Ocean Surface Salinity from SMAP
[18-Nov-2015] Meissner, T., Wentz, F., Lagerloef, G., and Le Vine, D.
Presented at the 2015 Aquarius/SAC-D Science Team Meeting
With the demise of Aquarius the ability of SMAP to measure ocean salinity has gained importance. We discuss the adaption of the Aquarius salinity retrieval algorithm to SMAP and address important differences between the Aquarius and SMAP: 1. The 360 degree look capability of SMAP makes it possible to take observations from the forward and backward looking direction basically at the same instance of time. 2. The spatial resolution of a SMAP radiometer measurement is about 40 km compared with 100 km for Aquarius. This higher resolution is associated with a higher noise for SMAP. Averaging is essential to reduce the noise in order to still achieve the accuracy goal of 0.2 psu. 3. Due to the failure of the radar, SMAP does not provide valuable L-band scatterometer wind speeds. Therefore the SMAP salinity retrieval needs to use wind speeds from WindSat and SSMIS for correcting the surface roughness effect. 4. Other than Aquarius the SMAP antenna is slightly emissive. The emissivity of 1% causes significant spurious biases in the SMAP salinity data that correlate with the physical temperature of the antenna, which depends on solar heating. It is therefore necessary to develop a correction for this emissivity signal.