Working Groups of Sub-Commission 2.3

JWG 2.3.1: Spatial Leakage Mitigation in Satellite Gravimetry

(joint with ICCC)

Chair: Eva Boergens (Germany)
Vice-Chair: Bramha Dutt Vishwakarma (India)

Terms of Reference

An inherent and well-known problem of satellite gravimetry is the limited spatial resolution of the sensors observing the functionals of the Earth’s gravity field. The problemis particularly present for mass change applications from GRACE and GRACE-FO. That is due to the limited amount of sensor data available to calculate monthly gravity fields, the signal attenuation due to the distance between the sensor (the satellites) and observable, and the typically applied global mathematical basis functions. The limited spatial resolution leads to apparent mass loss or gain in regions by mass signals from neighbouring regions and is called the spatial leakage effect. Although future gravity missions are planned to increase the spatial resolution with additional satellite pairs in inclined orbits (e.g. ESA’s MAGIC), the spatial leakage effect will only be reduced.

Over the last 20 years of the GRACE and GRACE-FO mission lifetime, numerous methods have been proposed by various research groups to mitigate the disadvantageous effects of leakage. Some of these approaches focus on specific regions, while others provide a global mitigation scheme.

The approaches can be grouped into the following categories:

• Estimates obtained from Earth system models of the most prominent surface mass processes;
• Forward-modelling approaches, where the geometry of surface mass change is assumed a-priori and parameters are estimated to fit the gravity field data (in a least-squares sense);
• Data-driven approaches that only rely on the geodetic data themselves;
• Regional integration approaches that use apriori covariance information on the surface mass change signal and accordingly optimize the weight function (or sensitivity kernel) used for the regional integration;
• Methodologies based on (non-geodetic) satellite remote sensing data.

Further, spatial leakage is treated very differently for individual surface mass change applications and across international research institutions. In some cases, leakage isreadily corrected before providing mass anomalies to non-geodetic users. In other cases, only some leakage approximation is provided to inform users about this systematic error source. Furthermore, leakage is sometimes not even treated at all. Thus, consolidating spatial leakage approaches across the geodetic community will guide geodetic and non-geodetic users and increase the accessibility of satellite mass anomaly data to the latter group.

Objectives

• Collect existing leakage approximation and mitigation methods;
• Develop a common and independent validation approach;
• Recommend best practices in communicating spatial leakage to non-geodetic users of surface mass change data derived from satellite gravimetry. Planned timeline with deliverables The planned time frame of the working group is four years.
• Year 1:
  • Collection and review of existing leakage mitigation methods (A review paper);
  • Definition of community-accepted validation criteria and requirements for validation data set (Tech report or a white paper);
  • Apply for a grant/fellowship-scheme for a PhD student.
• Year 2:
  • Generation of validation data set (Paper to a data journal).
• Year 3:
  • Execution and evaluation of validation experiments.
• Year 4:
  • Analysis of the validation experiments (Research paper);
  • Recommendation to the user community (Tech report or a white paper).

Members

Eva Boergens (Germany); Chair
Bramha Dutt Vishwakarma (India); Vice-Chair
Christoph Dahle (Germany)
Balaji Devaraju (India)
Thorben Döhne (Germany)
Wei Feng (China)
Frank Flechtner (Germany)
Andreas Güntner (Germany)
Adrian Jäggi (Swizerland)
Felix Landerer (USA)
Bryant Loomis (USA)
Mahdiyeh Razeghi (Australia)
Ernst Schrama (Netherlands)
Michael Zemp (Swizerland)