Measurements of ocean wave spectra and modulation transfer function with the airborne two-frequency scatterometer
The results of this research show that the directional spectrum and the microwave modulation transfer function (MTF) of ocean waves can be measured with the airborne two-frequency scatterometer-microwave resonance technique. By combining two-frequency backscatter resonance intensity with estimates of the directional wave spectrum (obtained by the airborne surface contour radar) and the known radar beam geometry, it was possible to solve for the unknown MTF using a system equation that has been verified in previous studies. Similar to tower-based operations, the aircraft measurements of the MTF show that it is strongly affected by both wind speed and sea state. Also detected were small differences in the magnitudes of the MTF between downwind and upwind radar look directions, and variations with ocean wave number. Unexpected results were obtained, which indicate the MTF inferred from the two-frequency radar is larger than that measured using single-frequency/wave orbital velocity/Doppler techniques such as tower-based radars or ROWS (remote ocean wave spectrometer) from low-altitude aircraft. Possible reasons for this are discussed. When independent MTF data are combined with two-frequency resonance intensities over a suitable variety of azimuthal look directions, then estimates of the surface wave directional spectrum can be made, to within the accuracy of the uncertainties in the individual data sets.
Journal of Geophysical Research
- Pub Date:
- February 1986