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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.
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Electromagnetic Spectrum
Wavelength Type of
Radiation
1nm x-rays
10nm
100nm Ultraviolet (UV)
lμm Visible Light {0.4 to 0.7 μm)
l0μm Near Infrared
lOOμm Thermal Infrared
1mm Far Infrared
10mm Microwaves
100mm Radar
lm Rad io Waves
10m
100m AM Radio
Figure 9. Electromagnetic Spectrum as a Function of Wavelength.
ELECTROMAGNETIC METHODS
RADAR (Reflected Energy)
RADAR, or "radio detection and ranging," has been heavily used since World War II for the
detection of aircraft and sea vessels. First patented by Christian Hulsmeyer in 1904, this
technique was first demonstrated by Nikola Tesla in 1917; RADAR was exploited in the
defense of Britain through the Chain Home RADAR network initiated in the late 1930s. 8
RADAR uses an antenna or a dish to transmit pulses of microwaves or radio waves toward a
potential target. Energy reflected from the target is collected by the antenna and the time of
flight of the transmitted and reflected signals yields the distance to the target. Early RADAR
systems emitted radia t ion in the high-frequency band (HF) from about 10 to 30 MHz.
Modern systems can operate well above 300 GHz.
As a single pu lse travels at the speed of light toward a target, the time delay between the
generation of the pulse and the time that its echo is received is 2L/c where L is the distance
to the target and c is the speed of light. For a target located 30 km from the source, the
time delay is 200 microseconds, an easily measurable delay. By using microwave radiation
emitted from a dish, target distance and bearing can both be measured.
While it was possible to use low-frequency radio waves ( ~30 MHz) for RADAR systems in the
1940s, the wavelength of t hese waves (100 meters) made it difficult to resolve small targets,
includ ing aircraft. This made it desirable to develop systems t hat could operate at higher
frequencies. UHF energy (300 to 1,000 GHz, 0.3- to 1-meter wavelength) radiation is used
for long-range surveillance, includi ng t he detection of intercontinental ballistic missi les . Air
traffic control uses the L band (1 to 2 GHz, 0.15- to 0.3-meter wavelength). X-band (8 to
12 GHz, 25- to 37-millimeter wavelength) energy is now used for airport RADAR where the
ra nge to aircraft is short. Higher frequency radiation is used for imaging systems and for
meteorological data acquisition.
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 46 pages are in the text index: search them above, or from the library's search.