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The Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office (DSO) has issued a Disruption Opportunity (DO) that invites innovative basic or applied research concepts in the field of remote sensing, with a specific focus on surface-wave over-the-horizon radar (SWOTHR) and environmental characterization. This opportunity is part of DARPA’s broader Program Announcement (PA) for Disruptioneering, known as DARPA-PA-23-03. The program seeks to push the boundaries of current technologies and methodologies, offering researchers a chance to explore new frontiers in remote sensing.
Background
DARPA’s latest Disruption Opportunity (DO) targets advancements in two primary radar technologies: Surface-Wave Over-the-Horizon Radar (SWOTHR) and Passive Noise Radar. SWOTHR operates in the high-frequency (HF) band, specifically between 4 to 15 MHz, and is designed for long-range detection and tracking of air and maritime vehicles by utilizing surface waves that travel along the Earth’s surface. This enables the radar to detect targets beyond the horizon, making it highly valuable for maritime and air surveillance. However, its effectiveness can be hampered by spread-Doppler clutter, particularly at lower frequencies, which the program seeks to address through innovative clutter mitigation techniques.
In addition to SWOTHR, the program is exploring the potential of Passive Noise Radar—a radar technique that leverages naturally occurring environmental noise, such as acoustic or electromagnetic signals, for remote sensing. Unlike traditional radars that actively emit signals, passive noise radar relies on detecting reflections of these ambient noises from objects, making it inherently stealthier and less susceptible to jamming. DARPA’s initiative aims to develop advanced methods for using passive noise radar to detect and classify maritime and air vehicles, as well as for environmental characterization, without depending on the temporal properties of waveforms. This dual focus on SWOTHR and Passive Noise Radar reflects DARPA’s commitment to pushing the boundaries of radar technology for enhanced surveillance and environmental monitoring.
Program Overview
The DO issued under DARPA-PA-23-03 invites proposals that aim to advance remote sensing techniques, particularly those applicable to SWOTHR. The primary focus is on the high-frequency (HF) band, ranging from 4 to 15 MHz. Key applications in this frequency band include air and maritime vehicle tracking, oceanographic sensing, and ionospheric characterization.
DARPA’s program is structured around three core focus areas, each addressing critical challenges in radar technology:
Passive Noise Radar: This focus area explores the innovative use of environmental noise for remote sensing, inspired by techniques in geophysics, oceanography, and radio astronomy. Unlike traditional passive radar systems, which depend on the known temporal properties of waveforms, DARPA’s approach seeks to develop passive noise radar methods that operate without this requirement. By harnessing naturally occurring environmental noise, the program aims to enhance the detection and tracking of objects, offering a stealthier and potentially more resilient radar system.
Clutter Mitigation: Surface-wave radar technology, particularly in the HF band, is challenged by spread-Doppler clutter, which limits the effective tracking range of vehicles, especially at frequencies below 6 MHz. This clutter, often caused by ionospheric backscatter and turbulence, can significantly impair radar performance. DARPA’s program focuses on developing clutter mitigation techniques that utilize the underlying physics of surface waves and spread clutter propagation. These techniques are intended to extend the reliable tracking range of Surface-Wave Over-the-Horizon Radar (SWOTHR) systems, ensuring more accurate and longer-range surveillance capabilities.
Classification: Traditional high-frequency (HF) radars struggle with classifying maritime traffic due to their long wavelengths, which are typically not suited for identifying detailed platform features. DARPA aims to overcome these limitations by leveraging longer observation periods, multi-frequency data, and multi-angle observation processing. The goal is to improve the classification accuracy of maritime vehicles, even when using narrowband radar systems operating in the HF band. This focus area is expected to enhance the ability of HF radars to not only detect but also accurately identify different types of maritime vessels.
Technical Scope and Objectives
The program’s technical scope covers the development and demonstration of novel sensing and signal processing methods in three key areas: passive radar, clutter mitigation, and vehicle classification.
DARPA’s program is structured around three core focus areas, each addressing critical challenges in radar technology:
Passive Noise Radar: This focus area explores the innovative use of environmental noise for remote sensing, inspired by techniques in geophysics, oceanography, and radio astronomy. Unlike traditional passive radar systems, which depend on the known temporal properties of waveforms, DARPA’s approach seeks to develop passive noise radar methods that operate without this requirement. By harnessing naturally occurring environmental noise, the program aims to enhance the detection and tracking of objects, offering a stealthier and potentially more resilient radar system.
Clutter Mitigation: Surface-wave radar technology, particularly in the HF band, is challenged by spread-Doppler clutter, which limits the effective tracking range of vehicles, especially at frequencies below 6 MHz. This clutter, often caused by ionospheric backscatter and turbulence, can significantly impair radar performance. DARPA’s program focuses on developing clutter mitigation techniques that utilize the underlying physics of surface waves and spread clutter propagation. These techniques are intended to extend the reliable tracking range of Surface-Wave Over-the-Horizon Radar (SWOTHR) systems, ensuring more accurate and longer-range surveillance capabilities.
Classification: Traditional high-frequency (HF) radars struggle with classifying maritime traffic due to their long wavelengths, which are typically not suited for identifying detailed platform features. DARPA aims to overcome these limitations by leveraging longer observation periods, multi-frequency data, and multi-angle observation processing. The goal is to improve the classification accuracy of maritime vehicles, even when using narrowband radar systems operating in the HF band. This focus area is expected to enhance the ability of HF radars to not only detect but also accurately identify different types of maritime vessels.
Proposals should demonstrate the potential to meet these objectives, with metrics for passive radar, vehicle classification, and signal-to-clutter-and-noise ratio (SCNR) provided in the program’s guidelines.
Program Structure and Phases
The program is structured as a 15-month effort divided into two phases:
- Phase 1 (Feasibility Study):
- This 6-month phase focuses on mid-latitude data and initial algorithm development. Participants will work on exploiting natural environmental noise, detecting platform signals amidst surface and ionospheric clutter, and enabling vehicle classification. The feasibility of proposed methodologies will be evaluated using mid-latitude data provided by the DARPA team.
- Phase 2 (Proof of Concept):
- The 9-month Phase 2 will involve refining and expanding the algorithms developed in Phase 1. The focus will shift to low-latitude data, collected in equatorial regions, which presents more challenging conditions for SWOTHR systems. Successful performers from Phase 1 will continue to work towards meeting the program’s metrics and will be evaluated by an Independent Validation and Verification (IV&V) team.
Opportunities for Academia and Small Businesses
DARPA encourages participation from academia, small businesses, and other non-traditional organizations with expertise in passive and remote sensing methods, surface wave radar, radio propagation, ionospheric characterization, and spatial-polarimetric-temporal signal processing. This is a unique opportunity for these entities to contribute to cutting-edge research and development in remote sensing technologies.
Funding and Award Structure
The total award value for this program, including both Phase 1 and Phase 2, is capped at $2,000,000. This amount includes both government funding and performer cost share if required or proposed. The Phase 1 base effort has a maximum award value of $1,000,000, while the Phase 2 option is capped at $1,100,000. The program’s emphasis is on developing algorithms and methods rather than large-scale instrumentation or field test campaigns.
Conclusion
The DARPA Disruption Opportunity for SWOTHR and environmental characterization represents a significant opportunity for researchers and developers to contribute to the advancement of remote sensing technologies. By focusing on innovative approaches to passive radar, clutter mitigation, and vehicle classification, the program aims to overcome existing challenges and pave the way for more effective and reliable remote sensing systems. Interested parties are encouraged to submit proposals that align with the program’s objectives and technical scope.
