Geometics - Model MetalMapper - Advanced Transient Electromagnetic (TEM) Instrument
MetalMapper can be used in two different modes. In dynamic or mapping mode, the instrument is moved in a manner similar to existing TDEM instrumentation for UXO detection. To increase the data rate, shorter transient decays (3 ms) are measured and fewer transients are averaged to come up with the final result. In some cases only a single transmitter coil is measured. This mode is used to identify targets which require further investigation.
The second mode of operation is static or target mode. The instrument is positioned over a target and data is recorded for approximately 30 s. During this time multiple transients are recorded and averaged together to obtain adequate signal to noise. For the MetalMapper instrument, there are three transmitter coils and 7 off 3-component receiver cubes which results in 63 different recorded transients. The decays are measured for 8 to 25 ms and 40-60 data points are saved for each transient measurement.
By comparing the recorded x, y and z decay curves it is possible to demine whether the target has a uniform or irregular shape. 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 is more likely to be fragmented shrapnel and metallic debris (refer to Fig 1).
Each instrument is supplied with a pre-installed calibration curve derived from samples containing different concentrations of magnetite. Alternatively operators are able to formulate and save their own calibration curves.
Bandwidth: DC to 50 KHz for purposes of anti-aliasing. Effective bandwidth is dependent of data collection parameters.
Noise Floor: 4 nT/s/√Hz 1t 1000 Hz.
Transmitter Loops: Up to 200 A-m2, 120 A-m2 typical
Receiver Loops: Each receiver cube contains three 10cm x 10 cm orthogonal, co-located loops.
Data Acquisition Time Blocks: 33.33 ms, 100 ms, 300 ms, 900 ms, 2.7s
Operating System: Windows XP SP2, or Windows 7
Data Terminal/Display: Ruggedized, Day Light Readable Touch Screen.
Power: Four 12 A-h Li-Ion batteries. Requires +12V supply for data acquisition and ±12V supplies for the transmitter. Six hour operation with full charged batteries.
Environmental: 0 to 50°C.
Instrument Physical: 19.75”L x 8.5”W x 14.5”H. Weighs 48 lb including batteries.