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Kao, H-Y. and Lagerloef, G. (16-Apr-13)

The Aquarius instrument is designed to use three horns to measure the sea surface salinity (SSS) at the same time. Taking the advantages of this particular design, here we compare the SSS in three beams and attempt to identify the signal and noise within. It is noticed that the measured SSS in three beams can have significant difference due to the local rainfall, as the distances among the three horns are around a hundred kilometers. Therefore, the rain signals may be removed if the adjustments are done to unify the SSS values in three beams. On the other hand, the observed freshening caused by the regional rainfall is usually washed away in one day. Different from the small-scale inter-beam differences, which are hard to identify signal or noise, longwave (large scale) inter-beam differences are expected to be negligible in reality, as the distances of the footprints of the three horns at the same time cannot be longer than 390 km. As verified in the reference field from HYCOM, it's reasonable to consider the longwave inter-beam difference as bias. As a result of the longwave inter-beam bias removal, we are able to remove most of the stripes on the L3 gridded maps, suggesting the efficiency of bias removal using this simple method. Improvements in buoy matchup are also shown in the results. However, the ascending and descending differences are still an unsolved issue, and should be further investigated in the future.