This letter presents a multi-target tracking algorithm—thresholded Sequential Monte Carlo probability hypothesis density (TH-SMC-PHD) algorithm. The TH-SMC-PHD aims to overcome the problem that underwater multi-target tracking is prone to missing tracking on sonar images, resulting in the breakage of trajectories. First, CA-CFAR and K-means are employed to detect potential underwater targets from sonar images, respectively. Then TH-SMC-PHD is applied to the detection results for tracking, using a continuously lost frame threshold to reduce the missing tracking rate and the Minimum-Sampling-Variance (MSV) resampling to improve tracking accuracy. An actual underwater multi-target tracking experiment using a forward-looking sonar was contracted in a water tank to evaluate the tracking performance. Compared with the other two PHD tracking algorithms, the results demonstrate that the proposed algorithm achieves high-precision, non-fracture, non-missing tracking of three targets. In addition, the TH-SMC-PHD is more stable and less affected by different detection algorithms, which has the potential for practical applications.

The detection accuracy of the multibeam echo sounder (MBES) can be damaged severely and inevitably due to the mismachining tolerance of the transducer array. Therefore, it is necessary to demonstrate the performance of the multi-element transducer array to guarantee the accuracy of the processing algorithms. In this paper, a kind of multi-element MBES receiving transducer array self-calibrating method is proposed to manage the serious defocusing problem of the conventional methods. We analyze the error source and their effect on the MBES detection. The near-field beamforming and the least residual error criterion methods are employed to calibrate the average element spacing. The integrated self-calibrating method is managed to calibrate the transducer array, considering the coupling between the circuits and the element with a channel uniformity problem. An experiment is carried in a small-size tank to evaluate the method proposed. The outfield experimental data are compensated by the average element spacing and the beam response error estimated in the tank experiment. The simulations and the field data processing results indicate that the novel method proposed can effectively demonstrate the performance of the receiving transducer array and guarantee the coverage of the MBES system.

The integrated observation of seabed topography, sediment geomorphology and sub-bottom profile information is very important for seabed remote sensing and mapping. To improve the efficiency of seabed detection and meet the needs of portable development of detection equipment, we developed a portable seabed feature integrated detection sonar (PSIDS) with whcih a single sonar device can simultaneously detect the above three types of seabed information. The underwater transducer is mainly composed of the following three components: a parametric emission array as the sound source, a high frequency receiving linear array for multibeam echo signal collection, and a two-dimensional vector hydrophone for receiving the low-frequency sediment echo signal. Field experiments were conducted to validate the performance of the PSIDS on 11–17 January 2018 in Jiaozhou Bay, China. (1) PSIDS could perform the functions of both multibeam sonar and sub-bottom profiler; (2) The synchronously and integrated measurement of various seabed information was achieved by alternately emitting multibeam echo-sounding and sub-bottom profiling signal using parametric source. The detection results proved the feasibility and practicability of PSIDS to achieve multiple seafloor characteristics. PSIDS provides a new idea for developing integrated seabed detection sonar. In terms of convenience and data fusion, it is a good option to use this equipment for integrated seabed detection.

The Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation has been widely used in the simulation and calculation of nonlinear sound fields. However, the accuracy of KZK equation reduced due to the deflection of the direction of the sound beam when the sound beam is inclined incidence. In this paper, an equivalent sound source model is proposed to make the calculation direction of KZK calculation model consistent with the sound propagation direction after acoustic refraction, so as to improve the accuracy of sound field calculation under the inclined incident conditions. The theoretical research and pool experiment verify the feasibility and effectiveness of the proposed method.

Backscattered sound waves of seabed sediments are important information carriers in seafloor detection and acoustic characteristic parameters inversion. Most of the existing methods for estimating geoacoustic parameters are based on multiangle seabed backscattered signal processing and suitable for flat seafloor conditions with uniform sediment thickness. This usually deviates from the real field conditions and affects the accuracy of parameter estimation. In this paper, the sound ray propagation theory is studied and analysed under the condition of sloping seabed and uneven sediment thickness. Based on the phased parameter array sonar system, a method of acoustic parameters estimation of the sediment under inclined seabed conditions is proposed. The simulation results show that the new method shows good adaptability to different inclination angles of the seabed and solves the problem of accuracy of acoustic parameter estimation of the inclined seabed sediments. The model will greatly reduce the seafloor topography requirements in the sediment acoustic parameter inversion, such as velocity, layer thickness, and acoustic impedance.

Global navigation satellite system attitude determination based on carrier phase differencing technique is studied. A realistic stochastic model is followed to fully consider the correlations among different measurements in the least-squares problem formulation. A prior-free, computation-fixed, and averagely optimal solution is proposed suitable for real-time and high-dynamic situations. The prior-free property is achieved by developing an analytical sub-optimal solution. This solution follows first transforming the original problem into one with vector measurements and then further approximating it with a general Wahba’s problem. The fixed computation is guaranteed by performing only one or two rounds of correction of the analytical solution. Every single round follows a linearization-estimation-correction process. The process also provides an error or covariance analysis for the estimate. The average optimality in terms of the root mean squared errors is brought about by the relatively good quality of the analytical solution and the fast convergence of the correction processes. The numerical experiments, with three 4 m long baselines and 5 mm (standard deviation) carrier phase errors, show that the estimation errors (in magnitude) for all three channels are well below 0.4° for almost all epochs and within 0.2° for most epochs.