Study on Monitoring System of Chlorophyll-a Concentration and Water Temperature in Lake using NOAA/AVHRR Observed Data

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The Abashiri Lake consists of two strong stable layers of upper Oligohaline water and lower Polyhaline water, which is entirely a brackish lake. The boundary depth of two layers has gradually decreased with time. At the same time, this has led to an increase in salinity and eutrophication in upper layer and to an acceleration of deoxygenating of lower layer, attributed to the occurrence of algal bloom and the upwelling of bluish water. It is pointed out that the algal bloom occurs in the Abashiri Lake on condition that the water temperature is larger than 18 ℃ and the chlorophyll-a concentration is larger than 30 μg/l.At first, the vertical and seasonal variations of one dimensional water tempera in the Abashiri Lake were calculated using a surface boundary condition described by observed values, a bottom boundary condition with no-heat conduction and a vertical initial condition described by estimated values for January 1^<st>. The surface temperature can be estimated using the software, MCSST (Multi Channel Sea Surface Temperature) for NOAA/AVHRR data received on the condition of no-cloud.In the next, the spectral reflectance of Abashiri Lake surface was formulated by using NOAA/AVHRR data received in Kitami Institute of Technology, horizontal global and scattered solar radiation at the shore. In order to correlate the spectral radiance of NOAA/AVHRR Ch.1 with the spectral radiance emitted from water surface, transmittance and path radiance were calculated approximately by using the horizontal global and the scattered solar radiation. Then, the chlorophyll-a concentration in the center of the Abashiri Lake was estimated by the regression line of the chlorophyll-a concentration on the difference of spectral reflectance between fluorescence and absorption zone of phytoplankton.