Airborne Electromagnetic Survey
(Redirected from Airborne Time-Domain Electromagnetics)
Exploration Technique: Airborne Electromagnetic Survey
|Exploration Technique Information|
|Exploration Group:||Geophysical Techniques|
|Exploration Sub Group:||Electrical Techniques|
|Parent Exploration Technique:||Electromagnetic Techniques|
|Information Provided by Technique|
|Lithology:||provide data on rock type and mineral content|
|Hydrological:||can be used to detect changes in density of fluids and indicate if there is salt water intrusion|
|Low-End Estimate (USD):|| 48.274,827 centUSD |
4.827e-8 TUSD / mile
|Median Estimate (USD):|| 317.3831,738 centUSD |
3.1738e-7 TUSD / mile
|High-End Estimate (USD):|| 1,609.00160,900 centUSD |
1.609e-6 TUSD / mile
|Low-End Estimate:|| 0.11 days3.011636e-4 years |
0.00361 months / 100 mile
|Median Estimate:|| 0.98 days0.00268 years |
0.0322 months / 100 mile
|High-End Estimate:|| 4.66 days0.0128 years |
0.153 months / 100 mile
|Cost/Time Dependency:||Location, Size, Resolution, Terrain, Weather, # of Turns|
Airborne electromagnetic surveys are used to conduct a rapid survey at a relatively low cost of a broad area to search for metallic conductors. Graphite, pyrite and or pyrrhotite are present in the bedrock and are most commonly what provides the electromagnetic response. The conductivities which is determined through the electromagnetic method varies over seven orders of magnitude between various geologic materials. The strongest responses come from massive sulphides. Fresh water on the other hand is highly resistive and will provide responses very different from salt water.
Airborne electromagnetic surveys are used to rapidly characterize a geothermal field. The surveys can detect changes in rock type, fluid density, and even the presence of a fault carrying large amounts of water since the fault will create geologic noise compared to areas without faults. Better characterization of the geothermal field will aid with production and injection well placement.
A primary man-made alternating magnetic field is established by passing a current through a coil. The field is measured with a receiver which consists of a sensitive electronic amplifier and meter or a potentiometer bridge. If the source and receiver are flown over a more conductive zone, such as an area with higher metallic content, a measurable secondary magnetic field will be created. This secondary magnetic field is compared to the original and is usually reported proportionally to the primary magnetic field. For airborne electromagnetic systems, the receiver coils are usually in a towed bird and the transmitter may be a large coil encircling a fixed wing aircraft. Or another set up is with one or more small coils in the same bird that houses the transmitting coils.
In the case of airborne systems, the receiver coils are usually in a towed bird and the transmitter may be a large coil encircling a fixed wing aircraft, e.g. INPUT systems, or one or more small coils in the same bird that houses the transmitting coils
Some areas are not appropriate for airborne electromagnetic surveys. These include semi-arid areas, particularly with internal drainage, and tidal coasts and estuaries. Also the background conductivity can influence the accuracy of the results. For example, weathered maific flows can provide strongly conductive backgrounds masking other signals. There are multiple factors that can influence the detectability of the conductor which need to be accounted for when analyzing the data. These include among many coverage, resolution, and the penetration depth of the system.