On the radar imaging mechanism of Kelvin arms of ship wakes

The radar signatures of Kelvin arms of the wave pattern generated by a moving ship are studied by using an improved composite surface model for the calculation of the radar backscatter from the ocean surface. The modulation of the normalized radar backscattering cross section (NRCS) by the cusp waves forming the Kelvin arms is calculated as function of the ship heading relative to the radar look direction for different radar frequencies and polarizations. According to the model, the modulation depth of the NRCS increases with radar frequency and is larger at HH than at VV polarization. One example of an ocean scene with a moving ship is presented which was imaged by the 3-frequency/multipolarization SAR aboard the Space Shuttle “Endeavour” during the SLR-C/X-SAR mission. It is shown that the measured modulation depths agree quite well with the simulated ones