Precise Orbit Determination for Climate Applications of GNSS Radio Occultation including Uncertainty Estimation

Abstract

Global Navigation Satellite System (GNSS) Radio Occultation (RO) is a highly valuable remote sensing technique for probing the Earth's atmosphere, due to its global coverage, high accuracy, long-term stability, and essentially all-weather capability. In order to ensure the highest quality of essential climate variables (ECVs), derived from GNSS signal tracking by RO satellites in low Earth orbit (LEO), the orbit positions and velocities of the GNSS transmitter and LEO receiver satellites need to be determined with high and proven accuracy and reliability. Wegener Center's new Reference Occultation Processing System (rOPS) hence aims to integrate uncertainty estimation at all stages of the processing. Here we present a novel setup for precise orbit determination (POD) within the rOPS, which routinely and in parallel performs the LEO POD with the two independent software packages Bernese GNSS software (v5.2) and NAPEOS (v3.3.1), employing two different GNSS orbit data products. This POD setup enables mutual consistency checks of the calculated orbit solutions and is used for position and velocity uncertainty estimation, including estimated systematic and random uncertainties. For LEOs enabling laser tracking we involve position uncertainty estimates from satellite laser ranging. Furthermore, we intercompare the LEO orbit solutions with solutions from other leading orbit processing centers for cross-validation. We carefully analyze multi-month, multi-satellite POD result statistics and find a strong overall consistency of estimates within LEO orbit uncertainty target specifications of 5 cm in position and 0.05 mm/s in velocity for the CHAMP, GRACE-A, and Metop-A/B missions. In 92% of the days investigated over two representative 3-month periods (July to September in 2008 and 2013) these POD uncertainty targets, which enable highly accurate climate-quality RO processing, are satisfied. The moderately higher uncertainty estimates found for the remaining 8% of days (∼5-15 cm) result in increased uncertainties of RO-retrieved ECVs. This allows identification of RO profiles of somewhat reduced quality, a potential benefit for adequate further use in climate monitoring and research.

Performance of the Ionospheric Kappa‐Correction of Radio Occultation Profiles Under Diverse Ionization and Solar Activity Conditions

“…As a complementary RO dataset we used data from the Gravity Recovery and Climate Experiment (GRACE) (e.g., Wickert et al, 2005;Beyerle et al, 2005), using the GRACE-A mission data in the same time range. For the processing we used the Wegener Center (WEGC) reference occultation processing system (rOPS) (Kirchengast et al, 2016Schwarz et al, 2017Schwarz et al, , 2018Danzer et al, 2018;Innerkofler et al, 2020;Liu et al, 2020) [V. Proschek et al, WEGC Graz, rOPS refractivity and dry-air retrieval manuscript in preparation, pers. communications, 2021].…”

New Higher-Order Correction of GNSS RO Bending Angles Accounting for Ionospheric Asymmetry: Evaluation of Performance and Added Value

“…They feed the different processors of the ODP subsystem and contain several subsystems to do so. The daily system modeling (DSM) consists of two subsystems, the DSM geometry (DSM-Geo) including the orbit modeling [41] and the DSM atmosphere (DSM-Atm).…”

A Robust Adaptive Cubature Kalman Filter Based on SVD for Dual-Antenna GNSS/MIMU Tightly Coupled Integration

“…It has the advantages of being applicable in all weather with high accuracy, high efficiency, high reliability, low cost, etc. [7,8]. However, in semi-or fully shielded challenging environments, such as valleys, tree-lined roads, and tunnels, the positioning performance of GNSS will drop sharply due to insufficient reception of sufficient satellites.…”