Aerospace remote sensing monitoring of inland water quality

The potential of using remote sensing for the detection of chlorophyll-a (CHL), dissolved organic matter (DOM), and suspended matter (SM) concentrations in coastal and inland waters was investigated using near-surface measurements of upwelling and downwelling (IR) radiance spectra along with simultaneous earth-reference data obtained on the test areas. The range of CHL was 0.1 to 350 μg/l, suspended matter was 0.1 to 43 mg/l, and DOM absorption at the analyzed wavelength (380 nm) was 0.1 to 10^-1. Factor and signature analysis reveal allometric relationships between constituent concentrations C_k and functions of reflectance Z_k of the type C_k = aZ_k^b. Appropriate functions of reflectance were found for the different constituents to be: Z_chl1 = R(700)/R(675), Z _chl2 = R(700)/R(560), and Z_chl3 = [R(700)-R(675)]/[R(700)+R(675)]; and Z_sm1 = [R(560)-R(520)]/[R(560)+R(520)], Z_sm2 = R(560)/R(520); and Z_dom = {R(480)+k[R(700)/R(675)]}/R(630). The maximum estimation errors were: CHL - 3 μg/l, DOM - 0.065 μgC/l, and SM - 4 mg/l. The parameters a and b differ significantly over different water areas for CHL, but this can be adjusted by virtue of good correlation with the averaged local value of CHL (C_chlavg). By using local correction, as in the equation C_k = a(C_chlavg)Z^b(Cchlavg), it is possible to detect CHL in water areas of different trophic states with estimation errors varied between 1.75 and 8.34 μg/l. There is a wide range of wavelengths over which a simple reflectance function Z = R_i/R_j works quite well for CHL, permitting use of even such wide-band sensors as MSS Landsat. Band combinations MSS6/MSS4 and MSS6/MSS4 + 5 + 6 are suitable for remote sensing of CHL if the value of C_chl < 150 μg/l. For C_chl < 20 μg/l, MSS5/MSS4 and MSS5/MSS4 + 5 + 6 may be available. For estimating of water quality from space using future space systems like NIRIS and MODIS, suitable imaging wavelengths are derived to be 480, 500, 520, 560, 630, 650, 675, 700, and 710 nm.