Global Observations of Wind Speed and Sea Surface Features using SAR Wave Mode

• Main Authors: Susanne Lehner, Johannes Schulz Stellenfleth, Jochen Horstmann
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Asar; Sea ice
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.20.6020; http://earth.esa.int/pub/ESA_DOC/gothenburg/166lehne.pdf

To prepare for the globally available ENVISAT ASAR wave mode data comparable complex imagettes where processed from the synthetic aperture radar (SAR) wave mode raw data of the European remote sensing satellite ERS-2, using the research processor BSAR from the German Space Agency (DLR). Complex ERS-2 SAR wave mode imagettes have a size of 5 km x 10 km and are available every 200 km along the satellite track. The full high resolution image information of the wave mode imagettes opens up a large variety of oceanographic applications. In this study wind speed retrieval from imagettes using the CMOD4 model (originally developed for the scatterometer) is studied. Therefore a global comparison to 10 m wind fields from the European Center of medium Range weather Forecast (ECMWF) is given. As ERS wave mode SAR imagettes are available at the same time and location as the scatterometer (SCAT) data (with pixel size of 25 km x 25 km) the imagettes are used to test the SCAT flagging for land and sea ice. It is shown that seemingly wrong SCAT measurements of wind speed can be explained by surface features not dominated by the influence of wind e.g. surface slicks, sea ice. Several approaches, e.g. spectral filtering, derivation of entropy of the power spectrum, and estimation of the decrease of backscatter in range are carried out on the global data set to characterize SAR image features. The characteristic feature parameters are compared to wind data provided by ECMWF on a global scale and their relation to atmospheric effects is discussed. The whole analysis is a validation an improvement of the planned operational measurement of wind speed from ENVISAT ASAR wave mode data.