Smart, Digital Infrasound Monitoring Array System

Infrasonic monitoring is a key technology employed in Nuclear Test Ban Treaty monitoring. Detecting the infrasonic signature associated with a nuclear detonation requires the elimination of locally generated wind noise. One widely deployed technique is to perform spatial averaging in the acoustic domain by means of a rosette—a single microphone connected by tubes to many acoustic inlets spread across a large area. Such systems are bulky, requiring a large, flat land area, and can be difficult to calibrate and maintain. In the present work, we report our progress to develop a smart, digital infrasonic monitoring system based on arrays of inexpensive digital sensor nodes. Such a system may be deployed in difficult terrain, can span much larger areas, and can be more easily moved from location to location. Wind noise is handled in the digital domain rather than the acoustic domain, and sophisticated digital signal processing techniques may be employed, e.g., using a phased-array approach to determine directionality.

Owing to the high relative intensity of wind noise compared with signals of interest, an infrasound sensor with very high dynamic range and low noise is required. Our analysis indicates that 150 dB of intrinsic dynamic range is ideal for this application. To this end, we will present progress on a piezoelectric micromachined open-loop sensor, and a closed-loop sensor employing optical interferometric readout and magnetic actuation.

We have also developed a nodal system to collect data from these sensors. The system comprises a high-performance analog to digital converter which is synchronized using the global positioning system (GPS), thus all nodes in the array are coherent. Each node supports self-calibration via a piston driver located in the back cavity of the sensor, enabling in situ calibration of the array. Nodes support wired data connection to a central receiver node or local data archival for up to 60 days.