An Evaluation of Multispectral and Multi-Emulsion Aerial Photography for Soils, Vegetation and Land use Mapping

Abstract

This thesis evaluated multispectral and multi-emulsion (i.e. false colour, true colour and panchromatic) photography for various types of earth resources survey, primarily soil survey. Two test areas in upland Britain were used, one in Cumbria and one in North Yorkshire. Only one set of multispectral photographs became available, covering the area in Cumbria, at 1:15,000 scale. False colour vertical aerial photographs of both areas were taken at two different seasons (October/ November 1973 and May 1974), also at 1:15,000. The available panchromatic photographs were at different scales and dates. The multispectral photography was analysed using a stereoscope, and an additive viewer, and false colour photography was analysed using a stereoscope. Attempts were made to analyse the tones on the multispectral photography by densitometry, and on the false colour photography by densitometry and by the ISCC-NBS centroid colour charts. The lack of success of these experiments indicated that the methods could not be considered operational. It was found that soils could not be mapped directly from aerial photographs, whatever type of emulsion was used, ant it was recommended that panchromatic aerial photography be continued to be used for soil surveying. The multispectral photography had too many disadvantages to be of use for many types of survey and it is possible that these defects are inherent in the multispectral system. False colour photography was found to be useful and, on the whole, superior to both panchromatic and multispectral emulsions ‘for vegetation and land use mapping. However, it is important to choose the appropriate time of year for aerial photography and the use of ground photography is recommended to help predict the correct time of year for aerial survey and to monitor closely changes in crops and vegetation.