Abstract

We analyzed the impacts of islands on suspended sediment concentration (SSC) in Zhoushan Coastal waters based on data from HY-1C, which was launched in September 2018 in China, carrying Coastal Zone Imager (CZI) and Chinese Ocean Color and Temperature Scanner (COCTS) on it for offshore observation. A new SSC retrieved model was established based on the relationship between in situ SSC and the reflectance in red and near infrared bands of CZI image. Fifteen CZI images obtained from October to December 2019 were applied to retrieve SSC in Zhoushan coastal waters. The results show that SSC in study area is 100–1600 mg·L−1. The SSC near islands changes obviously. Upstream of the islands, SSC is lower than downstream. During the flood and ebb, when the current passes through the islands, circumfluence will appear, under certain geophysical factors, generating Karman vortex streets downstream of the islands. The sediments were stirred by the fast speed current at the outer side of vortex street to the sea surface inducing higher SSC at the outer side of the vortex street, while the central sediments of the vortex street were lower. In the direction of ocean currents, the SSC of the vortex street downstream of islands is changing regularly, i.e., increasing, then decreasing and increasing again and then decreasing in a snaking vortex street whose length downstream is between 1000 and 8000 m long.

Highlights

  • Dynamic processes, such as the ocean waves, currents, tides and eddies, are complex and influential [1]

  • We analyzed the impacts of islands on suspended sediment concentration (SSC) in Zhoushan Coastal waters based on data from HY-1C, which was launched in September 2018 in China, carrying Coastal Zone Imager (CZI) and Chinese Ocean Color and Temperature Scanner (COCTS) on it for offshore observation

  • Highlight findings of this paper include: (1) a new launched satellite HY-1C was applied for offshore observation; (2) a new SSC retrieved model was established based on CZI image from HY-1C; (3) the SSC near islands changes obviously, forming a snaking “SSC tape” with its length between 1000 and 8000 m downstream of the islands

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Summary

Introduction

Dynamic processes, such as the ocean waves, currents, tides and eddies, are complex and influential [1] These dynamic environmental factors should be considered for offshore marine management. Ocean color is another key factor in detecting the existence of eddies based on their impact on the concentration of suspended sediments, chlorophyll and organic matters as well as temperature in the ocean [11]. Based on the analysis mentioned above, can the Karman vortex street be detected from the satellite by the change in suspended sediment concentration (SSC)?. We analyzed the impacts of coastal islands on distribution of suspended sediment concentration based on satellite data obtained from a new launched satellite HY-1C, which has an advanced resolution in time and space.

Data and Method
Satellite Data
In Situ Data
Satellite Data Processing
Result
Applicability of New Model
The Factors Affecting Distribution of Suspended Sediment Concentration
Islands Induced Karman Vortex Streets Influenced SSC Distribution
Conclusions
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