Study On Estimation Of Early Attached Biomass And Drift State Parameters Of Green Tide In The Yellow Sea

Since 2007,the Yellow Sea green tide has broken out year after year,which has caused great harm to the coastal ecological environment and aquaculture.It is characterized by the difficulty in monitoring the early origin process,long drift time at sea,and rapid change of drift velocity and biomass.Therefore,the traditional methods are difficult to carry out high-precision and emergency monitoring.If the biomass of green algae attached to raft and the drift state parameters of the green tide can be estimated with high accuracy,it will be of great significance for the prevention and control of disaster and accurate early warning.Using the research ship deck as the Unmanned Aerial Vehicle(UAV)landing platform,this paper applied high-precision UAV remote sensing to the research of green tide.At the same time,combined with satellite remote sensing,field survey and other means,the methods for biomass estimation of green algae attached to nursery-nets and raft rope were proposed on the early development of green tide.For the drift stage of green tide,firstly,a novel vegetation index,namely,the Red-Green-Blue Floating Algae Index(RGB-FAI)using RGB images captured by UAV was developed for green-tide detection;Then,by using RGB-FAI,the Ulva prolifera biomass estimation model was constructed,which was applied to the estimation of green-tidal biomass from UAV aerial images.Finally,based on the dual-phase orthophoto of the green tide obtained by the ship-borne UAV,the green-tidal velocity was estimated and analyzed.The main conclusions are as follows:(1)In 2017,the biomass of green algae attached to nursery-net of raft on the Subei Shoal was 8877 tons,and the biomass of green algae and U.prolifera attached to rope was about 2981 and 447 tons respectively.From 2011 to 2013,the biomass of green algae attached to raft rope was 7617,4132,and 3465 tons,of which the biomass of U.prolifera was 2774,1672,and 2137 tons,respectively.The biomass of U.prolifera attached to rope from 2011 to 2013 was basically consisitent with that of the initial coverage area of green tide in the inter-annual change trend.(2)the RGB-FAI performed well in the detection of green tide from UAV-based RGB imagery and the accuracy was satisfactory(kappa=0.95).It is worthy to note that RGB-FAI has the highest extraction accuracy(kappa=0.93)among these competing indices for the declining green tide under a hazy atmospheric condition.(3)The green-tidal biomass in different growth stages were estimated by UAV remote sensing,and the results showed that the maximum value of RGB-FAI of green-tidal pixel decreased from 61.9 in the outbreak period to 44.1 in the decline period,and the biomass density also decreased from 0.92 kg/m² to 0.52 kg/m².(4)The green-tidal velocity of three sites estimated by UAV remote sensing were 0.256,0.439,and 0.257m/s,respectively.The drift direction was basically consistent with the tidal current of M₂,at 1°?62°to the right of wind direction.The UAV remote sensing method with high spatial-temporal resolution can help calibrate the results of satellite remote sensing such as GOCI.Based on the application of UAV remote sensing in marine scientific investigation,the high-precision estimation methods were carried out on the biomass of the green algae attached to the raft and the drift state parameters of the green tide.The paper is expected to provide new technical means and more accurate quantitative data support for the related research of green tide,as well as scientific support for the precise prediction,warning and control of green tide disaster.