GPS User Information
Rapid and ultra-rapid products:
USNO is an analysis center of the International GNSS Service (IGS). The “rapid” and “ultra-rapid” products provided by this website are identical to those submitted by USNO to the IGS for use in the IGS combined rapid and ultra-rapid products. The formats of the orbit (.sp3), clock (.clk) and earth-orientation-parameter (.erp) files follow the IGS standard format described here – see “sp3 version c,” “erp” and “clock RINEX”
As of December 2008, USNO products agree with IGS combined rapid estimates approximately as follows:
“Rapid” orbits: 30 mm
“Ultra-rapid” orbits, past 24 h: 22 mm
“Ultra-rapid” orbits, first 6 h of prediction: 45 mm
“Rapid” polar motion: 90·10-6 arc sec
“Ultra-rapid” polar motion, past 24 h: 220·10-6 arc sec
“Ultra-rapid” polar motion, 24-h prediction: 340·10-6 arc sec
To learn more about the IGS, visit the IGS website
UTGPS estimates:
UTGPS is a GPS-based UT1-like quantity used for extrapolating UT1-UTC past the most recent VLBI measurement. Computed by combining orbit integration with GPS-derived earth-orientation parameter estimates, its theory is explained in: P. Kammeyer, Celestial Mechanics and Dynamical Astronomy, 77: 241-72, 2000.