Parametric dependence of ocean wave-radar modulation transfer functions

During the Marine Remote Sensing experiment of 1979 (MARSEN 79), we employed microwave techniques at X and L band to determine the dependence of ocean-wave radar modulation transfer functions (MTFs) on various environmental and radar parameters. In this paper, we present these MTFs along with coherence functions between the AM and FM parts of the backscattered microwave signal and show that they both depend on several of these parameters. In addition to confirming many of the properties of transfer functions reported by previous authors, this work indicates that MTFs decrease with increasing angle between wave propagation and antenna-look directions but are essentially independent of small changes in air-sea temperature difference. Coherence functions are much smaller when the antennas are pointed perpendicular to long waves, however. X band transfer functions measured with horizontally polarized microwave radiation are found to have larger magnitudes than those obtained by using vertical polarization. Under conditions encountered in this experiment, transfer functions are independent of long-wave amplitude when waves and antennas are aligned. Coherence functions, however, depend strongly on long-wave amplitude. We show that this dependence implies that in addition to being modulated by long waves, short waves amplitudes fluctuate in response to environmental factors unrelated to long waves. Spectral densities of these fluctuations are shown to be comparable to those of modulations induced by long waves

[1]  W. Alpers,et al.  The modulation of the radar backscattering cross section by long ocean waves , 1978 .

[2]  D. Schuler,et al.  Remote sensing of the sea surface using one‐ and two‐frequency microwave techniques , 1980 .

[3]  W. Plant,et al.  Modulation of coherent microwave backscatter by shoaling waves , 1978 .

[4]  T. Barnett,et al.  Measurements of wind-wave growth and swell decay during the Joint North Sea Wave Project (JONSWAP) , 1973 .

[5]  J. Wright,et al.  Microwave scattering and the straining of wind‐generated waves , 1975 .

[6]  K. Hasselmann,et al.  The two-frequency microwave technique for measuring ocean-wave spectra from an airplane or satellite , 1978 .

[7]  D. Ross,et al.  On the detectability of ocean surface waves by real and synthetic aperture radar , 1981 .

[8]  J. Wright,et al.  Detection of ocean waves by microwave radar; The modulation of short gravity-capillary waves , 1978 .

[9]  William J. Plant,et al.  Ocean wave‐radar modulation transfer functions from the West Coast Experiment , 1980 .

[10]  John C. Daley,et al.  Variation of the NRCS of the sea with increasing roughness , 1971 .

[11]  J. Wright.  A new model for sea clutter , 1968 .

[12]  I. Ostrovsky,et al.  Very high frequency radiowave scattering by a disturbed sea surface Part II: Scattering from an actual sea surface , 1968 .

[13]  J. Ewing,et al.  Directional Wave Spectra Observed during JONSWAP 1973 , 1980 .

[14]  O. Shemdin,et al.  An investigation of the modulation of capillary and short gravity waves in the open ocean , 1980 .