Cl. Rino et Hd. Ngo, NUMERICAL-SIMULATION OF LOW-GRAZING-ANGLE OCEAN MICROWAVE BACKSCATTERAND ITS RELATION TO SEA SPIKES, IEEE transactions on antennas and propagation, 46(1), 1998, pp. 133-141
This paper presents the results of numerically simulating microwave ba
ckscatter from a deep-water breaking wave profile. Enhanced microwave
backscatter from the crests of breaking waves has been hypothesized as
the source of bright short-lived microwave radar echoes that are obse
rved at low-grazing angles (LGA's), The characteristics of these ''sea
spikes'' are distinctly different from the Bragg-scatter echoes that
dominate measurements made at moderate grazing angles, Of particular i
nterest is the high contrast that sea spikes present against ocean bac
kground backscatter when observed with horizontally polarized transmit
/receive configurations [horizontal (HH) versus vertical (VV)]. This H
H/VV contrast disparity has been attributed to polarization-selective
cancellation of the direct reflection from the wave crest by the surfa
ce reflection, This hypothesis is reinforced first by showing evidence
that VV polarization is suppressed in the intensity range that would
normally be populated by the brightest scatterers. Histograms of unave
raged Doppler-centroid measurements show further that the depleted VV
backscatter population is responding to scatterers that are moving muc
h more slowly than the HH scatterers. The Doppler-centroid histograms
provide a sharper delination between the two scattering populations th
an do the unconditionally averaged Doppler spectra that are more commo
nly reported, Finally, our numerical simulations show evidence of an i
nterference mechanism that selectively suppresses VV backscatter. In o
ur simulations, the polarization selectivity comes from the phase depe
ndence of the backscatter from the wave crest, A Brewster phenomenon a
t the surface reflection point is not necessary.