Water quality mapping of the major lakes in northern Italy using TM data

摘要

Spatially distributed inland quality parameters, such as suspended sediments, chlorophyll load, water transparency and surface temperature were evaluated in the four majors lakes of the sub-alpine region located in the northern Italy. These lakes alone account for 90 percent of the inland water resource of the entire country. Due to the agricultural and industrial uses of the lake water and their main economic relevance, linked to the recreational vacation of the entire sub-alpine environment, a large monitoring programme for their conservation is justified. Two Landsat-5 Thematic Mapper data acquired in March 1997 were used to compare the different behaviour of the lakes water in Spring, when the main algae bloom occurs. Water quality parameterswere extracted by means of the chromaticity analysis: Landsat Chromaticity System (LCS) uses absolute radiance values from the satellite and derive the trophic state of the waters in terms of "redness" X, "greenness" Y, and "blueness" Z of water colour,related to the suspended materials, to the chlorophyll concentration and to the water turbidity, respectively. Moreover water surface temperature was derived from radiometrically corrected TM band 6 and the influence of water volume and altitude on watersurface temperature and the relation among them were formalised.