Citation: Xie, Q.; Chi, C.; Jin, S.;
Wang, G.; Li, Y.; Huang, H.
Underwater Tone Detection with
Robust Coherently-Averaged Power
Processor. J. Mar. Sci. Eng. 2022, 10,
1505. https://doi.org/10.3390/
jmse10101505
Academic Editors: Jacopo Aguzzi,
Giacomo Picardi,
Damianos Chatzievangelou,
Simone Marini, Sascha Flögel,
Sergio Stefanni, Peter Weiss and
Daniel Mihai Toma
Received: 10 September 2022
Accepted: 12 October 2022
Published: 16 October 2022
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Journal of
Marine Science
and Engineering
Article
Underwater Tone Detection with Robust Coherently-Averaged
Power Processor
Qichen Xie
1,2,3
, Cheng Chi
1,2,
*, Shenglong Jin
1,2
, Guanqun Wang
1,2
, Yu Li
1,2
and Haining Huang
1,2
1
Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China
2
Key Laboratory of Science and Technology on Advanced Underwater Acoustic Signal Processing,
Chinese Academy of Sciences, Beijing 100190, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
* Correspondence: chicheng@mail.ioa.ac.cn
Abstract:
The detection of tonal signals with unknown frequencies is an important area of study in
underwater signal processing. A common approach to address this issue is to use the Discrete Fourier
Transform (DFT) for observations. When a tone does not lie precisely at the discrete DFT frequency
point, its energy will leak to adjacent frequency point. This phenomenon is known as scalloping loss
or Picket Fence Effect (PFE). PFE leads to the degradation of detection performance based on DFT.
This paper studies the problem of robust detection in the case of PFE. A coherently-averaged power
processor utilizing the information of adjacent frequency bins is designed. The results of simulations
and experiments show that the proposed method is robust against PFE, and is highly suitable for
tone detection in practical circumstances.
Keywords:
tone detection; phase compensation; coherent averaging; picket fence effect; passive sonar
1. Introduction
Over the past several decades, the detection of tonal (sinusoidal) signals embedded
in noise has continuously received attention in many fields, such as sonar, radar, commu-
nication, seismology, and ocean engineering. Noise radiated from vessels consists of a
mixture of broadband noise and tonal noise, mainly caused by mechanical vibration and
propeller propulsion [
1
]. The tonal component contains the characteristics of the ship and is
of great importance for target detection and recognition [
2
]. And marine experiments have
proved that low-frequency tonal signals can propagate over a long distance and maintain
remarkable phase stability [
3
]. Therefore, tone detection has received considerable attention
in acoustic signal processing.
The problem of detecting tonal signals with unknown parameters is usually expressed
as a problem of composite hypothesis testing [
4
,
5
]. There are several solutions to this
problem by utilizing the statistical characteristics of DFT in different segments. A common
and extensively used method is to reduce the variability in signals and noise and increase
the Signal-to-Noise Ratio (SNR) by averaging process, which is referred to as the Average
Power Processor (AVGPR) [
6
,
7
]. Another widely-used method is the Generalized Likeli-
hood Ratio Test (GLRT) [
8
] for composite hypothesis test, which performance close to the
optimal bound, especially under low probability of false alarm [
9
,
10
]. However, only the
amplitude information of the tonal signals is used in these two methods. Consequently, the
detection performance tends to decay due to the loss of phase information. In order to take
full advantage of the phase information, a phase estimation method has been proposed
and the performance of the GLRT has been greatly improved by compensating the phase
difference among segments, which is referred to as the Coherent Generalized Likelihood
Ratio Test (CGLRT) [
11
]. The AVGPR can also be enhanced by introducing phase compen-
sation to coherently average segments, and is named as the Coherently-Averaged Power
Spectral Estimate (CAPSE) [12].
J. Mar. Sci. Eng. 2022, 10, 1505. https://doi.org/10.3390/jmse10101505 https://www.mdpi.com/journal/jmse
