Have you ever wondered why the noise around an airport is measured? There are actually several reasons why. Airport officials need to know whether or not the noise levels are increasing, or lessening. If the noise levels are increasing, steps are then taken to decrease the airport noise. Measurements like this are taken year round, and at the end of each year, averaged out so that all the levels for a day, both high ones and low ones, are just one figure. The final noise measurement is in decibels. This gathering of information concerning noise is known as taking airport noise contours. Airport noise contours measure the noise level when planes are departing an airport as well as during a plane's landing. Airport noise contours also take the sounds of airplane takeoff into consideration. Airport noise contours are often used to help decide how the land around airports should be put to use. If the noise level is too high, nothing will be built in that location.