Lf. Bliven et al., AN ANALYSIS OF SCATTEROMETER RETURNS FROM A WATER-SURFACE AGITATED BYARTIFICIAL RAIN - EVIDENCE THAT RING-WAVES ARE THE MAIN FEATURE, International journal of remote sensing, 14(12), 1993, pp. 2315-2329
Both wind and rain roughen the sea surface, but whereas wind generates
waves, rain generates craters, stalks and ring-waves. Average backsca
ttered power for scatterometer returns from water surfaces is closely
related to small scale features on the water surface, so we use backsc
attered power from short wind-waves as a basis to evaluate the importa
nce of ring-waves. Experiments were conducted with a 13.5 GHz scattero
meter (30-degrees incidence angle, vertical polarization) in a wind-wa
ve tank that is enhanced by a rain simulator. Rain intensities ranged
from 3-30 mm h-1 and wind friction velocities were between 10 and 50 c
m s-1. The variance of sur-face elevation for small scale features xi(
sm)2, i.e., ring-waves and short wind-waves, was computed for each cas
e using data from a capacitance probe. Comparison of the data sets sho
ws that the range of xi(sm)2 for the rain cases is comparable to that
from light to moderate wind cases-so ring-wave amplitudes are not negl
igible. Analysis of the radar data provides evidence that ring-waves a
re the dominant feature contributing to the backscattered power. Thus
ring-waves need to be included in scatterometer numerical models that
contain rain effects.