| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系碩博士班 === 97 === Taiwan locates in a subtropical area with steep slopes and short rivers and receives an abundant annual rainfall of 2,493 mm. However, the precipitation with uneven distribution over time and space leads to frequent floods and droughts. The global average temperature is increasing by the globally climatic change. Due to the natural disasters and over-explorations, a considerable change has been observed in the water catchment areas of many rivers upstream in Taiwan during the past few years. When the heavy rain occurs, the debris flow and mudslides are usually flushed from the areas of steep terrain to the reservoir, resulting in a dramatic increase in turbidity and the shortage in supplying the use of domestic water. Therefore, how to keep abreast of suspended sediment concentration distribution, and carrying on the best management, decision-making and analysis are important.
There are a number of alternatives for the design of a case 2 water algorithm with the capability to decompose the inherent optical properties (IOPs) into contributions by different water constituents. Radiative transfer modeling provides a systematic means of determining the effect of changes in the optical properties of water on underwater light fields and remote sensing reflectance signals. One of the key solutions is under the IOPs of suspended sediment investigation and measurement. In recent years, the combination of commercially available software such as Hydrolight and new in situ spectrophotometer for measuring IOPs has enabled greatly improved radiative transfer models to be constructed.
The size of suspended sediment in the inland waters is an important factor for optical monitoring method. A water tank was used for all experiments, and the interior surfaces were painted black to minimize extraneous reflectance of light. This study made use of ac-s (WetLabs Inc.) to measure the absorption coefficients of different sediment sizes. The sediment size of #200 ~ #300(0.075 ~ 0.048 mm), #300 ~ #325(0.048 ~ 0.045 mm) and #325 ~ #400(0.045 ~ 0.038 mm) were choose to conduct water tank experiment. The purpose of the research was to investigate the relationships between and among IOPs, sediment size, and suspended sediment concentration (SSC).
The results of this study includes (1) the absorption coefficient and scattering coefficient increase with increasing SSC, then the specific absorption coefficient and specific scattering coefficient were inverse proportion relationship with particle size of suspended sediment; (2)the absorption spectrum generally decreases, often exponentially, with increasing wavelength. The scattering spectrum of coarse particles occurs clearly peak and trough phenomenon across the visible wavelength, and the wavelength of peak shifted from 430 to 463 nm as SSC increased from 450 to 660 mg/l. The scattering spectrum of fine-grain was linear with increasing wavelength; and (3) the results of retrieve particle size were that D1 was 0.062±0.0019 mm and then Sd was 0.0078; D3 was 0.040±0.0004 mm and then Sd was 0.0088.
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