It is very complicated to determine the noise level in an environment. After all, there are many foreground- and background noises, that you have to take into account. We all deal with foreground noise on a daily basis, for example coming from passing cars.
This form of noise can also have a natural source such as the rustling of the sea or the wind that stirs leaves or trees. Background noise is a more abstract concept. Its origin is sometimes more difficult to trace. In any case, determining the environmental level requires a high degree of expertise. KGI is the specialist in this field.