Abstract
Abstract. Classification of urban materials using remote sensing data, in particular hyperspectral data, is common practice. Spectral libraries can be utilized to train a classifier since they provide spectral features about selected urban materials. However, urban materials can have similar spectral characteristic features due to high inter-class correlation which can lead to misclassification. Spectral libraries rarely provide imagery of their samples, which disables the possibility of classifying urban materials with additional textural information. Thus, this paper conducts material classification comparing the benefits of using close-range acquired spectral and textural features. The spectral features consist of either the original spectra, a PCA-based encoding or the compressed spectral representation of the original spectra retrieved using a deep autoencoder. The textural features are generated using a deep denoising convolutional autoencoder. The spectral and textural features are gathered from the recently published spectral library KLUM. Three classifiers are used, the two well-established Random Forest and Support Vector Machine classifiers in addition to a Histogram-based Gradient Boosting Classification Tree. The achieved overall accuracy was within the range of 70–80% with a standard deviation between 2–10% across all classification approaches. This indicates that the amount of samples still is insufficient for some of the material classes for this classification task. Nonetheless, the classification results indicate that the spectral features are more important for assigning material labels than the textural features.
Highlights
Assessing the materials in the urban environment has in recent times increased in importance for several reasons and applications
For the assessment of the deep AE (DAE), we perform a comparison with the alternative spectral representations by firstly using the original spectra and secondly employing the Principal Component Analysis (PCA) (Tipping and Bishop, 1999) on the original spectra
The compressed spectral representations of the two samples are significantly distinct, which indicates that they can be utilized for material distinction
Summary
Assessing the materials in the urban environment has in recent times increased in importance for several reasons and applications This information is useful for researchers and city planners who deal with city simulations or models where knowledge about the existing materials is important. Observed in previous studies regarding urban material classification, the characteristic spectral features of different urban material classes can be similar which makes it challenging to distinguish them from each other (Ilehag et al, 2017b; Ouerghemmi et al, 2017; Deshpande et al, 2019) This is partly due to the high inter-class correlation which leads to misclassification. Few spectral libraries contain imagery of the samples (Kotthaus et al, 2014; Kokaly et al, 2017; Ilehag et al, 2019) which can provide additional information for material classification
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