Modeling Study On The Target Strength Of Ceratoscopelus Warmingii

· The biodiversity of the mesopelagic fishes of the South China Sea is high, rich in resources,they have the life habits of day and night vertical migration.The specials float to the surface to feed plankton at night,and as bait for the important economic fish in deep water during the day.The mesopelagic fishes play an important role in the deep sea ecological system of material circulation and energy flow.· Acoustic methods is an important technology of the Marine biological resources survey and evaluation method,and the target strength is the key parameter of converting the echo integration value for fish resources in Fisheries resource assessment.The research methods of TS mainly divides into the scene in situ measurement(in situ), laboratory controlled experiments(ex situ) and theory model predicts.Model evaluation method is not restricted by measuring conditions, with flexible, convenient and simple calculation,etc.· This thesis mainlyuses the model method to evaluate the target strength of the mesopelagic fishes of the south China sea, the main research content is as follows:·(1)Based on literature studies,the measurement of the target strength of fish and its adaptability are briefly introduced.For researching the target strength model method of mesopelagic fish, focuses on existing models at home and abroad are summarized and summary, detailed introduces the basic principle of several main models, and compares the advantages and disadvantages of various models.·(2)Studying the backscattering directivity characteristics of target strength of the mesopelagic fishes, the average effective target strength and the relationship between the target strength and depth change(i.e. the depth dependence of the target strength) using the model method.· The model of target strength: the fish body and the swimbladder were used respectively to ellipsoid model which is full of liquid and gas, calculation method is through the scattering intensity of infinite rule model to estimate the scattering intensity of finite long target model.· The determination of model parameters: according to the result of biological determination and the anatomy, using soft X-ray machine to photograph target fish samples.On this basis, using image processing software analysis model parameters of fish body and swimbladder(fish body length, widthand swimbladder long, high, wide and the angle relative to the fish bodyetc.)· Target strength model analysis: Ceratoscopelus warmingii the average effective target strength of Ceratoscopelus warmingii is obtained by using convolution of acoustic scattering directivityand the fish angle distribution, the Angle distribution function choice for N(5 °, 15 °) and(0 °,10 °).According to the established model, studying as in the different layer, theacoustic scatteringdirectivity of target fish, swimbladder backscattering area under different Angle distribution under different frequencies and different compression ratio, along with the change of the depth of the water, at the same time, using the body length of 7 tail fish and swimbladder, the linear relationship between the related parameters,received the regression curve of the target strength of Ceratoscopelus warmingii and body length.·(3)The testing results of biological sampling show that the average length of Ceratoscopelus warmingii individuals is 53.0 mm(fish length distribution standard deviation is 18.6).The results of x-ray processing show that the fish body width, swimbladder length and the swimbladder back width are 7.6 mm and 11.3 mm and 4.4 mmrespectively;The numerical simulation results of model of target strength show that the target strength of Ceratoscopelus warmingii are closely related with the incident wave frequency, Angle of incident wave( Angle distribution of fish) and water layer, etc. In 38 k Hz, 120 k Hz, and 200 k Hz, the inclination function of target fish is(5 °, 15 °), the TS of sea surface are-53.4 d B and-52.2 d B and-54.9 d B respectively, The experience formula of the effective target strength varies with the length respectively: TS=20log L-67.8, TS=20log L-67.9, TS=20log L-68.1; the inclination function of target fish is(0°,10°), the TS of sea surface are-53.3 d B and-51.2 d B and-53.8 d B respectively, The experience formula of the effective target strength varies with the length respectively: TS=20log L-67.6, TS=20log L-66.9, TS=20log L-66.8; Tilt function is(5 °, 15 °), the target strength gradually decreases with the increase of the depth of the water layer, 38 k Hz, the effective target strength in the 50 m and 200 m are respectively-60.3 d B and-65.7 d B, 120 k Hz, that in 50 m and 200 m are-57.9 d B and-62.4 d Brespectively, under the 200 k Hz, which are respectively-58.1 d B and-60.3 d B.· Based on theory model of target strength, this paper studies the target strength of Ceratoscopelus warmingii changes with acoustic frequency and Angle distribution of fish, and swimbladder volume and the change of water depth, and according to the biological sampling length distribution, obtained under different frequency the target strength of Ceratoscopelus warmingii and the experience formula of the body length, for later middle acoustic quantitative assessment of fish resources in our country provide key parameters.