The polar gap problem from the perspective of the Bender configuration

Abstract:

The Bender configuration comprises of two GRACE-like pairs, one in a polar orbit and the other in an inclined orbit. While the polar pair covers the entire globe, the inclined pair does not cover the higher latitudes leaving a local discontinuity around the poles in acquired signal (better known as the Polar Gap problem). Similarly, due to its north-south orientation, the polar pair can capture well the features that are predominantly oriented in the east-west direction. In contrast, the inclined pair does not have any such issues. We simulated a Bender configuration using ESA's Earth System Model to see how the two satellite pairs contributed to the spherical harmonic coefficients. The general pattern was that the polar orbit contributed strongly to the zonal coefficients and the tesserals around it (near- zonal coefficients) while the inclined orbit contributed strongly to the other tesseral and the sectorial coefficients, which is well known. We also found out that the weak zonal and near-zonal inclined pair contributions lay inside a wedge in the spectral space, very similar to the polar gap error wedge. We want to discern how the relative geometry of the satellites, particularly the polar gap issue in the inclined pair of a bender configuration, affects the solution's spectral resolution. In this study, we model the contribution coefficients of the polar and inclined pairs as a function of orbit geometries. We hope that this will help in the design of future satellite missions with geometries best suited for their objective based on the precise determination of essential spectral coefficients.