Integrated design of velocity measurement sonar system based on ACL and phased array ADL

Velocity sonar is usually used on the boat or the UUV, which can obtain velocity of a vessel, current velocities, and the depth of water. With the help of INS, it can help the vessel to locate its position and sail in the right direction. According to the principle of operation, there are two kinds of velocity sonar, which are acoustic Doppler log (ADL) based on the principle of Doppler phenomenon and acoustic Correlation log (ACL) based on the principle of “waveform invariance”. The method of ADL to calculate the vessel velocity is to estimate the Doppler frequency shift between the transmitting and receiving acoustic beams by the complex covariance algorithm, which has the advantages of highspeed measurement accuracy and small blind area; ACL obtains the velocity of a vessel by least-square fitting the theoretical correlation function and the data correlation function. Compared with ADL, ACL has a small transducer array, low power, less influence by the vessel attitude under the same working frequency. For a large depth range speed measurement navigation system, the current solution is to use separate combinations of different sonars for velocity measurement and navigation, but this will increase the complexity of the underwater vessel and is not conducive to system miniaturization. We propose a new solution, through a certain regular transducer design, the ADL and ACL transducers are integrated into the structural design so that the two transducers are nested in a plane. At the same time, ADL and ACL software and hardware systems are integrated into an integrated system design. Among them, the ADL transducer uses a phased array ADL (PAADL) planar structure transducer to replace the conventional 3-4 piston transducer structure of the JANUS type. In the principle prototype of this scheme design, the center operating frequency of the ACL is 23 kHz, and a “spatially correlated” uniform array is used, including one transmitting element and eight receiving elements; the center operating frequency of the PAADL is 300 kHz, and a single phased array is used to complete the formation of multiple beams. The size of the system's underwater plane array is less than 60cm, the theoretical dead zone distance is less than 2m, the maximum detectable seabed depth is greater than 4000m, the working depth range is within 1% of the speed measurement accuracy, and the 180m shallow speed measurement accuracy can be controlled within 0.5%, which can replace the current Large depth split integrated navigation equipment. Finally, the data of the lake and ocean experiments are analyzed. The experimental area is located in the Qiandao Lake, the South China Sea, and other sea areas in China. The results of the sea trial verify the theory system, design method, and signal processing method of the integrated speed sonar. In the test, the performance of the real-time system of the speed sonar is verified. The results show that the engineering prototype of the speed sonar has reached the international advanced level.