GPS Base Station Data Environmental Protection Agency

The US Environmentatal Protection Agency - Edison, New Jersey office operates a Trimble Pathfinder Community Base Station and is making the collected GPS base files freely available. The station is located at our Edison, New Jersey facility. The station produces base files in hourly blocks between 7:00 am and 8:00 pm daily, seven days per week. The base files are stored as executables (.exe) and when uncompressed are in Trimble's ssf format. The GPS receiver used to collect the Base Station files is a 12-Channel TRIMBLE PRO XR (with Maxwell chip). The antenna used is a compact L1 with ground plane.

EPA's Base Station Antenna's Location (updated on October 28, 2003):
Latitude 40° 30' 43.93991"
Longitude 74° 21' 34.24050" W
Elevation 2.681 meters HAE
Base Station elevation mask is set to 10
Tracking epoch (sec.): Position at 5 seconds; SYNC measure at 5 seconds
The above location is referenced to the NAD83 (1996) horizontal geodetic datum and is accurate to within a few centimeters. New hourly base files should be available for download fifteen minutes after the close of the hour. However, hourly Base Station files that are collected after 6:00 pm will not be available until 8:15 am the following morning, and Base Station files collected after Friday at 6:00 pm, will not be available for downloading until 8:15 am on Monday.

The File Format
The base stations files are formated as follows:
EYMMDDHH.EXE - is an individual correction file for a one hour period, where;
E = Base Station ID (E is for the EPA at Edison, NJ)
Y = the last digit of the current year
MM = the month
HH = the hour in GMT (Greenwich Mean Time) time.
EXE = files are compressed and self-extracting. File length is one hour.
Example file: E2091113.exe (the file for September 11, 2002, from 13:00 to 13:59:59 in GMT)

The GPS Base Station data is kept for 1 month before being removed from data storage. Previous Base Station data can be obtained from the EPA Regional GPS Coordinator.

October 28, 2003 Update
On October 28, 2003, a 12-Channel TRIMBLE PRO XR receiver was installed at the Edison, New Jersey site, in order to replace the old TRIMBLE PRO XL receiver. In addition, the location of the Base Station antenna was re-surveyed on October 16, 2003. These steps are expected to meaningfully improve the accuracy of the Base Station data. The updated location (see above) is referenced to the High Accuracy Reference Network (HARN). The Base Station antenna was also referenced to the Continuously Operating Reference Stations (CORS), which is operated by the National Geodetic Survey (NGS). The location of the antenna in the CORS reference network is:

Latitude 40° 30' 43.93975" N
Longitude 74° 21' 34.23988" W
Elevation 2.688 meters HAE

The difference between the updated HARN location, and the CORS location is 15 millimeters (1.5 centimeters) in distance, and 7 millimeters (0.7 centimeters) in height.

If you have questions, want to give feedback, or report problems, call the the US EPA Regional GPS Coordinator (Towana Joseph) at (732) 321-6607, or email at joseph.towana@epa.gov.

Disclaimer: The EPA provides this GPS base data as a convenience for users of GPS. No responsibility is assumed for damages or other expenses due to the use or misuse of this data.

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