Ocean wave-radar modulation transfer functions inferred from airborne synthetic aperture radar imagery

Estimates of the ocean wave-radar modulation transfer function (MTF) at X-, C-, and L-band are obtained from synthetic aperture radar (SAR) imagery acquired by the American NADC airborne 3-frequency SAR over the North Sea during the US/German SAXON-FPN experiment in November 1990. This is achieved by comparing measured SAR image spectra with simulated ones which are computed from measured ocean waveheight spectra. SAR simulations are carried out by taking the nondimensional modulus, |M^RAR|, and phase, η^RAR, of the MTF as free parameters. The phase, η^RAR, is defined in such a way that it is positive in front of the wave crest and negative behind the wave crest in the reference system of the long ocean wave. Best agreement is achieved when using the following values for |M^RAR | and η^RAR: |M^RAR|=8-15 (VV and HH polarization), η^RAR=60°-90° for the case that the wind is blowing in the direction of the long ocean waves, and η^RAR=0°-60° for the case that the wind is blowing against this direction