On the imaging of sea wave with coherent microwave radar

An idealized, coherent radar traveling at a speed, maps a scatterer at a range, R and position parallel to the direction of travel and measured from the axis of radar look) into an imaged position. where is the component of scatterer velocity along the line of sight. Since the number of scatterers , say, is conserved in this transformation. Image patterns will thus be formed if either or varies significantly with . The former case is analogous to ordinary incoherent optical imaging but the latter is uniquely coherent imaging. In a two scale model incoherent imaging of sea waves results from tilting of Bragg Scatterers by the large wave and by modulation of the Bragg wave amplitude through straining by the large wave. The tilting and straining effects have a similar dependence on large wave slope but the latter has a much different windspeed and Bragg wavenumber dependence. Since, in the two scale case, is derived from the orbital velocity of the large wave it is quasi-periodic and can also produce a wave-line image by coherent imaging. We have recently examined a number of examples of coherent imagery of the sea for evidence of the above outlined mechanisms and find that we are able to isolate the characteristics of both coherent and incoherent type imagery.