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.

UNCLASSIFIED/,SFOR. QFFIElal L: 1!ii 011! X
In this equation, q represents the amount of radiant energy emitted in watts, E is the
emissivity (a dimensionless quantity that gauges the relative ability of an object's surface to
emit energy by radiation), A is the surface area, a is the Stefan-Boltzmann constant (a
= 5.67 x 10-s J-s-1-m-2-K-4 ), and T is the temperature of the object's surface. A simple
example of emission of heat as radiant energy is an infrared bathroom heater where electric
current is passed through a metallic element that reaches several thousand degrees and
emits considerable thermal radiation.
All objects in the environment exchange radiant heat with each other and seek equil ibrium
temperatures. At high temperatures, many objects behave as "black body radiators" defined
by their surface emissivity, E = 1. The surface temperature of an object causes
electromagnetic radiation to be emitted with a spectrum given by Planck's Distribution Law,
equation 18, where the energy density is emitted by the surface of the object per
wavelength per unit volume:
u(A,T) = 8 n h c __1__5 (18)
A, h e
e AkT - 1
The terms in th is equation are as follows:
• c: speed of light, (3 x 108 m/s).
• h: Planck's constant, (6.62 x 10-34 J-s).
• A: wavelength of the emitted radiation, (m).
• k: Boltzmann constant, (1.38 x 10-23 J/K).
• T : surface temperature, (K).
• u(A,T): spectral energy density, (Jm-3-m- 1).
The surface of the sun behaves as a black body radiatora with a surface temperature of
5,778 K. For the sun, the Planck distribution of energy versus wavelength looks like that of
Figure 12. The horizontal axis is the wavelength in units of meters and shows that peak
energy occurs at a wavelength of about 5.02 x 10-7 meters or 0.502 microns (1 micron = 10·6
meters). This falls within the visible band (0.38 microns to 0.65 microns) and corresponds to
the yellow color of our sun. The peak wavelength, equation 19, is given by Wien's
Displacement Law:
A-.rnx = 2.8977685 X 10-3 (m · K) I T (19)
Th is shows that as the temperature of an object increases, the amount of radiant energy
released by the surface increases and the value of the peak wavelength becomes smaller.
a A black body is an idealized object that absorbs all electromagnetic radiation that falls on it.
Since a black body is a perfect absorber of radiant energy, by the laws of thermodynamics it must
also be a perfect emitter of radiation.
UNCLASSIFIED//FOR 0661El.t.L: W&&: OttLY
18