Development And Evaluation Of A Second-Generation Airborne Electromagnetic System For Detection Of Unexploded Ordnance

Field trials of a low‐flying time‐domain helicopter electromagnetic system designed for detection of unexploded ordnance have yielded positive and encouraging results. The system is able to detect ordnance as small as 60‐mm rounds at 1‐m sensor height. We examined several transmitter and receiver configurations. Small loop receivers gave superior signal‐to‐noise ratios in comparison to larger receiver loops at low heights. Base frequencies of 90 Hz and 270 Hz were less affected than other base frequencies by noise produced by proximity to the helicopter and by vibration of the support structure. For small ordnance, a two‐lobed, antisymmetric transmitter loop geometry produced a modest signal‐to‐noise enhancement compared with a large single rectangular loop, presumably because the antisymmetric transmitter produces smaller eddy currents in the helicopter body, thereby reducing this source of noise. In most cases, differencing of vertically offset receivers did not substantially improve signal‐to‐noise ratios at very low sensor altitudes. Signal attenuation from transmitter to target and from target to receiver causes signals from smaller ordnance to quickly become indistinguishable from geological background variations, so that above a sensor height of about 3 m only large ordnance items (e.g., bombs and large caliber artillery rounds) were consistently detected.

Download Full-text

An example of 3D conductivity mapping using the TEMPEST airborne electromagnetic system

Exploration Geophysics ◽

10.1071/eg00162 ◽

2000 ◽

Vol 31 (1-2) ◽

pp. 162-172 ◽

Cited By ~ 60

Author(s):

Richard Lane ◽

Andy Green ◽

Chris Golding ◽

Matt Owers ◽

Phil Pik ◽

...

Keyword(s):

Electromagnetic System ◽

The Tempest ◽

Airborne Electromagnetic

Download Full-text

MAPPING EARTH CONDUCTIVITIES USING A MULTIFREQUENCY AIRBORNE ELECTROMAGNETIC SYSTEM

Geophysics ◽

10.1190/1.1440837 ◽

1978 ◽

Vol 43 (3) ◽

pp. 563-575 ◽

Cited By ~ 7

Author(s):

H. O. Seigel ◽

D. H. Pitcher

Keyword(s):

Thin Sheet ◽

Radar Altimeter ◽

Electromagnetic System ◽

Near Surface ◽

Quantitative Estimates ◽

Simple Geometry ◽

Airborne Electromagnetic ◽

Groundwater Mapping ◽

Actual Field ◽

Depth Of Burial

The Tridem vertical coplanar airborne electromagnetic system provides simultaneous in‐phase and quadrature information at frequencies of 500, 2000 and 8000 Hz. The system can map a broad range of earth conductors of simple geometry and provide quantitative estimates of their conductivities and dimensions. Computer programs have been developed to automatically interpret the six channels of Tridem data, plus the output of an accurate radar altimeter, to determine the depth of burial, conductivity and thickness of a near‐surface, flat‐lying conducting horizon. In limiting cases, the interpretation provides the conductance (conductivity‐thickness product) of a thin sheet (ranging from 100 mmhos to 100 mhos) or the conductivity of a homogeneous earth (ranging from 1 mmhos/m to 10 mhos/m). Two actual field examples are presented from Ontario, Canada; one relating to the mapping of overburden conditions (sand, clay and rock, etc) and the other to the mapping of the distribution of a buried lignite deposit. Other areas of potential application of the system to surficial materials would include groundwater mapping, permafrost investigations, and civil engineering studies for roads and pipelines.

Download Full-text

27. Viability of an Airborne Electromagnetic System for Mapping of Shallow Buried Metals

Near-Surface Geophysics ◽

10.1190/1.9781560801719.ch27 ◽

2005 ◽

pp. 653-662

Author(s):

William E. Doll ◽

T. Jeffrey Gamey ◽

J. Scott Holladay ◽

James L. C. Lee

Keyword(s):

Electromagnetic System ◽

Airborne Electromagnetic

Download Full-text

COMPUTER DATA PROCESSING AND QUANTITATIVE INTERPRETATION OF AIRBORNE RESISTIVITY SURVEYS

Geophysics ◽

10.1190/1.1440570 ◽

1975 ◽

Vol 40 (5) ◽

pp. 818-830 ◽

Cited By ~ 9

Author(s):

G. J. Palacky ◽

F. L. Jagodits

Keyword(s):

Electric Fields ◽

Simultaneous Recording ◽

Quantitative Interpretation ◽

Geologic Mapping ◽

Electromagnetic System ◽

Computer Data ◽

Type Curves ◽

Intermediate Data ◽

Processing Cost ◽

Airborne Electromagnetic

The recently constructed airborne electromagnetic system called E-Phase measures the intensity of the vertical and horizontal electric fields. Standard broadcasting, VLF, and LF navigation aid transmitters are used as sources of the primary EM field. A system of this kind responds best to horizontal layers of large extent and therefore is suitable for geologic mapping and for the detection of resistive materials such as gravel and permafrost. A successful application of the system would not have been possible without digital recording of the data and subsequent computer processing. An efficient algorithm consisting of three processing steps assures low processing cost and provides for two intermediate data checks. Final outputs are printer plots of apparent resistivity for all flight lines and maps of stacked profiles or contours. Quantitative interpretation was made possible by the simultaneous recording of the data at three transmitter frequencies and by the availability of theoretical solutions for layered media. Instead of generating an atlas of type curves, an interactive program was written which enables the geophysicist to rapidly obtain apparent resistivities assuming a three‐layer model. A close match with the measured data is easy to achieve when a reasonable estimate of two of the parameters (resistivities, thicknesses) can be made initially. The interpretation procedure is demonstrated on a case history, a 1973 survey conducted near Wadena, Saskatchewan.

Download Full-text