README

OpenWind depends on Nansat (https://github.com/nansencenter/nansat).

Installation

• Add the top level folder openwind/ to your PYTHONPATH
• Add the subfolder openwind/openwind/ to your PATH (for command line usage)
• Test the installation by running the test script (test_sarwind.py) in openwind/tests

Command line usage:

./sar_wind.py -s SAR_filename -w winddir -f figure_filename -n netCDF_filename -p pixelsize

• SAR_filename is a file readable by Nansat, containing Normalised Radar Cross Section (NRCS)

• winddir is either:

  • a file readable by Nansat, containing wind direction (U10 and V10)
  • an integer indicating constant wind direction (0 from North, 90 from East etc)
  • name (string) of a mapper with functionality to find a wind file (online or on local disk) matching the SAR image time [DEFAULT: 'ncep_wind_online']

• pixelsize is given in meters (500 m by default). Use pixelsize='fullres' for no resizing (usually not recommended, unless image is small or cropped).

To see explanation of all features:

./sar_wind.py -h

Python usage:

>>> from openwind import SARWind

>>> s = SARWind(SAR_image, winddir, pixelsize)

See above (command line usage) for specification of the input parameters. SAR image may here also be a Nansat SAR object (containing NRCS, incidence angle and look direction)

To plot the result and save as figure:

>>> s.plot() # to plot SAR wind overlaid wind vectors.

>>> s.plot(filename, show=False) # Save to file

Notes:

• GDAL might need to be compiled with the option --with-jasper to be able to read the downloaded NCEP GFS GRIB2-files

Acknowledgments

OpenWind is developed with support from the Norwegian Space Centre.

Thanks to the Royal Netherlands Meteorological Institute (http://www.knmi.nl/scatterometer/cmod5/) for making the cmod5 software available.

References

Mouche A.A., Collard F., Chapron B., Dagestad K.-F., Guitton G., Johannessen J.A., Kerbaol V., Hansen M.W. (2012). On the use of Doppler shift for sea surface wind retrieval from SAR. IEEE Transactions on Geoscience and Remote Sensing, Vol. 50, No. 7, pp 2901-2909, doi:10.1109/TGRS.2011.2174998.

Hersbach, H., Comparison of C-Band Scatterometer CMOD5.N Equivalent Neutral Winds with ECMWF J. Atm. Oceanic Technol., 2010, 27, 721-736, doi:10.1175/2009JTECHO698.1.

Portabella, M. and A.C.M. Stoffelen, On Scatterometer Ocean Stress J. Atm. Oceanic Technol., 2009, 26, 2, 368-382, doi:10.1175/2008JTECHO578.1.

Verhoef, A., M. Portabella, A. Stoffelen and H. Hersbach, CMOD5.n - the CMOD5 GMF for neutral winds Document external project: 2008, SAF/OSI/CDOP/KNMI/TEC/TN/165, EUMETSAT, 2008.

Hersbach, H., A. Stoffelen and S. de Haan, An Improved C-band scatterometer ocean geophysical model function: CMOD5 J. Geophys. Res., 2007, 112, C03006, doi:10.1029/2006JC003743.

Portabella, M., Wind field retrieval from satellite radar systems. Thesis: University of Barcelona, 2002, Barcelona, Spain, 207p.

Haan, S. de and A. Stoffelen, CMOD5 Document external project: 2001, SAF/OSI/KNMI/TEC/TN/140, EUMETSAT, 2001.