Assessment of the updated Envisat ASAR ocean surface wave spectra with buoy and altimeter data

The advanced synthetic aperture radar (ASAR) on board the European Space Agency (ESA) Envisat satellite is an important resource for observation of global ocean surface wave spectra. The ESA retrieval procedure for the fast-delivery level 2 ASAR wave spectra has undergone an important update since October 2007. Testing the benefit of the new procedure against ground truth is not straightforward, due to a lack of other independent ocean wave spectral observations; however an indirect comparison of the ASAR wave spectra with altimeter and buoy observations is made possible via a wave model. In addition to the conventional significant wave height (SWH), four spectral sub-range wave heights (SRWHs) are used to illustrate the spectral characteristics of these observations. The indirect comparison is applied on the updated ASAR wave spectra for over one year (November 2007 to December 2008). Results indicate that the updated ASAR spectra are better than the pre-October 2007 data since the updated procedure removes erroneous long waves, and improves the treatment of short waves beyond the detection range of the instrument.