Estimation of soil colour through spectral reflectance characteristics

Abstract

Surface samples (Ap horizon) of twenty one soils widely differing in their physical appearance of colour were collected from different parts of India. Air-dried soils, passed through 2 mm sieve, were packed in black round trays for reflectance measurements. Soil colour of air-dry soils was designated using Munsell colour charts. Spectral reflectance patterns were obtained by a portable spectroradiometer using sunlight as the illuminant. For each sample, the XYZ tristimulus values; x,y chromaticity coordinates were obtained from reflectance patterns using the CIE standard methods. Munsell. notations were also converted to tristimulus and chromaticity coordinates using published tables of Wyszecki and Stiles (1982). The RGB colour coordinates obtained from both the systems were compared. The RGB values from spectral data were well correlated with reflectance in TM bands, while those from Munsell notation were correlated to a lesser extent. The tristimulus values were used to designate each soil with specific set of values to locate them in Universal Colour Space.