FEASIBILITY STUDY FOR THE ESTIMATION OF CHLOROPHYLL-A USING MEASURED SPECTRAL REFLECTANCE IN THE EUTROPHIC LAKE-LAKE KOJIMA CASE STUDY IN FY2009

摘要

The objective of this study is to evaluate the performance of the two-band model in estimating Chl.a in Lake Kojima, Okayama Prefecture, Japan as representive example of Case II waters, and to assess the accuracy of Chl.a estimation. To evaluate the model's performance, a portable spectroradiometer (MS 720) was used to measure surface spectral radiance reflectance in the visible and near-infrared range of the spectrum using a small vessel in April 2009, July 2009, October, 2009, and January 2010. Water samples were collected to measure Chl.a (2.6-20.0 (mu)g/1) and Secchi disk transparency (0.5-1.5 m). Thirty-two data sets of spectral reflectance/Chl.a were collected. After normalized processing had been conducted, the reflectance data were compared with the Chl.a data. As a result, a strong linear relationship was established between the analytically measured Chl.a and two-band model R(700)/R(670), where R is reflectance at wavelength n (r velence 0.80). RMSE of Chl.a estimation using the two-band model was below 2.7 (mu)g/1. This result corresponds to past case studies in Chesapeake Bay, USA and Kasumigaura, Japan. Chl.a estimation techniques such as the single-band model, two-band model, and the LCI model using a data set in Lake Kojima are tested for the determination material of a SGLI Chl.a model. As a result, even when some models were applied, the correlation with observed Chl.a was about r velence 0.5. However, the correlation of the area average in the lake was very high (r velence 0.9 or more). Therefore, we recommend incorporation of this technique for routine monitoring of water quality using hyper-spectral sensor data such as Hyperion or SGLI in coastal and large estuarine waters like Lake Kojima in the future.