Data - GNSS & Archive Glossary
An evolving glossary of terms (continually under development ...)
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4-character ID: four printable ASCII characters (usually case-insensitive alphanumeric plus underscore) which traditionally have been used to designate a monument or site, so with a-z, 0-9, and _ there are 37^4 = 1874161 unique 4-character IDs possible; see also in the best documented cases, the monument code, visit code, and raw file code are identical, though in some cases the documentation (forms, etc.) and the raw data files may indicate different 4-character IDs even though all information is for the same survey point of a monument
antenna: (for the GNSS community:) a resonant device that detects the GHz GPS, GLONASS, Galileo, or SBAS microwave signals and converts them to electrical signals for processing by a GNSS receiver; see also text documentation: and other:
antenna cable: a 50-ohm impedence, RF-shielded, co-axial cable used to connect the antenna to the receiver
antenna dome or antenna radome: a thin, almost microwave-transparent material placed over a GNSS antenna, often in the shape (or nearly so) of a simple geometrical surface (e.g. hemisphere, cone, paraboloid, etc.); use of an antenna dome slightly alters the effective phase center(s) of the antenna for high-precision geodetic positioning due the dielectric contact of the dome and the dome's geometry relative to the true phase centers of the antenna, thus requiring the exact type of dome used to be known (see dome designations at end of IGS Central Bureau receiver & antenna table)
antenna height: vertical distance from the survey point of a monument to the antenna reference point (ARP) of the antenna; this may be calculated using the geometry of the antenna and the antenna slant height
antenna orientation: the antenna is usually rotated into a standard orientation, often so that the antenna cable connector is toward geographic north, though often in the field only the local magnetic north direction is known, requiring the local magnetic declination to be known
antenna reference point: or ARP; an established point on the antenna choke ring, ground plane, or base from which the L1 and L2 phase centers are measured; see also text documentation: for more information
Archive Database: a relational database management system (RBDMS) used by the UNAVCO Boulder Facility Data Group to track and retrieve archived data files and metadata; uses Oracle engine
Archive process: the steps undertaken to archive GNSS data, logs, and/or other forms at the UNAVCO Boulder Facility Archive, which roughly are:
ARGO: "Automated Reformatter of GPS Observations"; both the software and the resulting fixed-format ASCII exchange representation of GPS data and metadata, similar to RINEX, created and made available by the National Geodetic Survey, U.S. Department of Commerce
ARP: antenna reference point
BARD: "Bay Area Regional Deformation" Northern California Continuous GPS Network; see also: for more information
BDT: "BeiDou Time"; analogous to GPS time, the time in seconds, skipping UTC leap seconds, since 1.0 Jan 2006 UTC — therefore an offset from GPST of 1356 weeks of exactly 604800 seconds each
Beidou-1 Navigation System: a specific spaceborne radionavigation system financed and to be operated by the People's Republic of China, Phase I, consisting of three validation geosynchronous (GEO) satellites; Phase I launches (all dates UTC):
Beidou-2 Navigation System — also known as Compass: a specific spaceborne radionavigation system financed and to be operated by the People's Republic of China to be completed in two phases: Phase II (planned to be completed by 2012) to consist of 14 satellites: 5 of which will be in geostationary (GEO) orbit, 5 in inclined geosynchronous orbit (IGSO), and 4 in MEO — broadcasting 5 signals; Phase III (planned to be completed by 2020) to consist of 35 satellites: 5 of which will be in geostationary (GEO) orbit, 3 in inclined geosynchronous orbit (IGSO), and 27 in MEO — broadcasting 10 signals; in both phases the SVs are arranged in three orbital planes with inclinations of about 55-56° with the MEO approximately 21540 km above the Earth (orbital period of 12h 53m, or 13 orbits every 7 sidereal days) using code-division multiple access with right-hand circularly polarized carriers centered at:
Phase II:
BINEX: "Bininary Exchange"; binary exchange representation of GNSS data and metadata which allows for encapsulation all or most of the information currently exchanged with the ASCII formats of RINEX, SINEX, IONEX, SP3, and so on as various BINEX records are defined; see also: for more information
calendar: calendars from 1980 - 2019 showing the day-of-year (ordinal date) and GPS week. On each calendar for each week, the day-of-year is on the left in square brackets [ddd] for the first day of the given week and month, and the GPS week in on the right in pointy brackets <wwww>.
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campaign: a well-defined number of visits to a group of geographically- or scientifically-related monuments over a well-defined time interval, typically several months in length
campaign data: data from one or more sites from a campaign
CBIS: IGS "Central Bureau Information System"
CDDIS: "Crustal Dynamics Data Information System" of NASA; see also:
CGCS2000: "China Geodetic Coordinate System 2000"; spatial reference system of Beidou-1 and Beidou-2; consistent with ITRF
choke ring: concentric rings of metal around and below the ground plane of the antenna, perhaps separated by microwave-absorbing foam, for the purpose of reducing multipath effects produced by the local geometry of the antenna relative to the site
Compass: see Beidou-2
continuous data: data from a continuous site
continuous monitoring: round-the-clock receiver collection of data at a setup/station, probably at a regular sampling interval
continuous site: a site at which continuous monitoring is occurring for one or more monuments
continuous station: one permanent station at a continuous site
contract: the legal agreement to fund a project
Coordinated Universal Time: see UTC
CORS: "Continuously Operating Reference Station" network of NOAA's National Geodetic Survey; see also:
country: a geo-political region, e.g. Antarctica, Chile, Russia, USA, etc.
data: (one of several possible meanings depending on context:)
data file: (a bit of a misnomer since:) persistent storage on media of at least GNSS data (observation data, navigation data, associated meteorological data, and/or other possible data types), and usually also associated metadata, where the data is generally grouped into a time window for a specific antenna/receiver combination for a specific survey point; e.g. a typical raw data file or RINEX file; the metadata in a data file is always treated as suspect until verified by information on a log
data format: data recorded in one of a number of manufacturers' raw data specifications, or in BINEX, RINEX, RTCM 2.3 or 3.0, ARGO, FICA, or one of a number of other possible specifications
data-logging: data from a GNSS receiver is streamed in near real-time, usually via serial RS-232, to a device (the "data-logger") which stores the data on media and/or in random access memory (RAM)
data set: the second-highest level of organization of data at the UNAVCO Boulder Facility Archive, with one or more data set with each data group; the data set allows division by when the data and forms were deposited and who deposited them, media information, whether the data in the data set is public or not, and a notes area
datum (or geodetic datum): a set of constants specifying a coordinate system used for geodetic control; if a datum is modeled on a reference ellipsoid of revolution (such as WGS-84), then 8 constants are needed to specify a complete datum, e.g. 3 to specify the origin, 3 to specify the orientation of the coordinate system, and 2 to specify the dimensions of the ellipsoid
datum transformation: a mathematical transformation between two datums, some of which are the 7-parameter Helmert transformation, the 5-parameter Molodensky or 3-parameter Abridged Molodensky transformations, the 10-parameter (7+3) Molodensky-Badekas transformation; see datum transformations and coordinate conversions and transformations including formulas
day-of-year: sometimes incorrectly called the Julian day, the day-of-year is a sequential numbering of the days of the year such that Jan 1 is day-of-year 1, Jan 2 is day-of-year 2, ending with Dec 31 being day-of-year 365 in non-leap years and day-of-year 366 in leap years; also called the ordinal date; see also calendar
DCB: see "differential code bias"
differential code bias: SV or receiver time-dependent correction to pseudocode observables of GNSS data, agreed upon by the IGS to modify data from older receivers to be compatible with newer generation receivers, where typically older GPS-capable receivers used cross correlation to determine the P-code when antispoofing was activated on the GPS SV; see also:
dome: see antenna dome
DOMES number: world-wide unique designation for a particular monument assigned by IERS; application for a DOMES number for a permanent station (for SLR, VLBI, DORIS, GPS, etc.) is made to the IERS TRF section using the DOMES request form
download: a defined protocol transaction between a receiver and computer to obtain one or more data files stored in the receiver for a completed set of GNSS measurement epochs (compare with data-logging)
EarthScope: earth science initiative in the USA with funding (proposed) from FY2003 - FY2012 to investigate the structure and evolution of the North American continent and the physical processes controlling earthquakes and volcanic eruptions; see also:
ECEF: "Earth-centered, Earth-fixed"
email: "electronic mail"; see smtp
epoch: a specific time instance using either the GPS time basis, GLONASS time basis, or Galileo system time
FICA: "Floating Integer Character ASCII"; ASCII exchange representation of GPS data and metadata developed by the Applied Research Laboratory of the University of Texas, Austin which preserves all the information found in the raw data from various receivers
form: one of the documents to record metadata about a campaign, a site, a monument, a antenna, a receiver, a visit, or installation of a continuous site; a standardized form for any of the above is made available by the UNAVCO Boulder Facility Data Group; see forms for:
ftp: "file transfer protocol"; used for pulling (getting) or pushing (putting) ASCII or binary files between two nodes on a TCP/IP network; if set up, can be either be anonymous or via a user account
Galileo: a specific spaceborne radionavigation system financed and to be operated by ESA (European Space Agency) to consist of 27 satellites with 3 active on-orbit spares arranged in three MEO orbital planes at 56° inclination, approximately 23616 km above the Earth (orbital period of 14h 22m, or 5 orbits every 3 sidereal days), using code-division multiple access with right-hand circularly polarized carriers centered at E2-L1-E1 = 1575.42 MHz, E5a = 1176.45 MHz, E5b = 1207.14 MHz, and E6 = 1278.75 MHz; will develop and use its own time standard and own spatial reference ellipsoid frame; the Galileo constellation should be operational some time in the early 21st century. The first phase is Galileo In-Orbit Valiation Element (GIOVE) satellites, with GIOVE-A and -B launched in Dec 2005 and Apr 2008; the GIOVE user interface is defined in the GIOVE-A+B (#102) Navigation Signal-in-Space Interface Control Document (8 Aug 2008). The second phase is In-Orbit Validation (IOV) satellites, with launches starting in 2011. The IOV and Full Operations Capability (FOC) Galileo user interface is defined in the OS SIS ICD: Galileo Open Service Signal-In-Space Interface Control Document. See also
GBAS: "Ground Based Agmentation System"; a set of ground transponders to augment GNSS use for civilian applications, which includes:
geocode: a published GHAM geocode definition is pending, but roughly speaking this is a even-byte, big-endian alphanumeric code which specifies the latitude and longitude to a certain precision; each two bytes specifies a certain level, where e.g. on the Earth:
GLONASS: "Global Navigation Satellite System"; a specific spaceborne radionavigation system financed and operated by the Soviet Commonwealth planned to consist of 21 satellites with 3 active on-orbit spares arranged in three MEO orbital planes at 64.8° inclination, approximately 19130 km above the Earth (orbital period of 11h 16m, or 17 orbits every 8 sidereal days), using frequency-division multiple access with right-hand circularly polarized carriers at G1 = 1602.00 MHz + n · 9/16 MHz and G2 = 1246.00 MHz + n · 7/16 MHz (n = "frequency number" integer, have values 0,1,...,24 from 1982 to 1998, 0,1,...,13 from 1998 to 2005 and -7,-6,...,6 after 2005; G2 is 7/9 of G1) currently using GLONASS time as the time standard and PZ-90 as the spatial reference ellipsoid frame. The public user interface is defined in the ICD-GLONASS: Global Navigation Satellite System (GLONASS): Interface Control Document, Navigational radiosignal in bands L1, L2.
GLONASS time: time system used by GLONASS, based on the UTC(SU) time frame generated by Russian organizations, referred to the Moscow Standard Time which has an offset of three hours from Greenwich time; besides differences of full hours and full leap seconds (which GLONASS time includes), the difference between the GPS and GLONASS time frames have been computed to differ by 20-30 microseconds
GNSS: "Global Navigation Satellite System"; any of, or some combination of, the operational spaceborne radionavigation systems, at this time being Navstar GPS, GLONASS, Galileo, Compass, SBAS, and/or QZSS
GPS: "Global Positioning System"; a specific spaceborne radionavigation system financed and operated by the U.S. Department of Defense consisting of Navstar satellites, a minumum of 21 operational and 3 active in-orbit spares, arranged in six MEO orbital planes at 63° (Block I SVs) and 55° (Block II SVs) inclinations, approximately 20197 km above the Earth (orbital period of 11h 58m, or 2 orbits every 1 sidereal day), using code-division multiple access with right-hand circularly polarized L-band carriers centered at L1 = 1575.42 MHz, L2 = 1227.60 MHz (= 120/154 of L1), and L5 = 1176.45 MHz (= 115/154 of L1; L5 in test mode one Block IIR-M SV, and operational in upcoming Block IIF and Block III SVs), and currently using GPS time as the time standard and WGS-84 as the spatial reference ellipsoid frame; the unclassified user interface of which is defined in the IS-GPS-200: Navstar GPS Space Segment/Navigation User Interfaces
GPS time: time in seconds, skipping UTC leap seconds, since 6.0 Jan 1980 using UTC as defined by the master clock of the U.S. Naval Observatory, UTC(USNO,MC) (see also any recent "Time and Frequency Bulletin" published by the National Institute of Standards and Technology, U.S. Department of Commerce) (see also GPS time of week, GPS week, calendar)
GPS time of week: the seconds since the beginning of a GPS week; this will not exceed 604800 even for weeks containing positive UTC leap seconds since GPS time skips UTC leap seconds
GPS week: complete weeks, skipping UTC leap seconds, since 6.0 Jan 1980; e.g. week starting Sunday 6 Jan 1980 was GPS week 0, week starting Sunday 13 Jan 1980 was GPS week 1, and so on; only 10 bits are used to represent the GPS week modulo 1024 in the broadcast navigation messages from the GPS SVs, leading to a modulo 1024 rollover problem on 22.0 Aug 1999 (GPS week 1024), 7.0 Apr 2019 (GPS week 2048), 21.0 Nov 2038 (GPS week 3072), and so on (see also calendar)
group: or data group; the top level of organization of data at the UNAVCO Boulder Facility Archive, each group being made up of data from probably from one or more projects; usually a group is related on a one-to-one basis to a campaign a network of permanent stations, or a single field support effort for multiple regional projects; subdivision of the group is by data sets; storage of removable media, log sheets, etc. in the Physical Repository is by group ID number
group ID: for the purposes of the UNAVCO Archive, a unique number specifying a specific group
GSAC: "GPS Seamless Archive Center"; participant in the Seamless Archive initiative promoted as an activity for the UNAVCO community by NSF; see also GSAC overview and GSAC-WS overview
Hatanaka (compression/decompression): a compression/decompression scheme of a RINEX observation file into a smaller ASCII format used by the IGS. The Hatanaka-compressed ASCII format version of a RINEX observation file is frequently used in conjuction with the UNIX compress, zip, gzip or other generalized compression utilities to create a very small file for Internet transfer. (see also Hatanaka Format Information at UNAVCO)
ICD-GLONASS: the public "interface specification" document for GLONASS; see:
IERS: "International Earth Rotation and Reference Systems Service"; see also:
IGS: "International GNSS Service", formally the "International GPS Service (for Geodynamics)"; a voluntary federation of more than 200 worldwide agencies that pool resources and permanent GNSS station data to generate precise GNSS products, established by the International Association of Geodesy (IAG) to aid high-precision geodetic positioning by providing phase and pseudorange RINEX data from permanent stations around the world, high-precision orbits for all tracked GNSS satellites (~20 cm or better in accuracy), earth rotation parameters, etc.; Central Bureau of IGS at igscbigscb.jpl.nasa.gov;
also see:
IGS log: a combination site and visit history log developed by the IGS for recording permanent station metadata in an ASCII format; see:
inspection: going to a setup/station for the purpose of checking equipment, general maintainance, etc. without modifying any of the setup (see also visit)
International Atomic Time: see TIA
IONEX: "Ionosphere map Exchange"; ASCII exchange representation of 2- and 3-dimensional TEC-value maps given in a geographic grid; see also
IS-GPS-200: the unclassified "interface specification" document for the Navstar GPS Space Segment/Navigation User Interfaces; see: and related:
IS-QZSS: the public "interface specification" document for QZSS; see:
ITRF: "International Terrestrial Reference Frame"; a specific realization of the International Terrestrial Reference System (ITRS), produced by the IERS ITRS Centre; see details for specific frames:
Julian date: solar days since 1.5 Universal Time (i.e. noon on the 1st) Jan 4713 BCE (on the proleptic Julian calendar); the start of GPS time (i.e. GPS standard epoch) 6.0 Jan 1980 is exactly equivalent to Julian date 2444244.5 (i.e. GPS time and UTC were essentially the same (to ±1 microsecond) from 6.0 Jan 1980 to 1.0 Jul 1981 when the first UTC leap second offset was introduced during GPS time at the end of 30 Jun 1981); compare with modified Julian date; see also U.S. Naval Observatory's Julian Date Converter
Julian day: same as Julian date, though sometimes incorrectly used to refer to the day-of-year or ordinal date of the year
LAAS: "Local Area Agmentation System", being developed by the Federal Aviation Administration (FAA) in the USA; see LAAS Program
lcode: "location code"; a lexically-sortable, non-unique, case-insensitive, 6-character alphanumeric string which geographically locates a Earth-based surface monument to at least a 100m x 100m square on the Earth
LDM: "Local Data Manager"; product of UCAR's Unidata group that allows secure pushing and/or pulling of files between two nodes of a TCP/IP network; establishing LDM on a group of nodes allows the establishment of a secure data flow topology; see also:
leap second: second added (or subtracted) to keep the UTC time scale within ±0.9 second of the UT1 time scale, which changes due to changes in the rotation rate of the Earth; since the introduction of leap seconds into UTC (with the first on 1972 Jun 30), only positive leap seconds have been included which begin at 23 h 59 min 60 s UTC and end at 0 h 0 min 0 s UTC demarking the beginning of the next day; positive leap seconds since the beginning of GPS time have been inserted at the end of:
The leap second: its history and possible future, Nelson et al., Metrologia, 38, 509-529, 2001.
Articles discussing the lack of leap seconds between the end of 1998 and the end of 2005:
LEO: "Low Earth Orbit"; any orbit with an orbital period of less than about two hours
log: documentation of a site description and/or a visit (see also form)
log file: electronic version of a log sheet, e.g. an on-line IGS site log
log sheet: a blank or filled-in log on paper
magnetic declination: offset between the direction of true geographic north and the local direction of magnetic north; see NOAA/NGDC's geomagnetic calculators:
marker: if it exists, an identifiable and distinct component of a monument having a survey point, e.g. a USGS brass cap
media: or physical media; best explained by example: 9-track, QIC (1/4" cartridge tape), audio cassette tape, 3.5" or 5.25" floppy disk, 4mm DAT, 8mm data tape, 8mm video tape, optical disk, magneto-optical disk, PC-Card (PCMCIA), Zip disk, Jazz disk, CD-R, CD-ROM, hard disk, etc.
MEO: "Medium Earth Orbit"; any orbit with an orbital period of about two to sixteen hours
metadata: ancillary information required for the accurate processing of observation and navigation data to determine the position, velocity, and/or acceleration of a single or set of survey points; e.g. antenna phase center position relative to a survey point (if no horizontal offset, this is just the "antenna height"), antenna type, receiver type, approximate WGS-84 coordinates, etc.; most of the information in a RINEX file header is metadata
MJD: "modified Julian date"; see modified Julian date for definition
modified Julian date: an offset version of the Julian date obtained by subtracting 2400000.5 days from the Julian date; thus the start of GPS time (i.e. GPS standard epoch) 6.0 Jan 1980 is equivalent to a modified Julian date of 44244.0
monument: a physical object for which one is trying to collect data for a determination of position, velocity, and/or acceleration for one or more survey points on or very near that object. (In the case of a zero offset for the antenna, the survey point of measurement is the phase center(s) of the antenna, which may or may not actually correspond to a physical point on the object.) (see also lcode, marker, monument code, monument ID, monument name, monument setting, site)
monument code: a non-unique, case-insensitive, 4-character alphanumeric string to identify a specific survey point on a specific monument, e.g. "PEAK" = "peak"; also known as the 4-character ID of a survey point of a monument, obtained from the monument record form or something similar
monument ID: for the internal purposes of the UNAVCO Archive, a unique number specifying a specific survey point on a specific monument; if multiple survey points are used on a single monument, then multiple monument IDs would be assigned corresponding to each survey point used
monument name: a (hopefully) descriptive name for a particular monument; a 60-character version of which could be used in the RINEX Observation file for the non-optional MARKER NAME field
monument setting: a date stamp associated with a monument or a marker on a monument indicating either 1) when the monument was established, or if that time is not known 2) when the monument was first known to be used
Navstar: "Navigation Satellite Timing And Ranging"; the official name of the GPS satellites, e.g. see NASA SPACEWARN Bulletin No. 653 describing Navstar 62 launched in March 2008
network: an array of GNSS setups and/or stations operating at the same time for the purpose of collecting more or less continuous data over the extent of the array; the spatial extent of the array can be global or anything smaller
observable: any measurement between the space segment and the user segment of the GPS, GLONASS, Galileo or SBAS, e.g. receiver clock epoch time, and at the epoch: carrier-phase (L1 or L2) measurements, pseudorange or code (C/A, P1, or P2) measurements, doppler measurements of L1 or L2, signal-to-noise measurements, etc.
observation: a set of carrier-phase and/or pseudorange observables for an individual Navstar GPS, GLONASS, Galileo or SBAS SV for a specific epoch
occupation: a visit (depending on whether you prefer a militaristic or pacific term)
off-site: someplace other than the site
ordinal date: same as day-of-year
On-line Repository: dedicated electronic RAID storage of archived data files at the UNAVCO Boulder Facility Archive
OS SIS ICD: the unclassified "interface specification" document for the Galileo Open Service Signal-In-Space Interface Control Document; see:
PANGA: "Pacific Northwest Geodetic Array"; see also:
PBO: "Plate Boundary Observatory"; one of the main components of EarthScope, this is a set of surface (GPS permanent stations) and subsurface (strainmeters) to measure the crustal motion and deformation in the plate boundary between the North American and Pacific plates in the western USA and Alaska; see also EarthScope & PBO
permanent station: very long-term setup at a continous site; implies long-term power and possibly other infrastructure such as communication
permanent station data: data from one or more permanent stations
phase center: relative to the active antenna element and ground plane, where a specific carrier-phase frequency from GNSS SVs seem to be received; the phase center may be modeled as averaged over all possible directions, modeled as a function of elevation from the ground plane, or even modeled as a function of elevation and azimuth (see phase center pattern)
phase center pattern: the elevation and azimuthal offset of the effective phase center of the antenna; see also
Physical Repository: dedicated storage room(s) for physical media, log sheets, etc. at the UNAVCO Boulder Facility Archive, organized by group ID number
principal investigator: the big cheese/head honcho/primary cognizant entity associated with a project
PRN: "Pseudo-Random Noise" (or sometimes Number); an integer sequence number, 1-32, assigned to each of the Navstar GPS SVs to indicate its own unique C/A-code and its own unique P-code; this is the GPS SV number that is used in a RINEX observation or navigation file that is used to distinguish each satellite, e.g. PRNs for GPS, GBAS, and SBAS:
project: proposed or realized work in one or more of the following: site reconnaissance, monument installation (or monumentation), permanent station installation, campaign or permanent station data collection
PZ-90: "Parameters of the Earth 1990" (PZ-90 in Russian); formerly known as Soviet Geodetic System 1990 (SGS-90) and nearly identical to SGS-85; the ECEF spatial coordinate system used by GLONASS; the estimated transformation between SGS-85 and WGS-84 included a 4 meter offset of the z-axis and a 0.6" (3e-6 radian) rotation about the z-axis, whereas the transformation between PZ-90 and WGS-84 is only a 0.33" to 0.40" (1.6e-6 to 1.9e-6 radian) rotation about the z-axis, with perhaps a 2.5 meter offset of the y-axis; the system is defined as:
QZSS: "Quasi- Zenith Satellite System"; a specific spaceborne radionavigation system financed and operated by the Japan planned to consist of up to 18 geosynchronous satellites (mean height of approximately 35786 km above mean sea level but in a highly elliptical orbit, with an orbital period of 23h 56m 04.1s, or 1 orbit every sidereal day) using code-division multiple access with a right-hand circularly polarized carrier centered at L1 = 1575.42 MHz, L2 = 1227.60 MHz, L5 = 1176.45 MHz, and LEX = 1278.75 MHz; operational and proposed satellites of PRN 193 to 202 (with 203-210 as potential spares):
radome: see antenna dome
raw data: lowest-level, proprietary or non-proprietary data file(s) available from a GNSS receiver containing both data and metadata; e.g. Trimble's DAT, EPH, ION, and MES download files, AOA's ConanBinary or TurboBinary files, Ashtech's B-, E-, and S-download files, etc.; usually a majority of the data and metadata in a data file is in an encoded binary format.
raw file code: a non-unique, case-insensitive, 4-character alphanumeric string to identify a specific survey point on a specific monument, e.g. "PEAK" = "peak"; also known as the 4-character ID of a survey point of a monument, obtained from the raw data file itself (see also monument code and visit code)
real-time monitoring: continuous data is transferred near-real-time via one or more communication paths off-site for near-real-time data collection, quality checking, and/or processing; time delay should generally be no more than a few minutes
receiver: device used to decode the digital and analog components of the GNSS signal supplied by the antenna, as specified in part by the IS-GPS-200 for GPS, or the analog for GLONASS, Galileo or SBAS
reference point: a special case of a survey point usually used to locate a primary survey point or serve as a backup to a primary survey point especially in cases where the primary survey point has been lost or destroyed
RINEX: "Receiver Independent Exchange"; ASCII exchange representation of GNSS data and metadata currently conforming to the specification given in "RINEX: The Receiver Independent Exchange Format Version 2(.xx)" available from the Astronomical Institute, University of Berne (AIUB); one of several general file types:
RTCM: "Radio Technical Commission Maritime Services"; for example, RTCM Special Committee 104 (SC-104) recommends standards for differential GPS/GNSS data exchange
SBAS: "Satellite Based Agmentation System"; the component of a set of geostationary satellites (one orbital plane at 0° inclination, approximately 35786 km above mean sea level at the equator, with an orbital period of 23h 56m 04.1s, or 1 orbit every sidereal day) to augment GNSS use for civilian applications using code-division multiple access with a right-hand circularly polarized carrier centered at L1 = 1575.42 MHz and a (proposed) L5 = 1176.45 MHz; the operational and proposed satellites of PRN 120 to 138 include:
see also:
SCEC: "Southern California Earthquake Center"; see also SCIGN and:
SCIGN: "Southern California Integrated GPS Network"; see also:
session: a pre-definable time during which a GNSS receiver will record observations according to some pre-defined parameters, such as sample interval or data format
semi-continuous site: a site with a continuous station that has significant data gaps by design, for example so that the equipment can be moved to another similar site
semi-continuous site data: data from one or more semi-continuous sites
setting: monument setting
setup: (not necessarily limited to): the antenna dome (if any), the antenna, antenna's LNA (low-noise amplifier), the choke ring (if any), tripod or other antenna support, antenna cable, in-line surge suppressor (if any), receiver, receiver firmware, (and any other item in the signal path) established around a monument for the purpose of collecting GNSS data; modification of anything (see the above items, or a change in antenna height) that could effect positioning results constitutes a new setup (see also station, visit)
sidereal day: time for the Earth to rotation 360° on its axis; 23h 56m 4.098904s, based on the WGS-84 angular velocity of Earth == 7.2921151467e-5 radians/second
signal: both the analog and binary components of the electromagnetic radiation emitted by either the Navstar GPS, GLONASS, Galileo, or SBAS space segments; the signal is centered at one or more microwave frequencies
SINEX: "Solution Independent Exchange": see specification for 2.00 (24 May 2002) and 2.01 (25 Mar 2005):
site: the general, immediate area around one or more monuments or where one or more monuments may be installed
site description: the general description of a site, primarily to identify how to find the site from surrounding towns, roads, landmarks, etc.
smtp: "simple mail transfer protocol"; normal email transfer protocol
SOPAC: "Scripps Orbit and Permanent Array Center" of the Scripps Institution of Oceanography, University of California of San Deigo; see also:
SP3: "Standard Product 3" Orbit Format for GPS (also now known as SP3-a), an ASCII exchange format for representing GPS satellite orbits; see also
SP3-b: "Standard Product 3" Orbit Format for GPS and GLONASS, an ASCII exchange format for representing GPS and GLONASS satellite orbits
SP3-c: Extended "Standard Product 3" Orbit Format for GPS and GLONASS, an ASCII exchange format for representing GPS and GLONASS satellite orbits; see also
station: a long-term setup; antenna support is usually more permanent than just a tripod; a station probably includes the setup plus power, communication, and/or other infrastructure
Setup and station imply two ends of the time spectrum. A setup is generally more short-term (on the order of hours to days) and a station is more long-term (on the order of months to years). On occasion, a setup (plus long-term power) is pushed into long-term use (many months), but it still does not have the permanence and survivability implied by the term "station".
survey point: a precisely definable location (down to millimeter or sub-millimeter levels) to which an antenna is located for the purpose of receiving GNSS signals; this may be a physical point such a dimple or cross-hair intersection on a marker, or may a virtual (non-physical) point (see also marker, monument, site)
survey mark: in our terminology the same as survey point
SV: "Space Vehicle", referring originally to a specific Navstar GPS satellite, but now used to refer to any one of the Navstar GPS, GLONASS, Galileo, or SBAS satellites
TEC: "total electron count" of the ionosphere, which dominates the ionospheric refraction
teqc: "translate, edit, and quality check" software, a UNAVCO Boulder Facility data/metadata toolkit; see also
TIA: "Temps Atomique International" or "International Atomic Time", based on the weighted average of a large number of atomic clocks, where since 1967 the second is defined as the period of time equal to 9192631770 cycles of the radiation corresponding to the transition between the two hyperfine energy levels of the ground state of the cesium-133 atom (Cs-133); available since 1955, but TIA was defined as being equal UT1 at the epoch 1.0 Jan 1958
TRANSIT: full name of Navy Navigation Satellite System (NNSS) TRANSIT, this was the immediate predecessor of the Navstar GPS system; a specific spaceborne radionavigation system financed and operated by the U.S. Department of Defense consisting of 6-10 satellites (3-5 providing navigation service and 3-5 acting as in-orbit spares) in near-circular LEO polar orbits approximately 1075 km above the Earth (orbital period of 1h 46m, or about 27 orbits every 2 sidereal days) transmitting phase modulated navigation signals at 0.150 and 0.400 GHz; any signals after 31 Dec 1996 should not be used for timing or position; used WGS-72 until 27 Jan 1989 as its ECEF spatial coordinate system, whereupon this was switched to WGS-84
UNAVCO: "University Navstar Consortium" up until 30 Sept 2003, after which UNAVCO is just a name (i.e. not an acronym) representing the non-profit membership-governed organization that supports and promotes Earth science by advancing high-precision geodetic and strain techniques and technologies such as the Global Positioning System; see also:
UNIX epoch: time base for UNIX operating systems, based on the number on non-leap seconds since 1.0 Jan 1970 UTC; many current systems store the UNIX time internally as a 4-byte 2's complement integer, so that the maximum number of seconds that can be dealt with is 2^31 - 1 = 2147483647, equivalent to 2038 Jan 19 03:14:07 -- though any potential problem with this end date will probably be dealt with long before it's reached (probably by switching to a 8-byte 2's complement integer)
Universal Time: see definitions for the various realizations: UT0, UT1, UT2, and UTC
UT0: Universal Time base defined as precise solar time at the zero meridian (Greenwich)
UT1: UT0 corrected for the Earth's polar motion
UT2: UT1 corrected for seasonal variations in the Earth's rotation rate
UTC: not an acronym, but "Coordinated Universal Time", a hydrid time scale defined where the rate of UTC is based on atomic frequency standards (currently using TIA) but the epoch of UTC is synchronized to be within ±0.9 sec of UT1; this synchronization was defined as UTC = TIA - 10 seconds on 1.0 Jan 1972, and further synchronized since then by the insertion of leap seconds; some of the various realizations of UTC being:
visit: also site visit; establishing a setup/station at a monument for the purpose of collecting data; the UNAVCO Data Group maintains a GPS site visit form to be filled out for each visit, the information on which corresponds to the visit table in the Archive Database; if something about a setup changes during data collection (for example a change of receiver, receiver firmware, antenna, antenna height, etc.), the earlier visit ends and a new visit begins at the time of the change (see also inspection, occupation)
visit code: a non-unique, case-insensitive, 4-character alphanumeric string to identify a specific survey point on a specific monument, e.g. "PEAK" = "peak"; also known as the 4-character ID of a survey point of a monument, usually the same as the monument code, obtained from the survey log — monument visit logsheet, monument record logsheet, or something similar
visit ID: for the purposes of the UNAVCO Archive, a unique number specifying a specific visit
WGS-72: "World Geodetic System 1972"; the spatial coordinate system used by GPS through 21 Jan 1987 (see also WGS-84) Some of the major constants in WGS-72, which models the Earth as an ellipsoid of revolution, are:
WGS-84: "World Geodetic System 1984"; the ECEF spatial coordinate system used by GPS since 22 Jan 1987 (see, for example, "Session 2: World Geodetic System 1984" pp. 67-134, in Proceedings of the Fourth International Geodetic Symposium on Satellite Positioning, Apr. 28 - May 2, 1986, Volume 1); defined in the IS-GPS-200 as:
An evolving glossary of terms (continually under development ...)
If you don't find the term you need explained, send us (archive
unavco.org) a request.
0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
4-character ID: four printable ASCII characters (usually case-insensitive alphanumeric plus underscore) which traditionally have been used to designate a monument or site, so with a-z, 0-9, and _ there are 37^4 = 1874161 unique 4-character IDs possible; see also in the best documented cases, the monument code, visit code, and raw file code are identical, though in some cases the documentation (forms, etc.) and the raw data files may indicate different 4-character IDs even though all information is for the same survey point of a monument
antenna: (for the GNSS community:) a resonant device that detects the GHz GPS, GLONASS, Galileo, or SBAS microwave signals and converts them to electrical signals for processing by a GNSS receiver; see also text documentation: and other:
- GPS antenna calibrations by the staff of the Instrumentation and Methodologies Branch, Geodetic Services Division, National Geodetic Survey, NOAA, Dept. of Commerce
antenna cable: a 50-ohm impedence, RF-shielded, co-axial cable used to connect the antenna to the receiver
antenna dome or antenna radome: a thin, almost microwave-transparent material placed over a GNSS antenna, often in the shape (or nearly so) of a simple geometrical surface (e.g. hemisphere, cone, paraboloid, etc.); use of an antenna dome slightly alters the effective phase center(s) of the antenna for high-precision geodetic positioning due the dielectric contact of the dome and the dome's geometry relative to the true phase centers of the antenna, thus requiring the exact type of dome used to be known (see dome designations at end of IGS Central Bureau receiver & antenna table)
antenna height: vertical distance from the survey point of a monument to the antenna reference point (ARP) of the antenna; this may be calculated using the geometry of the antenna and the antenna slant height
antenna orientation: the antenna is usually rotated into a standard orientation, often so that the antenna cable connector is toward geographic north, though often in the field only the local magnetic north direction is known, requiring the local magnetic declination to be known
antenna reference point: or ARP; an established point on the antenna choke ring, ground plane, or base from which the L1 and L2 phase centers are measured; see also text documentation: for more information
Archive Database: a relational database management system (RBDMS) used by the UNAVCO Boulder Facility Data Group to track and retrieve archived data files and metadata; uses Oracle engine
Archive process: the steps undertaken to archive GNSS data, logs, and/or other forms at the UNAVCO Boulder Facility Archive, which roughly are:
- taking receipt of incoming data and or logs, whether by physical media or by electronic transfer and this receipt entered in the Archive Database; the physical media (or tape copies for electronic transfers) are stored in the Physical Repository; this step is referred to as data/log check-in;
- extracting metadata about the received data files and entering this information into the Archive Database; the data files are compressed and copied into the On-line Repository; the data files handled in this way can be raw data or RINEX or some combination of the two (though a copy of the raw data is always desired at a minimum); this step is referred to as data injection;
- the visit metadata is extracted from the logs and entered into the Archive Database;
- and finally the visits are associated with the injected data, often requiring a reexamination of the metadata of the visits and of the data in order to resolve discrepancies; this step is referred to as validation
ARGO: "Automated Reformatter of GPS Observations"; both the software and the resulting fixed-format ASCII exchange representation of GPS data and metadata, similar to RINEX, created and made available by the National Geodetic Survey, U.S. Department of Commerce
ARP: antenna reference point
BARD: "Bay Area Regional Deformation" Northern California Continuous GPS Network; see also: for more information
BDT: "BeiDou Time"; analogous to GPS time, the time in seconds, skipping UTC leap seconds, since 1.0 Jan 2006 UTC — therefore an offset from GPST of 1356 weeks of exactly 604800 seconds each
Beidou-1 Navigation System: a specific spaceborne radionavigation system financed and to be operated by the People's Republic of China, Phase I, consisting of three validation geosynchronous (GEO) satellites; Phase I launches (all dates UTC):
-
BD-1A (GEO) on 30 Oct 2000
BD-1B (GEO) on 20 Dec 2000
BD-1C (GEO) on 24 May 2003
BD-1D on 2 Feb 2007
Beidou-2 Navigation System — also known as Compass: a specific spaceborne radionavigation system financed and to be operated by the People's Republic of China to be completed in two phases: Phase II (planned to be completed by 2012) to consist of 14 satellites: 5 of which will be in geostationary (GEO) orbit, 5 in inclined geosynchronous orbit (IGSO), and 4 in MEO — broadcasting 5 signals; Phase III (planned to be completed by 2020) to consist of 35 satellites: 5 of which will be in geostationary (GEO) orbit, 3 in inclined geosynchronous orbit (IGSO), and 27 in MEO — broadcasting 10 signals; in both phases the SVs are arranged in three orbital planes with inclinations of about 55-56° with the MEO approximately 21540 km above the Earth (orbital period of 12h 53m, or 13 orbits every 7 sidereal days) using code-division multiple access with right-hand circularly polarized carriers centered at:
Phase II:
-
B1-2/E1 = 1589.74 MHz
B1/E2 = 1561.098 MHz
B3/E6 = 1268.52 MHz
B2/E5b = 1207.14 MHz
-
B1/L1 = 1575.42 MHz
B3/E6 = 1268.52 MHz
B2/E5b = 1191.795 MHz
-
Beidou DW1 (MEO 1) on 13 Apr 2007
Beidou DW12 (MEO 3) on 29 Apr 2012
Beidou DW13 (MEO 4) on 29 Apr 2012
-
Beidou DW2 (GEO 2) on 14 Apr 2009
Beidou DW3 (GEO 1) on 16 Jan 2010
Beidou DW4 (GEO 3) on 2 Jun 2010
Beidou DW5 (IGSO 1) on 31 Jul 2010
Beidou DW6 (GEO 4) on 31 Oct 2010
Beidou DW7 (IGSO 2) on 17 Dec 2010
Beidou DW8 (IGSO 3) on 9 Apr 2011
Beidou DW9 (IGSO 4) on 26 Jul 2011
Beidou DW10 (IGSO 5) on 1 Dec 2011
Beidou DW11 (GEO 5) on 24 Feb 2012
-
Inside GNSS, News Update Sept/Oct 2008
Inside GNSS News, 10 Aug 2009
Inside GNSS News, 2 Mar 2011
Encyclopedia Astronautica: Beidou
BINEX: "Bininary Exchange"; binary exchange representation of GNSS data and metadata which allows for encapsulation all or most of the information currently exchanged with the ASCII formats of RINEX, SINEX, IONEX, SP3, and so on as various BINEX records are defined; see also: for more information
calendar: calendars from 1980 - 2019 showing the day-of-year (ordinal date) and GPS week. On each calendar for each week, the day-of-year is on the left in square brackets [ddd] for the first day of the given week and month, and the GPS week in on the right in pointy brackets <wwww>.
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
campaign: a well-defined number of visits to a group of geographically- or scientifically-related monuments over a well-defined time interval, typically several months in length
campaign data: data from one or more sites from a campaign
CBIS: IGS "Central Bureau Information System"
CDDIS: "Crustal Dynamics Data Information System" of NASA; see also:
CGCS2000: "China Geodetic Coordinate System 2000"; spatial reference system of Beidou-1 and Beidou-2; consistent with ITRF
choke ring: concentric rings of metal around and below the ground plane of the antenna, perhaps separated by microwave-absorbing foam, for the purpose of reducing multipath effects produced by the local geometry of the antenna relative to the site
Compass: see Beidou-2
continuous data: data from a continuous site
continuous monitoring: round-the-clock receiver collection of data at a setup/station, probably at a regular sampling interval
continuous site: a site at which continuous monitoring is occurring for one or more monuments
continuous station: one permanent station at a continuous site
contract: the legal agreement to fund a project
Coordinated Universal Time: see UTC
CORS: "Continuously Operating Reference Station" network of NOAA's National Geodetic Survey; see also:
country: a geo-political region, e.g. Antarctica, Chile, Russia, USA, etc.
data: (one of several possible meanings depending on context:)
- information that can be used to reconstruct GNSS observables or a representation of the observables themselves produced by a GNSS receiver, otherwise known as "observation data";
- observation data plus any of a variety of related ancillary data collected by a GNSS receiver, e.g. navigation data (SV-broadcast orbit information), meteorological or other geophysical data (collected at the site and input to the receiver, such as air temperature, air pressure, air relative humidity, earth tilt, earth strain, etc.);
- any output from a GNSS receiver, especially raw data;
- any format in addition to raw data which endeavors to preserve the information content of raw data from a GNSS receiver necessary for processing, e.g. FICA, ARGO, RINEX
data file: (a bit of a misnomer since:) persistent storage on media of at least GNSS data (observation data, navigation data, associated meteorological data, and/or other possible data types), and usually also associated metadata, where the data is generally grouped into a time window for a specific antenna/receiver combination for a specific survey point; e.g. a typical raw data file or RINEX file; the metadata in a data file is always treated as suspect until verified by information on a log
data format: data recorded in one of a number of manufacturers' raw data specifications, or in BINEX, RINEX, RTCM 2.3 or 3.0, ARGO, FICA, or one of a number of other possible specifications
data-logging: data from a GNSS receiver is streamed in near real-time, usually via serial RS-232, to a device (the "data-logger") which stores the data on media and/or in random access memory (RAM)
data set: the second-highest level of organization of data at the UNAVCO Boulder Facility Archive, with one or more data set with each data group; the data set allows division by when the data and forms were deposited and who deposited them, media information, whether the data in the data set is public or not, and a notes area
datum (or geodetic datum): a set of constants specifying a coordinate system used for geodetic control; if a datum is modeled on a reference ellipsoid of revolution (such as WGS-84), then 8 constants are needed to specify a complete datum, e.g. 3 to specify the origin, 3 to specify the orientation of the coordinate system, and 2 to specify the dimensions of the ellipsoid
datum transformation: a mathematical transformation between two datums, some of which are the 7-parameter Helmert transformation, the 5-parameter Molodensky or 3-parameter Abridged Molodensky transformations, the 10-parameter (7+3) Molodensky-Badekas transformation; see datum transformations and coordinate conversions and transformations including formulas
day-of-year: sometimes incorrectly called the Julian day, the day-of-year is a sequential numbering of the days of the year such that Jan 1 is day-of-year 1, Jan 2 is day-of-year 2, ending with Dec 31 being day-of-year 365 in non-leap years and day-of-year 366 in leap years; also called the ordinal date; see also calendar
DCB: see "differential code bias"
differential code bias: SV or receiver time-dependent correction to pseudocode observables of GNSS data, agreed upon by the IGS to modify data from older receivers to be compatible with newer generation receivers, where typically older GPS-capable receivers used cross correlation to determine the P-code when antispoofing was activated on the GPS SV; see also:
- IGSMAIL-2744
- cc2noncc.f code
- p1c1bias.hist: bias history file for cc2noncc
- AIUB's CODE DCB archive
- MIT GAMIT/GLOBE-K rcvant.dat
dome: see antenna dome
DOMES number: world-wide unique designation for a particular monument assigned by IERS; application for a DOMES number for a permanent station (for SLR, VLBI, DORIS, GPS, etc.) is made to the IERS TRF section using the DOMES request form
download: a defined protocol transaction between a receiver and computer to obtain one or more data files stored in the receiver for a completed set of GNSS measurement epochs (compare with data-logging)
EarthScope: earth science initiative in the USA with funding (proposed) from FY2003 - FY2012 to investigate the structure and evolution of the North American continent and the physical processes controlling earthquakes and volcanic eruptions; see also:
- EarthScope homepage
- SAFOD (deep drilling component)
- PBO (geodetic component)
- USArray (seismic component)
ECEF: "Earth-centered, Earth-fixed"
email: "electronic mail"; see smtp
epoch: a specific time instance using either the GPS time basis, GLONASS time basis, or Galileo system time
FICA: "Floating Integer Character ASCII"; ASCII exchange representation of GPS data and metadata developed by the Applied Research Laboratory of the University of Texas, Austin which preserves all the information found in the raw data from various receivers
form: one of the documents to record metadata about a campaign, a site, a monument, a antenna, a receiver, a visit, or installation of a continuous site; a standardized form for any of the above is made available by the UNAVCO Boulder Facility Data Group; see forms for:
ftp: "file transfer protocol"; used for pulling (getting) or pushing (putting) ASCII or binary files between two nodes on a TCP/IP network; if set up, can be either be anonymous or via a user account
Galileo: a specific spaceborne radionavigation system financed and to be operated by ESA (European Space Agency) to consist of 27 satellites with 3 active on-orbit spares arranged in three MEO orbital planes at 56° inclination, approximately 23616 km above the Earth (orbital period of 14h 22m, or 5 orbits every 3 sidereal days), using code-division multiple access with right-hand circularly polarized carriers centered at E2-L1-E1 = 1575.42 MHz, E5a = 1176.45 MHz, E5b = 1207.14 MHz, and E6 = 1278.75 MHz; will develop and use its own time standard and own spatial reference ellipsoid frame; the Galileo constellation should be operational some time in the early 21st century. The first phase is Galileo In-Orbit Valiation Element (GIOVE) satellites, with GIOVE-A and -B launched in Dec 2005 and Apr 2008; the GIOVE user interface is defined in the GIOVE-A+B (#102) Navigation Signal-in-Space Interface Control Document (8 Aug 2008). The second phase is In-Orbit Validation (IOV) satellites, with launches starting in 2011. The IOV and Full Operations Capability (FOC) Galileo user interface is defined in the OS SIS ICD: Galileo Open Service Signal-In-Space Interface Control Document. See also
- GIOVE — first phase: definition (Galileo In-Orbit Validation Element)
- IOV — second phase: development (In-Orbit Validation)
- FOC — final phase: Full Operations Capability
- Galileo — European Satellite Navigation System (quick overview of Galileo)
- Status of Galileo Frequency and Signal Design
- Galileo Mission High Level Definition
GBAS: "Ground Based Agmentation System"; a set of ground transponders to augment GNSS use for civilian applications, which includes:
- LAAS (Local Area Augmentation System)
geocode: a published GHAM geocode definition is pending, but roughly speaking this is a even-byte, big-endian alphanumeric code which specifies the latitude and longitude to a certain precision; each two bytes specifies a certain level, where e.g. on the Earth:
- Level 4 (8 characters) delineate a region approximately 480 meters on each side
- Level 6 (12 characters) delineate a region approximately 1.9 meters on each side
- Level 8 (16 characters) delineate a region approximately 1 mm on each side
GLONASS: "Global Navigation Satellite System"; a specific spaceborne radionavigation system financed and operated by the Soviet Commonwealth planned to consist of 21 satellites with 3 active on-orbit spares arranged in three MEO orbital planes at 64.8° inclination, approximately 19130 km above the Earth (orbital period of 11h 16m, or 17 orbits every 8 sidereal days), using frequency-division multiple access with right-hand circularly polarized carriers at G1 = 1602.00 MHz + n · 9/16 MHz and G2 = 1246.00 MHz + n · 7/16 MHz (n = "frequency number" integer, have values 0,1,...,24 from 1982 to 1998, 0,1,...,13 from 1998 to 2005 and -7,-6,...,6 after 2005; G2 is 7/9 of G1) currently using GLONASS time as the time standard and PZ-90 as the spatial reference ellipsoid frame. The public user interface is defined in the ICD-GLONASS: Global Navigation Satellite System (GLONASS): Interface Control Document, Navigational radiosignal in bands L1, L2.
GLONASS time: time system used by GLONASS, based on the UTC(SU) time frame generated by Russian organizations, referred to the Moscow Standard Time which has an offset of three hours from Greenwich time; besides differences of full hours and full leap seconds (which GLONASS time includes), the difference between the GPS and GLONASS time frames have been computed to differ by 20-30 microseconds
GNSS: "Global Navigation Satellite System"; any of, or some combination of, the operational spaceborne radionavigation systems, at this time being Navstar GPS, GLONASS, Galileo, Compass, SBAS, and/or QZSS
GPS: "Global Positioning System"; a specific spaceborne radionavigation system financed and operated by the U.S. Department of Defense consisting of Navstar satellites, a minumum of 21 operational and 3 active in-orbit spares, arranged in six MEO orbital planes at 63° (Block I SVs) and 55° (Block II SVs) inclinations, approximately 20197 km above the Earth (orbital period of 11h 58m, or 2 orbits every 1 sidereal day), using code-division multiple access with right-hand circularly polarized L-band carriers centered at L1 = 1575.42 MHz, L2 = 1227.60 MHz (= 120/154 of L1), and L5 = 1176.45 MHz (= 115/154 of L1; L5 in test mode one Block IIR-M SV, and operational in upcoming Block IIF and Block III SVs), and currently using GPS time as the time standard and WGS-84 as the spatial reference ellipsoid frame; the unclassified user interface of which is defined in the IS-GPS-200: Navstar GPS Space Segment/Navigation User Interfaces
GPS time: time in seconds, skipping UTC leap seconds, since 6.0 Jan 1980 using UTC as defined by the master clock of the U.S. Naval Observatory, UTC(USNO,MC) (see also any recent "Time and Frequency Bulletin" published by the National Institute of Standards and Technology, U.S. Department of Commerce) (see also GPS time of week, GPS week, calendar)
GPS time of week: the seconds since the beginning of a GPS week; this will not exceed 604800 even for weeks containing positive UTC leap seconds since GPS time skips UTC leap seconds
GPS week: complete weeks, skipping UTC leap seconds, since 6.0 Jan 1980; e.g. week starting Sunday 6 Jan 1980 was GPS week 0, week starting Sunday 13 Jan 1980 was GPS week 1, and so on; only 10 bits are used to represent the GPS week modulo 1024 in the broadcast navigation messages from the GPS SVs, leading to a modulo 1024 rollover problem on 22.0 Aug 1999 (GPS week 1024), 7.0 Apr 2019 (GPS week 2048), 21.0 Nov 2038 (GPS week 3072), and so on (see also calendar)
group: or data group; the top level of organization of data at the UNAVCO Boulder Facility Archive, each group being made up of data from probably from one or more projects; usually a group is related on a one-to-one basis to a campaign a network of permanent stations, or a single field support effort for multiple regional projects; subdivision of the group is by data sets; storage of removable media, log sheets, etc. in the Physical Repository is by group ID number
group ID: for the purposes of the UNAVCO Archive, a unique number specifying a specific group
GSAC: "GPS Seamless Archive Center"; participant in the Seamless Archive initiative promoted as an activity for the UNAVCO community by NSF; see also GSAC overview and GSAC-WS overview
Hatanaka (compression/decompression): a compression/decompression scheme of a RINEX observation file into a smaller ASCII format used by the IGS. The Hatanaka-compressed ASCII format version of a RINEX observation file is frequently used in conjuction with the UNIX compress, zip, gzip or other generalized compression utilities to create a very small file for Internet transfer. (see also Hatanaka Format Information at UNAVCO)
ICD-GLONASS: the public "interface specification" document for GLONASS; see:
- version 5.1 (2008) (in English)
- version 5.0 (2002) (in English)
IERS: "International Earth Rotation and Reference Systems Service"; see also:
- IERS Central Bureau homepage
- IERS Publications: Messages, Bulletins, Technical Notes, Annual Reports
IGS: "International GNSS Service", formally the "International GPS Service (for Geodynamics)"; a voluntary federation of more than 200 worldwide agencies that pool resources and permanent GNSS station data to generate precise GNSS products, established by the International Association of Geodesy (IAG) to aid high-precision geodetic positioning by providing phase and pseudorange RINEX data from permanent stations around the world, high-precision orbits for all tracked GNSS satellites (~20 cm or better in accuracy), earth rotation parameters, etc.; Central Bureau of IGS at igscb
igscb.jpl.nasa.gov;
also see:
- IGS Central Bureau homepage
- IGS FAQs
- IGS Data and Products
- IGS Mailing lists
- GeoForschungsZentrum (GFZ) summary of the last 100 days of IGS sites
IGS log: a combination site and visit history log developed by the IGS for recording permanent station metadata in an ASCII format; see:
inspection: going to a setup/station for the purpose of checking equipment, general maintainance, etc. without modifying any of the setup (see also visit)
International Atomic Time: see TIA
IONEX: "Ionosphere map Exchange"; ASCII exchange representation of 2- and 3-dimensional TEC-value maps given in a geographic grid; see also
IS-GPS-200: the unclassified "interface specification" document for the Navstar GPS Space Segment/Navigation User Interfaces; see: and related:
- IS-GPS-705A (8 Jun 2010) User Segement L5 Interfaces (PDF — 1.2 Mb)
- IS-GPS-800A (8 Jun 2010) User Segement L1C Interfaces (PDF — 0.8 Mb)
IS-QZSS: the public "interface specification" document for QZSS; see:
- version 1.4 (draft) (15 July 2011)
- version 1.2 (draft) (19 March 2010)
- version 1.1 (31 July 2009)
ITRF: "International Terrestrial Reference Frame"; a specific realization of the International Terrestrial Reference System (ITRS), produced by the IERS ITRS Centre; see details for specific frames:
ITRF2008 ITRF2005 ITRF2000 ITRF(19)97 ITRF(19)96 ITRF(19)94 ITRF(19)93 ITRF(19)92and realizations ITRF(19)89, ITRF(19)90, ITRF(19)91, and ITRF(19)95 (see also WGS-84, PZ-90)
Julian date: solar days since 1.5 Universal Time (i.e. noon on the 1st) Jan 4713 BCE (on the proleptic Julian calendar); the start of GPS time (i.e. GPS standard epoch) 6.0 Jan 1980 is exactly equivalent to Julian date 2444244.5 (i.e. GPS time and UTC were essentially the same (to ±1 microsecond) from 6.0 Jan 1980 to 1.0 Jul 1981 when the first UTC leap second offset was introduced during GPS time at the end of 30 Jun 1981); compare with modified Julian date; see also U.S. Naval Observatory's Julian Date Converter
Julian day: same as Julian date, though sometimes incorrectly used to refer to the day-of-year or ordinal date of the year
LAAS: "Local Area Agmentation System", being developed by the Federal Aviation Administration (FAA) in the USA; see LAAS Program
lcode: "location code"; a lexically-sortable, non-unique, case-insensitive, 6-character alphanumeric string which geographically locates a Earth-based surface monument to at least a 100m x 100m square on the Earth
LDM: "Local Data Manager"; product of UCAR's Unidata group that allows secure pushing and/or pulling of files between two nodes of a TCP/IP network; establishing LDM on a group of nodes allows the establishment of a secure data flow topology; see also:
- Unidata's LDM homepage
leap second: second added (or subtracted) to keep the UTC time scale within ±0.9 second of the UT1 time scale, which changes due to changes in the rotation rate of the Earth; since the introduction of leap seconds into UTC (with the first on 1972 Jun 30), only positive leap seconds have been included which begin at 23 h 59 min 60 s UTC and end at 0 h 0 min 0 s UTC demarking the beginning of the next day; positive leap seconds since the beginning of GPS time have been inserted at the end of:
-
1981 Jun 30
1982 Jun 30
1983 Jun 30
1985 Jun 30
1987 Dec 31
1989 Dec 31
1990 Dec 31
1992 Jun 30
1993 Jun 30
1994 Jun 30
1995 Dec 31
1997 Jun 30
1998 Dec 31
2005 Dec 31
2008 Dec 31
2012 Jun 30
The leap second: its history and possible future, Nelson et al., Metrologia, 38, 509-529, 2001.
Articles discussing the lack of leap seconds between the end of 1998 and the end of 2005:
- Goddard Space Flight Center Top Story: Satellites reveal a mystery of large change in Earth's gravity field
- National Geographic News: Why is Earth's Girth Bulging?
LEO: "Low Earth Orbit"; any orbit with an orbital period of less than about two hours
log: documentation of a site description and/or a visit (see also form)
log file: electronic version of a log sheet, e.g. an on-line IGS site log
log sheet: a blank or filled-in log on paper
magnetic declination: offset between the direction of true geographic north and the local direction of magnetic north; see NOAA/NGDC's geomagnetic calculators:
- magnetic declination + rate
- 3-d magnetic field orientation + rate
- current field grid, 1 of 7 parameters
marker: if it exists, an identifiable and distinct component of a monument having a survey point, e.g. a USGS brass cap
media: or physical media; best explained by example: 9-track, QIC (1/4" cartridge tape), audio cassette tape, 3.5" or 5.25" floppy disk, 4mm DAT, 8mm data tape, 8mm video tape, optical disk, magneto-optical disk, PC-Card (PCMCIA), Zip disk, Jazz disk, CD-R, CD-ROM, hard disk, etc.
MEO: "Medium Earth Orbit"; any orbit with an orbital period of about two to sixteen hours
metadata: ancillary information required for the accurate processing of observation and navigation data to determine the position, velocity, and/or acceleration of a single or set of survey points; e.g. antenna phase center position relative to a survey point (if no horizontal offset, this is just the "antenna height"), antenna type, receiver type, approximate WGS-84 coordinates, etc.; most of the information in a RINEX file header is metadata
MJD: "modified Julian date"; see modified Julian date for definition
modified Julian date: an offset version of the Julian date obtained by subtracting 2400000.5 days from the Julian date; thus the start of GPS time (i.e. GPS standard epoch) 6.0 Jan 1980 is equivalent to a modified Julian date of 44244.0
monument: a physical object for which one is trying to collect data for a determination of position, velocity, and/or acceleration for one or more survey points on or very near that object. (In the case of a zero offset for the antenna, the survey point of measurement is the phase center(s) of the antenna, which may or may not actually correspond to a physical point on the object.) (see also lcode, marker, monument code, monument ID, monument name, monument setting, site)
monument code: a non-unique, case-insensitive, 4-character alphanumeric string to identify a specific survey point on a specific monument, e.g. "PEAK" = "peak"; also known as the 4-character ID of a survey point of a monument, obtained from the monument record form or something similar
monument ID: for the internal purposes of the UNAVCO Archive, a unique number specifying a specific survey point on a specific monument; if multiple survey points are used on a single monument, then multiple monument IDs would be assigned corresponding to each survey point used
monument name: a (hopefully) descriptive name for a particular monument; a 60-character version of which could be used in the RINEX Observation file for the non-optional MARKER NAME field
monument setting: a date stamp associated with a monument or a marker on a monument indicating either 1) when the monument was established, or if that time is not known 2) when the monument was first known to be used
Navstar: "Navigation Satellite Timing And Ranging"; the official name of the GPS satellites, e.g. see NASA SPACEWARN Bulletin No. 653 describing Navstar 62 launched in March 2008
network: an array of GNSS setups and/or stations operating at the same time for the purpose of collecting more or less continuous data over the extent of the array; the spatial extent of the array can be global or anything smaller
observable: any measurement between the space segment and the user segment of the GPS, GLONASS, Galileo or SBAS, e.g. receiver clock epoch time, and at the epoch: carrier-phase (L1 or L2) measurements, pseudorange or code (C/A, P1, or P2) measurements, doppler measurements of L1 or L2, signal-to-noise measurements, etc.
observation: a set of carrier-phase and/or pseudorange observables for an individual Navstar GPS, GLONASS, Galileo or SBAS SV for a specific epoch
occupation: a visit (depending on whether you prefer a militaristic or pacific term)
off-site: someplace other than the site
ordinal date: same as day-of-year
On-line Repository: dedicated electronic RAID storage of archived data files at the UNAVCO Boulder Facility Archive
OS SIS ICD: the unclassified "interface specification" document for the Galileo Open Service Signal-In-Space Interface Control Document; see:
- OS SIS ICD Issue 1 Revision 1 (1 Sept 2010) (PDF — 3 Mb)
PANGA: "Pacific Northwest Geodetic Array"; see also:
- PANGA, Central Washington University homepage
- University of Washington GPS Geodesy homepage, including PANGA
PBO: "Plate Boundary Observatory"; one of the main components of EarthScope, this is a set of surface (GPS permanent stations) and subsurface (strainmeters) to measure the crustal motion and deformation in the plate boundary between the North American and Pacific plates in the western USA and Alaska; see also EarthScope & PBO
permanent station: very long-term setup at a continous site; implies long-term power and possibly other infrastructure such as communication
permanent station data: data from one or more permanent stations
phase center: relative to the active antenna element and ground plane, where a specific carrier-phase frequency from GNSS SVs seem to be received; the phase center may be modeled as averaged over all possible directions, modeled as a function of elevation from the ground plane, or even modeled as a function of elevation and azimuth (see phase center pattern)
phase center pattern: the elevation and azimuthal offset of the effective phase center of the antenna; see also
- GPS antenna calibrations by the staff of the Instrumentation and Methodologies Branch, Geodetic Services Division, National Geodetic Survey, NOAA, Dept. of Commerce
- igs_01.pcv: IGS antenna phase center offsets and variations
Physical Repository: dedicated storage room(s) for physical media, log sheets, etc. at the UNAVCO Boulder Facility Archive, organized by group ID number
principal investigator: the big cheese/head honcho/primary cognizant entity associated with a project
PRN: "Pseudo-Random Noise" (or sometimes Number); an integer sequence number, 1-32, assigned to each of the Navstar GPS SVs to indicate its own unique C/A-code and its own unique P-code; this is the GPS SV number that is used in a RINEX observation or navigation file that is used to distinguish each satellite, e.g. PRNs for GPS, GBAS, and SBAS:
-
1 – 32 are used for the current constellation of GPS SVs
33 – 37 are reserved for other uses, such as ground transmitters
38 – 63 are reserved for future GPS SVs
64 – 119 are reserved for future GBAS amd other augmentation systems
120 – 158 are reserved for SBAS
159 – 210 are reserved for other GNSS applications
project: proposed or realized work in one or more of the following: site reconnaissance, monument installation (or monumentation), permanent station installation, campaign or permanent station data collection
PZ-90: "Parameters of the Earth 1990" (PZ-90 in Russian); formerly known as Soviet Geodetic System 1990 (SGS-90) and nearly identical to SGS-85; the ECEF spatial coordinate system used by GLONASS; the estimated transformation between SGS-85 and WGS-84 included a 4 meter offset of the z-axis and a 0.6" (3e-6 radian) rotation about the z-axis, whereas the transformation between PZ-90 and WGS-84 is only a 0.33" to 0.40" (1.6e-6 to 1.9e-6 radian) rotation about the z-axis, with perhaps a 2.5 meter offset of the y-axis; the system is defined as:
- the origin is the center of mass of the Earth
- z-axis is directed to the average North pole of the 1900-1905 epoch
- x-axis is in the equator plane of the 1900-1905 epoch, the XOZ plane being parallel to the average Greenwich meridian
- y-axis completes the system as a right-handed rectangular system
QZSS: "Quasi- Zenith Satellite System"; a specific spaceborne radionavigation system financed and operated by the Japan planned to consist of up to 18 geosynchronous satellites (mean height of approximately 35786 km above mean sea level but in a highly elliptical orbit, with an orbital period of 23h 56m 04.1s, or 1 orbit every sidereal day) using code-division multiple access with a right-hand circularly polarized carrier centered at L1 = 1575.42 MHz, L2 = 1227.60 MHz, L5 = 1176.45 MHz, and LEX = 1278.75 MHz; operational and proposed satellites of PRN 193 to 202 (with 203-210 as potential spares):
- L1-SAIF performance enhancement signal on 183-192, though 188-192 are used for QZS maintenance/test purposes and must not be used by users
- LEX performance enhancement signal on 193-202, though 198-202 are used for QZS maintenance/test purposes and must not be used by users
- other QZSS signals on 193-202, though 198-202 are used for QZS maintenance/test purposes and must not be used by users
- thus normal user PRNs for initial QZSS without L1-SAIF are 193-197
radome: see antenna dome
raw data: lowest-level, proprietary or non-proprietary data file(s) available from a GNSS receiver containing both data and metadata; e.g. Trimble's DAT, EPH, ION, and MES download files, AOA's ConanBinary or TurboBinary files, Ashtech's B-, E-, and S-download files, etc.; usually a majority of the data and metadata in a data file is in an encoded binary format.
raw file code: a non-unique, case-insensitive, 4-character alphanumeric string to identify a specific survey point on a specific monument, e.g. "PEAK" = "peak"; also known as the 4-character ID of a survey point of a monument, obtained from the raw data file itself (see also monument code and visit code)
real-time monitoring: continuous data is transferred near-real-time via one or more communication paths off-site for near-real-time data collection, quality checking, and/or processing; time delay should generally be no more than a few minutes
receiver: device used to decode the digital and analog components of the GNSS signal supplied by the antenna, as specified in part by the IS-GPS-200 for GPS, or the analog for GLONASS, Galileo or SBAS
reference point: a special case of a survey point usually used to locate a primary survey point or serve as a backup to a primary survey point especially in cases where the primary survey point has been lost or destroyed
RINEX: "Receiver Independent Exchange"; ASCII exchange representation of GNSS data and metadata currently conforming to the specification given in "RINEX: The Receiver Independent Exchange Format Version 2(.xx)" available from the Astronomical Institute, University of Berne (AIUB); one of several general file types:
- RINEX observation (OBS) file
- RINEX navigation (NAV) file (e.g. for GPS, GLONASS, and SBAS)
- RINEX meteorological (MET) file
- RINEX clock (CLK) file
- RINEX documentation listing at IGS Central Bureau
- RINEX Ver. 2(.00) (Apr 1993)
- RINEX Ver. 2.10 (10 Dec 2007)
- RINEX SBAS NAV Ver. 2.10 (19 Dec 2003)
- RINEX Ver. 2.11 (10 Dec 2007)
- RINEX Ver. 2.12 (22 Jun 2009)
- RINEX Ver. 3.00 (latest: 28 Nov 2007)
- RINEX Ver. 3.01 (22 Jun 2009)
- IONEX Ver. 1.00 (25 Feb 1998)
- Earth Rotation Parameters Ver. 2 (10 Jul 1998)
- Clock Ver. 3.00 (14 Nov 2006)
- Clock Ver. 3.02 (02 Sep 2010)
- IGS antenna and receiver designations for RINEX, available at JPL's IGS Central Bureau ftp site; these RINEX entries for receiver and antenna types are not part of the RINEX specification, but, rather, represent an effort by the IGS to standardize the ASCII strings used to describe various common receiver and antenna types and are widely accepted
RTCM: "Radio Technical Commission Maritime Services"; for example, RTCM Special Committee 104 (SC-104) recommends standards for differential GPS/GNSS data exchange
SBAS: "Satellite Based Agmentation System"; the component of a set of geostationary satellites (one orbital plane at 0° inclination, approximately 35786 km above mean sea level at the equator, with an orbital period of 23h 56m 04.1s, or 1 orbit every sidereal day) to augment GNSS use for civilian applications using code-division multiple access with a right-hand circularly polarized carrier centered at L1 = 1575.42 MHz and a (proposed) L5 = 1176.45 MHz; the operational and proposed satellites of PRN 120 to 138 include:
- WAAS (Wide-Area Augmentation System) for the USA and Canadian area
- CWAAS (Canadian WAAS)
- EGNOS (European Geostationary Navigation Overlay Service) a joint project of the European Space Agency (ESA), the European Commission (EC) and Eurocontrol, the European Organisation for the Safety of Air Navigation for the European area
- MSAS (MTSAT-Based Augmentation System) Japan MTSAT (Multi-functional Transport Satellite)
- GAGAN (Indian GPS And GEO Augmented Navigation)
- SNAS (Chinese Satellite Navigation and Augmentation Service)
| Inmarsat 3 F2, AOR-E | 15.33°W | PRN 120 | EGNOS |
| Inmarsat 3 F4, AOR-W | 53.98°W | PRN 122 | WAAS |
| ESA Artemis | 21.67°E | PRN 124 | EGNOS |
| Inmarsat 3 F5, IND-W | 25.06°E | PRN 126 | EGNOS |
| Inmarsat 4 F1 | 143.61°E | PRN 127 | GAGAN |
| Insat-NAV | (tbd) | PRN 128 | GAGAN |
| MTSAT-1R | 140.17°E | PRN 129 | MSAS |
| Inmarsat 3 F1, IOR | 65.5°E | PRN 131 | EGNOS |
| Inmarsat 3 F3, POR | 178.06°E | PRN 134 | WAAS |
| PanAmSat Galaxy XV | 132.87°W | PRN 135 | WAAS |
| MTSAT-2 | 144.75°E | PRN 137 | MSAS |
| Telesat Anik F1R | 107.17°W | PRN 138 | WAAS |
- SX Blue GPS: SBAS Resources
- GPS World: Innovation: The WAAS L65 Signal
- Satellite Based Augmentation System
- C-Nav LBand Communication Satellite Locator
SCEC: "Southern California Earthquake Center"; see also SCIGN and:
SCIGN: "Southern California Integrated GPS Network"; see also:
session: a pre-definable time during which a GNSS receiver will record observations according to some pre-defined parameters, such as sample interval or data format
semi-continuous site: a site with a continuous station that has significant data gaps by design, for example so that the equipment can be moved to another similar site
semi-continuous site data: data from one or more semi-continuous sites
setting: monument setting
setup: (not necessarily limited to): the antenna dome (if any), the antenna, antenna's LNA (low-noise amplifier), the choke ring (if any), tripod or other antenna support, antenna cable, in-line surge suppressor (if any), receiver, receiver firmware, (and any other item in the signal path) established around a monument for the purpose of collecting GNSS data; modification of anything (see the above items, or a change in antenna height) that could effect positioning results constitutes a new setup (see also station, visit)
sidereal day: time for the Earth to rotation 360° on its axis; 23h 56m 4.098904s, based on the WGS-84 angular velocity of Earth == 7.2921151467e-5 radians/second
signal: both the analog and binary components of the electromagnetic radiation emitted by either the Navstar GPS, GLONASS, Galileo, or SBAS space segments; the signal is centered at one or more microwave frequencies
SINEX: "Solution Independent Exchange": see specification for 2.00 (24 May 2002) and 2.01 (25 Mar 2005):
site: the general, immediate area around one or more monuments or where one or more monuments may be installed
-
A site is the top layer in a hierarchy (after monument installation):
a site has one or more monuments,
a monument has zero or more markers,
a marker has one or more survey points.
site description: the general description of a site, primarily to identify how to find the site from surrounding towns, roads, landmarks, etc.
smtp: "simple mail transfer protocol"; normal email transfer protocol
SOPAC: "Scripps Orbit and Permanent Array Center" of the Scripps Institution of Oceanography, University of California of San Deigo; see also:
SP3: "Standard Product 3" Orbit Format for GPS (also now known as SP3-a), an ASCII exchange format for representing GPS satellite orbits; see also
SP3-b: "Standard Product 3" Orbit Format for GPS and GLONASS, an ASCII exchange format for representing GPS and GLONASS satellite orbits
SP3-c: Extended "Standard Product 3" Orbit Format for GPS and GLONASS, an ASCII exchange format for representing GPS and GLONASS satellite orbits; see also
- Extended Standard Product 3 Orbit Format (SP3-c) (5 Sep 2002)
- IGSMail-5008 (7 Sep 2004) Some information on the error codes given in the SP3-c
station: a long-term setup; antenna support is usually more permanent than just a tripod; a station probably includes the setup plus power, communication, and/or other infrastructure
Setup and station imply two ends of the time spectrum. A setup is generally more short-term (on the order of hours to days) and a station is more long-term (on the order of months to years). On occasion, a setup (plus long-term power) is pushed into long-term use (many months), but it still does not have the permanence and survivability implied by the term "station".
survey point: a precisely definable location (down to millimeter or sub-millimeter levels) to which an antenna is located for the purpose of receiving GNSS signals; this may be a physical point such a dimple or cross-hair intersection on a marker, or may a virtual (non-physical) point (see also marker, monument, site)
survey mark: in our terminology the same as survey point
SV: "Space Vehicle", referring originally to a specific Navstar GPS satellite, but now used to refer to any one of the Navstar GPS, GLONASS, Galileo, or SBAS satellites
TEC: "total electron count" of the ionosphere, which dominates the ionospheric refraction
teqc: "translate, edit, and quality check" software, a UNAVCO Boulder Facility data/metadata toolkit; see also
TIA: "Temps Atomique International" or "International Atomic Time", based on the weighted average of a large number of atomic clocks, where since 1967 the second is defined as the period of time equal to 9192631770 cycles of the radiation corresponding to the transition between the two hyperfine energy levels of the ground state of the cesium-133 atom (Cs-133); available since 1955, but TIA was defined as being equal UT1 at the epoch 1.0 Jan 1958
TRANSIT: full name of Navy Navigation Satellite System (NNSS) TRANSIT, this was the immediate predecessor of the Navstar GPS system; a specific spaceborne radionavigation system financed and operated by the U.S. Department of Defense consisting of 6-10 satellites (3-5 providing navigation service and 3-5 acting as in-orbit spares) in near-circular LEO polar orbits approximately 1075 km above the Earth (orbital period of 1h 46m, or about 27 orbits every 2 sidereal days) transmitting phase modulated navigation signals at 0.150 and 0.400 GHz; any signals after 31 Dec 1996 should not be used for timing or position; used WGS-72 until 27 Jan 1989 as its ECEF spatial coordinate system, whereupon this was switched to WGS-84
UNAVCO: "University Navstar Consortium" up until 30 Sept 2003, after which UNAVCO is just a name (i.e. not an acronym) representing the non-profit membership-governed organization that supports and promotes Earth science by advancing high-precision geodetic and strain techniques and technologies such as the Global Positioning System; see also:
UNIX epoch: time base for UNIX operating systems, based on the number on non-leap seconds since 1.0 Jan 1970 UTC; many current systems store the UNIX time internally as a 4-byte 2's complement integer, so that the maximum number of seconds that can be dealt with is 2^31 - 1 = 2147483647, equivalent to 2038 Jan 19 03:14:07 -- though any potential problem with this end date will probably be dealt with long before it's reached (probably by switching to a 8-byte 2's complement integer)
Universal Time: see definitions for the various realizations: UT0, UT1, UT2, and UTC
UT0: Universal Time base defined as precise solar time at the zero meridian (Greenwich)
UT1: UT0 corrected for the Earth's polar motion
UT2: UT1 corrected for seasonal variations in the Earth's rotation rate
UTC: not an acronym, but "Coordinated Universal Time", a hydrid time scale defined where the rate of UTC is based on atomic frequency standards (currently using TIA) but the epoch of UTC is synchronized to be within ±0.9 sec of UT1; this synchronization was defined as UTC = TIA - 10 seconds on 1.0 Jan 1972, and further synchronized since then by the insertion of leap seconds; some of the various realizations of UTC being:
- UTC(USNO) — U.S. Naval Observatory (Washington D.C., USA)
- UTC(GPS) — GPS time automatically steered to UTC(USNO) on a daily basis to keep system time within ±1 microsecond of UTC(USNO)
- UTC(NIST) — National Institute of Standards and Technology (Boulder, Colorado, USA)
- UTC(NPL) — National Physical Laboratory (Middlesex, UK)
- UTC(PTB) — Physikalisch-Technische Bundesanstalt (Braunschweig, Germany)
- UTC(BIPM) — Bureau International des Poids et Mesures (Sèvres, France)
- UTC(SU) — (Vniftrii, Russia)
- UTC(CRL) — Communications Research Laboratory (Koganei/Tokyo, Japan)
- UTC(Europe Lab)
visit: also site visit; establishing a setup/station at a monument for the purpose of collecting data; the UNAVCO Data Group maintains a GPS site visit form to be filled out for each visit, the information on which corresponds to the visit table in the Archive Database; if something about a setup changes during data collection (for example a change of receiver, receiver firmware, antenna, antenna height, etc.), the earlier visit ends and a new visit begins at the time of the change (see also inspection, occupation)
visit code: a non-unique, case-insensitive, 4-character alphanumeric string to identify a specific survey point on a specific monument, e.g. "PEAK" = "peak"; also known as the 4-character ID of a survey point of a monument, usually the same as the monument code, obtained from the survey log — monument visit logsheet, monument record logsheet, or something similar
visit ID: for the purposes of the UNAVCO Archive, a unique number specifying a specific visit
WGS-72: "World Geodetic System 1972"; the spatial coordinate system used by GPS through 21 Jan 1987 (see also WGS-84) Some of the major constants in WGS-72, which models the Earth as an ellipsoid of revolution, are:
- semimajor axis (origin to equator on x-y plane) = 6378.135 km
- semiminor axis (origin to either pole) = 6356.7505 km
- flattening = 1/298.26
- angular velocity of Earth = 7.292115147e-5 radians/s
- G x mass of Earth = 3.986008e14 m**3/s**2
WGS-84: "World Geodetic System 1984"; the ECEF spatial coordinate system used by GPS since 22 Jan 1987 (see, for example, "Session 2: World Geodetic System 1984" pp. 67-134, in Proceedings of the Fourth International Geodetic Symposium on Satellite Positioning, Apr. 28 - May 2, 1986, Volume 1); defined in the IS-GPS-200 as:
- origin is the center of mass of the Earth
- z-axis is parallel to the direction of the Conventional International Origin (CIO) as defined by the Bureau International de'l Heure (BIH), and passes through instantaneous pole of epoch 1984.0
- x-axis is the intersection of the reference meridian plane and the plane of the mean astronomic equator, with the reference meridian being parallel to the zero meridian defined by the BIH
- y-axis completes the system as a right-handed rectangular system
- semimajor axis (origin to equator on x-y plane) = 6378.137 km
- semiminor axis (origin to either pole) = 6356.7523142 km
- flattening = 1/298.257223563
- angular velocity of Earth = 7.292115e-5 radians/s
- angular velocity of Earth (untruncated) = 7.2921151467e-5 radians/s
(for precise satellite applications) - G x mass of Earth = 3.986005e14 m**3/s**2
Comments or questions about this page? Send e-mail to Lou Estey (louunavco.org).
Last modified Tuesday, 08-May-2012 13:52:06 UTC