Mapping plastic materials in an urban area: Development of the normalized difference plastic index using WorldView-3 superspectral data

Accurate and regularly updated information on plastic distribution in urban areas is of great significance for understanding the potential impact of plastic materials on human health and the environment. Remote sensing provides abundant data to identify and map plastics in the natural environment, such as marine plastic debris, and in a heterogeneous urban environment. In existing studies, airborne hyperspectral data were used to map plastic in urban areas. Recently available WorldView-3 data, with superspectral resolution, high spatial resolution and global coverage, have been used in mineral mapping and hydrocarbon detection in non-urban areas. These data provide new opportunities for plastic mapping in urban areas. This study proposes a novel plastic spectral index using WorldView-3 shortwave infrared bands, termed the Normalized Difference Plastic Index (NDPI), to quantify and map plastic materials in urban areas. The NDPI was evaluated in a dense urban area by comparing with the established hyperspectral Hydrocarbon Index (HI) and WorldView-3 Relative-absorption Band Depth (RBD) index. The results demonstrate that the NDPI was effective in visual evaluation, separability analysis and plastic material mapping, with superior performance than the HI and RBD indices. Thus, the proposed NDPI provides a useful measure for urban plastics mapping and analysis.