Impact of Sun Glint on Salinity Remote Sensing: An Example With the Aquarius Radiometer

The Aquarius/SAC-D mission will employ three L-band (1.41 GHz) radiometers dedicated to the remote sensing of sea surface salinity. The radiation from the Sun reflected at the ocean surface toward the radiometer is an important source of interference for retrieving salinity; in fact, the mission will be in a dawn/dusk Sun-synchronous orbit with the beams oriented toward the night side of the orbit in order to limit this signal. In this paper, the effect of ocean surface roughness on the reflected radiation is examined. The reflected Sun radiation can be separated into two components: 1) a quasi-specular component and 2) a scattered component, due largely to small-scale roughness. We show that the first component has a large brightness temperature but, in the Aquarius geometry, is located far from the antenna boresight. The scattered component has relatively small brightness temperature but can extend to the antenna boresight where the gain is maximum. This can occur at high latitude near the summer solstice when the antenna footprint is not in shadow and can cause significant contamination. While the calculations have been done for the specific geometry of the Aquarius instrument, the conclusions drawn regarding the effect of roughness on the reflected solar radiation are characteristic of remote sensing at L-band.