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Data - GNSS & Archive Glossary
An evolving glossary of terms (continually under development ...)

If you don't find the term you need explained, send us (archiveunavco.org) a request.

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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:
  • GPS antenna calibrations by the staff of the Instrumentation and Methodologies Branch, Geodetic Services Division, National Geodetic Survey, NOAA, Dept. of Commerce
for more information

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 GAGE 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 GAGE Facility Archive, which roughly are:
  1. 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;
  2. 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;
  3. the visit metadata is extracted from the logs and entered into the Archive Database;
  4. 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
although the exact steps vary on a case by case basis

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 plus the 14 seconds inserted into UTC between the start of GPST, 6.0 Jan 1980 UTC, and the start of BDT, 1.0 Jan 2006 UTC

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 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 UTC
(see Encyclopedia Astronautica: Beidou)

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, the range code numbers being:
    1-5 for GEO
    6-37 for MEO/IGSO
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
Phase III:
    B1/L1 = 1575.42 MHz
    B3/E6 = 1268.52 MHz
    B2/E5b = 1191.795 MHz
Beidou-2 will use BDT (Compass/Beidou Time) as the time standard and CGCS2000 as the spatial reference frame. Originally planned as a purely military system, China announced on 2 Nov 2006 that in 2008 a free open service would allow civilian use with position accuracy of 10 meters, clock synchronization to an accuracy of 50 ns, and speeds to within 0.2 m/s. Launches to populate the MEO portion have been (all dates UTC):
    Beidou DW1 (M1) on 13 Apr 2007
    Beidou DW12 (M3) and and DW13 (M4) on 29 Apr 2012
    Beidou DW14 (M5) and DW15 (M6) on 18 Sep 2012
Launches to populate the GEO and IGSO portions have been (all dates UTC):
    Beidou DW2 (GEO2) on 14 Apr 2009
    Beidou DW3 (GEO1) on 16 Jan 2010
    Beidou DW4 (GEO3) on 2 Jun 2010
    Beidou DW5 (IGSO1) on 31 Jul 2010
    Beidou DW6 (GEO4) on 31 Oct 2010
    Beidou DW7 (IGSO2) on 17 Dec 2010
    Beidou DW8 (IGSO3) on 9 Apr 2011
    Beidou DW9 (IGSO4) on 26 Jul 2011
    Beidou DW10 (IGSO5) on 1 Dec 2011
    Beidou DW11 (GEO5) on 24 Feb 2012
    Beidou DW16 (GEO6) on 25 Oct 2012
Version 1 of the Beidou ICD was released Dec 2012: (English version) BeiDou Navigation Satellite System Signal In Space Interface Control Document, Open Service Signal B1I, Version 1.0 BDS-SIS-ICD-B1I-1.0; an earlier test version of the Beidou ICD was released 27 Dec 2011: (English version) BeiDou Navigation Satellite System Signal In Space Interface Control Document (Test Version) BeiDou-SIS-ICD-Test; see also

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:)
  1. 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";
  2. 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.);
  3. any output from a GNSS receiver, especially raw data;
  4. 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 GAGE 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 GAGE 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:
  • LAAS (Local Area Augmentation System)
see also:

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 GAGE 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: and text documentation:

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

IRNSS: "Indian Regional Navigation Satellite System"; a specific spaceborne radionavigation system developed by the Indian Space Research Organisation (ISRO) planned to expand to seven satellites, four in 29° inclined geosynchronous orbits centered in pairs at 55°E and 111°E and three in geostationary orbit at 34°E, 83°E, and 132°E with an expected accuracy for positioning of 10 meters or better in the Indian subcontinent and 20 meters or better in the Indian Ocean, probably using code-division multiple access with a right-hand circularly polarized L-band carrier centered at L5 = 1176.45 MHz and an S-band carrier centered at S1 = 2492.028 MHz; 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:
and 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:

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
so, between 1.0 Jan 1999 UTC and 1.0 Jan 2006 UTC, GPS - 13 seconds = UTC; between 1.0 Jan 2006 UTC and 1.0 Jan 2009 UTC, GPS - 14 seconds = UTC; between 1.0 Jan 2009 UTC and 1.0 Jul 2012 UTC, GPS - 15 seconds = UTC; and as of 1.0 Jul 2012 UTC (and before the next leap second is inserted), GPS - 16 seconds = UTC. See NIST Time Scale Data Archive for the latest leap second listing (updated monthly); see USNO EO Database Search to obtain a daily listing of UT1-UTC (observed and/or predicted); see also USNO leap second page for more background. Note: A positive leap second was inserted at the end of June 2012.

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 GAGE 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
  • 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 GAGE 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
(see also WGS-84, ITRF)

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
The public user interface is defined in the IS-QZSS: Quasi-Zenith Satellite System Navigation Service: Interface Specification for QZSS.

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
also see documentation: and related: and see
  • 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 142 include:
  • 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
  • GAGAN (GPS And GEO Augmented Navigation) — India
  • MSAS (MTSAT-Based Augmentation System) — Japan MTSAT (Multi-functional Transport Satellite)
  • SDCM (System for Differential Correction and Monitoring) — Russia
  • SNAS (Satellite Navigation and Augmentation Service) — China
  • WAAS (Wide-Area Augmentation System) — USA, for the USA and Canadian area
where the current operational or proposed satellites are (ordered by PRN):

Inmarsat 3 F2, AOR-E 15.5°W PRN 120 EGNOS
ESA Artemis 21.5°E PRN 124 EGNOS
Luch-5B 16.0°W PRN 125 SDCM
Inmarsat 3 F5, IND-W 25.0°E PRN 126 EGNOS
GSAT-8 55.0°E PRN 127 GAGAN
GSAT-10 83.0°E PRN 128 GAGAN
MTSAT-1R 140.0°E PRN 129 MSAS
Inmarsat 4 F3 98.0 PRN 133 WAAS
PanAmSat Galaxy XV 133.0°W PRN 135 WAAS
Sirius-5 SES-5 5.0°E PRN 136 EGNOS
MTSAT-2 145.0°E PRN 137 MSAS
Telesat Anik F1R 107.3°W PRN 138 WAAS
Luch-5V 95.0°E PRN 140 SDCM
Luch-5A 167.0°E PRN 141 SDCM
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
    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.
If a physical marker is not part of a particular monument, that monument still must have at least one identifiable survey point. The equipment to collect GNSS data at a particular survey point is either a setup or a station.

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 GAGE 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: and see listings of the delta between standardized UTC and various realizations

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
Some of the major constants in WGS-84, which models the Earth as an ellipsoid of revolution, are:
  • 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
(see also ITRF, PZ-90)

Comments or questions about this page? Send e-mail to Lou Estey (louunavco.org).

Last modified Friday, 28-Mar-2014 13:32:46 UTC