Precise Ephemeris Orbit Determination Process Notice!!!


Starting on February 16, 2014, the NGA will switch to the IERS Technical Note 36/IERS Conventions (2010) (TN36) for all tidal corrections, ocean loading, and tropospheric corrections with Global Mapping Function for its GPS orbit and clock estimates. These changes should not visibly affect either the output of our orbits/clocks or the subsequent Precise Point Positioning which uses them. Instead, they are another step in NGA's effects to conform to the latest geophysical models, constants and procedures used in the Earth sciences embodied in the IERS Conventions.

This update follows the October 16, 2013 release of the NGA and USAF GPS tracking site coordinates which aligned the WGS 84 reference frame to the ITRF2008(IGb08).

The final installments, CIO based tidal variation in the Earth's rotation and GNSS antenna phase variation calibrations, have larger and more obvious effects with NGA's end users and are awaiting coordinating efforts before implementation. If there are any questions regarding this issue, please contact NGA’s Office of Geomatics at the contact information below.

The Earth Orientation portion of the Orbit Determination process will remain in the IERS Technical Note 21/IERS Conventions (1996) (TN21) at this time. This is covered in TN21/Chapter 8. We will be transitioning to the Earth Orientation portion of TN36/Chapter 8 at a later date.

We will also transition to a 32-bit file compression/extraction algorithm (originally from a 16-bit) for our data storage.

Any questions, please use the contact information below.


Point of Contact: GPS Division
Phone Numbers:
  Com. (314)676-9140/676-9142
  DSN 846-9140/846-9142

Document last modified 02/18/2014Tuesday, 18-Feb-2014 12:50:18 EST