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Surveillance, detection, and tracking of multiple high-speed projectiles, particularly bullets, RPGs, and
artillery shells, can help military forces immediately locate sources of enemy fire and trigger countermeasures. The
traditional techniques for detection and tracing of fast moving objects typically employ various types of radar, which has
inherently low resolution for such small objects. Fast moving projectiles are aerodynamically heated up to several
hundred degree Kelvin temperatures depending on the speed of a projectile. Thereby, such projectiles radiate in the Mid-
Infrared (MWIR) region, where electro-optical resolution is far superior, even to microwave radars. A new passive
electro-optical tracker (or PET) uses a two-band IR intensity ratio to obtain a time-varying speed estimate from their
time-varying temperatures. Based on an array of time-varying speed data and an array of azimuth/ elevation angles, PET
can determines the 3D projectile trajectory and back track it to the source of fire. Various methods are given to
determine the vector and range of a projectile, both for clear and for non-homogeneous atmospheric conditions. One
approach uses the relative intensity of the image of the projectile on the pixels of a CCD camera to determine the
azimuthal angle of trajectory with respect to the ground, and its range. Then by using directions to the tracked projectile
(azimuth and elevation angles of the trajectory) and the array of instant projectile speeds, PET determines the distance to
the projectile at any point on its tracked trajectory or its predicted trajectory backwards or forwards in time. A second
approach uses a least-squares optimization technique over multiple frames based on a triangular representation of the
smeared image to yield a real-time trajectory estimate. PET's estimated range accuracy is 0.2 m and the azimuth of the
trajectory can be estimated within 0.2°.
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