Estimation of chlorophyll-a concentration and trophic states for inland lakes in Northeast China from Landsat TM data and field spectral measurements

Landsat TM data and field spectral measurements were used to evaluate chlorophyll-a (Chl-a) concentration levels and trophic states for three inland lakes in Northeast China. Chl-a levels were estimated applying regression analysis in the study. The results obtained from the field reflectance spectra indicate that the ratio between the reflectance peak at 700nm and the reflectance minimum at 670nm provides a relatively stable correlation with Chl-a concentration. Their determination of coefficients R-2 is 0.69 for three lakes in the area. From Landsat TM data, the results show that the most successful Chl-a was estimated from TM3/TM2 with R-2=0.63 for the two lakes on 26 July 2004, from TM4/TM3 with R-2=0.89 for the two lakes on 14 October 2004, and from the average of TM2, TM3 and TM4 with R-2=0.72 for the three lakes tested on 13 July 2005. These results are applicable to estimate Chl-a from satellite-based observations in the area. We also evaluate the trophic states of the three lakes in the region by employing Shu's modified trophic state index (TSIM) for the Chinese lakes' eutrophication assessment. Our study presents the TSIM from different TM data with R-2 more than 0.73. The study shows that satellite observations are effectively applied to estimate Chl-a levels and trophic states for inland lakes in the area.