Abstract：The Forel-Ule scale was introduced to record the colors of oceans and inland waters. It classified natural water colors into 21 grades ranging from dark blue to reddish brown. With satellite data, it has been possible to extract the Forel-Ule index (FUI) , which correspond to 21 levels of the Forel-Ule scale. Based on Sentinel-3OLCI satellite data, the monthly and annual FUI of the Bohai Sea for the past five years from 2018 to 2022 was extracted. In addition, spatial and temporal variations in water color conditions were investigated. As can be seen from the results, both the spatial and temporal variation of FUI in the Bohai Sea was significant. High FUI values were observed in the coastal waters of Liaodong Bay, Bohai Bay, and Laizhou Bay. This indicated turbid water and poor water color. In contrast, low FUI values were observed in Qinhuangdao and other offshore waters, reflecting relatively clear water and good water color. A "V" shaped change, i.e., the FUI varied from large to small and then to large, from January to December, in the variation of the monthly FUI average in the Bohai Sea was captured, illustrating the process of the Bohai Sea's water color condition from turbid to clear and then to turbid. An overall decreasing trend in the annual FUI average value was detected, corresponding to the water color condition getting better, from 2018 to 2022. During this period, the highest decreasing rate happened from 2018 to 2019, subject to the Bohai Sea comprehensive management battle. The lowest level was in 2020, followed by a slight rebound in 2021. The annual FUI average value reached its lowest level in 2022. Compared with 2020, the percentage of sea area with improved, stable, and deteriorating water color in 2022 was 36.05%, 50.45%, and 13.50% respectively. This was the best performance in five years. Therefore, it was seen that comprehensive management of the Bohai Sea had played an active role in improving its ecological environment. Monitoring FUI with remote sensing increased the capacity for regular inspections and supervision of China's marine ecological environment. This was of great practical importance.
王林, 王祥, 陈艳拢, 高思雯, 曾怡乐, 孟庆辉, 王新新. 基于Sentinel-3 OLCI数据的渤海水色状况时空变化特征[J]. 中国环境科学, 2023, 43(9): 4828-4836.
WANG Lin, WANG Xiang, CHEN Yan-long, GAO Si-wen, ZENG Yi-le, MENG Qing-hui, WANG Xin-xin. Spatiotemporal variation of water color conditions in the Bohai Sea based on Sentinel-3OLCI data. CHINA ENVIRONMENTAL SCIENCECE, 2023, 43(9): 4828-4836.
马本昌.基于色度角的中国近海水色要素遥感研究[D]. 南京:南京信息工程大学, 2022. Ma B C. Remote sensing of ocean color elements in the Chinese offshore based on chromaticity angle[D]. Nan Jing:Nanjing University of Information Science and Technology, 2022.
[2]
Prieur L, Sathyendranath S. An optical classification of coastal and oceanic waters based on the specific spectral absorption curves of phytoplankton pigments, dissolved organic matter, and other particulate materials[J]. Limnology and Oceanography, 1981,26(4):671-689.
[3]
O'Reilly J, Maritorena S, Mitchell B G, et al. Ocean color chlorophyll algorithms for SeaWiFS[J]. Journal of Geophysical Research:Oceans, 1998,103(C11):24937-24953.
[4]
Tang J W, Wang X M, Song Q J, et al. The statistic inversion algorithms of water constituents for the Huanghai Sea and the East China Sea[J]. Acta Oceanologica Sinica, 2004,23(4):617-626.
[5]
Lee Z P, Shang S L, Hu C M, et al. Secchi disk depth:A new theory and mechanistic model for underwater visibility[J]. Remote Sensing of Environment, 2015,169:139-149.
[6]
Silsbe G M, Beherenfeld M J, Halsey K H, et al. The CAFE model:A net production model for global ocean phytoplankton[J]. Global Biogeochemical Cycles, 2016,30:1756-1777.
[7]
Bonelli A G, Loisel H, Jorge D S F, et al. A new method to estimate the dissolved organic carbon concentration from remote sensing in the global open ocean[J]. Remote Sensing of Environment, 2022,281:113227.
[8]
Alföldi T T, Munday J. Water quality analysis by digital chromaticity mapping of Landsat data[J]. Canadian Journal of Remote Sensing, 1978,4(2):108-126.
[9]
Bukata R P, Bruton J E, Jerome J H. Use of chromaticity in remote measurements of water quality[J]. Remote Sensing of Environment, 1983,13(2):161-177.
[10]
Bukata R P, Pozdnyakov D V, Jerome J H. et al. Validation of a radiometric color model applicable to optically complex water bodies[J]. Remote Sensing of Environment, 2001,77(2):165-172.
[11]
Wernand M R, van der Woerd H J. Spectral analysis of the Forel-Ule ocean colour comparator scale[J]. Journal of the European Optical Society Rapid Publications, 2010,5:10014s.
[12]
Novoa S, Wernand M R, Van der Woerd H J. The Forel-Ule Scale revisited spectrally:Preparation protocol, transmission measurements and chromaticity[J]. Journal of the European Optical Society:Rapid Publications, 2013,8:13057.
[13]
Wernand M R, Hommersom A, van der Woerd H J. MERIS-based ocean colour classification with the discrete Forel-Ule scale[J]. Ocean Science, 2013,9(3):477-487.
[14]
van der Woerd H J, Wernand M R. True colour classification of natural waters with medium-spectral resolution satellites:SeaWiFS, MODIS, MERIS and OLCI[J]. Sensors, 2015,15(10):25663-25680.
[15]
van der Woerd H J, Wernand M R. Hue-angle product for low to medium spatial resolution optical satellite sensors[J]. Remote Sensing, 2018,10(2):180.
[16]
Wernand M R, van der Woerd H J, Gieskes W W. Trends in ocean colour and chlorophyll concentration from 1889 to 2000, worldwide[J]. Plos One, 2013,8(6):e63766.
[17]
Garaba S P, Badewien T H, Braun A, et al. Using ocean colour remote sensing products to estimate turbidity at the Wadden Sea time series station Spiekeroog[J]. Journal of the European Optical Society-Rapid Publications, 2014,9:14020.
[18]
Garaba S P, Voß D, Zielinski O. Physical, bio-optical state and correlations in North-Western European Shelf Seas[J]. Remote Sensing, 2014,6(6):5042-5066.
[19]
Garaba S P, Friedrichs A, Voss D, et al. Classifying natural waters with the Forel-Ule Colour Index System:results, applications, correlations and crowdsourcing[J]. International Journal of Environmental Research and Public Health, 2015,12(12):16096-16109.
[20]
Pitarch J, van der Woerd H J, Brewin R J W, et al. Optical properties of Forel-Ule water types deduced from 15years of global satellite ocean color observations[J]. Remote Sensing of Environment, 2019, 231:111249.
[21]
Chen Q, Huang M T, Tang X D. Eutrophication assessment of seasonal urban lakes in China Yangtze River Basin using Landsat 8-derived Forel-Ule index:a six-year (2013~2018) observation[J]. The Science of the total environment, 2020,745:135392.
[22]
王胜蕾.基于水色指数的大范围长时序湖库水质遥感监测研究[D]. 北京:中国科学院大学, 2018. Wang S L. Large-scale and long-time water quality remote sensing monitoring over lakes based on water color index[D]. Bei jing:University of Chinese Academy of Sciences, 2018.
[23]
Wang S L, Li J S, Shen Q, et al. MODIS-based radiometric color extraction and classification of inland water with the Forel-Ule scale:a case study of Lake Taihu[J]. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015,8(2):907-918.
[24]
Wang S L, Li J S, Zhang B, et al. Changes of water clarity in large lakes and reservoirs across China observed from long-term MODIS[J]. Remote Sensing of Environment, 2020,247:111947.
[25]
Wang S L, Li J S, Zhang B, et al. Trophic state assessment of global inland waters using a MODIS-derived Forel-Ule Index[J]. Remote Sensing of Environment, 2018,217:444-460.
[26]
Li M J, Sun Y H, Li X J, et al. An improved eutrophication assessment algorithm of estuaries and coastal waters in Liaodong Bay[J]. Remote Sensing, 2021,13:3867.
[27]
Zhou Y D, He B Y, Fu C J, et al. An improved Forel-Ule index method for trophic state assessments of inland waters using Landsat 8 and sentinel archives[J]. GIScience & Remote Sensing, 2021,58(8):1316-1334.
[28]
张海波,王丽莎,石晓勇,等.渤海中部营养盐季节变化及限制统计分析[J]. 中国环境科学, 2019,39(4):1579-1588. Zhang H B, Wang L S, Shi X Y, et al. Spatial distributions and seasonal variations of nutrients and statistical analysis of nutrient limitation in the center of the Bohai Sea, China[J]. China Environmental Science, 2019,39(4):1579-1588.
[29]
王利明,马蕾,杨晓飞,等.渤海环境污染的治理与保护对策[J]. 中国资源综合利用, 2020,38(3):109-111. Wang L M, Ma L, Yang X F, et al. The countermeasures for the pollution control and protection in the Bohai Sea[J]. China Resources Comprehensive Utilization, 2020,38(3):109-111.
[30]
于春艳,朱容娟,隋伟娜,等.渤海与主要国际海湾水环境污染治理成效比较研究[J]. 海洋环境科学, 2021,40(6):843-850. Yu C Y, Zhu R J, Sui W N, et al. Comparative study on the effectiveness of water environmental pollution control between Bohai Sea and major international bays[J]. Marine Environmental Science 2021,40(6):843-850.
[31]
王林,王祥,王新新,等.基于Sentinel-3 OLCI影像的秦皇岛海域悬浮物浓度遥感反演[J]. 中国环境科学, 2022,42(8):3867-3875. Wang L, Wang X, Wang X X, et al. Retrieval of suspended particulate matter concentration from Sentinel-3 OLCI image in the coastal waters of Qinhuangdao[J]. China Environmental Science, 2022,42(8):3867-3875.
[32]
CIE. Commission internationale de l'eclairage proceedings 1931[R]. Cambridge:Cambridge University Press, 1932:19-29.
[33]
Chen X D, Liu L Y, Zhang X, et al. An assessment of water color for inland water in China using a Landsat 8-Derived Forel-Ule Index and the Google Earth engine platform[J]. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2021, 14:5773-5785.
[34]
任惠茹,李国胜,郭腾蛟,等.1950~2011年渤海地区海表风场的季节特征与多尺度变化分析[J]. 地理科学, 2017,37(9):1430-1438. Ren H R, Li G S, Guo T J, et al. Multi-scale variability of surface wind direction and speed on the Bohai Sea in 1950~2011[J]. Scientia Geographica Sinica, 2017,37(9):1430-1438.
[35]
孟庆辉,王林,陈艳拢,等.2002~2021年渤海叶绿素a浓度变化及环境响应分析[J]. 中国环境监测, 2022,38(6):228-236. Meng Q H, Wang L, Chen Y L, et al. Change of chlorophyll a concentration and its environmental response in the Bohai Sea from 2002 to 2021[J]. Environmental Monitoring in China, 2022,38(6):228-236.
