Impacts of High Rate GNSS Satellite Clock Estimation on Radio Occultation Bending Angle Retrievals: Preliminary Report

A high-rate estimation of GNSS satellite clock offsets has been reported to be critical to the retrieval of bending angles in the GNSS radio occultation (RO) processing, particularly for GLONASS [1]. [1] finds that theoretically the bending angle uncertainty at a high altitude (e.g., > 50 km) reduces by more than 20% for all GLONASS satellites and GPS Cs-clock satellites, and by ~ 8% for GPS Rb-clock satellites if using a 3 sec interval GNSS-satellite-clock product rather than the conventional 30 sec interval clock product. Inspired by this finding, we at UCAR generate in-house high-rate GNSS satellite clock products at intervals of 1 second, 2 seconds, 5 seconds, and 30 seconds using the GINAN GNSS software, based on observations from a set of globally-distributed ground stations. The performance of our clock products is evaluated by comparing to the clock products oflntemational GNSS Service (IGS) analysis centers such as the Center for Orbit Determination in Europe (CODE). To demonstrate that high-rate clock estimation does impact the bending angle uncertainty as pointed out theoretically by [1], we perform radio-occultation (RO) bending angle retrievals for the COSMIC-2 mission using the aforementioned clock products as well as JPL's 1-sec, 2-sec, 3-sec, 5-sec, and 30-sec clock products. We then conduct statistical comparisons to the NCAR climatology model [2] and find that the fundamental noise of the RO technique has been reduced slightly for GPS and 15% - 45% for GLONASS, using 2-sec clock products rather than 30-sec clock products. Reducing the RO noise can improve the sensitivity ofRO remote sensing, benefiting weather and space weather monitoring & forecast.