Determination and localized analysis of intersatellite line of sight gravity difference: Results from the GRAIL primary mission

Abstract

AbstractThe line of sight (LOS) gravity difference between two coorbiting spacecrafts is determined in terms of intersatellite range‐acceleration measurements available from the Gravity Recovery and Interior Laboratory (GRAIL). The precise orbit data are crucial for retrieving gravity difference from range acceleration and aligning the LOS data particularly in altitude. A relative orbit error of a few centimeters in position and a few tens µm/s in velocity is commensurate with the GRAIL‐ranging instrument noise at a few μGal in LOS gravity difference. The power spectrum, as well as the topography correlation and admittance, is quantified by upward continuing the topographic potential, forward modeling the LOS gravity along the spacecraft trajectory (i.e., Bouguer correction) and comparing with the GRAIL LOS observations. Based on the data analysis from the primary GRAIL mission, I found that the LOS gravity difference observation produced near unity correlation with topography potential out to degree 550, higher than the global estimate, over the areas covered by the low‐altitude orbit (~20 km). The crustal density was estimated to be 2500–2600 kg/m3 with regional variations of about 10%, by minimizing the Bouguer coherence of the GRAIL data at the degree band 150–300. Systematic decrease in the density estimates by 3–4% or 100 kg/m3 was observed at shorter wavelengths (degree band 300–500). It implies the inadequacy of a uniform density model across the entire lithosphere and suggests radial stratification of the bulk density (or porosity). Due to spatially localized characteristic, the LOS gravity difference data are well suited to regional analysis at the highest‐possible resolution.