Optimized Synthetic Aperture Radar (SAR) processing for Airborne UWB FMCW Radar

Abstract

Remote Sensing of snow covered sea ice in melting Polar Regions has become crucial in estimating the results of increased global warming and to overcome the Earth’s energy imbalance. And to accurately map the snow models over sea ice, it has become essential to build radar systems that has increased sensitivity and to use post processing techniques that enhance the performance. The Center for Remote Sensing of Ice Sheets (CReSIS) at KU has developed ultra-wideband snow radar system that operates over 2-18 GHz frequency range to effectively measure the snow thickness including very thin snow cover and map the snow-ice and snow-ice interfaces precisely. Synthetic Aperture Radar (SAR) processing is one of the post processing technique employed to further increase the sensitivity of the radar in terms of resolution and SNR. In this thesis, a time domain correlation SAR technique which is essentially a matched filter application is described and implemented. It is verified initially with an ideal simulated point target data and then with point target data collected by the snow radar system over sea-ice. Both gave the results as expected with the theoretical values. It is also shown how noise is multiplied with increasing synthetic aperture length. The effect of aircraft motion non-linearities on SAR processing are also studied at different altitudes. To overcome the effect of non-linearities and multiplicative noise, a multilooking SAR processing is proposed and explained. This is then applied to the field data collected by the snow radar in 2014 to 2017 over sea ice and observed that the azimuth resolution is improved by 4 m approximately. The optimum parameters like SAR aperture length and the number of looks are extracted based on the results of SAR processing on various data sets. Finally, a comparison of SAR application to low and high altitude data sets collected in 2016 over the same region is also provided to show that longer apertures are required for high altitude to achieve same amount of improvement in SNR and azimuth resolution.