| In polar regions,due to the cover of ice,the acoustic signals of underwater targets received by ice-based sensors from the ice surface will be affected by water,ice,and air.Therefore,the estimation of underwater target orientation across ice layers will more difficult.In the current direction of arrival estimation technology,the uniform linear array is the most widely used type of array structure.In order to ensure that the result of the direction of arrival estimation has no phase ambiguity,the element spacing of the uniform linear array is subject to spatial Nyquist sampling.the constraints of the theorem.Therefore,if we want to obtain higher resolution,we can only increase the aperture of the array by increasing the number of elements in the array.Due to the harsh environment on ice,the deployment of ice-based sensors is very difficult,so people expect to achieve higher resolution under the premise of using the same number of array elements.Coprime array not only has the characteristics of coprime,but also has the advantage of sparse array,so it can obtain higher resolution than traditional uniform linear array under the condition of using the same number of array elements,and will not produce spatial aliasing.This paper will study the direction of arrival estimation of underwater target across ice based on coprime arrays.The specific work includes:(1)Establish a cross-ice reception signal model.First of all,we give a model of acoustic information transmission across the ice layer.The underwater acoustic signal is transmitted through the ice layer to the upper surface of the ice layer.The layer transmission coefficient is used to calculate the displacement response of the upper surface of the ice layer.Then,we introduce the reflection and refraction of sound waves at the water-ice and ice-air interfaces.According to the boundary conditions of the wave field displacement potential function,we can calculate the transmission coefficient of the ice layer,and then we can get the ice The received signal model of the array placed on the surface.(2)Study the direction of arrival estimation of underwater target across ice based on coprime arrays.We use the extended coprime array to receive the signal on the ice,use the method based on the idea of sub-array decomposition to process the signal received by the extended coprime array.The simulation results verify that it is feasible to use the coprime array to estimate the azimuth of the underwater target across the ice.Considering the loss of DOF performance based on the idea of sub-array decomposition,we establish a received signal model of an extended coprime array to achieve target orientation estimation without DOF performance loss.The signal received by the extended coprime array is processed by a method without performance loss of degrees of freedom,and the azimuth estimation result of the underwater target across the ice layer is obtained.Compared with traditional uniform linear array and sparse uniform linear array,the results show that: when the frequency of the incident signal is high,the distance between two adjacent array elements of the sparse uniform linear array with the same aperture size as that of the extended coprime array is greater than the half wavelength of the signal,which does not satisfy the Nyquist sampling theorem and cannot be used.Orientation estimation of underwater targets across ice;In the case of using the same number of array elements,the extended coprime array has higher resolution than the traditional uniform linear array.The signal received by the extended coprime array is processed by the method based on virtual domain signal processing,and compared with the method without performance loss of degree of freedom,the results show that:for the extended coprime array,when using conventional beamforming algorithm and Capon algorithm,compared with the method without performance loss of degrees of freedom,the azimuth estimation results of underwater targets based on virtual domain signal processing have no advantages.When using the spectral peak search PM algorithm and the MUSIC algorithm,compared with the method without performance loss of degrees of freedom,the azimuth estimation result of the underwater target across the ice layer based on the virtual domain signal processing has higher resolution.(3)Investigate the effect of the environmental parameters on the estimation of the underwater target orientation across the ice.We use the extended coprime array to receive the signal on the ice surface,change the signal-to-noise ratio,the sound speed in the ice layer,the sound speed gradient in the water,the structure of ice,the frequency of the incident signal and the thickness of the ice layer,and use the maximum virtual uniform linear array space to smooth the spectral peak search PM algorithm and The maximum virtual uniform linear array spatial smoothing MUSIC algorithm processes the signal received by the extended coprime array.The results show:when the above two methods are used to process the signal received by the extended coprime array,the signal-to-noise ratio has little effect on the results of azimuth estimation of underwater targets across ice.The speed of sound in the ice layer,the gradient of the speed of sound in water,the structure of ice,the frequency of the incident signal and the thickness of the ice layer all have a certain influence on the estimation results of the underwater target azimuth across the ice layer.(4)Study the underwater target orientation across ice in Songhua River.The feasibility of azimuth estimation of underwater targets across ice layers based on coprime array is verified;When the frequency of the incident signal is high,the spacing between the adjacent two array elements of the sparse uniform linear array with the same aperture size as the extended coprime array is greater than the half wavelength of the signal,which does not satisfy the Nyquist sampling theorem and cannot be used to measure the trans-ice The azimuth estimation of the underwater target of the layer is carried out.In the case of using the same number of array elements,the extended coprime array has higher resolution than the traditional uniform linear array.For the extended coprime array,when using the maximum virtual uniform linear array space smoothing spectral peak search PM algorithm and the maximum virtual uniform linear array spatial smoothing MUSIC algorithm to process the received signal,the signal-to-noise ratio has little effect on the results of azimuth estimation of underwater targets across ice.The frequency of the incident signal and the distance between the transmitting transducer and the array all have a certain influence on the results of the azimuth estimation of the underwater target across the ice. |
