Wednesday (Group 2) - SERDP-ESTCP - Strategic Environmental ...

Munitions Management (MM)
Poster Number 47 – Wednesday
Ground Based Detection and Discrimination — EMI & Magnetometers / Sensors
REFINEMENTS IN THE ALLTEM UXO DETECTION
AND DISCRIMINATION SYSTEM
TED ASCH
U.S. Geological Survey
Denver Federal Center
Building 20, MS-964
Denver, CO 80225
(303) 236-2489
tasch@usgs.gov
CO-PERFORMERS: David Wright, Craig Moulton, and Trevor Irons (U.S. Geological Survey)
A
n advanced multi-axis electromagnetic induction system, ALLTEM, was specifically
designed for detection and discrimination of unexploded ordnance (UXO) with funding
from SERDP Project MM-1328. Refinement of the acquisition electronics, survey platform and
system orientation, and interpretation and analysis software is continuing with funding from
ESTCP Project MM-0809. ALLTEM uses a continuous triangle-wave excitation that measures
the target step response rather than the more common impulse response. An advantage of using a
triangle-wave excitation is that the responses of ferrous and non-ferrous metal objects have
opposite polarities. The system multiplexes through all three orthogonal (H x , H y , and H z axes)
transmitting loops and records a total of 19 different transmitting (Tx) and receiving (Rx) loop
combinations. ALLTEM data acquisition is dynamic with a spatial data sampling interval of 15
cm to 20 cm at a constant 100 kilosamples/s rate with 24-bit precision. Using an early-time pick
of 275 μs, late enough that the step response of an analog low-pass filter has settled, amplitude
difference data and maps are produced. These data are almost free of ground response and
system drift effects while retaining good sensitivity to UXO. The improvement in the signal-tonoise
ratio greatly enhances the ability to detect small or deep targets. The new ALLTEM
platform is a cart made of composite fiberglass and plastic that will substantially reduce the
weight of the cart. The electronics have been redesigned to be more compact and more energy
and heat efficient. The Crown amplifier that has been the backbone of the system has been
replaced with Class D amplifiers. This has resulted in an increased current output from +/- 8
Amps to +/- 11 Amps with much less heat put off by the amplifier. The ALLTEM data analysis
has now been incorporated into the Oasis Montage platform. This includes basic data processing,
system noise analysis, automated target selection, orientation analysis, and calls to an inversion
algorithm that has been developed and refined over the last year. The algorithm uses a physicsbased
forward model and non-linear inversion. While GPS position errors and additional errors
from cart roll, pitch, and yaw were often small enough that previous survey inversions still
provided good estimates of target position, depth, and orientation, and reasonable and
reproducible values for dipole moments of these targets, the addition of an AHRS unit should
reduce some of these errors. A demonstration at the Yuma Proving Ground is scheduled for
winter 2009.
G-15