Arnold G. Dekker

Quantitative modeling of inland water quality for high-resolution MSS systems

For a lake system in The Netherlands, Secchi disk transparency, seston dry weight, vertical attenuation coefficients, chlorophyll-a, and phaeopigments were determined. Inherent optical properties were estimated from measured apparent optical properties. Subsurface spectroradiometric measurements and airborne (non)-imaging spectrometric measurements were performed. This made it possible to model the performance of high-resolution multispectral scanning systems. Results of multivariate statistical modeling of water quality parameters versus simulated spectral band ratios for a water quality spectral bandset of the programmable multispectral imager (PMI), also known as the fluorescence line imager (FLI), are presented. >

Remote sensing as a tool for assessing water quality in Loosdrecht lakes

The underwater light field in 7 lakes in the Loosdrecht lake area was measured in situ. Subsurface upwelling irradiance and irradiance reflectance, together with estimations of scattering and laboratory measurements of absorption by aquatic humus and particulate matter, enabled an analysis of the spectral signature of these waters. Aircraft imaging spectrometer measurements of upwelling radiance at 1 km altitude were used to simulate the PMI Chlorophyll #1, the CAESAR Inland Water Mode spectral bandsets and the Thematic Mapper bands 1 to 4. This made it possible to compare the effects of spectral band width and selection on the estimation of water quality parameters. Correlations increased to r > 0.94, at a significance level of 1% for the simulated C-IWM data with the 6 water quality parameters. Images of the PMI Chlorophyll #1 and of the TM were analysed and found to be in accordance with the statistical modelling results.A significant increase in correlation of remote sensing data with water quality parameters can be achieved through the selective use of 10 to 20 nm wide bands in the spectral range of 500 to 720 nm in these eutrophic waters. Sum of chlorophyll a and phaeopigments, seston dry weight, Secchi disc transparency, and coefficients for vertical attenuation of light, absorption and scattering can be estimated accurately. TM image data for water quality assessment is of limited use due to the relatively low spectral and radiometric resolution. However, the revisit capability and relatively low price per area are positive aspects of these satellite images.

An assessment of the importance of emergent and floating-leaved macrophytes to trophic status in the Loosdrecht lakes (The Netherlands)

The potential importance of the six major emergent and floating-leaved macrophyte species in recycling of sediment phosphorus in the Loosdrecht lakes was studied. Representative plant samples were collected at the time of maximum biomass, and analysed for biomass and carbon, nitrogen and phosphorus contents. Species cover was determined by aerial photography.

Application of remote sensing techniques for water quality monitoring

A detailed study and experimental work performed to establish the properties of multispectral remote sensing techniques as applied to the monitoring of water quality, is hihhly desirable since direct synoptic field measurements concerning the quantity and type of pollutants in water is not possible at present.The multispectral characteristics of the signal received from water are a function of hydrological, biological and chemical characteristics of water, and the physical properties of the remote sensor related environment. Spectral data encompassing of the spectral region 0.36 μm and 2.36 μm showed that the detectibility of water pollutants, using spectral signatures in the 0.4 to 0.9 μm range, is promising and feasible.