Abstract
Abstract. In order to meet the demand of obtaining chlorophyll a concentration distribution in the offshore waters of Hong Kong on a rapid and large scale, based on the daily measured chlorophyll a concentration data and the HJ-1A/B satellite multispectral data in 2009–2019. Taking Modis-Aqua and Himawari series chlorophyll a concentration of remote sensing products as comparative data. Through per-process to extracted the reflectivity of each band combined and statistical correlation analysis with measured data, select the highest correlation band combination as the characteristic variable to statistical regression analysis with two-thirds of the measured chlorophyll a concentration data, constructing multiple regression algorithms. Determination of the best inversion algorithm by verified accuracy of the remaining one-third of the measured data. Inversion of chlorophyll a concentration in the offshore waters of Hong Kong from 2009 to 2019, the results show: 1). The best inversion algorithm is a univariate cubic regression algorithm, R2 is 0.942, RMSE is 0.285 μg/L, RPD is 33%; 2). The overall trend of remote products is the same as the measured data, but the value is slightly higher than the measured data;3). The distribution characteristics in the offshore waters of Hong Kong in the recent ten years are “high in the east and low in the west”, and the average concentration in the western waters is about 5 μg/L lower than the eastern waters.
Highlights
Ocean chlorophyll a concentration is the highest pigment in algae and plankton
Remote sensing inversion of chlorophyll a concentration can meet the needs of water quality monitoring and eutrophication evaluation, marine productivity and other studies to quickly obtain large-scale ocean chlorophyll a concentration distribution, and make up for the shortage of observed sample points in traditional marine monitoring(Watanabe, et al 2018; Xu, et al 2018), which makes it possible to monitor the change of chlorophyll a concentration in long time series
The reasons are that the exchange and renewal capacity of semi-closed waters is weak, coupled with the discharge of domestic sewage, the polluted water bodies can not exchange with other water bodies in time, and the accumulation of water quality index leads to the increase of chlorophyll a concentration
Summary
Ocean chlorophyll a concentration is the highest pigment in algae and plankton. As the concentration is closely related to the number of algae in the water, it is the main index of the evaluation of the eutrophication of the water(Lu, et al 2015). Chlorophyll a concentration remote sensing inversion data products such as Modis-Aqua Chlor_a and Himawari Chlor_a have been widely used in the monitoring and analysis of marine environment in China(Shanmugam, et al 2018; Yao, et al 2017), but limited by the lack of high quality and long time series measured data, the. With a view to better service to the ocean biological chemistry and climate research
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