Quantitative near-surface remote sensing of wastewater quality in oxidation ponds and reservoirs: A case study of the naan system

This study develops a remote sensing technique for real-time monitoring of wastewater effluents stored before irrigation. Reflectance and attenuation coefficients for downwelling irradiance spectra (400 to 950 nm spectral resolution of 2 nm) were acquired simultaneously with turbidity, chlorophyll, organic matter, and total suspended matter concentrations in the Naan wastewater system, Israel. High-spectral-resolution spectrometric data were used to select the most suitable spectral bands for remote sensing of `optically active' constituent concentrations. Algorithms for remote estimation of wastewater quality expressed as chlorophyll-a, bacteriochlorophyll-a, and total suspended matter concentrations were developed. Reflectance height at 720 nm and an area above the base line from 670 to 950 nm was used in algorithms for chlorophyll-a assessment (r²>0.83). For bacteriochlorophyll-a assessment, an area under the base line through 780 to 900 nm was used, allowing its quantitative estimation (r²>0.94). Reflectance of approximately 570 and from 400 to 950 nm correlated closely with total suspended matter concentration (r²>0.82) and was used to retrieve it from reflectance spectra. This is the first reported study on the quantitative remote assessment of wastewater quality. The results suggest that four spectral bands be used for real-time monitoring of wastewater ponds quality.