QUANTITATIVE INVERSION OF CHLOROPHYLL A CONCENTRATION AND ANALYSIS OF TEMPORAL AND SPATIAL CHARACTERISTICS IN HONGKONG OFFSHORE WATERS BASED ON TIME-SERIES HJ-1A/B MULTISPECTRAL DATA

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.