Showing papers by "Frank G. Lemoine published in 2023"

VGOS VLBI Intensives between MACGO12M and WETTZ13S for the rapid determination of UT1-UTC

Abstract: In this work, we present a status update and results of the designated research and development VLBI Intensive program VGOS-INT-S, observed between MACGO12M and WETTZ13S for the rapid determination of the Earth's phase of rotation, expressed via UT1-UTC. The main novelty of these sessions is the use of a special observation strategy, rapidly alternating between high- and low-elevation scans, enabling an improved determination of delays caused by the neutral atmosphere. Since 2021, 25 Intensive sessions have been observed successfully. In early 2022, VGOS-INT-S was among the most accurate Intensive programs with an average formal error $\sigma_{UT1-UTC}$ of 3.1 $\mu$s and a bias w.r.t. IERS C04 of 1.1 $\mu$s. Later, the session performance decreased due to multiple technical difficulties.

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 systemenabled 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 highprecision 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.