Mapping terrestrial macroplastics and polymer-coated materials in an urban watershed using WorldView-3 and laboratory reflectance spectroscopy.

The presence and abundance of synthetic polymers can be used to map mismanaged waste, housing quality, and other development indicators. For various common urban plastic polymers, spectral absorption features in the shortwave infrared (SWIR) wavelengths can be captured using laboratory reflectance spectroscopy. In addition, SWIR bands of the WorldView-3 (WV3) satellite sensor are known to capture absorptions specific to these polymers. The ≈4-m ground sampling distance of WV3 offers the potential to spatially resolve urban aggregations of polymer-based debris and differentiate these from natural and other anthropogenic materials. Synthesizing field work, laboratory reflectance spectroscopy, and satellite image analysis, we mapped suspected polymer-based materials in a complex urban watershed on the coastal US-Mexico border. Field surveys identified several large (80-150 m) unmanaged waste aggregations in stream channels. 1024-band laboratory reflectance spectra of field-collected macroplastics (25-1000 mm) showed consistent absorption features that were often preserved when convolved to the 8-band spectral response function of the WV3 SWIR sensor. Laboratory spectra for high- and low-density polyethylene, polyethylene terephthalate, and polyvinyl chloride correlated closely (r = 0.95; p < 0.01) and had high spectral similarity with an independently derived endmember selected from a bounding apex of the spectral feature space of a WV3 image of the area. Matched filtering identified areas corresponding to infrastructure inferred to be of polymer-based or -coated materials as well as waste aggregations. Mapping precision scores ranged from 0.92 to 0.95. Our study suggests that some common plastic polymers may be distinguishable in this study area using a generalized WV3 SWIR image endmember.