Tracking and orbit determination performance of the GRAS instrument on MetOp-A

Abstract

The global navigation satellite system receiver for atmospheric sounding (GRAS) on MetOp-A is the first European GPS receiver providing dual-frequency navigation and occultation measurements from a spaceborne platform on a routine basis. The receiver is based on ESA's AGGA-2 correlator chip, which implements a high-quality tracking scheme for semi-codeless P(Y) code tracking on the L1 and L2 frequency. Data collected with the zenith antenna on MetOp-A have been used to perform an inflight characterization of the GRAS instrument with focus on the tracking and navigation performance. Besides an assessment of the receiver noise and systematic measurement errors, the study addresses the precise orbit determination accuracy achievable with the GRAS receiver. A consistency on the 5 cm level is demonstrated for reduced dynamics orbit solutions computed independently by four different agencies and software packages. With purely kinematic solutions, 10 cm accuracy is obtained. As a part of the analysis, an empirical antenna offset correction and preliminary phase center correction map are derived, which notably reduce the carrier phase residuals and improve the consistency of kinematic orbit determination results.

GPS-derived orbits for the GOCE satellite

“…It has to be emphasized that the low latency solutions are optimized for the quick delivery and not for the best possible result with the involved software packages. As shown by Montenbruck et al (2008), the orbits from DEOS are at the same level of accuracy as the AIUB solutions when the same input data are used and the same requirements are met on both sides. Figure 12 shows the 3D RMS values for the differences between the RD orbits (Fig 12a, mean offset: radial −1.22 cm, along-track 0.39 cm, cross-track 2.43 cm) and between the KIN orbits (Fig 12b, 0.24, 0.04, 6.37 cm).…”

“…The POD strategy is based on an undifferenced approach, using rapid GPS orbits and 30 s clock corrections computed by the Center for Orbit Determination in Europe (CODE, Dach et al 2009). This approach was already successfully used for POD of, e.g., MetOp-A (Montenbruck et al 2008). The KIN orbit processing is done in 24 h batches and the resulting orbit consists of position information only, with a 1 s sampling.…”

“…The method to generate RD orbits for LEOs with the Bernese GPS Software has already been successfully used for POD for several LEOs, e.g., CHAMP (Jäggi et al 2006), GRACE ), TerraSAR-X , and MetOp-A (Montenbruck et al 2008) and is described in detail in Jäggi et al (2006). KIN orbits (Švehla and Rothacher 2005) have also already successfully been generated with the Bernese GPS Software and have been used for gravity field recovery (see, e.g., Gerlach et al 2003;Prange et al 2010).…”

“…The requirement in latency is 2 weeks with an accuracy of 2 cm (1D, Visser et al 2006). The two institutions have proven their ability for LEO POD in, e.g., Jäggi et al (2007Jäggi et al ( , 2009van den IJssel et al (2003); Montenbruck et al (2005Montenbruck et al ( , 2008 and have shown in Bock et al (2007) and Visser et al (2009) that the POD requirements for the GOCE mission can be met with their procedures.…”

GPS Radio Occultation: Results from CHAMP, GRACE and FORMOSAT-3/COSMIC

“…1, 35-50, February 2009doi: 10.3319/TAO.2007 2500 pro files per day are ex pected. The Eu ro pean op er ational weather sat el lite MetOp was launched on 19 Oc to ber 2006 and ini tial results of the GRAS (GNSS Re ceiver for At mo spheric Sound ing; see, e.g., Montenbruck et al 2008) on 27 Oc to ber, in di cated the po ten tial for pro vid ing more than 600 mea sure ments per day (www.eumetsat.int; von Engeln et al 2007). This multi-sat el lite con fig u ra tion was fur ther extended by the Ger man TerraSAR-X with an In te grated GPS Oc cul tation Re ceiver (IGOR) re ceiver on board when it was launched on 15 June 2007 via a Rus sian Dnepr-1 rocket from Baikonur (Russia).…”