Relationship between spectral reflectance and chlorophyll-a concentration in the eutrophic Lake Togo-ike

The objective of this study is to investigate the relationship between spectral reflectance and Chla in the lake. The spectral reflectance and upper-layer water sampling was performed from onboard on May 30, August 8, 2013, and March 7, 2014 at the 10 to 11 points in the lake. MS720 (EKO Ltd.) was used for spectral reflectance measurement. The wavelength range of reflectance measurement is 400 to 900 nm. Chla was quantified by the UNESCO method after the filtering of upper-layer water and acetone extraction in the laboratory. The range of Chla is 6 to 145 mu g L-1. The spectral-reflectance characteristic in the lake is the low reflectance near 670 nm (strong absorption), and the high reflectance near 700 nm (including fluorescence). Such the characteristic is the same as the eutrophic lakes such as Chesapeake Bay in the United States, or Lake District in Germany. A correlation analysis using the two band algorithm for Chla estimation was conducted using 32 obtained datasets. An optimal combination of two bands was the case of 648 nm and 700 nm (R-2=0.81). However, the latest earth observation satellites are not observed at these bands. Then, the Chla estimation using Landsat-8 OLI bands which was launched in Feb., 2013 was examined. As a result, it became clear that the technique adapting OC2 and OC3 model of the operational algorithm was comparatively reasonable.