ANU GRACE Data Analysis: Characteristics and Benefits of Using Irregularly Shaped Mascons

The estimation of mass anomalies using Gravity Recovery and Climate Experiment (GRACE) data involves parameterizing the temporal gravity field using basis functions. In this study, we show that the use of irregularly shaped mass concentration (mascon) tiles that follow land/ocean boundaries reduces the leakage of land signals into ocean regions and vice versa. Leakage of signal from continents to oceans in mascons that cross the coastline affect the integrated mass changes at a regional scale. For example, the calculated mass loss in 2016 is ∼5% greater for Greenland when using mascons that follow coastlines. We describe efficient algorithms for computing the accelerations acting on the satellites caused by mass changes on mascons, along with the partial derivatives relating the mass changes to the inter-satellite observations. Through simulation, we quantify the impact of different mascon geometries, spatial resolution and regularization. The variations of mass change signals within mascons, which we call “intra-mascon variability,” contribute to errors in estimates of mass variation from GRACE data. While this can be mitigated through the regularization of the inversions, it cannot be removed entirely. The use of irregularly shaped mascons that follow land/ocean boundaries reduces the “intra-mascon leakage” of land signals into ocean regions and vice versa. This approach can also be applied to hydrological basins for calculating integrated mass changes on catchment scales.