Tongji‐Grace02s and Tongji‐Grace02k: High‐Precision Static GRACE‐Only Global Earth's Gravity Field Models Derived by Refined Data Processing Strategies

Abstract

In order to derive high‐precision static Gravity Recovery and Climate Experiment (GRACE)‐only gravity field solutions, the following strategies were implemented in this study: (1) a refined accelerometer calibration model that treats monthly accelerometer scales as a third‐order polynomial and daily accelerometer biases as a fifth‐order polynomial was developed to calibrate accelerometer measurements; (2) the errors of the acceleration and attitude data were estimated together with the geopotential coefficients and accelerometer parameters on the basis of the weighted least squares adjustments; (3) a nearly complete observation series of GRACE mission was used to decrease the condition number of normal equation; and (4) the GRACE data collected in lower orbit altitude were also included to decrease the condition number. Our results show that (1) the refined accelerometer calibration model with much less parameters performs as well as previous methods (i.e., solving daily scales and hourly biases or estimating biases along with bias rates every 2 hr). However, it provides a system of more stable normal equation and less high‐frequency noise in gravity field solutions; (2) high‐frequency noise in the gravity field solution is reduced by modeling the errors of the acceleration and attitude data; (3) the geopotential coefficients at all degrees is greatly enhanced by using longer GRACE time series (especially the data by the end of 2010); and (4) due to lower orbit altitude, the GRACE data collected since 2014 lead to a significant improvement of the gravity field solution as the satellites are more sensitive to higher‐frequency signal. Using the refined strategies, an unconstrained static solution (named Tongji‐Grace02s) up to degree and order 180 was derived. For further suppressing the high‐frequency noise, a regularization strategy based on the Kaula rule is applied to the degrees and orders beyond 80, leading to a regularized model Tongji‐Grace02k. To validate the quality of the derived models, both Tongji‐Grace02s and Tongji‐Grace02k were compared to the latest GRACE‐only models (i.e., GGM05S, ITU_GRACE16, ITSG‐Grace2014s, and ITSG‐Grace2014k) and validated using independent data (i.e., Global Navigation Satellite Systems (GNSS)/Leveling data and DTU13 oceanic gravity data). Compared to other models, much less spatial noise in terms of global gravity anomalies with respect to the state‐of‐the‐art model EIGEN6C4 and far higher accuracy at high degrees are achieved by Tongji‐Grace02s. The same conclusions can be drawn for Tongji‐Grace02k when the same analyses were applied to the regularized solutions ITSG‐Grace2014k and Tongji‐Grace02k. Validations with independent data confirm that Tongji‐Grace02s has the least noise among the unconstrained GRACE‐only models and Tongji‐Grace02k is the one with the best accuracy among the regularized GRACE‐only solutions. For the tests up to degree and order 180 using GNSS/Leveling data, the improvements of Tongji‐Grace02s with respect to ITSG‐Grace2014s reach 13% over ...

An Optimized Short‐Arc Approach: Methodology and Application to Develop Refined Time Series of Tongji‐Grace2018 GRACE Monthly Solutions

“…In physical sense, the spatial distributions of stripes to some extent are related to the GRACE orbit configuration. As explained in previous studies (e.g., Chen et al, Dobslaw et al, ), the large orbit inclination (about 89°) for GRACE satellites leads to oversampling in the polar areas and sparser ground track coverage over medium and low latitude areas. As a consequence, much more striping errors over the medium‐ and low‐latitude areas exist in all the models in contrast to over the polar areas.…”

“…Chen et al () showed that accurately modeling the time‐related variations in accelerometer parameters can lead to improvements on gravity field models. Here we present the statistics (mean values and standard deviations) of the estimated accelerometer scales and biases for the period April 2002 to August 2016 in Figure .…”

“…Note that both IGG RL01 and HUST‐Grace2016 are based on RL05 processing standards, but the others are all based on RL06 processing standards. It is well known that the GRACE‐based geopotential coefficients at low degrees (particularly below degree 30) are generally dominated by gravity field signals, while the high‐degree coefficients are contaminated by noise (Chen et al, ; Meyer et al, ). As presented in Figure , the signal levels (approximately below degree 30) of Tongji‐Grace2018 for both months are in good agreement with those models on the basis of the RL06 processing standards.…”

“…Even though all the local parameters are eliminated from the final normal equation, the corresponding gravity field result is mathematically equivalent to the case of retaining the local parameters in the final normal equation. Chen et al (2018) showed that accurately modeling the time-related variations in accelerometer parameters can lead to improvements on gravity field models. Here we present the statistics (mean values and standard deviations) of the estimated accelerometer scales and biases for the period April 2002 to August 2016 in Figure 9.…”

Combination Analysis of Future Polar-Type Gravity Mission and GRACE Follow-On

“…Along with the KBR, other important sensors onboard GRACE satellites include Global Positioning System (GPS) receivers for precise orbit determination (POD), high-precision accelerometers for measuring non-gravitational forces and star cameras for attitude determination [4][5][6]. Based on the precise data collected by the above sensors, many scientific institutions have produced high-quality static and temporal gravity field models [7][8][9][10][11], which are successfully adopted for quantitative researches concerning the Earth's mass changes, such as global mean sea-level variations [12,13], continental water balance [14,15], and the Tibetan Plateau and Antarctic regional ice losses [16,17].…”