Abstract
Chlorophyll-a (Chl-a) is an objective biological indicator, which reflects the nutritional status of coastal waters. However, the turbid coastal waters pose challenges to the application of existing Chl-a remote sensing models of case II waters. Based on the bio-optical models, we analyzed the suppression of coastal total suspended matter (TSM) on the Chl-a optical characteristics and developed an improved model using the imagery from a hyper-spectrometer mounted on an unmanned aerial vehicle (UAV). The new model was applied to estimate the spatiotemporal distribution of Chl-a concentration in coastal waters of Qingdao on 17 December 2018, 22 March 2019, and 20 July 2019. Compared with the previous models, the correlation coefficients (R2) of Chl-a concentrations retrieved by the new model and in situ measurements were greatly improved, proving that the new model shows a better performance in retrieving coastal Chl-a concentration. On this basis, the spatiotemporal variations of Chl-a in Qingdao coastal waters were analyzed, showing that the spatial variation is mainly related to the TSM concentration, wind waves, and aquaculture, and the temporal variation is mainly influenced by the sea surface temperature (SST), sea surface salinity (SSS), and human activities.
Highlights
IntroductionThe ocean accounts for 71% of the Earth’s total area and has 97% of the world’s water resources
The ocean accounts for 71% of the Earth’s total area and has 97% of the world’s water resources.Ocean waters, especially coastal waters, are important ecosystems and provide a lot of essential ecosystem services for people
We demonstrated the process of using a unmanned aerial vehicle (UAV) equipped with a hyperspectral imager to image coastal waters in Qingdao and successfully estimated the Chl-a concentration
Summary
The ocean accounts for 71% of the Earth’s total area and has 97% of the world’s water resources. Especially coastal waters, are important ecosystems and provide a lot of essential ecosystem services for people. With the rapid development of the coastal economy, the coastal water quality has gradually deteriorated in the past decades. After 1950, the development of aquaculture has led to significant degradation of the ecological environment, which has threatened biological resources and human health [1,2,3]. Since 2007, green tides have occurred in the Yellow Sea every year due to the water eutrophication caused by ocean pollution.
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