Use this link NGS GPS Antenna Calibrations and then scroll down on the page.

* Select the "Complete" Relative Antenna Calibration Results link under Antenna Calibration Resources.

* Right-click on the "Complete Relative Antenna Calibration File" link and save it to your hard disk.

* Open up SKI-Pro and go to the Antenna Management page. Right-click in either the Contents area or the Antenna list area and select "Import Antenna File...".

* Locate, select and import the file. It is typically named Ant_info.003.txt.

This happens when the antenna name in the RINEX observation file is not exactly the same as the name in the SKI-Pro database. To fix it, perform the following steps:

* Go to the View/Edit page in SKI-Pro and delete the observation for the CORS site.

* Delete the antenna from the project in the Antennas page.

* Delete this antenna from the SKI-Pro database. (SKI-Pro adds it as a new antenna with the zero offsets.)

* Edit the antenna name in the RINEX observation file so that is exactly the same as the name in the SKI-Pro database. (This includes number of spaces between the antenna number and a modifier such as SNOW or DOME.)

* Re-import the RINEX data into the project.

* Verify that the project antenna has the proper phase center offsets.

Note: It is easiest to verify the antenna name, and correct it if necessary, prior to importing the RINEX file the first time.

Some of the CORS sites, especially scientific sites that are not part of the NGS CORS network, use ITRF (International Terrestrial Reference Frame) positions and not NAD 83 positions. This is especially prevalent in Southern California where many scientific sites exist to monitor plate tectonics.

Always use the NAD 83 position for your CORS site if it has one. If it doesn't you will have to convert the ITRF positions to NAD 83. NGS lists both ITRF 97 and NAD 83 positions for its CORS stations. Use the NAD 83 position for the ARP (Antenna Reference Point).

Note: You can use the HTDP part of the NGS Geodetic Tools to convert from ITRF to NAD83. http://www.ngs.noaa.gov/TOOLS.

The ARP (Antenna Reference Position) position is the position of the part of the antenna from which the phase center offsets are calculated. This is the position that should be used to properly apply the phase center offsets in the processing.

If you do not have phase center information for the antenna and the offsets are set to zero, then you should use the L1 phase center position. However, you will get the best results by using the ARP and the phase center offsets. (See CORS FAQ #1 for information on how to obtain phase center offsets for most antennas.)