A spectral based recognition of the urban environment using the visible and near-infrared spectral region (0.4-1.1 m). A case study over Tel-Aviv, Israel

This work examines the feasibility of using detailed spectral information in the visible (VIS) and near-infrared (NIR) spectral region (0.4-1.1 m) for recognizing the urban environment. This was done by carefully studying pure and mixed spectral based materials from laboratory and airborne imaging spectroscopy (IS) data. The motivation for this study is the fact that although the IS technique has introduced a promising quantitative capability in many applications, it has not yet received attention in urban-related studies. For this study the Compact Airborne Spectral Imager (CASI) IS sensor (which operates in the VIS- NIR region) and the city of Tel-Aviv (Israel's largest city) were selected. A pure spectral library of Tel-Aviv's urban objects within the CASI channel configuration was generated from an existing spectral library. It was shown that even though the VIS-NIR spectral region is rather featureless, objects in the urban environment are characterized by spectral fingerprints. Examining this observation under a real, complex urban IS domain showed that minor spectral variations among targets could be easily used to spatially distinguish similar objects. Water bodies, asphalt pavement, shade, vegetation species and soil in the urban area can be spectrally and spatially recognized and mapped. For the purpose of spectral recognition the IS data must be of high quality (spectrally and spatially), the sensor status should be evaluated and the atmospheric attenuation should optimally be removed. These factors were carefully considered in the performance of this study, and the results, validated on the ground, showed remarkable agreement with reality. It was concluded that the IS technique is promising for use in the urban environment, and it is hoped that this paper will serve as a precursor for future urban-related IS studies.