Intelligence experts ask industry for signal processing to help detect and locate electromagnetic events

May 6, 2024
Low-frequency radio signals below 30 MHz are for global communications, and for their ability to reach underground facilities and submarines.

WASHINGTON – U.S. intelligence experts are reaching out to industry for new signal processing approaches to analyze the so-called D-region of the atmosphere to detect and locate variations in the Earth's magnetic field caused by humans.

Officials of the U.S. Intelligence Advanced Research Projects Activity (IARPA) in Washington issued a request for information (IARPA-RFI-24-05) on Wednesday for the Opportunities for Observing and Sensing Atmospheric Electromagnetic Anomalies project.

The D-region of the atmosphere exists at altitudes of about 37 and 56 miles; remote sensors characterize this region by comparing very low frequency (VLF) signals with modeling results. The problem today is poor accuracy in efforts to detect and locate electromagnetic events.

This approach is considered to be an ill-posed nonlinear problem; it's difficult to solve, and does not yield a unique one-to-one correspondence between electron density profiles in the Earth-ionosphere waveguide and receiver signals.

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Scientists have tried to resolve these shortcomings with machine learning and artificial neural networks using information from sensors that are uncoordinated and loosely networked, yet this cannot provide real-time estimates of the D-region, which is necessary for accurate electromagnetic event detection, geolocation, and classification.

IARPA researchers seek to characterize and better understand the D-region and its interaction with electromagnetic anomalies typically caused by space weather, lightning, and human-caused electromagnetic events. One objective is to characterize the D-region to help identify, map, and track these electromagnetic anomalies.

Today's capabilities do not divide the D-region quickly into neat parameters, and any methodology that could do this is of interest, IARPA researchers say.

Low-frequency radio signals below 30 MHz are useful for strategic communications because these radio waves propagate at global distances, and can reach underground facilities and submarines.

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While the electrical properties of the Earth’s surface and Earth’s magnetic field are reasonably stable and well-understood, the electrical and magnetic properties of the D-region are not, because of electron density irregularities.

The D-region is unpredictable, and contains irregularities that occur across latitude, longitude, and elevation, and are time-varying across the day and time of year. The D-region also reacts to electromagnetic anomalies from electron density irregularities.

Despite the difficulty, developing the ability to characterize the volatility of the D-region could help improve real-time identification and geolocation of variations in the Earth's magnetic field caused by humans.

Signal processing approaches that use data from various uncoordinated ionospheric sensors can help study electron density irregularities, yet today's signal processing is unlikely to help characterize the D-region quickly enough for real-time domain awareness of manmade electromagnetic anomalies.

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Instead, IARPA researchers are asking industry for new signal-processing approaches that could separate the D-region quickly into understandable parameters.

Of particular interest are existing or newly proposed signal processing techniques; networked ground sensors; RF sensors able to detect signals at 3 MHz and below; electrostatic discharge, electric field perturbations, magnetic field perturbations, and radio waves that interact with the surrounding regions of the ionosphere and the Earth's surface; specialized sensor collection; low-signal detection techniques; and improved resolution of data assimilation.

Companies interested should email white papers no later than 17 June 2024 to [email protected].

Email questions or concerns to [email protected]. More information is online at

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