Abstract
Over the 15 years of the Gravity Recovery and Climate Experiment (GRACE) mission, various data processing approaches were developed to derive time-series of global gravity fields based on sensor observations acquired from the two spacecrafts. In this paper, we compare GRACE-based mass anomalies provided by various processing groups against Global Navigation Satellite System (GNSS) station coordinate time-series and in-situ observations of ocean bottom pressure. In addition to the conventional GRACE-based global geopotential models from the main processing centers, we focus particularly on combined gravity field solutions generated within the Horizon2020 project European Gravity Service for Improved Emergency Management (EGSIEM). Although two validation techniques are fully independent from each other, it is demonstrated that they confirm each other to a large extent. Through the validation, we show that the EGSIEM combined long-term monthly solutions are comparable to CSR RL05 and ITSG2016, and better than the other three considered GRACE monthly solutions AIUB RL02, GFZ RL05a, and JPL RL05.1. Depending on the GNSS products, up to 25.6% mean Weighted Root-Mean-Square (WRMS) reduction is obtained when comparing GRACE to the ITRF2014 residuals over 236 GNSS stations. In addition, we also observe remarkable agreement at the annual period between GNSS and GRACE with up to 73% median WRMS reduction when comparing GRACE to the 312 EGSIEM-reprocessed GNSS time series. While the correspondence between GRACE and ocean bottom pressure data is overall much smaller due to lower signal to noise ratio over the oceans than over the continents, up to 50% agreement is found between them in some regions. The results fully confirm the conclusions found using GNSS.
Highlights
During the 15 years of the Gravity Recovery and Climate Experiment (GRACE) mission [1], a number of GRACE data processing approaches have been developed and greatly advanced to derive global geopotential models (GGMs) from the raw sensor data observed by the twin GRACE satellites
As an essential part of the European Gravity Service for Improved Emergency Management (EGSIEM) project, this study has successfully demonstrated the capabilities of the Global Navigation Satellite System (GNSS) time series and in-situ ocean bottom pressure (OBP) records for validating GRACE monthly gravity fields
By comparing the six monthly gravity field products to the three independent GNSS datasets, we can conclude that strong agreements between GNSS and GRACE have been clearly observed at both the full and the annual signals
Summary
During the 15 years of the Gravity Recovery and Climate Experiment (GRACE) mission [1], a number of GRACE data processing approaches have been developed and greatly advanced to derive global geopotential models (GGMs) from the raw sensor data observed by the twin GRACE satellites. For the majority of those approaches, different releases exist thanks to successive refinements of the methodology, re-processed Level-1 sensor data, or improved geophysical background models. A number of post-processing options were developed over the years that are necessary to transform gravity fields into global surface mass estimates. To evaluate the quality of different gravity field solutions, two types of external datasets, i.e., GNSS time series and in-situ ocean bottom pressure (OBP) measurements, have been used
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