Spectroscopic Characterization of Built Environments in China

Spectral mixing space characterization is especially important for studies of built environments because of the range of materials around which humans establish residence. With the launch of NASA’s EMIT imaging spectrometer in 2022, spectroscopic characterization of a variety of built environments using atmospherically corrected imagery collected by a common instrument became feasible. The recent availability of four cloud-free EMIT granules imaging Beijing, Chongqing, Guangzhou and Shanghai in early 2025 allows us to address a critical limitation of a 2023 study of built environments using EMIT. The 3D topology of an EMIT mixing space combining all four cities and their surrounding environments shows the familiar ternary structure with Substrate, Vegetation, Dark endmember apexes but extends it to a 3D tetrahedral structure with the addition of a non-photosynthetic vegetation (NPV) endmember. In contrast to multispectral characterizations, EMIT spectra distinguish a variety of anthropogenic substrates not resolvable with broadband sensors. However, semivariogram analysis of coincident 10 m Sentinel-2 and 1.2 m WorldView-3 imagery confirms extensive spectral mixing at the ~50 m scale of the EMIT IFOV. As a result, some of the spectral diversity resolvable with meter resolution spectroscopy is certainly attenuated by decameter resolution sensors.