Study On Apparent Optical Parameters In Lake Taihu

Water environment study has been a hot topic. Ocean remote sensing has many characteristics, such as the large range, fast and periodical. So, Oceanremote sensing promotes water environment study, and water quality monitoring. Any optical remote sensing needs further research of the optical properties of target object. Water signal of water-leaving radiance occupies10%of the received total signal by remote sensors. Water color inversion algorithm is sensitive to the error of water-leaving radiance. And light transmission and reflection characteristics are very important to obtain water-leaving radiance.Taihu lake, the large shallow inland lake, was taken as example in this paper. Through the field optical experiment, we all-roundly measured radiance and irradiance of five different depth between20cm and100cm.Then apparent optical properties of air-water interface was studied systematically.The results indicate that, firstly, parameter f has no relationship with wavelength and the value of f is depend on solar zenith angle and backscattering coefficient. Secondly,the mean value of parameter Q is about4.5.Q changes little with wavelength and its relationship with solar zenith angle is not obvious. Thirdly,between440nm and700nm, parameters t+and t also have no relationship with wavelength. Fourthly, Transmittance r of the gas-water interface in the non-storm conditions, with the solar zenith angle increases, the gas-water interface reflectivity r gradually increases between0-55°, r in the range0.02-0.045storm conditions between the air-water interface reflectivity r with the solar zenith angle, the observer’s zenith angle and wind speed increases.The mean value of parameter Kd changes from2to12. The fluctuation range of parameter Kd is4-6in the same wavelength. The great values of Kd appear at about415nm,750nm,and900nm,and the minimum at810nm.From profile changes respect the great values of Kd appear between20cm and40cm or between40cm and60cm.Along with the change of the depth the value of kd increases gradually, then levels off or decreases rapidly. In the space, Kd value of southern is bigger than the northern. From South to the north it appears in the form of belt. Between400nm and900nm,in spring Kd value is bigger than in autumn obviously. And the former is about1bigger than the later. Between in the depth of20cm to40cm,Kd value of turbidity water is the biggest, and the difference with other depth is big. Kd value of even water changes not obvious with depth relatively. Besides, part of the turbidity water shows more significant layered characteristics and even water doesn’t. Further more, the paper comparatively analysis parameter kd, k1and ku.The bottom reflectance of Taihu lake is range of0.05-0.24. Due to the lack of greater depth than one meter of the actual radiation measured values,the projections of the lake reflectance spectral shape is still the performance of the spectral characteristics of algae chlorophyll.Typical albedo space analysis revealed that the lake’s bottom reflectance spatial distribution of basic present south of the northern trend. In the440nm-800nm range, the value of the lake’s bottom reflectance in the autumn is greater than the spring; between440nm-740nm, the average difference is about2%, while compared to1%above740nm.Finally,this paper studies the apparent optical properties of air-water interface of Taihu lake, determines the value of optical parameters, lays the foundation of establishing lakes color remote sensing mechanism model.