Analysis Of Fish Acoustic Scattering Characteristics And Research On Acoustic Biomass Monitoring Method

The 21st century is the century of the ocean,and vigorously developing marine fishery resources is of great significance to my country’s construction of a powerful marine economy and technology.In recent years,my country’s offshore cage fish culture has developed rapidly,but due to the increasing number of cages,the load on the offshore waters is becoming more and more serious.The use of industrial ship cabins for fish farming in the deep sea has many advantages such as expanding the aquaculture area,reducing the pressure on the marine environment,and improving the quality of fish.Acoustic methods are used to monitor farmed fish,to evaluate the size and quantity of fish in the cabin,and to provide technical support for intelligent farming.Based on the sound scattering characteristics of fish,this paper establishes the formula for the change of fish target intensity with body length as a theoretical basis for estimating the size and quantity of fish.At the same time,the fish positioning method is studied to obtain the position of the fish,which is convenient for estimating the target of the fish.Intensity,and suppress the reverberation in the cabin environment,realize the estimation of the size and number of fish in the cabin.First,the sound scattering mechanism of fish is analyzed.The Kirchhoff model(KRM)is used to model the fish morphology,and the rationality of the model is verified by the scattering of the free boundary sphere.The sound frequency and the influence of the angle of incidence and the body length of the fish on the target intensity of the fish is fitted with the empirical formula of the target intensity-body length of the fish.The analysis results show that the scattering of the swim bladder plays a major role in the scattering of the swim bladder.When the sound wave frequency is much higher than the swim bladder resonance frequency,the target intensity of the fish fluctuates slightly with the sound wave frequency,and fluctuates greatly with the incident angle of the sound wave;The sound scattering characteristics test of the KRM model shows that the KRM model method is reasonable.The sound scattering characteristics of fish are used as the theoretical basis for estimating the size and quantity of fish.On this basis,the distribution of fish in the fish school in the cabin is simulated,and the scattered echo signal of the fish school is obtained by the simulation,which is given in a noisy environment The estimated result of the size and quantity of fish.Secondly,study the fish positioning method based on split beam.The generalized cross-correlation method based on quadratic correlation is used to estimate the time delay difference between the array elements,and the linear array and planar array model are combined with the split beam idea to orient and locate the fish in the cabin,and estimate the fish and the transducer It also studied the influence of array parameters,signal-to-noise ratio and other factors on orientation and positioning accuracy,and used a four-element array to process fish’s echo signals.The results verified the effectiveness of the split beam positioning algorithm.Position the fish in order to accurately obtain the target intensity of the fish.Finally,a reverberation model was established according to the cabin structure,and the spectrum characteristics and time correlation of the cabin reverberation signal were analyzed.A cabin reverberation suppression algorithm based on the fractional Fourier transform is proposed.According to the energy accumulation characteristics of the LFM signal in the fractional Fourier transform domain,the distribution of the reverberation signal in the fractional Fourier transform domain is rather messy.FRFT can be used to separate the reverberation signal and the fish’s scattered echo signal in the fractional Fourier transform domain to achieve the effect of suppressing reverberation.On this basis,the echo energy integration method is used to estimate the size and number of fish on the separated fish scattering echo signal.Under the cabin reverberation,a better estimation effect of the size and number of fish is achieved.