Low frequency sound – infrasound – in the atmosphere travels over vast distances carrying information about its source and the state of the atmosphere. To date measurements of infrasound have been restricted to earth’s surface.
Dr. Alexey Titovich, a research scientist at Naval Surface Warfare Center Carderock Division, saw this as an opportunity to research an avenue of implementing infrasonic wave detection on aircraft. In his time within the command’s Structural Acoustics and Targeting Strength Branch, Titovich worked on related projects when he realized that the Navy could benefit from such equipment. Almost four years ago, he began an investigation into how the Navy could utilize infrasonic sensors on aircraft and in July 2019, was granted a patent for, “Atmospheric infrasonic sensing from an array of aircraft” (U.S. Patent No. 10,365,089).
“The underlying uniqueness of this sensor is that although scientists have made fiber optical interferometers for measuring infrasound on earth, no such measurement of infrasound has been achieved in the atmosphere,” Titovich said. “Researchers have attempted measuring infrasound in the atmosphere with a microphone-like point sensor. The idea here is to combine the benefit of distributed sensing that fiber optic interferometry gets you with a very large spatial aperture provide by the platform.”
The issue with a point measurement of infrasound, according to Titovich, is incoherent noise such as pseudo-noise. He said a more effective way of measuring low frequency waves in the atmosphere is with a distributed sensor that cancels out the incoherent noise. Waves that originate from sources that are more distant become harder to detect because they decay as they propagate away from the source. One of Titovich’s goals in his research included creating a lower noise floor for the sensor, increasing the distance from which infrasonic activity can be detected.
In the beginning of his experimental process, Titovich participated in the development of a fiber optic sensor through a Small Business Innovation Research project for structural health monitoring. While analyzing an odd blip in the test data, he realized and proved that it was due to a very small earthquake over 350 miles away, which piqued his interest in discovering new applications of such sensing. Weather monitoring became a primary point of emphasis for Titovich, who noticed that current weather prediction technologies could benefit from infrasonic measurement, which unlike LIDAR captures the vibrational state of the atmosphere. Particularly, infrasound generated by severe weather phenomenon such as tornadoes can be localized earlier than with traditional weather warning systems, which has the potential of saving lives.
“The weather aspect to me was absolutely interesting,” he said. “Severe weather events that cause infrasound, why would the Navy care about that? Because we either have to sail or fly through it.”
Getting the sensor on aircrafts is the next big step for Titovich’s invention, and it is a step that is sure to take some considerable time. Following the disclosure for this patent, he worked with Dr. Joseph Teter, Carderock’s Director of Technology Transfer, to participate in the FedTech program, where he met with labs and industry representatives to gauge interest in his idea. Other steps to refine the sensor are taking place, such as working to utilize the structural vibrations of the aircraft and the impact of altitude and temperature on the sensors’ accuracy.
“One of the things we identified through the FedTech program was those corporate partners and government labs that were interested in pursuing this further,” Titovich said. “It needs development and next level demonstration, so we’ll be working on that.”