A Literature Survey on Ambient Noise Analysis For underwater Acoustic Signals

Abstract

Transmitting data with water as the medium is called underwater communication. Electromagnetic signals are better attenuated in water than sound. Hence it is the most reliable and versatile means of communication underwater. The acoustic signals will be affected by ocean driven noise during transmission. Ambient noise is the background noise which has to be subtracted from the acoustic signal for smooth transmission. Hence the recognition and reduction of ambient noise is the essential part of underwater signal transmission. Studies and research are being carried out extensively in this area. There are many works reported and the research is still in progress. This literature survey presents the work done on the research front of ambient noise affecting acoustic signals.

Feature identification using acoustic signature of Ocean Researcher III (ORIII) of Taiwan

“…There are different strategies to enhance the detection accuracy. First, regarding signal processing and noise reduction [4], Wang enhanced the target signal by Hilbert-Huang transform [5]. Weiss also applied a noise reduction and reconstruction technique to high-frequency acoustic signals by wavelet transforms [6].…”

“…Data quality control also is challenging, with problems of ambient noise by time/space-varying multipaths arising when the underwater acoustic propagation is influenced by ever-changing sound speed profiles under different topography or sea state conditions [4,9]. The biggest noise masking issue is shipping noise masking, as it is a continuous low-frequency anthropogenic sound [10,11], but its acoustic signatures are valuable features in antisubmarine warfare or harbour security systems.…”

How can ports act to reduce underwater noise from shipping? Identifying effective management frameworks

“…Noise can attain up to 220 dB re 1μPa at 1 m(Sadaf et al, 2015).3 Noise from nearby shipping may be present in a wide spectrum of frequencies, but only the lower frequencies below about 200 Hz attain a certain distance since high frequencies are attenuated in deep water(Jasny, 2014).4 Such ships produce noise levels in the range of 165 to 180 re 1μPa at 1 m which contribute to marine ambient noise to varying degrees depending on their age and level of maintenance (OSPAR, 2009a).5 They may produce noise levels of the order of 160 to 175 dB re 1 μPa at 1 m(Tejedor et al, 2012).6 On a broader scale, the long-term consequences of anthropogenic underwater noise on marine animals at the level of the population as a whole are still largely unknown, both when considering this stressor alone and when accounting for cumulative impacts (CBD, 2012; NOAA, 2016; IMO, 2018a).…”