Monitoring mine tailings revegetation using multitemporal hyperspectral image data

Abstract

This paper investigates the use of hyperspectral remote sensing imagery in the 400–2500 nm wavelength range for the extraction of information suitable for monitoring mine tailings revegetation. The objectives were twofold: (i) demonstrate the usefulness of fractional texture for monitoring mine tailings revegetation using visible and near-infrared (VNIR) hyperspectral data, and (ii) investigate the benefit of adding the short-wave infrared (SWIR) bands. Compact Airborne Spectrographic Imager (casi) data were acquired over the Copper Cliff mine tailings impoundment area in the VNIR bands during the summers of 1996 and 1998. In addition, Probe-1 data were collected in the VNIR-SWIR region during the summer of 1999. Surface reflectance was retrieved from the three datasets, and spectra of the 1996 and 1998 casi datasets were resampled to match the 1999 Probe-1 spectral sampling characteristics, which resulted in 30 bands covering the 450–890 nm range. The three datasets were concatenated into one file, and 30 endmember spectra were automatically selected. Constrained linear spectral unmixing was performed using the 30 endmembers, which were then grouped into the six endmember categories, namely water, lime, fresh and oxidized tailings, and low and high photosynthetic vegetation. Image fractions were then normalized and image texture was extracted from the total vegetation fraction. Total vegetation fraction (high/low photosynthetic), total tailings fraction (fresh/oxidized), and texture of the vegetation fraction were used in a K-mean unsupervised classification, which produced the best results using seven classes (78.13% overall accuracy, Kappa coefficient of 0.74). Classification results were validated using a set of 34 ground estimates of vegetation cover and tailings. The full set of 128 bands of the 1999 Probe-1 dataset was used to investigate the contribution of the SWIR bands to monitoring the reclamation of mine tailings. A new vegetation endmember was identified as plant litter, which in many cases replaces areas labelled as low photosynthetic vegetation when using the VNIR bands only. Oxidized tailings could be separated into jarosite and goethite endmembers and lime into agricultural lime (CaMgCO3) and calcium oxide (CaO), also known as quicklime.