Laboratory measurements of the effects of viscosity on short water wave spectra and implication for radar remote sensing of the ocean surface

AbstractUsing anX-band radar and a mechanical short wave generator, we measured the dependence of radar return power on the viscosity of water which was adjusted by changing the water temperature. From the measurements we drew two inferences: (1) the spectral density of short water waves,F, depends strongly on the viscosity of water $$F(v) = F_0 \tilde v^m $$ where $$\tilde v$$ is normalized viscosity, andm=−1.72; and (2) the normalized radar cross section,σ0(dB), depends strongly on the water temperature $$\Delta \sigma _0 (dB) = 0.217 \Delta T$$ Analyses indicate that these dependencies can be observed in the field only at low wind conditions at which the Bragg scattering is a dominant mechanism for producing the radar return signals. The results of this study can be used to interpret the sharp variability in radar cross section across a water temperature front and SAR images of oceanic phenomena.