QUANTITATIVE REMOTE-SENSING METHODS FOR REAL-TIME MONITORING OF INLAND WATERS QUALITY

Spaceborne remote sensing of inland water quality is based on the assu mption that the relationship between the reflectance and the concentra tion of relevant water quality constituents is known a priori. Simulta neous measurements of the- upwelling and downwelling irradiances, alon g with phytoplankton chlorophyll-a, suspended matter and dissolved org anic matter concentration at over 20 water bodies throughout former US SR, Hungary, Germany and Bulgaria, are reported in this article. The m easurements cover different trophic states of water bodies, from oligo trophic to hypertrophic, and different climatic conditions. The range of chlorophyll-a is 0.1 to 350 Mg m-3, suspended matter is 0.1 to 66 m g l-1, and dissolved organic matter absorption at the wavelength 380 n m is 0.1 to 12 m-1. All radiometric measurements are performed with a single radiometer in the 400-750 nm range with spectral resolution bet ter than 1 nm. Factor and signature analysis, as well as multi-spectra l statistical modelling of water quality parameters versus simulated s pectral band ratios, makes possible the determination of appropriate f unctions of reflectance for estimating phytoplankton chlorophyll-a, su spended matter, and dissolved organic matter concentrations. One set o f measurements is used to develop empirical relationships among the sp ectral reflectance and the above-mentioned water quality parameters. T he other sets of measurements are used to test these relationships. Th e maximum error of estimation are: 3 mg m-3 for chlorophyll-a, 4 mg l- 1 for suspended matter and 0.065 mg Cm-3 (mg of carbon per m3) for dis solved organic matter. The results are used to develop an appropriate methodology for monitoring of eutrophication process in inland waters and to test concepts of inland water quality monitoring from space.