Phy. Lee et al., POWER SPECTRAL LINESHAPES OF MICROWAVE-RADIATION BACKSCATTERED FROM SEA SURFACES AT SMALL GRAZING ANGLES, IEE proceedings. Radar, sonar and navigation, 142(5), 1995, pp. 252-258
Analysis of recent small-grazing-angle microwave backscattering data i
ndicate that the Bragg mechanism alone cannot explain the experimental
results. The authors investigate the issue of scattering mechanisms b
y studying the lineshapes of the backscattered microwave power spectra
. It is found that spectral lineshapes can be decomposed into physical
ly meaningful basis functions which are Gaussian, Lorentzian or Voigti
an. Generally, the spectral component corresponding to the lower frequ
ency peak in the power spectral density (PSD) of the vertical polarisa
tion is well described by a Gaussian profile, while the spectral compo
nent due to the higher frequency peak in the horizontal polarisation P
SD is well described by either a Lorentzian or a Voigtian profile, dep
ending on the size of the radar footprint. These quantitative results
provide compelling evidence that several entirely different mechanisms
, corresponding to different surface features of the dynamic sea surfa
ce, are active in contributing to microwave backscattering returns. Th
ese mechanism comprise: first, scattering from free Bragg waves, chara
cterised by a Gaussian distribution in scatterer speeds and a Gaussian
component in the PSD; secondly, scattering from sporadically appearin
g, fast moving, short lifetime, facet-like scatterers, characterised b
y an exponential distribution in scatterer lifetime and a Lorentzian c
omponent in the PSD; and finally, scattering from fast-to-intermediate
speed bound-Bragg waves, or not-so-fast facets, characterised by a co
nvolution of the Gaussian and Lorentzian processes, resulting in a Voi
gtian component in the PSD.