Reduction of aliasing errors in gravity field recovery by means of covariance information for ocean tide models

The GRACE and GRACE-FO missions are fundamental in establishing a near-continuous time series of global mass transport since 2002. However, monthly gravity field recovery using these mission data includes errors limiting the spatial and temporal resolution of the estimated gravity field solutions. The major error contributions, besides the noise of the accelerometer instruments, arise from temporal aliasing errors due to undersampling of signals to be recovered (e.g. hydrology), uncertainties in the de-aliasing models (e.g., non-tidal atmosphere and ocean) and imperfect ocean tide models. Especially the latter will also remain one of the most limiting factors in determining high-resolution temporal gravity fields from Next-Generation Gravity Missions (NGGM).

In this context, recent developments have been made within the Research Unit NEROGRAV (New Refined Observations of Climate Change from Spaceborne Gravity Missions) funded by the German Research Foundation DFG. One of the projects within NEROGRAV deals with the stochastic modeling regarding ocean tide background models by the utilization of covariance information for eight major tidal constituents. The repeatable pattern of the tidal signal enables the extraction of uncertainty information by an ensemble of different ocean tide models. This information can be introduced into the gravity field recovery process in terms of a covariance matrix while expanding the parameter space by additional tidal parameters to be estimated.

This presentation provides an overview of the recovered monthly gravity fields from GRACE/GRACE-FO when applying covariance information of ocean tide errors. Furthermore, results from simulations representing a GRACE-FO type mission as well as an NGGM double-pair scenario (polar plus inclined pair) are presented. The results show reduced tidal aliasing errors as well as more realistic formal uncertainties.