**3. Ambient noise due to intermittent sources**

The influence of intermittent sources on ambient noise is significant, which includes various factors such as marine life, rain noise, shipping noise, etc.

#### **3.1 Marine life**

A distinct and innumerous variety of sounds are produced by marine life. Humpback whales, dolphins, and other marine mammals generate sounds of a broad range of frequencies, and these sounds can be treated as infrasonic or ultrasonic. Specific categories of fish and marine invertebrates are also sources of sound. For example, special species of fish includes toadfish and croaker, and some of the marine invertebrates are snapping shrimp. Information pertained to surroundings is obtained by marine animals using sound. This dependency on sound extends in communicating, navigating, and even feeding. For example, dolphin depends on sound to search food and smell enemies. This is done by transmitting sound pulses for short intervals, and then with the echo received, dolphins detect objects in sea. Most of the time, this kind of communication contributes to raise in ambient noise levels for a maximum value of 25 dB. In the case of whales, noise levels are up to 190 dB at 10–25 Hz frequencies [6].

Sound produced by snapping shrimp inhabiting in shallow waters contributes to background noise. In general, prevalence of this can be seen in semitropical and shallow tropical waters which contain seabed with rock and shell, as they provide the necessary concealment. Colonies of snapping shrimp produce sounds at frequencies of 2–15 KHz. Individually these have peak-to-peak source levels of 189 underwater dB at 1 m.

**155**

*Underwater Ambient Noise*

**3.2 Natural physical processes**

**3.3 Human activities**

identified.

acoustics.

energy."

rain noise.

**3.5 Shipping noise**

**3.6 Wind-generated noise**

**3.4 Rain noise**

*DOI: http://dx.doi.org/10.5772/intechopen.93057*

35 underwater dB from few Hz to beyond 20 KHz.

It is also possible that the sounds that are known to humans and pertained to underwater have the sources that include more than the species that have been

Most of the physical processes produce higher levels of sounds with source levels

Human activity is one of the important sources of background noise. Sounds in underwater are used for many purposes like communication, navigation, and fishing, and the point of observation is that one act is source for the other activity. Several by-products can also be seen like noise generation by offshore activities such as oil drilling, manufacturing, and other industrial acoustic pollutions. Incidentally and evidently, all of these factors, more or less, have a human hand in it. So, it is very clear that human activities also contribute to ambient noise of the underwater

Nicolaas Bom [8] studied the influence of rain on undersea noise level. Experiments were conducted in Italy at the lake of Sarzana near La Spezia. Data is analyzed between 300 Hz and 96 KHz. The observation and inference of this work reflected the effect of rain on noise, i.e., noise level increases w.r.t to increased rainfall rate. It was concluded that "it corresponded to higher frequency

In 1986, Nystuen [9] reported that a light rain with total rainfall of <2.5 mm per hour produced a spectral peak at 15 KHz (broadband wind sensitive). And, a heavy rain where a total rainfall was more than 7.5 mm per hour produced a wideband noise ranging from 4 to 21 KHz. A similar type of study and data analysis was done by Deane [10] for a period of 1 year, and this work also revealed the effect of

Shipping noise can exhibit both spatial and temporal variability. The spatial variability is largely governed by the distribution of shipping routes in the oceans. Temporal variability can be due to the seasonal activities of fishing fleets. The noise generated by coastal shipping and by high-latitude shipping can contribute to the noise field in the deep sound channel in tropical and subtropical ocean areas. Specifically, coastal shipping noise is intruded into the deep sound channel through the process of downslope conversion. High-latitude shipping noise is generated through the latitudinal dependence of the depth of the sound channel axis.

Noise due to wind is a major contributor of the total ambient noise. Windassociated ambient noise was predicted and analyzed earlier by many researchers. Ambient noise depends on varying wind speeds over the frequency range of 500 Hz

up to 260 underwater dB at 1 m. Rain, undersea earthquakes, and underwater volcanoes generate intermittent sounds in the ocean. Heavy rain raises noise level by

It is also possible that the sounds that are known to humans and pertained to underwater have the sources that include more than the species that have been identified.
