Recently in Japan, airports tend to be constructed or relocated offshore to reduce aircraft noise impact to inland residential areas, consequently the necessity of aircraft noise monitoring at such distant areas from airplanes which fly above sea has increased. However, in such areas where generally the signal to noise ratio (S/N) is low and occasional louder noise events than aircraft noise are frequently observed, monitoring only aircraft noise events by distinguishing other non-aircraft noise events are more difficult than in general areas near airports or flight paths. Because conventional aircraft noise detecting methods are not always effective under such monitoring situation, therefore, new technologies have been desired.

In such situation, it is important to separate each noise and identify which noise is the loudest. Therefore, we have focused our attention to 'the omni-directional noise source analyzing technology'. This is an existing technology and is used for noise source identification. This system analyzes the positions, intensity levels and frequency characteristics of multiple noises by using a beam-forming method with a sphere-baffled microphone array, we call this SBM. By analysis of such information, this system will evaluate each source separately, then, will judge whether the dominant source is an aircraft noise or not by comparing each intensity level.

DL-SBM has been adopted by the Ministry of Land, Infrastructure and Transport and has been recognized as an automated accurate aircraft noise monitoring in combination with aircraft noise discriminator type-I and II.