Author(s): Haruna Takahashi; Yosei Yamasaki; Shoji Okada
Linked Author(s):
Keywords: Pera River; Turbidity; Water sampling; Measurement; Experiment; Sentinel-2
Abstract: Turbidity or suspended sediment concentration measurements to understand sediment dynamics in rivers are generally “point observations” in which water is collected with a bucket and measured with a turbidity meter. Therefore, it is time-consuming and labor-intensive to measure the temporal variation and areal distribution at a certain time. On the other hand, a method has been proposed to estimate turbidity on a watershed scale by calculating the surface reflectance of turbid water from near-infrared images taken by satellites, but this method has some problems, such as the fact that Sentinel-2 images are taken approximately every five days, and it is impossible to estimate turbidity when there are many clouds. To solve the above problem, the authors are developing a non-contact method to estimate the turbidity of water surfaces by calculating the surface reflectance from near-infrared images (wavelength: 840 nm, bandwidth: 40 nm) taken by a small multispectral camera that can be mounted on a UAV. As the results, we have experimentally measured the surface reflectance of various types of turbid water using fine sediment deposited in the river to obtain an equation that can be used in a local river and have shown that the surface reflectance obtained from satellite images (Sentinel-2) is comparable. This method was applied to the tidal area of the Pera River in Malaysia, where turbid water flows constantly, and water samples and turbidity measurements were taken in the Pera River at the time of Sentinel-2 passing. Using the collected fine sediment from the Pera River, an equation for estimating turbidity from the near-infrared wavelength reflectance of the water surface was experimentally developed. The equation was applied to past Sentinel-2 images, and the relationship with the water level of the Pella River at that time was used to clarify the spatiotemporal variation characteristics of turbidity in the tidal zone.
Year: 2024