Study on the Exploration of Spaceborne GNSS-R Raw Data Focusing on Altimetry

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.