Variation Characteristics Of Attenuation Coefficient Of Upwelling Radiance And Attenuation Mechanism In Lake Taihu

Upwelling radiance was the signal source of ocean color remote sensing. It also was the key parameter that could reflect water quality conditions. The research object was the variation characteristics of attenuation coefficient of upwelling radiance and attenuation mechanism in Lake Taihu from spring to autumn. Based on the data of upwelling radiance and water quality parameter in Lake Taihu, the spectral characteristics in different seasons, spatial distribution characteristics in different areas of attenuation coefficient of upwelling radiance, and the multiple liner regression relationship between the concentration of organic and inorganic suspended matter, chlorophyll a and attenuation coefficients of upwelling radiance were analyzed. According to multiple scattering radiative transfer model, this study calculated the attenuation coefficient of upwelling radiance in the condition of different zenith angles, absorption and scattering coefficient, then discussed attenuation mechanism of upwelling radiance. The results of this research provided the corresponding theoretical basis for the research of optical properties in Lake Taihu and the precision improvement of ocean color remote sensing inversion. The main conclusions on this research were as follows:(1) The spectral characteristics of attenuation coefficient of upwelling radiance in different seasons in Lake TaihuAttenuation coefficient of upwelling radiance basically decreased with the wavelengths in most locations from430-600nm, above700nm the spectral shape of attenuation coefficient of upwelling radiance started to rise. And the spectral shape of attenuation coefficient of upwelling radiance was mainly controlled by the spectrum of absorption coefficient.(2) The spatial distribution characteristics of attenuation coefficient of upwelling radiance in different areasSpatial distribution of the average of attenuation coefficient of upwelling radiance was different between spring and autumn by the different composition of water body, wind and other factors. The high value of attenuation was different from spring to autumn. The attenuation trend in spring was:open water area> grass type zone> typical algae type zone> grass, algae type zone; in autumn was:grass, algae type zone> open water area> grass type zone> typical algae type zone.(3) The multiple liner regression relationship between the concentration of organic and inorganic suspended matter, chlorophyll a and attenuation coefficient of upwelling radianceTaking the concentration of organic and inorganic suspended matter, chlorophyll a, as independent variables and doing multiple liner regression analysis relationship with attenuation coefficient of upwelling radiance, a good linear relationship was found that using the concentration of inorganic suspended matter could get better effect than other factors. It showed that the concentration of inorganic suspended matter did a significant positive contribution to attenuation coefficient of upwelling radiance.(4) The mechanism discussion of variation regularity of attenuation coefficient of upwelling radianceAttenuation coefficient of upwelling radiance basically increased linearly with the increase of absorption coefficient, the slope of attenuation coefficient of upwelling radiance rose with the increase of absorption coefficient when scattering coefficient became larger; scattering effect on attenuation coefficient of upwelling radiance existed two different influence of enhancement and weakened. At a large zenith angle, attenuation coefficient of upwelling radiance gradually decreased and subsequently increased with the increase of scattering coefficient when absorption was less. Meanwhile, at a small zenith angle, attenuation coefficient of upwelling radiance increased approximately linearly with the increase of scattering coefficient; along with the larger absorption, this trend gradually disappeared. When the ratio of scattering/absorption was from0.5to37, absorption coefficient did the greatest contribution to attenuation coefficient of upwelling radiance, and the corresponding contribution rate was in the range of90.3%-98.5%; when the ratio was less than1.5, the contribution of the zenith angle to attenuation coefficient of upwelling radiance was greater than that of scattering coefficient, and the corresponding contribution rates respectively ranged from2.2%to7.3%and from3.7%to17.9%; with the increasing ratio, the contribution of scattering coefficient was bigger than the zenith angle, and the tendency tended to be stable.