Page "Ambient noise level" Paragraph 2

Ambient sound levels are often measured in order to map sound conditions over a spatial regime to understand their variation with locale.

In this case the product of the investigation is a sound level contour map.

Alternatively ambient noise levels may be measured to provide a reference point for analyzing an intrusive sound to a given environment.

For example, sometimes aircraft noise is studied by measuring ambient sound without presence of any overflights, and then studying the noise addition by measurement or computer simulation of overflight events.

Or roadway noise is measured as ambient sound, prior to introducing a hypothetical noise barrier intended to reduce that ambient noise level.