Abstract
This article discusses the sea level determination using raw intermediate frequency data transmitted from the Global Navigation Satellite System (GNSS) and received by spaceborne GNSS-Reflectometry satellites, TechDemoSat-1. The reflected signals scattered from a sea ice surface and a rough sea surface are investigated. The altimetry method based on the bistatic group delay (code phase) from GNSS signals for sea level estimation are introduced. The two raw IF datasets recorded on January 18 and 27, 2015 for a duration of 40 s are analyzed to drain more information than Level 1 data. The results show a good consistence with mean sea surface (MSS) model. The orbit error of the GNSS-R satellite is corrected by a proposed method that combines the MSS and the least squares solution, which help evaluate the actual altimetry precision. The defect of fixed temporal resolution and fixed four onboard processing channels of Level 1 data can be improved by postprocessing using software define receiver to mine more information, so as to explore the potential. At the end, fake high signal-to-noise ratio Doppler delay maps from the raw data are analyzed, which provides a reference for the altimetry of GNSS-R technique using raw data.
Highlights
Global Navigation Satellite System (GNSS)-Reflectometry (GNSS-R) technique has received an extensive attention since its introduction in 1993[1]
Due to the high signal-to-noise ratio (SNR) in the RD15 dataset with the signals reflected from sea ice, the altimetry results at each millisecond can be got, while the weak scattering and large sampling interval can result in poor accuracy
It is found that the error between the specular point and the GNSS satellite is greater than the specular error between the point and the GNSS-R satellite, which is related to the altitude difference between them
Summary
GNSS-Reflectometry (GNSS-R) technique has received an extensive attention since its introduction in 1993[1] It was first proposed for sea level determination, which is similar in principle to the traditional altimetry method but different in technique. Similar to the GNSS positioning technique, GNSS-R requires precise time measurement of signal propagation to obtain the change of the reflecting surface. The GNSS-R altimetry can be divided into code phase and carrier phase altimetry, and both can be carried on different platforms, including ground-based, airborne and spaceborne. With the further developments in GNSS signal processing algorithms and the GNSS-R specific instrumental, the sea level altimetry technique of an airborne platform can reach accuracy of sub-decimeter level. Yu[17], Semmling[18], Mashburn[19] and others carried out various projects on near-shore sea level monitoring and got satisfactory results with higher precision
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