Steps towards a SAR-based wind atlas in the Baltic Sea

摘要

In the EU-Norsewind project (2008-2012) one task was to assess the wind climate in the Baltic Sea using Synthetic Aperture Radar (SAR) observations. The presentation outlines the methodology and key results. The Baltic Sea has been mapped relatively frequently by Envisat ASAR since 2002 and during these years several offshore meteorological masts have been in operation.The first step was to assess the accuracy of SAR-based wind mapping in this region. We compared SAR-based wind maps retrieved from ANSWRS the APL/NOAA SAR Wind Retrieval System. The NOGAPS wind direction data were interpolated in space and time prior to input in CMOD-5. Around 900 collocated pairs of observations were found between the SAR-based wind maps and the 10 offshore meteorological masts. The statistical comparison on wind speed (direction) showed root mean square error 1.17 m/s (6.29°), bias of -0.25 m/s (7.75°), standard deviation of 1.88 m/s (20.11°), and linear correlation coefficient R2 of 0.783 (0.95°).The second step was estimation of the mean wind speed, the Weibull scale and shape parameters, and energy density based on over 1000 SAR-based wind maps for the Baltic Sea. The results were compared to the FINO-2 meteorological mast data.The SAR-based results from the 12 existing and 42 planned offshore wind farm sites within the study area including parts of Danish, Swedish, German, and Polish Seas were extracted and showed variability in wind energy density from 300 to 800 W m-2. The wind energy density as a function of distance to nearest coast was also investigated (Hasager et al. 2011).The third step is focused on lifting SAR-based winds from 10 m to hub-height using a method proposed and applied to a data set in the North Sea by Badger et al. 2012 (EWEA 2012 conference). In brief, the method is based on information of the atmospheric stability and the boundary layer height using WRF mesoscale results and applying this information to a model for the vertical profile in the marine boundary layer between 10 m and hub-height (Peña et al. 2008). The results of step 3 are currently in progress but no results can be presented.