Abstract
High resolution imaging spectroscopy data have been recognised as a valuable data resource for augmenting detailed material inventories that serve as input for various urban applications. Image-specific urban spectral libraries are successfully used in urban imaging spectroscopy studies. However, the regional- and sensor-specific transferability of such libraries is limited due to the wide range of different surface materials. With the developed methodology, incomplete urban spectral libraries can be utilised by assuming that unknown surface material spectra are dissimilar to the known spectra in a basic spectral library (BSL). The similarity measure SID-SCA (Spectral Information Divergence-Spectral Correlation Angle) is applied to detect image-specific unknown urban surfaces while avoiding spectral mixtures. These detected unknown materials are categorised into distinct and identifiable material classes based on their spectral and spatial metrics. Experimental results demonstrate a successful redetection of material classes that had been previously erased in order to simulate an incomplete BSL. Additionally, completely new materials e.g., solar panels were identified in the data. It is further shown that the level of incompleteness of the BSL and the defined dissimilarity threshold are decisive for the detection of unknown material classes and the degree of spectral intra-class variability. A detailed accuracy assessment of the pre-classification results, aiming to separate natural and artificial materials, demonstrates spectral confusions between spectrally similar materials utilizing SID-SCA. However, most spectral confusions occur between natural or artificial materials which are not affecting the overall aim. The dissimilarity analysis overcomes the limitations of working with incomplete urban spectral libraries and enables the generation of image-specific training databases.
Highlights
Accurate differentiation and identification of urban surface materials is an important requirement for area-wide land cover mapping, and for subsequent derivation of further urban data products.Due to their high spectral and spatial information content [1], very-high resolution airborne imaging spectroscopy data have been recognised as a valuable data resource for augmenting surface material inventories [2,3]
Three data sets are needed for the dissimilarity analysis, (I) a very-high resolution image image (Section 2.1); (II) a basic spectral library (Section 2.2); and (III) a class hierarchy that groups the (Section 2.1); (II) a basic spectral library (Section 2.2); and (III) a class hierarchy that groups the surface materials in the BSL
The final result is a scene-specific spectral spectral library with categorised spectrally homogeneous unknown material classes that can serve as library with categorised spectrally homogeneous unknown material classes that can serve as a basis a basis for precise labelling of the materials, e.g., by field surveys (Figure 1)
Summary
Accurate differentiation and identification of urban surface materials is an important requirement for area-wide land cover mapping, and for subsequent derivation of further urban data products. Due to their high spectral and spatial information content [1], very-high resolution airborne imaging spectroscopy data have been recognised as a valuable data resource for augmenting surface material inventories [2,3]. For successful and reliable surface material mapping using very-high resolution airborne imaging spectroscopy data, spectral mixture analysis has been frequently used. Most success has been achieved with image-specific endmembers since they comprise all scene-based structural and compositional information, sensor artefacts, and acquisition-based data characteristics [26]
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