Coastal winds from synthetic aperture radar sea surface images of the North West of Baja California, México

One of the key advantages of synthetic aperture radar (SAR) images of the sea surface is the achieved spatial resolution with the possibility of providing useful information for limited area models of winds in the coastal region. Several SAR images of the North West of Baja California are being analyzed to estimate the wind field by using a typical wind retrieval algorithm such as CMOD-4, and with wind direction information deduced directly from the image. While most of the time low to moderate wind conditions are encountered, the presence of characteristic sea surface features suggests the influence of other processes. Surface streaks are rather common and their association with near surface currents and/or winds is investigated for they might either induce uncertainty or might help for wind direction estimations. Sea surface streaks prevail even under moderate wind and active wave fields, as observed in our ERS-2 SAR images acquired on September 30th, and on December 9th 1998, as well as in that one acquired on February 17th, 1999. Fronts are easily detected in some of our images and can be considered of great assistance for a very detailed wind direction estimation, when trying to reproduce spatial characteristics with typical scales of the order of few to tens of kilometers in the wind field. In some cases these fronts show a clear separation between areas with very low wind from those with low to moderate winds. Our results will show that in some cases, certain sea surface features would contribute for a better wind direction estimation, in particular for wind patterns with spatial scales of the order of few kilometers. While a C-band VV polarization wind retrieval model is being use, access to HH polarization images requires a modified algorithm to estimate wind speeds. The possible influence of polarization ratio used elsewhere is addressed.