Royal Dutch Meteorological Institute; Ministery Of Infrastructure And The Environment

The C-band geophysical model function, CMOD5, is developed by ECMWF and KNMI for use with the ERS and ASCAT scatterometers. It has been developed using advanced empirical methods, ECMWF model winds tied to buoy measurement data, and measurements in extreme wind conditions (hurricanes) from the unique Imaging Wind and Rain Airborne Profiler (IWRAP) instrument aircraft campaigns.

The CMOD5.N function is related to equivalent neutral ocean vector winds rather than to real 10-m winds (CMOD5). Retrieved vector winds from CMOD5.N are thus more representative of the ocean surface conditions and make it possible to avoid errors related to atmospheric stratification, see the paper of Portabella and Stoffelen, On Scatterometer ocean stress, in J. Atm. Oceanic Technol. In addition to an enhancement of 0.2 m/s, which describes the average difference between neutral and real wind, CMOD5.N accounts for a known low bias of 0.5 m/s in CMOD5. The GMF changes are described in the ECMWF Technical Memorandum CMOD5.N: A C-band geophysical model function for equivalent neutral wind (2008), see under 'Related links' on the right hand side.

The CMOD5 function is described in detail in the ECMWF Technical Memorandum CMOD5 - An improved geophysical model function for ERS C-band scatterometry (2003), see under 'Related links' on the right hand side. We used such geophysical model function in C-band SAR wind processing, as described in Chapter 4 of the thesis by M. Portabella.
IDL and Fortran 90 code (10 kB, use the "gunzip" and "tar -xf" commands to unpack on Unix/Linux). The package contains a Fortran routine to compute the CMOD5.N geophysical model function and an IDL sample program that uses the Fortran routine.

A Python version of this software is available from the Nansen Environmental and Remote Sensing Center in the openwind project:
Available documents
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.
Abstract (html)  Complete text (pdf: 758 KB)
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.
Abstract (html)  Complete text (pdf: 521 KB)
Portabella, M., Wind field retrieval from satellite radar systems
Thesis: University of Barcelona, 2002, Barcelona, Spain, 207p.
Complete text (pdf: 3 MB)
Haan, S. de and A. Stoffelen, CMOD5
Document external project: 2001, SAF/OSI/KNMI/TEC/TN/140, EUMETSAT, 2001.
Abstract (html)  Complete text (pdf: 6 MB)
Further information
Please contact the KNMI scatterometer team.

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