Calibration of GRACE on-board accelerometers for thermosphere density derivation

Low Earth Orbit satellite on-board accelerometers play an important role in improving our understanding of thermosphere density; however, the accelerometer-derived densities are subject to accelerometer calibration errors. In this study, two different dynamic calibration schemes, the accelerometer parameter-incorporated orbit fitting and precise orbit determination (POD), are investigated with the Gravity Recovery And Climate Experiment (GRACE) satellite accelerometers for thermosphere density derivation during years 2004–2007 (inclusive). We show that the GRACE accelerometer parametrization can be optimized by fixing scale coefficients and estimating biases every 60 min so that the orbit fitting and POD precision can be improved from 10 cm to 2 cm in the absence of empirical acceleration compensations and as a result the integrity of calibration parameters may be reserved. The orbit-fitting scheme demonstrates similar calibration precision with respect to POD. Their bias estimates in the along-track and cross-track components exhibit an offset within 0.1% and a standard deviation (STD) less than 0.3%. Correspondingly, a bias of 2.20% and a STD of 5.75% exists between their thermosphere density estimates. The orbit-fitting and POD-derived thermosphere densities are validated through the comparison against the results published by other institution. The comparison shows that either of them can achieve a precision level at 6%. To derive thermosphere density from the rapid-increasing amount of on-board accelerometer data sets, it is suggested to take full advantage of the orbit-fitting scheme due to its high efficiency as well as high precision.