Application of Remote Sensing Technique to Suspended Sediment Estimation of Pinan River, Eastern Taiwan

Abstract:

Because of the rapid compression between the Eurasian Plate and the Philippine Sea Plate, the Central Range of the Taiwan Island continued to quickly uplift. Moreover, because of being located in the subtropical area, Taiwan has abundant rainfall, and has distinct wet and dry season. Typhoons which almost brought violent rain, struck Taiwan average four times a year during the summer. This extreme tectonic and weather condition makes that a large number of sediments easily to be taken away from the mountainous area and output to the downstream estuary in a short time. These eroded sediments can be classified into two categories. One is bedrock sediments, and the other is suspended sediments which could be detected by the satellite remote sensing technique. In previous studies, some suspended sediment concentration (SSC) predictions were carried out by using optical satellites imagery in different areas. As we know, the more suspension sediment in water can directly reflect the higher reflectance of solar radiation. In addition, the exact form of the relationship between SSC and reflectance also depends on the mineralogy, color, and size of the sediments. Therefore, most studies developed unique relationships by relating field measurements of SSC to reflectance data from satellite imagery. The Pinan River is the largest river in eastern Taiwan. It rises in the Central Range and flows through Taitung County for 84 kilometers. Statistically, in Taiwan, more than 40 percent typhoons struck and landed from the Pinan River watershed. Abundant rainfall coupled with short channel caused plenty of sediments output from the Pinan River. In this study, we focus on Pinan River estuary by using SSC field data which was got from the Hydrological Year Book of Taiwan published by Water Resources Agency every year. Because of lack of field data, we got daily river discharge to establish the Rating Curve and predict daily SSC. Moreover, we also used FORMOSAT-2 imagery in band 3 and band 4 to monitor suspended sediments and identify an appropriate SSC-reflectance model. According to this model, we could estimate suspended sediments which depended on the rainfall, after typhoons passing through the Taiwan. Furthermore, we discussed the behavior of suspended sediments, including concentration, direction, and distribution.