Detection of naturally heavy-metal-poisoned areas by LANDSAT-1 digital data

Abstract Natural poisoning of soil and vegetation due to heavy metals originating from sulphide deposits in the bedrock has been demonstrated at several locations in Norway. At some of these, the features of poisoning are rather widespread, suggesting that the recognition of such naturally poisoned areas by means of satellite imagery and satellite digital tapes might be possible. An occurrence of natural Cu poisoning near Karasjok, northern Norway, was selected as a training area. LANDSAT-1 computer compatible tapes were used to prepare enhanced colour ratio images and to calculate ratios of calibrated channel reflectances. Ground reflectance measurements were also carried out using radiometers with band passes equivalent to those on the LANDSAT multispectral scanner system. Compared with the surroundings the LANDSAT data over the training area showed unique spectral characteristics. These are also indicated on the enhanced ratio images, and the digital data can be utilized in supervised discriminant analysis and unsupervised “cluster” analysis. In particular, the area of the natural Cu poisoning shows low values in the band 7/band 5 reflectance ratio. At present, a detailed, precise numerical correlation between the ground and satellite reflectance data is not possible due to differences in resolution, although spatial correlation of spectral trends can be established. It appears that features of natural heavy metal poisoning can be located with the 0.45-hectare resolution of the LANDSAT multispectral scanner system. The search for such features might therefore be used as a tool in mineral exploration. The current resolution limitation can be overcome by utilizing scanners at aircraft altitudes.