Computing underwater downward irradiance of fish aggregation lamps in class I ocean water based on Monte Carlo method

In this paper,a computing model of underwater irradiance of fish aggregation lamps was developed based on Monte Carlo method by using chlorophyll concentration and wind speed with characteristic parameters of the lamps.The absorption and scatter character of chlorophyll concentration and pure sea water in class I waters were used to compute beam attenuation coefficient including absorption coefficient and scatter coefficient,and scattering cumulative distribution function.Wind speed was used to construct windblown capillary wave surface which would have a great influence on light fields for large air-incident angles.Compared with the traditional computing model,this model has the following advantages:(1) the model took the difference of beam attenuation coefficient over wavelength into account without a constant assumption or using guessing value;(2) the model can provide the spectral distribution of fishing lights for different depths which was important for design of fishhook and researches of fish behavior to light;(3) the scattering of the light was calculated,so the model can provide downward irradiance under the shadow area of fishing vessels;(4) the influence of the windblown capillary wave surface on the reflectance for large air-incident angle was taken into account,so that the model was more reasonable in computing underwater light field of fish aggregation lamps;(5) the chlorophyll and wind speed can be drawn from remote sensing data,which make the model easy to use.Comparing with the in situ measure data,the value computed by model was larger,the relative root mean error was 37.6%,but the correlation between the two data was significant(P<0.001).Finally,the difference between the two data was discussed.