Improving quantitative remote sensing for monitoring of inland water quality

Simultaneous measurements of the upwelling and downwelling irradiances, along with phytoplankton chlorophyll-α, suspended matter and dissolved organic matter concentration at over 20 water bodies throughout the CIS, Hungary, Germany and Bulgaria, are reported in this paper. The measurements cover different trophic states of water bodies, from oligotrophic to hypertrophic, and different climatic conditions. The range of chlorophyll-α is 0.1-350 mg m^-3, suspended matter is 0.1-66 mg 1^-1 and dissolved organic matter absorption, at a wavelength of 380 nm, is 0.1-12 m^-1. All radiometric measurements were performed with a single radiometer in the 400-750 nm range with spectral resolution better than 1 nm. Factor and signature analysis, as well as multispectral statistical modeling of water quality parameters versus simulated spectral band ratios, made possible the determination of appropriate functions of reflectance for estimating phytoplankton chlorophyll-α, suspended matter and dissolved organic matter concentrations. One set of measurements was used to develop empirical relationships between the spectral reflectance and the above-mentioned water quality parameters. The other sets of measurements were used to test these relationships. The maximum errors of estimation are: 3 mg m^-3 for chlorophyll-α, 4 mg l^-1 for suspended matter and 0.065 mgC m^-3 for dissolved organic matter. The results are used to develop an appropriate methodology for monitoring of eutrophication processes in inland waters.