Spatiotemporal Validation of Mass-Change Products over Greenland and Antarctica Using GRACE-FO Laser Ranging Instrument

Abstract

Observations of mass changes in the cryosphere are critical to understanding the impact of climate change and constraining global projections of sea-level rise. Observations from satellite gravimetry missions, satellite altimetry, and Surface Mass Balance (SMB) models provide differing estimates of mass change at different temporal and spatial scales making intercomparison challenging. GRACE-FO is equipped with two sensors to track the inter-satellite distance; a baseline K-band microwave ranging system (KBR) and an experimental Laser Ranging Interferometer (LRI). The improved ranging precision of the LRI enables Line-of-Sight Gravity Difference (LGD) observations with substantially greater sensitivity to short-wavelength gravity signals than is possible with the KBR and at a range of temporal scales. Building on previous work demonstrating enhanced high-frequency sensitivity over Greenland and Antarctica, we apply LGD as a validation tool for GRACE-FO mascon products, ICESat-2-derived mass-change estimates, and two versions of the RACMO SMB model over the same region. This tests products commonly used for mass-change observations in the cryosphere over a range of spatial and temporal scales. LRI-derived LGD uniquely enables an independent direct frequency domain validation of the effective gravity signals from different mas change products without the limiting effects of temporal aliasing. By forward modeling gravity from monthly mass-change solutions and comparing the resulting synthetic LGD with LRI LGD observations, we assess the ability of different mass-change products to recover signals over multiple spatial and temporal scales. The results demonstrate that the effective spatial resolution of mass-change products is not characterized by a single spatial scale but instead depends on the interaction between the magnitude of the mass-change signal, the spatial and temporal scale of mass changes, and the measurement or modeling technique. This validation is particularly important for the cryosphere where understanding the effective spatial and temporal resolution of products can change the interpretation of the data. Validation of mass-change products using LGD provides a new approach for evaluating existing mass-change products in Greenland and Antarctica as well as guiding the development of future mass-change products.