Comparison of accelerometer data calibration methods used in thermospheric neutral density estimation

Abstract

Abstract. Ultra-sensitive space-borne accelerometers on board of low Earth orbit (LEO) satellites are used to measure non-gravitational forces acting on the surface of these satellites. These forces consist of the Earth radiation pressure, the solar radiation pressure and the atmospheric drag, where the first two are caused by the radiation emitted from the Earth and the Sun, respectively, and the latter is related to the thermospheric density. On-board accelerometer measurements contain systematic errors, which need to be mitigated by applying a calibration before their use in gravity recovery or thermospheric neutral density estimations. Therefore, we improve, apply and compare three calibration procedures: (1) a multi-step numerical estimation approach, which is based on the numerical differentiation of the kinematic orbits of LEO satellites; (2) a calibration of accelerometer observations within the dynamic precise orbit determination procedure and (3) a comparison of observed to modeled forces acting on the surface of LEO satellites. Here, accelerometer measurements obtained by the Gravity Recovery And Climate Experiment (GRACE) are used. Time series of bias and scale factor derived from the three calibration procedures are found to be different in timescales of a few days to months. Results are more similar (statistically significant) when considering longer timescales, from which the results of approach (1) and (2) show better agreement to those of approach (3) during medium and high solar activity. Calibrated accelerometer observations are then applied to estimate thermospheric neutral densities. Differences between accelerometer-based density estimations and those from empirical neutral density models, e.g., NRLMSISE-00, are observed to be significant during quiet periods, on average 22 % of the simulated densities (during low solar activity), and up to 28 % during high solar activity. Therefore, daily corrections are estimated for neutral densities derived from NRLMSISE-00. Our results indicate that these corrections improve model-based density simulations in order to provide density estimates at locations outside the vicinity of the GRACE satellites, in particular during the period of high solar/magnetic activity, e.g., during the St. Patrick's Day storm on 17 March 2015.

Extended forward and inverse modeling of radiation pressure accelerations for LEO satellites

“…We here speculate that the mean difference in the along-track direction is caused by a mean bias in the modeled drag acceleration. In the cross-track direction, the mean differences between modeled and calibrated accelerations according to Vielberg et al (2018) are about 4 × 10 −10 m/s 2 , which is about three orders of magnitude smaller than in the comparison above. Interestingly, the mean difference between modeled and our calibrated accelerations increases by about one order of magnitude when adding the instantaneous thermal reradiation.…”

“…is here computed for different model extensions RMSD 2 with respect to the standard model RMSD 1 , i.e., the positive results mean that accelerations from the extended model version are closer to calibrated accelerations than the standard model. In the comparison against calibrated accelerations from Vielberg et al (2018), we found that extended ERP and SRP accelerations have no impact on the modeled along-track acceleration because here the drag dominates. Interestingly, visible and infrared fluxes in the SRP model bring the modeled cross-track accelerations about 5.5% closer to calibrated observations from Vielberg et al (2018).…”

“…In the comparison against calibrated accelerations from Vielberg et al (2018), we found that extended ERP and SRP accelerations have no impact on the modeled along-track acceleration because here the drag dominates. Interestingly, visible and infrared fluxes in the SRP model bring the modeled cross-track accelerations about 5.5% closer to calibrated observations from Vielberg et al (2018). Including the variation in the solar flux and the physical shadow function has no significant impact on the total acceleration.…”

“…In the following, we model the drag acceleration [in Eq. (15)] as described in Vielberg et al (2018). The model is the same for all scenarios and accounts for drag and lift forces as in Doornbos (2012) with an energy accommodation coefficient of 0.93.…”

“…Future work will address the problem of joint inversion of thermosphere and radiation pressure errors. We also assume that accelerometers have been calibrated, e.g., within a POD procedure (Van Helleputte et al 2009;Vielberg et al 2018).…”