BCI: A biophysical composition index for remote sensing of urban environments

Understanding urban environments and their spatio-temporal changes is essential for regional and local planning and environmental management. To facilitate monitoring and analyzing urban environments, remotely sensed data have been applied extensively because of its synoptic view and repeat coverage over large geographic areas. Compared with traditional per-pixel and sub-pixel image analyses, spectral indices have apparent advantages due to their easy implementation. However, most spectral indices are designed to highlight only one land cover, and confusion between other land cover types, in particular impervious surfaces and bare soil, has not been successfully addressed. This study proposes a biophysical composition index (BCI) for simple and convenient derivation of urban biophysical compositions for practical applications following Ridd's conceptual vegetation – impervious surface – soil triangle model by a reexamination of the Tasseled Cap (TC) transformation. Further, this research explores the applicability of BCI in various remotely sensed images at different spatial resolutions. Results indicate that, BCI has a closer relationship with impervious surface abundance than those of normalized difference vegetation index (NDVI), normalized difference built-up index (NDBI) and normalized difference impervious surface index (NDISI), with correlation coefficients of approximately 0.8 at various resolutions. Also, the performances of BCI in quantifying vegetation abundance are comparable with NDVI at all three spatial scales. Additionally, with much higher values of separability metrics than any other index, the study confirms that BCI was shown to be the most effective index of the four evaluated for separating impervious surfaces and bare soil.

► We develop a biophysical composition index (BCI) to characterize urban environments. ► We compare the performances of BCI with NDVI, NDBI, and NDISI at three resolutions. ► BCI is among the best in representing impervious surfaces abundance at each scale. ► BCI is also effective in quantifying vegetation abundance when compared to NDVI. ► With BCI, impervious surfaces and bare soil can be moderately separated.