Automatic detection of underwater propeller signals using cyclostationarity analysis

The second order Cyclostationarity Analysis (CA) is gaining attention for detection and classification of marine vehicles driven by propellers in broadband passive sonar systems, in which the Detection of Envelope Modulation On Noise (DEMON) is a standard tool for the same purpose. In this paper both CA and DEMON are discussed in the form of discrete digital formulae. It is shown that the three cyclo-spectra obtained by the DEMON analysis, the coherent integration of the Cyclic Modulation Spectra (CMS) and the coherent integration of the Cyclic Modulation Coherence (CMC) are equivalent to each other when the same frequency band and duration are chosen for calculating all of them. This equivalence is further explained based on the physical characteristic of cyclic modulation (also called amplitude modulation), that is, the same harmonic of cyclic modulation at different carrier frequencies is in-phase. For detection and/or classification of propeller signals a Coherent Integration and Quadratic Detection Law (CIQDL) is proposed to construct cyclo-spectra from the CMS and CMC. The performance of the thus constructed cyclo-spectra are compared with that of cyclo-spectra constructed using the Quadratic Detection Law (QDL). The SNR gain of the CIQDL over the QDL is derived theoretically and the gain is always larger than unity, indicating that the CIQDL outperforms the QDL. Both simulation and seatrial data are used to demonstrate the in-phase characteristic. The performances of the CIQDL and the QDL are also quantitatively assessed using both simulation and sea-trial data. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

This paper discusses the second order Cyclostationarity Analysis (CA) and Detection of Envelope Modulation On Noise (DEMON) for detection and classification of marine vehicles driven by propellers in broadband passive sonar systems. A Coherent Integration and Quadratic Detection Law (CIQDL) is proposed for constructing cyclo-spectra, which outperforms the Quadratic Detection Law (QDL) with a theoretically-derived SNR gain larger than unity. The in-phase characteristic is demonstrated using both simulation and sea-trial data, and the performance of CIQDL and QDL is quantitatively assessed.