On the influence of the ground track on the gravity field recovery from high–low satellite-to-satellite tracking missions: CHAMP monthly gravity field recovery using the energy balance approach revisited

Abstract

In this paper, the influence of the ground track coverage on the quality of a monthly gravity field solution is investigated for the scenario of a high-low satellite-tosatellite tracking mission. Data from the CHAllenging Minisatellite Payload (CHAMP) mission collected in the period April 2002 to February 2004 has been used to recover the gravity field to degree and order 70 on a monthly basis. The quality is primarily restricted by the accuracy of the instruments. Besides, CHAMP passed through a 31 /2 repeat mode three times

An improved sampling rule for mapping geopotential functions of a planet from a near polar orbit

“…Several publications showed that this causes a severe quality degradation of the monthly gravity field solutions, e.g. Sneeuw et al (2003Sneeuw et al ( , 2005; Weigelt et al (2009). As a consequence, the sampling at the equator and in the longitude direction is of primary concern in the following.…”

“…Especially during repeat cycles with low relative prime numbers β and α, the sampling in longitude direction becomes sparse. An example for CHAMP taken from Weigelt et al (2009) is shown in Fig. 1.…”

“…For a time series, this is defined by the Nyquist rule. For the sampling of the sphere, the ruleof-thumb needs refinement as shown by Weigelt et al (2009) and Visser et al (2012). The first choice at hand is then to try to use the Nyquist criterion itself.…”

“…It is also an open question how to optimally avoid signal aliasing from outside the bandlimitation given by equation (18). One possibility was explored by Weigelt et al (2009) by reducing this part of the signal using a priori information. Besides, the signal-to-noise ratio and the quality of background models are other limiting factors for the maximum resolvable spatial resolution but are not considered here.…”

“…They concluded that the ideal maximum degree is L = 30 which is in agreement with the rule-ofthumb. Klokočník et al (2008) extended the investigations of Wagner et al (2006) to the cases of CHAMP and GOCE and predicted future periods of degraded performance of GRACE. Recently, Weigelt et al (2009) noted a discrepancy between the maximum recoverable degree for CHAMP as the satellite passed on several occasions through the 31 /2 repeat cycle. The rule-of-thumb predicts a maximum recoverable degree of 15 but the solutions remained valid approximately till degree and order of 35.…”