MetalMapper 2x2 Electromagnetic Land Geophysical Equipment

MetalMapper 2x2 is the most advanced Transient Electromagnetic (TEM) instrument available for Unexploded Ordinance (UXO) detection. Through analysing the 3D EM decay curves of buried metallic targets the instrument permits an operator to differentiate between intact UXO, fragmented shrapnel and metallic debris. This is achieved through illuminating a buried object from different locations and recording the three-axis electromagnetic decay.

The instrument consists of four 35cmx35cm transmitter loops, producing 30A-m2 magnetic moment, positioned in a two by two array. Located in the centre of each transmitter coil is a three-axis receiver. Each transmitter is sequentially triggered and the decay curves from each receiver coil recorded, producing in total 48 decay curves.

MetalMapper 2x2 being used to locate UXO on a US DoD test range. Image Courtesy of Geometrics Inc.

By inverting the recorded x, y and z decay curves it is possible to determine the local (X,Y,Z) location of the target beneath the array, the orientation of its principal axes, and the principal axis polarizability with high degrees of accuracy. From which the following discriminating factors can be can be derived for each anomaly;

Location
Measure of size
Depth of burial
Symmetry of object (i.e. cylindrical, spherical, plate like or asymmetrical)
3 polarizability decays indicating target shape

Target classification is based on a library matching procedure. Intact UXO are fundamentally a cylinder of metal, therefore if the UXO target is intact two of the decay curves should present the same gradient.

However if the all three decay curves are dissimilar then the object has an irregular shape and the object is more likely to be fragmented shrapnel and metallic debris. Recorded decay curves are statically matched against the object library to determine the nature of the target. This procedure takes on average thirty seconds to complete.

The system exploits external GNSS positioning and an Inertial Measurement Unit (IMU) to pin point each discovered anomaly.

By analysing the decay curves in such a way it is possible to discriminate multiple targets located within the footprint of the system.

Post-processing and inversion of the decay curves is undertaken using the UX-Analyses module developed by Geosoft as part of their Oasis Montaj. Classification is the process of analyzing data to decide whether the source of an anomaly is a hazardous target of interest (TOI), and in some cases, even deciding which specific type of munition may be present. During munition clean-up projects, most of the items excavated are harmless scrap metal (or ‘clutter’). If geophysical targets can be determined to be non-hazardous without digging, they can be left unexcavated.

For UXO projects using advanced electromagnetic (EM) geophysical data such as that from the MetalMapper, UX-Analyze provides a software solution for data processing, modelling and target classification. UX-Analyze allows you to select target signatures of interest, model the data and classify the results from static (cued over known targets) or dynamic surveys. These capabilities are incorporated into a complete workflow with easy to use tools for the following main functions:

Prepare Data for Analysis - Import data, quality checks, apply data corrections
Find Targets - Automated and manual target picking including “Informed source selection”
Analyze- Inversions (solvers), target libraries
Classify and Rank - Find targets matching signature library and find unexpected TOI, classify and rank targets for excavation or for follow-up static survey.

UX-Analyze includes modelling tools developed in partnership with Acorn Science & Innovation. UX-Analyze is an extension of Oasis montaj and requires Oasis montaj and the UXO Land extension as prerequisites.

Tech Specs
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Product Dimensions

Physical	Dimensions (L x W x H)	Weight
MetalMapper 2x2 (instrument only)	1.4cm x 110cm x 120cm	50kg

Technical Specifications

Configuration:	Four transmitter loops, four 3-component MetalMapper receiver cubes/loops, field modifiable configuration for cart-mounted wheeled transport or skid-steer mounted sled.
A/D Conversion:	Up to 24, 16-bit A/D channels simultaneously sampled and operation at 250kHz.
Bandwidth:	DC to 50kHz for purposes of anti-aliasing. Effective bandwidth is independent of data collection parameters.
Noise Floor:	4nT/s/√Hz at 1000Hz.
Stacking Trigger Accuracy:	All timing accurate to one sample interval (4 μs).
Maximum Input Signal:	Receivers withstand any transient capable of being produced by the transmitter.
Effective area of each receiving loop / preamplifier:	100m²
Transmitter loops:	Four loops oriented in a 2x2 horizontal array , each 35cm x 35cm.
Transmitter loop moment:	30 A-m² typical.
Receiver loops:	Each receiver cube contains three 10cm x 10cm orthogonally-oriented, co-located loops.
Data acquisition time blocks:	33.33 ms, 100 ms, 300 ms, 900 ms, 2.7s
Data point acquisition and storage rate:	30, 10, 3.33, 1, 0.37 data points/s.
Cycles of time-domain signal in each data-acquisition block:	1, 3, 9, 27, 81, 243.
Transient-decay length:	Selectable based on data-acquisition block time and cycles within that block. Useful decay lengths can vary from 103 μs to 675ms long.
Data acquisition modes:	- Full wave (stores all data samples for each channel, i.e. 4 μs samples). - Decays (stores data samples in one decay curve after stacking multiple decays from a data-acquisition block). - Decimated decays (stores decays after stacking time gated decays and computing average amplitude in each time gate).
Transmitter turn-off and primary die-away time including receivers’ response:	100 μs maximum after initiating transmitter turn-off. After background subtraction, secondary decay transients can typically be observed at 50 ms. Transmitter turn-off to 1% is on the order of 10 ms.
Decimation time gates:	The gate widths are determined by applying an (operator selectable) fraction of the delay time at each gate , with a one sample minimum. Gating begins after a selectable hold-off time.
Transmit Current Monitoring channel::	One digital channel records digitized transmitter current to same sampling specifications as receiver channels.
Console:	Rugged Tablet PC running Debian (Linux-based).
Power::	Three 12 A-h Li-Ion batteries. Requires +12V supply for data acquisition and ±12V supplies for the transmitter.
Operating time on full battery charge::	Up to 8 hours.
Environmental:	0 to 50 degrees C.
Personal:	2 operators required.