Target positioning of dual forward looking sonars based on orthogonal detection

Accurate positioning of underwater targets is an important basis for many underwater tasks. As an imagery equipment, forward-looking sonar (FLS) can overcome the problem of poor brightness in underwater environment, and has a longer detection distance than the camera, which plays an important role in oceanic target positioning. However, there remain two challenging problems: (1) due to the complex underwater environment and the propagation characteristics of sound waves in the water, there are a lot of noises in the FLS images, which impair the accuracy of positioning; (2) FLS can only obtain two-dimensional information, which is insufficient for target positioning. Aiming at these two problems, a three-dimensional underwater target positioning algorithm based on dual FLSs is proposed in this paper. Firstly, a Threshold-Mask-Guided Filter (TMGF) image denoising algorithm is designed to deal with the obvious background noises and same-pitch noises in FLS images, which greatly improves the denoising effect compared with the original guided filter algorithm. Secondly, a target positioning algorithm based on orthogonal vertical placement of dual sonars is proposed to calculate the three-dimensional position of the target. Finally, pool experiments and sea trial tests are carried out respectively to verify the effectiveness of TMGF algorithm in denoising and the accuracy and stability of positioning algorithm.