| Lighting fishery is one of the important fishing methods in China,including light-seine fishery,light falling net fishery,stick held lift net fishery,squid jigging and so on.However,with the continuous development of lighting fishery,a number of problems have emerged,such as blindly increasing the light power,the light field between neighboring light fishing vessels interfere with each other and the problems are becoming increasingly serious.How to solve the above problems through lamp selection,configuration adjustment and setting a reasonable operating spacing threshold are the purposes of this research.In this paper,by establishing a numerical calculation model for the beam transmission of fish collection lights,the transmission characteristics of the fishing lamp beam at the sea surface,in clear seawater and turbid seawater media were analyzed.Further combined with the typical light fishing vessel light configuration and the parameters of sea conditions,the attractive water volum around vessel and the operational spacing between fishing vessels were discussed,the main results are as follows:Firstly,to accurately calculate the light field distribution on the sea surface for fishing lamp,Metal halide lamp（Metal halide lamp,MHL）as an example,a numerical computational optimization model（MC-Cox-Munk model）for the light field distribution on the sea surface of fishing lamp is proposed,based on Monte Carlo（MC）method and the sea surface capillary slope probability formula proposed by Cox&Munk.Different from the traditional method,this chapter proposes a new numerical simulation method Monte Carlo（MC）principles.The light beam was dispersed into a large number of photons and then we calculate the light intensity in the target area by tracing the transmission path of photons after reflection or bouncing off the sea surface.Meanwhile,we presented a photon emission optimization model based on luminosity distribution data of fishing lamp and verified by the measured data.The results show:（1）The MC-Cox-Munk model was applied to calculate the light field illuminance of fishing vessels in the actual operating environment,and the simulated values were closer to the measured values;（2）The larger the value of the simulated photon number,the better the stability of the simulation result.Taking the point which distance from lamp 5.0 m as an example,when the value exceeds1e8,the coefficient variance（CV）of the result is 0.07%and when the value exceeds 1e10,the CV is 0.05%;（3）By using the optimization model,the mean relative error（MRE）between the simulated and measured data reduces from 0.0512 to 0.0453.Secondly,to investigate the effects of fishing lamp color,power,placement depth and seawater chlorophyll mass concentration on light field distribution in clear seawater,the underwater LED（Light Emitting Diode）fishing lamp was used as the research object,and the numerical calculation model of underwater beam transmission was established based on MC method.The distribution of underwater light field under different conditions was calculated by the control variable method.The relative effective illumination range（REIR）-the ratio of the area surrounded by the 0.1～10 lx isoline to the computational domain was taken as an evaluation index.The results showed that:（1）under the same light power,the REIR value from high to low was green light,white light and blue light,and when the light power was 420 W and the seawater chlorophyll concentration was 0.1mg/m3,the ratio of REIR values of the three light colors was 1.58:1.31:1;（2）under the same light color and when the seawater chlorophyll concentration was 0.1mg/m3,as the power of fishing lamp increased from 420 to 1200 W,the REIR value of blue,green,and white light lamp increased from 31.68%,50.27%and 41.78%to 38.59%,56.91%and 50.15%respectively;while the power of lamps increased nearly three times,the increase of REIR was limited;（3）As depth of lamp increased,the REIR of lamps increased at first and then kept stable.The maximum value of green and white lamp was about9.69%～9.84%when the depth of lamp reached 20 m under water,while the maximum value of blue lamp was about 5.60%when the depth of lamp reached 15 m under water;（4）As the chlorophyll concentration increased from 0.1mg/m3 to 5.0mg/m3,the REIR value of green,white and blue lamp decreased from 31.89%,48.25%and 42.05%to 1.65%,2.09%and 2.22%respectively.The study in this chapter can provide reference for the selection of fishing lamp color,underwater fishing lamp placement depth,and power configuration.Thirdly,to explore the transmission characteristics of light beams in turbid seawater medium,a new numerical calculation model of light field transmission was constructed based on MC method by using collector lamp spectral data,luminosity distribution data and the inherent optical parameters of seawater and attenuation and scattering models,and the calculation model was verified by collecting water samples for water tank tests.The Ads—area of closed region which enclosed by 0.1 lx contour line in marine section which ds m away from underwater fishing lamp and the Ids—maximum illuminance value in marine section were used to characterize the spatial distribution of light field in water.In this paper,the effect of chlorophyll concentrations,scattering type in the marine water and the scattering asymmetry parameters on the illumination distribution of LED fishing lamp and MHL fishing lamp were analyzed through numerical simulation.The results showed:（1）with the chlorophyll concentration increases from 1mg/m3 to 5mg/m3,the A5 m of LED lamp decreased from 1073.90 m2 to 292.87 m2,which means A5m has reduced by 72.73%;the A5 m of MHL lamp decreased from 1094.51 m2 to 304.57 m2,which means A5mhas reduced by 72.17%;the I5m of MHL decreased from 972.76 lx to 454.42 lx,which means the I5 m has reduced by 53.29%;the I5m of LED decreased from 956.48lx to 318.60 lx,which means the I5m has reduced by 66.69%.（2）when scattering type of the ocean water is Mie scattering and Rayleigh scattering,the I5m of MHL is956.48 lx and 318.60 lx,respectively;the I5m of LED is 1057.96 lx and 992.42 lx,respectively.（3）with the scattering asymmetry parameters increases from 0.8 to 0.99,the A5m of MHL lamp decreased from 1094.89 m2 to 1336.40 m2,A5m increased22.05%;the A5m of LED lamp decreased from 1076.52m2 to 1325.21m2,A5mincreased 23.10%;the I5m of MHL increased from 962.52 lx to 1122.48 lx,I5mincreased 16.62%;the I5m of LED increased from 980.74 lx to 1123.22 lx,I5mincreased 14.53%.It was found chlorophyll concentrations had a significant effect on illumination distribution of fishing lamp,while the scattering type and the scattering asymmetry parameters on the illumination distribution had no significant effects.The numerical simulation method proposed in this paper can accurately calculate the illumination distribution of fishing lamps in offshore waters,which would provide scientific basis for fishery supervision and reasonable application of fishing lamps.Fourthly,to estimate the volume of the effective attracted water around the fishing vessels,the relationship between the light configuration and the volume of the effective attracted water was explored based on the light configuration of the fishing vessels and the sea state parameters of the operation area,using the numerical calculation model established in the previous chapters.The results show that:（1）increasing the light height can effectively increase the effective volume,and it is suggested to increase the light height from 5.0 to 7.0 m;（2）under the conditions of120 k W light power and 5.0 m light height,the light spacing has no significant effect on the effective volume,and moving the fishing lamp group from the inner side of the ship to the outer side of the ship can increase the effective volume-the distance between the fishing lamp group and the ship amidships increases from 3.2 m to 4.2m,The effective water volume first increases and then remains constant,reaching a maximum of2.58 106 m3 at 3.7～3.8 m,in other word,fishermen are advised to try to hang the fish collection light set to the outer 0.1m of the ship’s side In production practice;（3）Under the condition of 5.0 m lamp height,the total power of the fishing lamp increases from 120 k W to 480 k W,the effective volume first increases and then decreases.When the total power of the fish collection lamp is 240 k W,it reaches the maximum effective volume of2.7 106 m3.Correspondingly,the recommended power of a single fish collection lamp is 2 k W.Fifthly,In order to study the reasonable spacing between fishing vessels to avoid or reduce the mutual interference effect between them,based on the light configuration of light-trapping squid fishing vessels and the wind speed data of the operating sea area,the reasonable operating spacing under the conditions of light configuration scheme and sea surface wind speed was discussed using the MC-Cox-Munk numerical calculation model established in the previous chapter.The results show that:（1）under the conditions of 5.0 m light height and 0.01 m/s wind speed,the relationship between reasonable operating distance and total light power can be expressed by the formula:Lz=9.90 10-4P2+1.30P+843.08;（2）under the conditions of 120 k W total light power and 0.01 m/s wind speed,the relationship between reasonable operating distance and operating sea surface wind speed can be expressed by the formula:Lz=-61819.07V-0.0 015+63096.69;（3）changing the light height or Spacing between the fishing lamp set and the ship amidships line has no obvious effect on the operating distance.For the production practice,the anchoring distance should be increased when the wind speed or the power of fishing lamp increases in the operation area.According to the current light configuration,combined with the average wind speed data of three fishing grounds in the North Pacific,Peruvian and Argentinean fishing grounds,the operating distance is recommended to be at least1268.1 m,1404.0 m and 1255.1 m respectively.In summary,this paper established an effective numerical calculation model based on MC method for the transmission of fishing lamp beams in the sea surface and seawater,analyzes the beam transmission law and range by simulating the transmission path of photons in complex media,and analyzed the light field distribution around the fishing vessel from the microscopic level in relation to the seawater parameters and light configuration.Combining the light configuration of typical fishing vessels and the actual conditions of sea conditions,the problems of the volume of effective attracted water around fishing vessels and the operational spacing between fishing vessels were further discussed,and optimal adjustment schemes or reference value were given. |
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