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Development & Testing - L1 Receiver
Overview
The relatively high cost of dual-frequency receivers and installations (~$15,000-$25,000) makes it too expensive to deploy small dense GPS networks
needed to investigate volcanoes, individual fault zones, landslides, fluid reservoirs, glaciers, and atmospheric measurements such as volcanic plumes,
and severe storm prediction.
L1 is a low cost single frequency GPS receiver system which can be deployed in dense arrays to monitor small scale crustal deformations and to
provide data for tomographic estimation of three-dimensional atmospheric water vapor fields. The system design combines a commercial class of
inexpensive single-frequency L1 GPS carrier phase sensors with a Time Delay Multiple Access (TDMA) radio modem network. The data is continuously
sent to a central collection and processing site from typically up to 25 remote receivers per single base station. There are currently networks
of systems in Hawaii, the Philippines, California, Mexico, and Oklahoma.
The monument design, shown above at the UNAVCO Facility, is a 2 3/8" galvanized water pipe cemented into a borehole drilled into the rock. The solar
panel support contains a regulator as well as the radio modem/GPS receiver package. The GPS antenna is mounted on a fiberglass rod and the radio
whip antenna is mounted on the pipe below it. The height of the GPS antenna is about 2 meters above the ground.
Each L1 network is specific to it's
surroundings and functionality, and where possible, as many example as possible will be provided.
Monumentation
UNAVCO's monumentation specification table
characterizes various monuments including information on multipath, physical attributes, and approximate costs.
Specific Examples
L1 Volcano Monitoring Monument in Rock, Hawaii
L1 Volcano Monitoring Monument in Soil, Hawaii
L1 Weather Monument, Oklahoma
L1 Volcano Monitoring Monument - Popocatepetl Volcano, Mexico
1. Monument Only
2. Monument with solar panel
Other Resources
UNAVCO's Monumentation Diagrams
Other resources for monumentation
Antenna Mounts
3 Examples to Illustrate an L1 network
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Figure 1: Figure 1 illustrates a simple example of a TDMA network with 4 slave modems that have a direct line of sight with the master modem. The data is then transferred directly from the master modem to a data logging computer. |
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Figure 2: This next example illustrates having a base station in order to relay the data to a data logging computer that can not be set up close to the slaves, for example on a volcano. There are still 4 slave radio modems that have a direct line of sight with the master TDMA
radio modem. The 4 slave radio modems transmit their data to the master TDMA
modem, and the master TDMA modem then transmits it's data to a Point-to-Point slave radio modem, this makes up the base station. From the Point-to-Point
slave radio modem, the data then gets transmitted to a Point-to-Point master radio modem which then transmits the data to the data logging computer.
Base stations are primarily used when it is impossible to have the data logging computer close to the slave radio modems.
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Figure 3: This next example illustrates an L1 network that has slave repeaters in it. A slave repeater is used when there is some obstruction and one or more of the slave radio modems does not have a direct line of sight with the master TDMA radio modem. As you can see in the diagram, there are 2 radio modems that cannot see the master. Therefore, they must send their data to a slave radio (line of sight), and that slave radio must repeat the other slave radio's data, as well as it's own. Again the data gets transmitted to the master TDMA radio modem, on to the Point-to-Point slave,
which then gets transmitted to the Point-to-Point master and then the data logging computer. A good example of where to use repeaters is again on a volcano where sometimes line of sight is not always possible with every radio modem. |
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Ongoing Project Pages
The link below will take you to the Popocatepetl permanent station page. Popo is an L1 network of 5 L1 receivers on a volcano in Mexico. This network will be upgraded and expanded by February 2001.
POPO L1
The link below will take you to the Hawaii L1 page. Hawaii L1 is a network of 12 L1 receivers on a volcano in Hawaii. This network will be upgraded and expanded by late February 2001.
Hawaii L1
The link below will take you to the Dive project page which is a Sea-Level monitoring network of L1 receivers.
Dive L1
Budget
Approximate cost for a remote site consisting of: receiver/radio modem enclosure, solar panel, GPS antenna, battery, radio communications antenna, and
miscellaneous wires and connectors is equal to $4,600.
Approximate cost for a base station consisting of: download and data logging computer, radio modems, antenna cables, miscellaneous wires and
connectors is equal to $6,800.
Software
The download and data logging computer uses a java application which manages the data flow and demultiplexes the data stream into individual binary data
files from each remote station. Each GPS data packet from a remote unit is identified by it's TDMA address. The CMC binary format data are then translated
using UNAVCO's TEQC software. The java application also performs error reporting and system control.
Please contact Victoria Andreatta (victoria unavco.org) if you are looking for the document that explains how to configure the receivers.
Send questions or comments about this page to Support (supportunavco.org)
Last modified Tuesday, 14-Feb-2006 01:09:15 UTC
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