This chapter is concerned with the problem of detecting and estimating the time delay between signals received at two spatially separated sensors together with noise. This problem has been of interest to many investigators since it has applications in varied fields. Basically, the solution has consisted of cross-correlating the sensor outputs and of calling the time argument that corresponds to the maximum peak in the output the time delay (Figure 1). Generalized cross-correlation. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351077446/ae9170a5-5bd6-492c-ad8d-19209ed7eda8/content/fig3_1.tif"/>