Detecting Coastal Aggregation of Macroplastic Litter Using Satellite X-Band SAR Imagery

This study summarizes the lessons learned during the July 2024 experimental campaign, where targets, consisting of floating plastic and natural debris, were jointly observed in a South Italy lake by drone and satellite instruments. The satellite layer consists of the X-band synthetic aperture radar (SAR) equipped onboard the Italian Cosmo-SkyMed Second Generation (CSG) constellation, while the drone layer consists of an optical camera. A set of multipolarization features, namely the co- and cross-polarized normalized radar cross section (NRCS), the SPAN, and the like-to-cross-polarization ratio, are extracted from the CSG SAR measurements. Their sensitivity to the plastic target, along with their ability to discriminate plastic from natural floating debris, is investigated using objective metrics. Experimental results, obtained under calm water conditions, show that floating plastic calls for co- and cross-polarized signals well above the system noise and well-distinguishable from the surrounding water using all the features. The plastic target appears as a spot brighter than the surrounding water in both the co- and the cross-polarized NRCS imagery. The copolarized NRCS calls for the largest plastic-to-water contrast and the largest separation between the plastic and the natural target. However, this separation is such that the discrimination remains a challenging task when using intensity-based dual-polarimetric features.