| Optical properies in the northern part of Lake Taihu were investigated in fourtypical months between 2005 and 2006. Based on field observation samples ofdifferent regions in the northern part of Lake Taihu and later laboratory analysis, thispaper studied spatio-temporal variation of the bio-optical properties (CDOM,particulate matter, irradiance ratio), and then developed the quantitative retrievalmodels of total suspended matter (TSM) and inorganic suspended matter (ISM) usinga semi-analytic method.The results indicated that the spatial pattern of CDOM absorption was: ZhushanBay＞Meiliang Bay＞Gonghu Bay＞Lake center. Furthermore, CDOM absorptionwas generally higher near the river inflow than the open water in Meiliang Bay.Seasonally, CDOM absorption gradually decreased from the winter to the followingautumn. The values of the exponential slope coefficient S had no significantdifference in time and space. In the seasons like winter and spring, no correlationswere found between CDOM absorption coefficient and chlorophyll a concentration,however, CDOM absorption coefficient consistent with the spatial distribution ofchlorophyll a concentration distribution significantly and positively correlated withchlorophyll a concentration during algal bloom in the two other seasons. Relativelyconstant linear relationship have been established between CDOM absorption andfluorescence intensity in four seasons. In natural light, UV radiation exposure inchief, a significant photochemical degradation occurred, and the degradation processto be consistent with a band attenuation reaction kinetics.The absorption spectra by total particulate in the four seasons are obviouslydifferent. Phytoplankton absorption properties had a marked effect on totalparticulate absorption in summer and autum. However, in winter total particulateabsorption was similar to that of detritus, with values of absorption coefficientdecreasing with wavelength. Distribution of all stations is also different,by the timeis highest in summer,higher in autumn,high in spring and lowest in winter. Nosignificant spatio-temporal variation was found for the values of the exponential slope coefficient S of detritus. Phytoplankton absorption coefficient significantlycorrelated with chlorophyll a concentrations in the same period, and the correlationwas lowest in winter and not very different between the other three seasons. Theabsorption coefficient of total particulate, detritus and phytoplankton respectivelysignificantly correlated total suspended solids, organic,and inorganic particles, andthe rank of the correlation coefficient is TSS＞ISS＞OSS, for season ranking winterand spring higher than summer and autumn. Phytoplankton absorption coefficientonly weakly correlated with organic particles.Significant spatio-temporal variation was found for the contributions of everycomponent in water to the total absorption coefficient.The largest contribution rate tothe total absorption was detritus, followed by CDOM, phytoplank-ton ranks third, thewater absorption contribution to a minimum.The detritus contribution rate washighest in winter, higher in spring,high in summer, and lowest in autumn, meanwhile,the contribution rate for the four seasons of CDOM was highest in winter, higher inspring, high in autumn, lowest in summer. The contribution rate of phytoplanktonwas highest in summer,higher in autumn,high in spring, and lowest in winter. Thecontribution rate of pure water was more or less the same in different seasonsranging between 6%～7%.Irradiance reflectance distribution was similar in the two seasons like winter andspring, varying between Lakes region. Numerical value in winter was significantlylarger than in summer, and the difference between spring and autumn was notsignificant. Estimation of the concentrations of TSM and ISM was reasonablyaccurate based on inherent optical properties measurement, and the RMSE and theaverage RE were 11.13mg/L, 6.0% for TSM, and 9.90 mg/L, 5.1% for ISM,respectively. Remote sensing accuracy compared with the expected effect was quitesatisfactory.
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