Network Turns Soldiers' Helmets Into Sniper Location System

Engineers at Vanderbilt University's Institute for
Software Integrated Systems (ISIS) have developed a system
that can give soldiers just such an edge by turning their
combat helmets into "smart nodes" in a wireless sensor
network.

ISIS developed this novel technology with the support of
the Defense Advanced Research Project Agency and the
university has patented two of the system's key elements.

Like several other shooter location systems developed in
recent years, the ISIS system relies on the sound waves
produced when a high-powered rifle is fired. These acoustic
signals have distinctive characteristics that allow the
systems to pick them out from other loud noises and track
them back to their source. Current systems, however, rely on
centralized or stand-alone sensor arrays. This limits their
accuracy and restricts them to identifying shooters at
line-of-sight locations.

By contrast, the ISIS system combines information from a
number of nodes to triangulate on shooter positions and
improve the accuracy of its location identification
process. It also uses a patented technique to filter out the
echoes that can throw off other acoustic detection systems,
explains Akos Ledeczi, the senior research scientist at ISIS
who heads up the development effort.

"When DARPA gave us the assignment of creating a shooter
location system using nodes with very limited capabilities,
they didn't think we could solve the technical problems,"
Ledeczi admits. "At first, I didn't think we could do it
either, but we figured out how to make it work!"

Retired U.S. Army Lieutenant Colonel Albert Sciarretta,
who assesses new military technologies in urban environments
for DARPA, is one of the experts who is impressed by the
ISIS system: "It's strong points are that it isn't limited
to locating shots fired in direct line-of-sight, it can pick
up multiple shooters at the same time, and it can identify
the caliber and type of weapon that is being fired."

Sciarretta adds, "A leader can use the information that
this system provides to react tactically to enemy shooters
in ways that limit the number of friendly force and
non-combatant casualties. The ISIS system could be easily
developed into an operational war-fighting system."

When a high-powered rifle is fired, it produces two
different kinds of sound waves. One is the "muzzle blast"
that expands outward in a spherical wave from the
muzzle. The second is a conical shock wave that is produced
by the bullet as it travels at supersonic speeds. Each node
of the shooter location system contains an array of four
sensitive microphones. If at least three of the microphones
in a single node detect the muzzle blast, the information
allows the nodes' microprocessor to calculate the direction
that the sound came from. If the same array also detects the
arrival time and angle of the bullet shockwave, a simple
calculation gives the shooter's location.

"Because the microphones on the helmet are so close
together, the precision is not very high," Ledeczi
says. "However, the nodes are continuously exchanging the
times and angles of arrival for these acoustic signals,
along with their own locations and orientations. When two or
more nodes detect the shot, they can provide the bearing
with better than one degree accuracy. The range is typically
within a few meters even from as far as 300 meters. The more
sensors that pick up the shot, the more accurate the
localization."

The ISIS system communicates its findings with the
personal digital assistants that the soldiers carry. The
PDAs are loaded with maps or overhead pictures of the area
upon which the shooter locations are displayed.

In 2006, a team from the National Institute of Standards
and Technology at the U.S. Army Aberdeen Test Center
independently determined the accuracy of the system. Firing
positions were located at distances of 50 to 300 meters from
a 10-node sensor network. Six different weapons were
used. The only shots that the system sometimes failed to
track accurately were those that passed to one side of all
of the nodes.

The field tests demonstrated that the system can pick out
the location of high-powered sniper rifles even when they
are firing at the same time as a submachine gun like the
AK-47. They also proved that it can identify the window
that a rifle is firing through even when the rifle is
completely inside the building, the technique preferred by
trained snipers.

These tests were performed with sensors in fixed
locations. One of the problems with using a mobile network
has been keeping track of the positions of the mobile nodes
with sufficient precision. Standard GPS locations are not
precise enough for this purpose and satellite coverage can
be spotty in urban environments. The ISIS team has recently
solved this problem by adding an inexpensive radio chip that
allows them to track the relative position of nodes using
high-precision radio interferometry. The university has
patented the technique that ISIS developed.

The ISIS shooter system uses wireless nodes invented at
UC Berkeley and produced by Crossbow Technology Inc. of San
Jose, Calif. These smart nodes, or motes, form
self-organizing wireless-sensor networks and are the
realization of the Pentagon's "smart-dust" concept of
radically reducing the size and cost of sensor networks for
military applications. Current commercial shooter location
systems are extremely expensive, with prices ranging from
$10,000 to $50,000 per unit. By contrast, an entire node for
the ISIS system weighs only slightly more than the four AA
batteries that power it and costs about $1,000 to construct
using currently available commercial hardware.

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NOTE TO EDITORS: A multimedia version of this story is
available on Exploration, Vanderbilt's online research
magazine, at
http://www.vanderbilt.edu/exploration/stories/shooterloc.html
. For more news about Vanderbilt, visit the Vanderbilt News
Service homepage on the Internet at
http://www.vanderbilt.edu/News .

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