As coalition forces faced the daunting task of helping Iraq rebuild its roads, bridges, pipelines, and other infrastructure, they were met with a unique challenge – Iraq had no established, consistent system to measure distances, pinpoint locations on maps, or determine elevations. Imagine building a bridge across a river without exact measurements to tell you where the two sections of the bridge should meet in the middle, and you’ll get a sense of the obstacles facing a successful Iraqi reconstruction. To meet this challenge, the National Geodetic Survey (NGS), an office of NOAA’s National Ocean Service, has collaborated with the U.S. Army to build the Iraqi Geospatial Reference System.
The Global Positioning System (GPS) includes a constellation of satellites that transmit radio signals, allowing us to compute positional coordinates anywhere on or above the surface of the Earth. While GPS does allow us to determine our position, a single GPS receiver alone is not accurate or reliable enough to yield precise measurements. To obtain the exact location of a point with an accuracy of a few centimeters requires at least two GPS receivers: one receiver whose exact location is already known and one receiver at the site in question. The receiver with known coordinates becomes a reference point for pinpointing the unknown location. Several “known” receivers, consistently and accurately installed and maintained, can link together to form a spatial reference system.
In the United States, NGS manages the National Spatial Reference System – a consistent coordinate system that defines position (latitude and longitude), elevation, distance and direction between points, and how these values change over time. At the backbone of the National Spatial Reference System is a network of more than 850 Continuously Operating Reference Stations (CORS). Managed by NGS in collaboration with over 155 partnering organizations, each station sits at a known, precise location and receives GPS radio signals 24 hours a day, seven days a week.
Information collected through the CORS network is processed by NGS and made available to surveyors, engineers, scientists, and others around the world. CORS data are essential for ensuring the reliability of transportation and communication systems, boundary and property surveys, land record systems, mapping and charting, and many scientific and engineering applications. In the U.S., we rely on an accurate spatial reference system everyday – it is a critical component of our national infrastructure.
When coalition forces arrived in Iraq, they found that Iraq had no established spatial reference system. Without such a system, reconstruction efforts in the war-torn country would be extremely difficult. So, the U.S. Army contacted experts from NGS to develop a framework reference system for Iraq modeled after the National Spatial Reference System. At the request of the Army, NGS developed a plan to comprehensively and effectively build such a system in Iraq.
The foundation of the designed Iraqi Geospatial Reference System (IGRS) is six GPS CORS sites, spread geographically throughout the country.
Each CORS site consists of a GPS receiver that has a permanently mounted antenna. Position and time data are logged 24 hours a day, seven days a week. Solar panels and large batteries power the stations and ensure that the receivers never fail. Data collected at each station are sent to NGS for analysis and publication. Data are also transferred to a global network of reference stations formed by the voluntary cooperation of agencies around the world.
Because each CORS site becomes a reference point from which distances and elevations are measured, it is important that each station is established to an exact horizontal and vertical position, defined by latitude, longitude, and height coordinates.
To provide the most accurate GPS information available, NGS has developed rigorous standards for installation and maintenance of each CORS. Following the same standards for each station helps to ensure a consistent, reliable, and cohesive network of sites that delivers precise measurements. These standards help to minimize GPS signal distortion and maximize the quality of calculated positions, in accordance with computer models used to process GPS data. This allows users to obtain centimeter to sub-centimeter accuracy. CORS standards cover factors such as location and stability of the GPS-receiving antenna and methods for transmitting and computing GPS data.
When the Army officials initially contacted NGS, they’d had no prior experience in establishing CORS sites. Further illustrating the power of technology, email allowed the NGS CORS project team to remotely (from the U.S.) guide the Army in installing each station. NGS guidance and expertise allowed the Army to follow the proper installation standards and procedures, ensuring the integrity of the IGRS within Iraq and relative to CORS sites around the world.
Currently, all six Iraqi CORS sites are fully operational and are amongst the most stable stations NGS has seen. Scientists at NGS continue to monitor and maintain the stations from the U.S. Data collected from these stations are helping coalition and Iraqi engineers to rebuild large portions of the Iraqi infrastructure, are aiding in military operations and protecting U.S. and coalition troops, and are filling a vital hole in the international spatial reference system.
The Army is continuing to work with coalition teams and Iraqi engineers to create a robust IGRS. To supplement the established CORS network, the Army is installing a nationwide High Accuracy Reference Network (HARN) of permanently mounted survey marks, which consist of steel rods driven into the hard Iraqi ground. The HARN is modeled after the network of permanent benchmarks the covers the U.S. and has its origins from NOAA’s ancestral organization, the Survey of the Coast. Installation of the full IGRS is expected to be completed in June, 2006. While the U.S. Army and NGS continue to maintain the CORS network, eventually, the goal is to train Iraqi engineers to maintain the stations.
According the U.S. Army, “[b]y using IGRS as a model to create similar programs…the army could effectively package what NGS developed as a successful multi-nation technical assistance program into a military reconstruction effort, [allowing] nations emerging from conflict to face the daunting task of rebuilding large portions of their infrastructure” (The American Surveyor, November, 2005).
- In the U.S. alone there are over 800 stations within the CORS system. Ninety percent of the CORS network was not built by NOAA – 158 organizations currently contribute to the network.
- The CORS program is an investment yielding high returns: While the estimated value of the program to the U.S. is $150 million per year, NGS spends only $2.5 million a year on the program.
- CORS data are available to anyone, anywhere – free of charge – via the Internet at: http://www.ngs.noaa.gov/CORS/.
- NGS provides a Web-based utility, called the Online Positioning User Service (OPUS), which allows users to submit their GPS data to be processed to determine the positional coordinates associated with the submitted data. Each submitted data file is processed with respect to three CORS sites using NGS computers and software. Within minutes, the computed coordinates are emailed to the user.
Article from Eric.Linzey and Emily Crum of NOAA.