The major drawback of Ka band, operating frequency of the AltiKa altimeter on board SARAL, is its sensitivity to atmospheric liquid water. Even light rain or heavy clouds can strongly attenuate the signal and distort the signal leading to erroneous geophysical parameters estimates.
A good detection of the samples affected by atmospheric liquid water is crucial. As AltiKa operates at a single frequency, a new technique based on the detection by a Matching Pursuit algorithm of short scale variations of the slope of the echo waveform plateau has been developed and implemented
prelaunch in the ground segment. As the parameterization of the detection algorithm was defined using Jason-1 data, the parameters were re-estimated during the cal-val phase, during which the algorithm was also updated. The measured sensor signal-to-noise ratio is significantly better than
planned, the data loss due to attenuation by rain is significantly smaller than expected (<0.1%). For cycles 2 to 9, the flag detects about 9% of 1Hz data, 5.5% as rainy and 3.5 % as backscatter bloom (or sigma0 bloom). The results of the flagging process are compared to independent rain
data from microwave radiometers to evaluate its performances in term of detection and false alarms.
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Document Type: Research Article
Institut Français de Recherche pour L'exploitation de la Mer (IFREMER), Laboratoire d’Océanographie Spatiale, Plouzane, France
Collecte Localisation Satellite (CLS), Space Oceanography Division, Saint Agne, France
Centre National d’Etudes Spatiales (CNES), Toulouse, France
Publication date: September 10, 2015
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