Buried object detection with parametric sonar
Description
Detection of buried objects with parametric sonar is studied using time-frequency methods. The sonar equation is used as a framework to assess the sonar system characteristics, the sediment response, and the buried object response. Field tests were conducted to measure the source levels of difference frequencies in the nearfield and spectral components at different ranges. The results of these tests were compared with the predicted values from the Moffett-Mellen model in the nearfield. The analysis reveals the nonstationary and nonlinear behavior of the sonar system and environment and shows that a linear systems approach is not realistic. Analysis of sediment variability and attenuation quantifies the nonstationarity of the media and motivates the use of gain correction techniques presented in this dissertation. The response of buried objects was found to exhibit resonances and time-frequency dependence. Acoustic resonance theory is used to explain the target response and is shown to be effective in estimating target size. The use of time-frequency techniques for object detection in such a system is discussed and it is shown that the Wigner-Ville distribution and the wavelet transform are particularly well suited to the interpretation of the data and detection of buried objects. Results are given for several buried objects and gas bubbles in sediment