NOAA Improves GPS Accuracy

Image showing CORS Web site.

High resolution (Credit: NOAA)

Did you know that Mt. McKinley in Alaska is still growing at a rate of about 1 millimeter per year due to continuous tectonic pressure? Or that Louisiana is losing up to 40 square miles of wetlands per year?

To help scientists and others monitor our ever changing planet, NOAA manages a network of advanced GPS receivers know as Continuously Operating GPS Reference Stations (CORS) that helps them obtain highly accurate positioning information.

These receivers help monitor even the minutest changes in the horizontal and vertical movement of the land across the U.S. and collect data that are used for a variety of other purposes. Knowing these changes enables scientists, engineers, land surveyors, and others to track subtle changes to the Earth’s surface — down to sub-centimeter levels.

Continuously Operating Reference Stations (CORS) station.

High resolution (Credit: NOAA)

“In the past, it was believed that geodetic markers — brass discs in the ground — could be used to permanently mark the vertical and horizontal location of any given point on land. Today, scientists realize that the Earth is dynamic — its surface moves both vertically and horizontally over time. This can potentially make geodetic markers position less accurate over time,” said Casey Brennan, program analyst at NOAA’s National Geodetic Survey. “Today, everyone can buy a GPS, but most of the common GPS units are only accurate to within a few meters.”

This level of accuracy may be fine if you’re hiking in the woods or driving a car, but there are many scientific, military, and engineering activities that require much more accurate positioning — fortunately CORS can help.

The Continuously Operating Reference Stations (CORS) system is a network of stations throughout the United States and its territories that continually record GPS signals, and then provide the data to GPS users over the Internet.

High resolution (Credit: NOAA)

What Makes CORS Different?

CORS enables NOAA and others to monitor the smallest changes in the Earth environment because it provides significantly more accurate vertical and horizontal positions than could ever be obtained from a single GPS unit or geodetic markers.

“Think of CORS as a network of very advanced GPS units that are permanently installed throughout the nation,” said Brennan. “Because there are so many of them and they collect data all the time, they provide much more accurate information for a variety of uses. For example, we can monitor subsidence, which is when the Earth’s crust sinks, like what is happening in many parts of coastal Louisiana. We also can monitor crustal movement and plate tectonics, create accurate storm surge models, and even improve our coastal habitat restoration efforts.”

NOAA even uses CORS data to monitor the quantity of water vapor in the atmosphere. This information helps meteorologists to better forecast the amount of precipitation associated with storms. GPS signals also can be used to map the total electron count in the ionosphere, enabling atmospheric scientists to better forecast the affects of space weather on power grids and telecommunications.

NOAA's Online Positioning Users Service (OPUS).

High resolution (Credit: NOAA)

How Can You Benefit from CORS?

If you have a GPS, you can get a more accurate, adjusted GPS reading using CORS. Just send your data to NGS’s On-line Positioning User Service (OPUS) via the Internet, where it is cross-referenced against three nearby national CORS sites. This improves data accuracy by taking out many of the errors inherent in GPS positioning such as signal distortion, clock errors, and satellite location information. NGS computers process the data, and then users receive an improved position (or “solution”) via e-mail usually within minutes.

The service is free, and CORS data is available to anyone via the Internet. To learn more about NOAA’s National Geodetic Survey and CORS, visit the Web site at http://www.ngs.noaa.gov. NOAA logo.