Towards a new IAG Working Group on Spatial Leakage Mitigation in Satellite Gravimetry

An inherent problem of satellite gravimetry is the limited spatial resolution of space-borne sensors observing various functionals of the Earth's gravity field. Due to the limited amount of sensor data available to calculate monthly gravity fields and the typically applied global mathematical basis functions, the problem is particularly severe for mass change applications from GRACE and GRACE-FO. That leads to apparent mass loss or gain in regions by mass signals from neighbouring regions and is called the spatial leakage effect.

The spatial leakage problem was identified well before GRACE's launch (see Wahr et al., 1998), and numerous methods have been proposed to assess and mitigate the adverse effects of spatial leakage. Available approaches can be grouped into

• estimates obtained from numerical models of the most prominent surface mass processes;
• data-driven approaches that only rely on the geodetic data themselves;
• methodologies based on (non-geodetic) satellite remote sensing data; and
• forward-modelling approaches, where a certain (time-invariant) geometry of surface mass change is assumed a priori and a limited set of (time-variable) parameters are estimated to fit the (spatially much smoother) gravity field data in a least-squares sense.

Despite the various approaches available, we note that spatial leakage is treated very differently for individual surface mass change applications and across the various international research institutions. Sometimes, leakage is readily corrected before providing mass anomalies to non-geodetic users. Other groups only provide some leakage approximation to inform users about this systematic error source. And in (increasingly rare) cases, leakage is not even treated at all. In order to consolidate approaches across the geodetic community, we propose to establish an IAG Working Group aiming to

• collect different leakage mitigation methods;
• develop a common and independent validation approach; and
• recommend best practices in communicating spatial leakage to non-geodetic users of surface mass change data derived from satellite gravimetry.

This contribution will summarize the current status of our ideas in order to invite all interested colleagues to contribute to this initiative.