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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RADAR systems are widely used for aircraft surveillance and can detect the distance to
objects and the position of an object (through triangulation); with Doppler RADAR, the
velocity can be directly measured. RADAR does have limitations. While low-frequency
RADAR systems are capable of following the curvature of the earth, the long wavelength of
this energy makes it difficult to resolve small objects. Higher frequency RADAR tends to be
more "line of sight." Since it depends upon reflected energy, several problems are
highlighted by the RADAR Equation:
p . = P,,·ansmilld GA a F4
(15)
rece,ved ( 4 1r)2 R/ R,2
In this equation, Ptransmitted represents the transmitted power, Preceived the received power, G
the transmitting antenna gain, A the aperture area of the receiving antenna, a the RADAR
cross section, F the pattern propagation factor, and Rt and Rr are the distance from the
transmitter to the target and the target to the receiver, respectively. If the RADAR
transmitter and receiver are in the same unit, the power returned as a reflection from a
target decreases as R4 . This means that energy received in reflected energy decreases by
94% every time the distance to the target is doubled.
RADAR depends upon the reflection of electromagnetic waves off of a target's surface,
thereby making objects with a small RADAR cross section difficult to detect (e.g., stealth
aircraft). Atmospheric phenomenon, including inversions and turbulence, can lead to
interference with RADAR reflections. Even with these limitations, RADAR is widely used to
monitor high-speed aircraft, meteors, and man-made objects reentering the atmosphere
from Earth orbit.
Velocity Vector
Radar Dish
Hypersonic Vehicle
Radial direction
I Rotat
Pedei
Reflected Energy Transmitted Energy
R= radial distance
Figure 10. Schematic of a RADAR System.
Doppler RADAR
Doppler RADAR systems yield velocity data for a target. Pulsed RADAR systems send out a
short burst of high-frequency radiation that is reflected from a target. The RADAR unit
processes the delay time between the transmitted pulse and the received echo to determine
the range or distance to the target. The energy reflected from the target is, however,
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