Assessing Thermospheric Neutral Density Models using GEODYN's Precision
Orbit Determination
Abstract
This study focuses on utilizing the increasing availability of satellite
trajectory data from global navigation satellite system-enabled
low-Earth orbiting satellites and their precision orbit determination
(POD) solutions to expand and refine thermospheric model validation
capabilities. The research introduces an updated interface for the
GEODYN-II POD software, leveraging high-precision space geodetic POD to
investigate satellite drag and assess density models. This work presents
a case study to examine five models (NRLMSIS2.0, DTM2020, JB2008,
TIEGCM, and CTIPe) using precise science orbit (PSO) solutions of the
Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2). The PSO is used
as tracking measurements to construct orbit fits, enabling an evaluation
according to each model’s ability to redetermine the orbit. Relative
in-track deviations, quantified by in-track residuals and
root-mean-square errors (RMSe), are treated as proxies for model
densities that differ from an unknown true density. The study
investigates assumptions related to the treatment of the drag
coefficient and leverages them to eliminate bias and effectively scale
model density. Assessment results and interpretations are dictated by
the timescale at which the scaling occurs. JB2008 requires the least
scaling (~-23%) to achieve orbit fits closely matching
the PSO within an in-track RMSe of 9 m when scaled over two weeks and 4
m when scaled daily. The remaining models require substantial scaling of
the mean density offset (~30-75%) to construct orbit
fits that meet the aforementioned RMSe criteria. All models exhibit
slight over or under sensitivity to geomagnetic activity according to
trends in their 24-hour scaling factors.