Sensing Thermospheric Density Using COSMIC-2 Satellite GNSS Data

A low-Earth orbit (LEO) satellite typically has an altitude of a few hundred kilometers, residing in the thermosphere. The UCAR COSMIC Program helps operate and manage the six-satellite COSMIC-2 constellation, a US-Taiwan partnership led by NOAA and the Taiwan Space Agency, which aims at GNSS radio occultation applications. In this paper we report a new application of COSMIC-2 satellite data for sensing thermospheric density. Thanks to advanced onboard GNSS receivers, we can compute the COSMIC-2 satellite orbits at a precision of around 8 cm (3D). As part of the precise-orbit-determination (POD) processing, we estimate the along-track acceleration every five minutes. After analyzing one month of daily-averaged along-track acceleration data of COSMIC-2 satellites, we find a similar pattern to the modeled thermospheric density, which verifies the feasibility of sensing thermospheric density using COSMIC-2. To improve the temporal (and thus spatial) resolution of thermospheric density, a major challenge is to de-couple the drag acceleration due to thermosphere from the solar radiation pressure (SRP) acceleration. By incorporating the satellite layout as well as the epoch-to-epoch attitude information, we can model the SRP acceleration and achieve a 5-min resolution of thermospheric-density sensing. This thermospheric density product can contribute to thermosphere monitoring, space weather forecast, modeling of the atmosphere, and orbit prediction for satellite collision avoidance.