Extending the GPS IIIA antenna calibration for precise orbit determination of low Earth orbit satellites

Abstract

High-precision applications of GNSS require accurate calibrations to correct for phase variations of the transmitting antennas. Calibrations distributed by the International GNSS Service (IGS), based upon observations from the global network of ground stations, are often used as the source of the transmitter calibrations as they are inherently linked to a specific definition of the International Terrestrial Reference Frame. The IGS provides antenna phase variations as a function of boresight angle for each basic block of navigation satellite. To support scientific missions operating in low Earth orbit, the antenna calibrations must be extended beyond the 14-degrees limit that can be observed by GNSS receivers on the Earth. Extended antenna calibrations to accommodate low Earth orbiting satellites have already been derived for the GPS Block II satellites. This paper derives an extension solution for the new GPS IIIA antenna calibration, based on a year of observations from the Sentinel-6 Michael Freilich altimetry mission and validated using Jason-3. These solutions are inherently consistent with the IGS-provided models of the Block II antenna calibrations. We use the new model for the GPS IIIA transmitter antenna calibration extensions to evaluate the impact on precise orbit solutions of both Sentinel-6 MF and Jason-3.

GNSS visibility and performance implications for the GENESIS mission

“…For the Earth coverage zone, GNSS transmit phase patterns are generally flat with peak variations of less than 10 mm relative to the mean phase center. Comparisons with estimated phase patterns from terrestrial receiver networks and selected LEO missions (Dilssner et al 2016;Conrad et al 2023;Dilssner et al 2023) show consistency at the oneto few-millimeter level with the Lockheed Martin antenna calibrations after adjustment of the individual phase center contributions. For 14 • ≤ θ ≤ 17 • , the lack of adequate LEO antenna patterns has resulted in IGS-specific, relative extensions of the GPS transmit antenna phase patterns (Jäggi et al 2010) that are not, however, representative of the absolute patterns and exhibit deviations of up to 15 mm from the factory calibrations in this region.…”