Line spectrum detection of airborne moving source by underwater horizontal array

Owning to the great difference of the acoustic characteristic impedances between the air and the sea water,energy of the sound propagating in water due to an airborne source suffers significant transmission loss.In addition,the existence of the interferences induced by the underwater sound sources makes it even more difficult to detect the air target from the water.An experiment for helicopter detection using underwater horizontal array was carried out in the northern South China Sea in January 2018.The data analysis shows that the helicopter noise is weak when it transmits into water,so it is difficult to detect helicopter effectively by using the conventional broadband beamforming method especially with frequent underwater interference.In view of the line spectrum characteristics of airborne source,line spectrum recognition,extraction,tracking and line spectrum encryption technology are used to analyze the received signal.Then,by eliminating the line spectrum of strong interference,the airborne source is successfully detected,and the longest distance is 16.8 km.The accuracy of the detection results is verified by experiment and theoretical analysis.