NGA Banner

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 efforts 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 has also switched to the IERS Technical Note 36/IERS Conventions (2010) (TN36) at this time. This is covered in TN36/Chapter 8. The Orbit Determination process uses the Gross zonal tide model along with the Oceans diurnal/semidiurnal model. At present, we restore a 41 Gross zonal tide model. We transitioned to the full 62 Gross zonal tide model on 14 June 2016.

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: NGA Public Affairs
Phone Numbers:
  Com. (571)557-5400
  DSN 846-9140

Document last modified