Triboelectric (frictional) and combustion processes impart electrostatic charge on projectiles as they are fired. Additional
charging and discharging processes alter the magnitude of charge
in-flight and are complex functions of a plethora of
environmental conditions. There is an interest in using electric-field sensors to help detect and track projectiles in
counter-sniper and projectile ranging systems. These applications require knowledge of the quantity of charge, as well as
the sensitivity of electric-field sensors.
The U.S. Army Research Laboratory (ARL) took part in multiple experiments at Aberdeen Proving Grounds (APG) to
simulate a battlefield-like environment. Sensors were placed in strategic locations along the bullets' paths and recorded
the electric-field signatures of charged small-arms bullets. The focus of this effort was to analyze the electric-field
signatures collected during the APG experiment in order to estimate electrostatic charge on the bullets. Algorithms were
written to extract electric-field bullet signatures from raw data; these signatures were further processed to estimate the
miss distance, velocity and charge. The estimates of range and velocity were compared to similar estimates from
acoustic signatures for verification. Ground-truth Global Positioning System (GPS) data were used to independently
calculate ranges, azimuths, and miss distances. Signatures were filtered to remove clutter signals from power lines and
other unwanted field sources. Closed-form equations were then fitted to the collected signatures to retrieve estimates for
the magnitude of charge on the bullets.
Test data, collected with sensors placed on a wall, showed enhanced E-field intensity. A Method of Moments (MoM)
model of the wall was created to improve signature simulation. Detectable charges on bullets were found to exist in the 1
pC to 1 nC (10-12 - 10-9 C) range. Relationships between estimated charge, gun type, bullet caliber, noise thresholds and
number of shots in sequence are presented and statistically analyzed.