A simple method for calibration of a scatterometer over the ocean

The absolute calibration of the backscatter signal of a scatterometer is es sential for the retrieval of optimum-quality geophysical products. The Euro pean Space Agency targeted a specification of 0.2 dB for the accuracy of th e European Remote Sensing Satellite scatterometers. A radiometric error of this amount leads to a wind speed error of roughly 0.25 m s(-1). An interbe am bias of the same amount may lead to notable wind direction effects. In t his paper, a method is discussed to obtain an accurate calibration of a sca tterometer over the ocean using an accurate backscatter-ro-wind transfer fu nction and collocated winds from a numerical weather prediction model. The method is estimated to be accurate to a precision of 0.1 dB. It can be used for instrument monitoring, and application of the calibration results has a demonstrable and beneficial impact on the wind inversion.