Book Description

This report shows how the Modulation Transfer Function, an important quantity for remote microwave sensing of ocean wave spectra, will vary with environmental conditions that control the air-sea interaction. The accuracy with which this quantity is known will determine the quality of remote measurements of ocean wave spectra. Microwave remote sensing of individual ocean wavelengths (and the complete directional spectrum) is based on synchronized reflectivity variations along each wave, that the radar can resolve spatially. This study demonstrates that the MTF, which is the ratio of this reflectivity (amplitude of variation) to the ocean wave amplitude, is affected by the air-sea interaction, in addition to the hydrodynamic interaction between capillary and long gravity waves. Recent measurements by the Naval Research Laboratory of the ocean wave-radar modulation transfer function (MTF) from fixed ocean platforms, over a period of several years, have demonstrated that the local hydrodynamic modulation of short centimeter waves is affected by the air-sea interaction. Results from widely separated ocean regions also show different individual properties, that make detailed measurements necessary.