Remote sensing of chlorophyll in Lake Kinneret using high-spectral-resolution radiometer and Landsat TM : spectral features of reflectance and algorithm development

High-resolution reflectance spectra in the range of 400-850 nm were obtained from Lake Kinneret during a period when dense populations of the dinoflagellate Peridinium gatunense dominated the phytoplankton. Chlorophyll (Chl) concentrations ranged from 5.1 to 185 mg m super(-3) and from 2.4 to 187.5 mg m super(-3) in the samples of two independent experiments. The most prominent features of the reflectance spectra were: (i) a wide minimum from 400 to 500 nm; (ii) a maximum at 550-570 nm, which did not surpass 3% in samples with high Chl concentration (>20 mg m super(-3)), indicating a strong absorption by pigments in the green range of the spectrum; (iii) a minimum at 676 nm; this was similar to 1% and was almost insensitive to variation in Chl concentration >10 mg m super(-3); (iv) a maximum reflectance showed near 700 nm; its magnitude and position were highly dependent on chlorophyll concentration. High-spectral-resolution data were used as a guideline for selection of the most suitable spectral bands for chlorophyll remote sensing. Models were devised, based on the calculation of the integrated area above the baseline from 670 to 850 nm and the reflectance maximal height within this range. Some algorithms already used in previous studies were tested and showed a plausible degree of accuracy when applied to the current data base. However, novel models devised in this study improved substantially the accuracy of Chl estimation by remotely sensed data, by reducing the estimation error from >11 to 6.5 mg m super(-3). Those models were validated by an independent data set where Chl concentration ranged over two orders of magnitude. The use of three relatively narrow spectral bands was sufficient for Chl mapping in Lake Kinneret. Therefore, a relatively simple sensor, measuring only a few bands will be employed in future applications for Chl monitoring in inland waters. Radiometric data were also used to simulate radiances in the channels of TM Landsat and to find the algorithm for Chl assessment. The ratio of channel 4 to channel 3 was used and enabled Chl estimation with an error of