High Altitude Infrasound

To address the Air Force need for a high-altitude (60,000 to 90,000 ft), low-noise, low size, weight, power, and cost (SWaP-C) infrasound sensor and data recorder, Intellisense Systems, Inc. (Intellisense) proposes to develop the new High-Altitude Infrasound (HERON) system based on a new design that utilizes previously developed mature components and a new three-axis, directional infrasound sensor. Specifically, innovations in self-mixing interferometry, an ultra-light, Mylar membrane with perimeter relief and overtravel limiter, multi-axis directional sensing, auto-correlation for noise reduction, low-power microelectronics, and spatial Fourier processing will enable HERON to measure faint acoustic signals not currently detectable with ground-based sensors. As a result, this system will overcome altitude, noise, and SWaP-C limitations of current commercial off-the-shelf technologies. In addition, because the HERON system does not rely upon omnidirectional, barometric operation, it operates as a three-dimensional directional sensor that can determine the angle of arrival of sound waves reaching the sensor without requiring an accelerometer and without being affected by vertical oscillation of the balloon platform in the atmosphere. Unlike systems that would require triangulation from multiple balloons, sensors, or accelerometers to determine angle of incidence, the HERON system can accurately determine the direction of origin of sound waves from a single, compact sensor package by measuring acceleration of the sensing membranes. In addition to benefits of size and weight, this approach leaves the remainder of the payload for batteries, recording equipment, signal processing, and telemetry, thus enabling HERON to meet all Air Force SWaP-C requirements. In Phase I, Intellisense will build a working sensor, an infrasound generator to perform initial ground-based studies of sensor performance, and provide performance measurements including sensitivity, noise level, directional accuracy, and frequency range, as well as cost estimates and resource requirements including size, weight, and power for both the sensor and the on-board signal processing. In Phase II, Intellisense plans to update the Phase I prototype and evaluate it in altitude chambers and on balloon flights. The results of these tests will be incorporated into low-rate initial production articles for testing.