PROCEEDINGS ARTICLE | April 26, 2010
Proc. SPIE. 7668, Airborne Intelligence, Surveillance, Reconnaissance (ISR) Systems and Applications VII
KEYWORDS: Radio optics, Data modeling, Sensors, Combustion, Black bodies, Infrared radiation, Explosives, Radiometry, Forward looking infrared, Temperature metrology
Continuum emission is predominant in fireball spectral phenomena and in some demonstrated cases, fine detail in the
temporal evolution of infrared spectral emissions can be used to estimate size and chemical composition of the device.
Recent work indicates that a few narrow radiometric bands may reveal forensic information needed for the explosive
discrimination and classification problem, representing an essential step in moving from "laboratory" measurements
to a rugged, fieldable system. To explore phenomena not observable in previous experiments, a high speed (10μs
resolution) radiometer with four channels spanning the infrared spectrum observed the detonation of nine home made
explosive (HME) devices in the < 100lb class. Radiometric measurements indicate that the detonation fireball is well
approximated as a single temperature blackbody at early time (0 < t ⪅ 3ms). The effective radius obtained from absolute
intensity indicates fireball growth at supersonic velocity during this time. Peak fireball temperatures during this initial
detonation range between 3000.3500K. The initial temperature decay with time (t ⪅ 10ms) can be described by a
simple phenomenological model based on radiative cooling. After this rapid decay, temperature exhibits a small, steady
increase with time (10 ⪅ t ⪅ 50ms) and peaking somewhere between 1000.1500K-likely the result of post-detonation
combustion-before subsequent cooling back to ambient conditions . Radius derived from radiometric measurements
can be described well (R<sup>2</sup> > 0.98) using blast model functional forms, suggesting that energy release could be estimated
from single-pixel radiometric detectors. Comparison of radiometer-derived fireball size with FLIR infrared imagery
indicate the Planckian intensity size estimates are about a factor of two smaller than the physical extent of the fireball.
