First shipborne GNSS-R campaign for receiving low elevation angle sea surface reflected signals

摘要

Global Navigation Satellite System Reflectometry (GNSS-R) was regarded as a promising way to observe atmospheric duct by utilizing low elevation angle ocean surface reflected signals. To invest the Delay maps' feature of low elevation angle reflected signals in the atmospheric duct, a shipborne GNSS-R campaign was conducted in July, 2015 by the scientific investigation ship called Shiyan 3 on the South China Sea. During the campaign, the atmospheric temperature, pressure, and relative humidity which were used to detect atmospheric duct were recorded by GPS radiosondes and meteorological recorder. The GNSS-R payload developed by National Space Science Center (NSSC) and fixed on the rail of Shiyan3 was used to generate Delay maps. Preliminary results showed that atmospheric duct, especially evaporation duct, existed almost all the time in the experimental ocean region. Ocean surface reflected signals with elevation angle less than 10° were received and formed delay maps successfully. Affected by the direct signal and specular reflected signal's strong interference, apparent code correlation peaks appeared on Delay maps' tail. The experimental values of correlation peaks and simulated code autocorrelation were synthetically used to fit the curve of direct signal and specular reflected signal's strong interference utilizing the least square method. After removing the interference, cleaner reflected signals without direct and specular reflection signals were obtained.