| Active sonar detection performance is greatly improved through the use of advanced pulse designs such as Costas waveforms. Costas waveforms are a class of waveforms having the form of frequency-hopped uniform pulse trains. They are superior in performance to conventional waveforms such as Continuous Wave (CW) pulses and Frequency Modulated (FM) pulses, as each Costas waveform provides both range and velocity information simultaneously. Matched-filtering is used to positively identify each individual Costas waveform from amongst a set of similar Costas waveforms received at the receiver, all of which are within the same frequency bandwidth. In this work, the Costas wideband ambiguity, cross-correlation and auto-correlation functions have been newly derived. These functions are used to generate ambiguity and matched-filter diagrams, thereby indicating the range and velocity resolutions achievable by a specific pulse or waveform. The Acoustic Signal Processing Program (ASPP) was developed and used to simulate the performance of CW pulses, Hyperbolic Frequency Modulation (HFM) pulses and Costas waveforms in deep, shallow and Pekeris water environments. Simulated performances are compared to actual trial data collected during the Defence Research and Development Canada (Atlantic) (DRDC(A)) at-sea Towed Integrated Active-Passive Sonar (TIAPS) trials of September 2003. Finally, it is shown that Costas waveforms are superior in performance to CW and HFM pulses. The unique characteristics of Costas waveforms allow for the more frequent insonification of a water mass for targets at moderate ranges, and therefore more frequent target tracking and analysis. |
