Distribution And Driving Mechanism Of The Drift Velocity Of Ulva Prolifera In The Yellow Sea Based On Remote Sensing

The green tides of Ulva prolifera in Yellow Sea broken out for many consecutive year since 2007 and gradually become the trend of the normalization, brought some impact to the marine ecological environment and the economic development in the region. The process of generation and elimination of Ulva prolifera is accompanied by a large-scale drift and the study of the drift velocity and driving mechanism can provide information to support disaster prevention and mitigation.In this thesis, extraction methods, temporal and spatial distribution characteristics and driving mechanism of the drift velocity of Ulva Prolifera in the Yellow Sea are researched based on satellite remote sensing data. Details are as follows.(1) The extraction methods of the drift velocity of Ulva Prolifera are developed based on the enhanced red-green-blue images (ERGB) and visual interpretation; the method is tested and the results are compared using polar orbit (MODIS) and geostationary orbit (GOCI) satellite data; the uncertainty of the extraction results is analyzed.(2) This paper uses the MODIS and GOCI satellite remote sensing data, making the 2013-2015 years a total of 57 days of remote sensing monitoring products about the drift velocity of Ulva Prolifera in the Yellow Sea. On this basis, the temporal and spatial distribution characteristics of drift velocity are analyzed from the different time scales of day, month and year.(3) Combined with the current and wind field data in the Yellow Sea, the drift driving mechanism of Ulva Prolifera is researched for different time periods and regions.The main conclusions include:(1) The extraction method of the drift velocity based on the satellite remote sensing proposed in this paper has high accuracy and universality. Test results based on MODIS and GOCI show that the drift velocity of Ulva prolifera has a better consistency and relative deviation is about 17%.(2) The drift velocity of Ulva Prolifera in the Yellow Sea (0.01-0.98 m/s,0.34± 0.18 m/s) exists spatial difference. The drift velocity of high value area (0.34-0.98 m/s, 0.50±0.12 m/s and N=303) are mainly distributed in the south and west of 121°E, 35°N; the low drift velocity zone (0.01-0.34 m/s,0.21±0.08 m/s and N=379) mainly in the north and east of 121°E,35°N.(3) The time variant characteristic of the drift velocity of Ulva Prolifera in the Yellow Sea is obvious.①Based on a case study of 8 scene GOCI images (June 28, 2014), daily amplitude of the drift velocity of Ulva Prolifera can reach 0.3 m/s.② For the comparison of different months, the drift velocity is smaller in late May (mean value:0.23±0.17 m/s and N=39) and rapid increase in early June (mean value:0.57 ±0.22 m/s and N=44), then it maintains at ～0.30 m/s from mid-June to late July.③ From 2013 to 2015, the annual mean drift velocity of Ulva Prolifera in the Yellow Sea decreases year by year (2013:0.38±0.16 m/s and N=135; 2014:0.34±0.18 m/s and N=310; 2015:0.30±0.17 m/s and N=235).(4) Sea surface wind and current field are important driver of the drift of Ulva Prolifera in the Yellow Sea, but the driving mechanism is different in time and space. ① The northern component of the drift velocity of Ulva Prolifera, wind field and current field are relevant from May to July; In May significantly related to the wind filed east (r=0.34 and N=35), the eastern component of drift velocity is significantly correlated to the current filed east component in June (r=0.32 and N=230). ②In the area of south of 35°N, the wind filed east component impact is remarkably effected in the eastern component of drift velocity (r=0.79 and N=48) and in the area of north of 35°N, the function of wind field north component is obviously influenced on the northern component of drift velocity (r=0.65 and N=380); In the area of west of 121°E, the current field north component is related to the northern component of the drift velocity of Ulva Prolifera (r=0.30 and N=74) and in the area of east of 121°E, the wind field north component is correlated to the northern component of the drift velocity (r=0.64 and N=354).