Observed impact of the GNSS clock data rate on radio occultation bending angles for Sentinel-6A and COSMIC-2
<p>Radio occultation (RO) measurements require the tracking of signals from a global navigation satellite system (GNSS) by a low-Earth-orbit (LEO) satellite as the signals travel through different layers of the atmosphere. The orbit and clock solutions for the GNSS constellations affect these...
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| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/18/3217/2025/amt-18-3217-2025.pdf |
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| Summary: | <p>Radio occultation (RO) measurements require the tracking of signals from a global navigation satellite system (GNSS) by a low-Earth-orbit (LEO) satellite as the signals travel through different layers of the atmosphere. The orbit and clock solutions for the GNSS constellations affect these measurements in two ways: they are needed to obtain a zero-differencing GNSS-based orbit and clock solution for the LEO, and they directly enter the processing of each single RO profile, where the orbit and clock information for the transmitter (GNSS) and receiver (LEO) satellites is required. In this work, we investigate how different GLONASS and GPS orbit and clock solutions affect the statistical properties of RO profiles by comparing our results with forward-modeled bending-angle profiles based on data from the European Centre for Medium-Range Weather Forecasts (ECMWF) short-range forecasts. Given that GNSS orbits are relatively smooth, this study focused on the effect of different transmitter clock data rates, and we tested the range from 1 to 30 s (specifically, the rates of 1, 2, 5, 10 and 30 s). The analysis is based on the reprocessing of Sentinel-6A data (4 months in 2021, September to December, or about 110 000 occultations) and of a smaller sample of recent COSMIC-2/FORMOSAT-7 data (5–7 August 2023, or about 9000 occultations). We find that at impact heights above about 35 km, GLONASS bending-angle statistics markedly improve with the use of higher-rate clock information. For GPS, the statistics are better for more recent GPS blocks, and a rate of 5 s provides a marginal improvement over the 30 s rate for all blocks. In the same impact height range, higher-rate GLONASS clocks also significantly reduce the vertical error correlation. These results are likely the manifestation of the different kinds of short-timescale behavior of the atomic clocks on board the GPS and GLONASS constellations.</p> |
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| ISSN: | 1867-1381 1867-8548 |