Research On Multi-target Distinguishing With Small Scale Vector Array

The direction-of- arrival (DOA) estimation is one of the most important parts in the technique of array signal processing. Traditionally the DOA estimation is implemented by beam-forming the acoustic signal received by the hydrophone array distributed in the water. But the general beam-forming technique has its Raleigh constraint, so when the length of the array is fixed, its resolution is fixed. If the low frequency signal is needed to be processed, it needs a big array which has enough length. Of course, this will increase the cost and bring us inconvenience in experience.Recently the technique of vector sensor array signal processing is becoming more and more mature. The vector hydrophone can measure pressure (scalar field) and particle velocity (vector field) of acoustic field simultaneously, so more information could be got than that from general array. By this way a narrower beam can be acquired, what's more, the ability to distinguish the target whether it is on left or on right of the boat is obtained. Thereby in the paper I study the topic of using the small-size vector hydrophone array to distinguish multiple targets.First in the paper I discuss the fundamental of vector array signal processing. The conclusion that the pressure and particle velocity is relevant in coherent-source radiant sound field and isotropic noisy sound field is reached. Next, the directivity of vector hydrophone is mentioned. The combination of pressure and particle velocity (p + v_c)v_c has been chosen as the beam-forming output because it can get the gain which doesn't change with the direction. Differing from traditional beam-forming, the method that the signal which is reconstructed based on adaptive Notch filter is beam-formed by phase is provided in the paper. The Notch filter is a narrow-band filter, it can track the frequency of signal and extract the signal in the noisy environment. Specially, the compensation of sensitivity and phase is more convenient than before.Aiming at improving target resolution in array signal processing, several methods are brought in, such as frequency division, imagined-sensor and constant beam-width. Dividing the broad-band signal into several narrow-band signals avoids the overlapping among signals with different intensity. The technique of imagined-sensor has a good effect upon removing second higher petals in beam-picture and get a narrower main beam for the array after being imagined becomes longer. The application of constant beam-width makes the beam in different frequency band have the same width, which creates the condition for later beams amalgamation. At the same time, the use of imagined-sensor removes phase ambiguity in estimating time-delay in constant beam-width.Finally, that the whole process of distinguishing multiple targets with small-size vector array is set forth in the paper, and the practical application of imagined-sensor and constant beam-width are given. Considering the practical project, it sets out some thresholds and judgments in order to reduce the probability of false alarm. These methods are proved effective by computer simulation and lake trial data.