Laboratory measurements of the joint dependence of radar frequency and water wavelength on sea-spike returns

Analysis of low grazing angle sea-spikes from breaking waves suggests the presence of a non-Bragg scaling law. The FMCW radar has a frequency chirp of 4-8 GHz. The water wavelength is 1-4 m. The frequency response of the radar cross section peaks in horizontal co-polarization has been investigated. The radar cross-section peaks are caused by the plunging jet and have the characteristics of non-Bragg scatterers; they are compact in range, short in duration and fast. The scaling law states that the product of water wavelength and radar frequency is constant; K=λ_water(m)f_radar(GHz)≈12. Alternatively this may be written as λ_water/λ_radar≈40. An overview of the calibration procedure for range profiles and frequency responses for FMCW radars is also given. The experiments were conducted in the large wind-wave tank at the University of California, Santa Barbara