Millimetre wave radar signatures of sea lions

Abstract

This study reports the millimetre wave radar signatures of sea lions collected from three animals in the outdoor seal pool available at the Sea Mammal Research Unit in St Andrews in the Autumn of 2021. The objective is to study the radar signatures of the animals when their full body or part thereof is above water. The data was collected using a 77 GHz Frequency Modulated Continuous Wave (FMCW) radar with linear polarisation. Both Horizontal-Horizontal (HH) and Vertical-Vertical (VV) polarisation data have been stored and analysed. It has been demonstrated that the sea lions were very clearly detected by the radar with SNR greater than 30 dB at a range of 40 m. The calculated radar cross section (RCS) of the sea lions in HH polarisation varies from −50 to −19 dBsm (modal) and −28 to −2 dBsm (maximum), corresponding to the different body parts and the amount of exposure to the radar beam. In VV polarisation, the modal RCS value range is from −47 to −25 dBsm and the maximum RCS varies from −26 to −15 dBsm. It is also shown that the recorded Doppler features have the potential for target classification, essential for autonomous operation of marine vessels.