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This Defense Intelligence Reference Document was prepared by the Defense Intelligence Agency's Defense Warning Office in fiscal year 2010 as part of the Advanced Aerospace Weapons System Applications program. It reviews how air flows around objects at subsonic, supersonic and hypersonic speeds, covering shock waves, wakes and ionization. It then compares ways to detect and track hypersonic vehicles, including radar, optical, infrared, LIDAR, infrasound and seismic methods. The report makes four recommendations, among them building a database of aircraft wake signatures and developing novel detectors.
From the source: Release of 2026-09-18 Incident: 11/20/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys how hypersonic vehicles may be detected and tracked by exploiting the physical effects they create in flight, especially shock waves, ionized gas, hot surfaces, and turbulent atmospheric wakes. The report reviews a broad set of detection methods, including radar, infrared sensing, optical imaging, LIDAR, passive radio reflection, infrasound, and seismic techniques, and argues that the most effective systems will likely combine multiple sensor types, because each captures different features of a high-speed vehicle’s passage through the atmosphere. It presents radar and infrared sensing as the strongest existing tools for operational detection, while giving particular attention to wake-based methods such as LIDAR and passive radio techniques for improving tracking, identification, and discrimination of future hypersonic aircraft. The paper identifies hypersonic vehicles as an evolving surveillance problem in which future progress will depend on better multi-sensor integration, improved wake characterization, and novel signature-exploitation techniques.
UNCLASSIFIED/fFOR. QFFIEl.t.L: Uii QD:I! X Chapter 3: Detection Technologies Hypersonic objects passing through the Earth's atmosphere leave traces that can be observed using a number of detection methods. The bow shock introduced by such objects reflects and refracts radio waves, RADAR pulses, and visible light. The ionized air surrounding the object also creates electromagnetic interference that is visible on RADAR and the emitted visible li ght in the wake is observable in photographs. The shock and turbulent wake also create low frequency sound that can be sensed by ground-based sensors. These detection methods can be characterized as electromagnetic, optical, and acoustic and seismic as shown in Figure 7. Each method will be discussed along with the limitations and advantages for the detection of hypersonic objects passing through the atmosphere. Electromagnetic RADAR Energy Reflection Doppler RADAR Radio Reflection Detection Optical Sky Cameras and Photographic Methods Infrared Detection LIDAR Chronograph Acoustic and Seismic Infrasound Seismic Figure 7. Hypersonic Vehicle Detection Techniques. One of the fundamental tools for detecting the velocity of high-speed objects is the chronograph. These devices are used to measure the velocity of automobiles using pneumatic tubes, and simple systems using laser diodes or LEDs are used to measure the velocity of bullets. Figure 8 outlines a laser-based chronograph that is commercially available for measuring the velocity of projectiles in two-stage gas guns capable of speeds in a vacuum of 12 km/h, or approximately Mach 36 if the projectile passed through air. As a high-speed object passes through the first laser beam followed rapidly by the second, photodetectors sense the change in intensity of the laser beam and send these signals to a storage oscilloscope or to a counter. The time delay between the two signals, Lit, is used to find the velocity of the object based on the distance between the two photodetectors, L. Digital clocks are capable of accurately measuring time delays to within a fraction of a nanosecond (10·9 seconds), so chronographs are capable of very high accuracy in determining the velocity of objects. As noted earlier, their use at gun ranges or in high speed gas guns requires that the path of the hypersonic object must pass through the laser beams for the chronograph to be effective, which limits their usage for the detection of hypersonic aircraft except at instrumented test ranges. UNCLASSIFIED//EQA: QlililEl.t.L: W&&: O,.L'l 11
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