Aero acoustics: Helicopter detection and classification (1998-2000)

Summary

This page highlights research into acoustic methods for identifying and categorizing helicopters. This project explored technologies to detect helicopters using their unique noise signatures, enabling classification based on rotor and engine acoustics. The study had applications in surveillance, military operations, and air traffic management, aiming to improve detection reliability and operational utility.

 

Helicopter detection and classification (1998-2000)

UNDER CONSTRUCTION

 
The Helicopter Detection and Classification Demonstrator project aimed to develop a helicopter detection and classification demonstrator. The first version consisted of a desktop PC, an analog-to-digital card, a Bruel & Kjaer amplifier and a measurement microphone. This first equipment version was used for development and testing. This was done at various air bases with helicopters and aircraft, including Soesterberg, Gilze Rijen and Volkel (during a large air show).
MatlabTM was used as the basis for the detection, pre-processing and classification software. The Matlab user interface was used to control, set and adjust the processing parameters.

The first helicopter detection system based on a PC, AD card and a Bruel & Kjaer microphone and amplifier.
The first helicopter detection system based on a PC, AD card and a Bruel & Kjaer microphone and amplifier.
A cross-section showing how the microphone detector is hidden underground.
A cross-section showing how the microphone detector is hidden underground.

A later version of the system ran on a laptop with a specially designed all-weather microphone, a low-pass filter and microphone amplifier???. The system contained an expandable collection of 11 helicopter sound profiles. This enabled the system to detect helicopters and automatically determine the exact type of helicopter. [1]

The second helicopter detection system was based on a laptop and a proprietary designed microphone, filter and amplifier.
The second helicopter detection system was based on a laptop and a proprietary designed microphone, filter and amplifier.

For the same purpose, a rig also stood at Valkenburg Naval Airfield for a year. That was to record wind noise and later use it to determine detection distances at different wind speeds with simulated helicopter noise. Processing several hours of measurement data was a mega calculation job that required 24 hours of batch processing time on a VAX. The processing time later went down to a few minutes with a DEC Alpha system. [2]
De foto’s van die opstelling stuur ik separaat.

Later, the intention was to link the whole thing to an unmanned ground sensor in collaboration with Dutch industry.
 
 

Sources
  1. A.C. van Koersel, The influence of wind noise on the performance of helicopter detection and classification algorithms, Proceedings of the Eighth International Symposium on Long-Range Sound Propagation, Penn State University, 1998.
  2. A.C. van Koersel, Helicopter detection and classification demonstrator. In: Unattended Ground Sensor Technologies and Applications, Edward M. Carapezza, Todd M. Hintz, Proceedings of SPIE Vol. 4040 (2000) <pdf>