AAWSAP DIRD, Detection and High-Resolution Tracking of Vehicles at Hypersonic Velocities, November 2010

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.

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LIDAR. By attaching a rotating mirror to vary the direction of the laser beam, it is possible to
traverse the laser across surfaces to develop 3-D maps of objects using "imaging LIDAR." As
an example, during the DARPA challenge held in the Nevada desert in 2005, autonomous
automobiles used LIDAR to build a map of all objects in front of the vehicle and used it for
collision avoidance and navigation. LIDAR systems have also been used to obtain accurate
maps of the surface of mars from the Mars Orbiting Global Surveyer. LIDAR systems for
meteorological studies are often mounted in aircraft and fired from the side of the fuselage to
obtain a two-dimensional horizontal map of the atmospheric conditions.
A measurement technique known as Laser Doppler Velocimetry (LDV) uses the Doppler shift
in the transmitted and reflected laser light to measure the velocity of the target and the
properties of the air along the axis of the laser beam.
LIDAR systems using pulsed YAG lasers are capable of measuring many properties of air
along the path of the laser beam. As shown in Figure 17, if a laser pulse is fired toward a
distant target, light is reflected from particles in the atmosphere and this light is collected
through a beamsplitter and directed to a photodetector. By knowing the time interval
between generation of the laser pulse and the time that each reflected signal is received, the
distance along the beam can be accurately determined for each data set. By recording this
optical information as a function of time, using Raman spectroscopy, particle light scattering,
and absorption theory, multiple properties of the air and particles in the air along the path of
the laser can be measured as a function of distance from the transmitter. Particle density,
velocity, and chemical species can be measured using pulsed LIDAR systems. Concentration
of airborne gas species (oxygen, nitrogen), air temperature, and air velocity can also be
measured in this fashion.
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Turbulent Wake
Figure 17. Schematic of a Pulsed LIDAR System.
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