Measurement of acoustic signals are possible if their amplitude exceeds a minimum threshold, determined partly by the signal processing used and partly by the level of background noise. Ambient noise is that part of the received noise that is independent of the source, receiver and platform characteristics. This it excludes reverberation and towing noise for example.
The background noise present in the ocean, or ambient noise, has many different sources and varies with location and frequency. At the lowest frequencies, from about 0.1 Hz to 10 Hz, ocean turbulence and microseisms are the primary contributors to the noise background. Typical noise spectrum levels decrease with increasing frequency from about 140 dB re 1 μPa²/Hz at 1 Hz to about 30 dB re 1 μPa²/Hz at 100 kHz. Distant ship traffic is one of the dominant noise sources in most areas for frequencies of around 100 Hz, while wind-induced surface noise is the main source between 1 kHz and 30 kHz. At very high frequencies, above 100 kHz, thermal noise of water molecules begins to dominate. The thermal noise spectral level at 100 kHz is 25 dB re 1 μPa²/Hz. The spectral density of thermal noise increases by 20 dB per decade (approximately 6 dB per octave).
Transient sound sources also contribute to ambient noise. These can include intermittent geological activity, such as earthquakes and underwater volcanoes, rainfall on the surface, and biological activity. Biological sources include cetaceans (especially blue, fin and sperm whales), certain types of fish, and snapping shrimp.
Rain can produce high levels of ambient noise. However the numerical relationship between rain rate and ambient noise level is difficult to determine because measurement of rain rate is problematic at sea.
Other articles related to "noise, ambient noise, ambient":
... Noise Criteria (NC) are noise-level guidelines applicable to cinema and home cinema ... application, it is a measure of a room's ambient noise level at various frequencies ... theater to be THX certified, it must have an ambient sound level of NC-30 or less ...
... Bad Sector is an ambient/noise project formed in 1992 in Tuscany, Italy by Massimo Magrini ... Bad Sector's music is considered a mixture of ambient, noise, minimal and experimental music ... Magrini himself describes it as "deeply emotional dark ambient noise" ...
... Some users have noted that ambient noise can be a problem ... The built-in microphone on the pen can pick up small amounts of noise from writing on paper, and adjacent ambient noise is often louder than a far away speaker ... However, the included headphones have embedded microphones that reduce this ambient noise ...
Famous quotes containing the word noise:
“It is as real
as splinters stuck in your ear. The noise we steal
is half a bell. And outside cars whisk by on the suburban street
and are there and are true.
What else is this, this intricate shape of air?
calling me, calling you.”
—Anne Sexton (19281974)