ASCAT scatterometer cal/val and winds

The first MetOp-A L2 product was released on 28 March 2007 by the Ocean & Sea Ice Satellite Application Facility (OSI SAF) at the Royal Netherlands Meteorological Institute (KNMI). Here we present the calibration procedure that lead to these 25-km ASCAT winds. The European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) is responsible for the absolute calibration of the new Advanced Scatterometer (ASCAT), onboard MetOp-A, which relies on the use of transponders. A complementary geophysical calibration method uses scatterometer measurements over the ocean. The method is based on the knowledge of the backscatter signal modulation by the ocean surface, which is derived from previous C-band scatterometer missions, and on the use of ancillary wind information as calibration reference. The method proves to be very useful in providing guidance to EUMETSAT calibration efforts and inherently provides continuity of the C-band scatterometers. Also, this so-called “cone” calibration results in very good quality winds visible at http://www.knmi.nl/scatterometer.The winds are declared pre-operational since 10 October 2007.