Sea surface salinity determination method assisted by spaceborne GNSS-R

Global navigation satellite system-reflectometry (GNSS-R) is a new remote sensing way which is passive radar and could be used to improve the retrieval precision of the sea surface salinity (SSS). The model of brightness temperature and the scattering power model of GNSS-R were reviewed, and the spaceborne simulation scenario was developed in this paper. Based on those, the performance of GNSS-R aiding radiometer to determine SSS was first explored. Although it is possible to decrease the mass and power consumption of spaceborne equipment by sharing the antenna and radio frequency font-end between GNSS-R and radiometer working on the frequency of GPS L1 1 575.42 MHz, when SSS is larger than 25 psu, the sensitivity of brightness temperature to SSS reduces by about 0.1 and 0.08 K/psu for the vertical and horizontal polarization signal respectively. The distortion of reflected GPS L1 signals on the measurement of the brightness temperature was analyzed. It is found that under the condition of the simulation scenario for 1 K variation of brightness temperature, reflected GPS L1 signals introduce error less than 2.5×10^-4 K. Subsequently, the sensitivity of the GNSS-R observable to the brightness temperature variation for the vertical and horizontal polarization signal was explored. The results show that when incidence angle increases, the sensitivity of the horizontal and vertical polarization signal show falling and rising tendency respectively. Finally, the relationship between the sensiti-vity of the observable to the brightness temperature variation and the spatial resolution was analyzed. The conclusion is that the study of retrieval algorithm having high accuracy and spatial resolution is crucial for spaceborne GNSS-R aiding radiometer to determine SSS.