We have developed two unique sensors for in-air acoustic applications:
VAWS - our state of the art noise cancellation enables ground vehicles to detect other sounds while rejecting its self-noise.
SSC has developed a
second-generation Vehicle Acoustic Warning and Surveillance (VAWS)
use in the Army’s next generation of ground vehicles, collectively
as the Future Combat Systems. (Phase II SBIR DAAD17-02-C-0018, Tien
(301) 394-4282). This system provides
all weather wide area acoustic queuing for imaging sensors such as
support of the Demo III Experimental Unmanned Vehicle program, SSC
automated queuing of staring FLIR sensors at Fort Indiantown Gap,
The VAWS system contains 12 custom-designed acoustic sensors, signal conditioning electronics, platform noise cancellation, adaptive beamforming, vehicle tracking, and counter sniper (impulse) algorithms. The output of the VAWS system is contact reports that are networked to other vehicles and command posts, where network-level data fusion and field tracking occur. SSC has developed, under Army funding, an LRD for our multi-node target detection/tracking system that incorporates passive air-coupled acoustic sensor reports from our VAWS system. This technology transition allows SSC to perform data fusion for our networked set of ground vehicle acoustic arrays. Each sensor contact report provides target bearing and sensor information such as identification, location and orientation to the LRD processor. The LRD has been ported to a C++ environment and currently runs in real time with a 1 Hz update rate. The LRD was successfully evaluated in the field at Aberdeen Proving Grounds (APG) in August 2003, and at the Eglin Air Force Base in September 2003. Both unmanned ground sensors, developed by SSC under DARPA/ONR funding, and ground vehicle acoustic sensors were evaluated and were able to successfully track ground targets of interest using the PRT technology.
ASU- a revolutionary compact (11 cm) sensor containing a unique chambered design with ultra-low power ASICs for detecting and localizing vehicles and gun-fire.
The purpose of the Acoustic Sensor Unit (ASU) which was developed by SSC under the DARPA-funded Smart Microphone Program is to detect, support reconnaissance, surveillance, and target acquisition using acoustic signature analysis. This is accomplished in real-time via self-contained electronic beamforming and signal processing algorithms that detect, localize, and identify potential threats. SSC’s small ASU produces line of bearing to a sound source (vehicles or gunfire) with the capability to employ unwanted noise reduction algorithms in real-time. The ASU is housed in a 4.5-inch circular “hockey puck” enclosure, which is a minimum of 1.5 inches in height. While small, the individual ASU node has been designed for high performance, and has demonstrated bearing accuracies of 5 degrees or less with standard algorithms (on the order of 1 degree with specialized algorithms).
The ASU is composed of four independent chambers or “horns”, each of which contain a water proof microphone sensor located at the focus or “throat”. The horn layout performs as if the microphones were outside the physical dimensions of the enclosure. The throat of the horn is the smallest portion of the chamber where all walls converge. Each horn directs the incoming wave front inward towards the microphone membrane; thus, the received signal is actually an average over an area larger than the membrane – this surface area is effectively the entire horn opening. This averaging is responsible for reduced wind, flow and/or turbulence-induced noise in the channels (de-correlation) and increased coherence of acoustic energy.
In addition to the composition of the ASU, SSC has incorporated open-cell foam to each horn and an optional faux fur “hat” to help with further passive wind noise reduction. It is theorized that the overabundance of long fibers or “hairs” on the fur “hat” acts as the obstruction for the air mass movement, distributing wind and flow energy as it arrives at the surface. The properties of the tiny hairs allow for inaudible variations, so that when presented with wind, these fibers translate the wind energy into silent movement, or sound outside the audible range. This absorption of energy reduces the effects of the wind on the sheltered microphone element, but allows desired sound pressure waves to pass.