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.
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
The GMF changes are described in the ECMWF Technical Memorandum CMOD5.N:
A C-band geophysical model function for equivalent neutral wind
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:
Comparison of C-Band Scatterometer CMOD5.N Equivalent Neutral Winds with ECMWF
J. Atm. Oceanic Technol., 2010, 27, 721-736,
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Please contact the
KNMI scatterometer team