Coherent Array Processing of GPS Sonobuoys

Underwater target tracking in ocean environment has attracted considerable interest in both military and civilian applications. Towards this purpose, sonobuoys are among the most capable sonar systems used in underwater environments. Sonobuoys are used to detect and track underwater objects emitting sounds. Recently GPS receivers have been integrated to sonobuoy systems to provide accurate information about sonobuoys positions. An accurate knowledge of geographic positions of deployed sonobuoys is critical for the conduct of antisubmarine warfare (ASW) operations and detected target localization. It enables processing array of GPS sonobuoys thus improving the target tracking accuracy. Considering that sonobuoy positions are accurately known, the main factors influencing the operation of sonobuoys would be the interference sources and background noise.;This research aims at: (1) Developing a high resolution spectral estimation algorithm to improve target detection and enhance the accuracy of bearing estimation; (2) Exploring the theoretical requirements for sonobuoy positioning in order to feasibly and coherently process a field of sonobuoys; (3) Designing a method for coherently processing uniform and arbitrary arrays of GPS sonobuoys; (4) Integrating frequency domain adaptive beamforming with artificial neural network (ANN) to resolve the ambiguity existing in bearing estimation when processing widely spaced array omnidirectional sonobuoys; (5) Developing a virtual array search method to enhance the bearing estimation when processing sparse array of directional sonobuoys.;The proposed methods are examined and their performances are verified using acoustic level simulated data development for different underwater environmental conditions. Comparisons to the conventional processing techniques are conducted to assess the benefits of the proposed methods. The results show the proposed methods are capable of enhancing the accuracy of target bearing estimation especially in cases of relatively low SNR. The merits and limitations of the proposed methodologies are discussed and analyzed in this thesis.;The background noise, the low sound pressure levels of some underwater targets, the sonobuoys drift, the attenuation of the sound pressure level, the sonobuoys deployment strategy and the self noise of hydrophones are among the main factors deteriorating the system accuracy and jeopardizing the overall performance. The present trend of decreasing signal of interest levels while increasing noise due to the growing ocean traffic has served to continually complicate ASW operations. Coherently processing an array of GPS sonobuoys can lead to noise reduction and hence higher signal to noise ratio (SNR). Some research activities targeted the utilization of an array of sonobuoys to utilize beamforming technology to reject unwanted noise and enhance the reception of desired signals. However, the limitation on the inter-element spacing was always considered the main factor affecting the system performance.