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GPS
Differential Corrections and GPS Basestations

Attention!

The inland portion of the Nationwide Differential Global Positioning Service (NDGPS) is in danger of being shut down. This not only will affect real-time differential operations but many parks ability to acquire high-quality, reliable GPS post-processing differential data. Select the appropriate area below to see if your park potentially will be impacted.

Northeast / Northwest / Midwest / Southeast / Southwest / Alaska

Existing Real-time NDGPS Coverage
Potential FY09 Coverage

How to submit your comments electronically to DOT-RITA concerning NDGPS decommissioning:
1) Go to Regulations.gov site http://www.regulations.gov/fdmspublic/component/main
2) Click on Search for Dockets. In the Docket ID field enter this number: 28836 and press submit.
3) Click on RITA-2007-28836. The next page will list all the comments to date on this issue.
4) On the first page of comments, row 1 is the Federal Register. Look to the far right and click on the yellow balloon in the Add Comments Column.



GPS Basestations in the U. S.

GPS basestations are used for differential corrections of field collected GPS data. Differential corrections are achieved by utilization of two GPS receivers, one collecting data on a known geodetic point (basestation) and one (rover) collecting project remote positioning data. The two resulting files are mathematically compared in a computer program and most of the errors are removed. Basestations must be placed on accurately surveyed positions or monuments. There is a network of horizontal and vertical monuments with varing survey accuracies throughout the U.S. that can be used for GPS basestation operations. They are administered and maintained by the National Geodetic Survey (NGS).


Ways to Acquire Differential Corrections

1) Set up your own basestation... More>>
2) Use "realtime" GPS broadcasts... More>>
3) Use a network of basestations operated by a variety of private and government entities... More>>