Summary of Geophysical Methods
- Gravity Survey Method
Survey Application - Airborne, ground, downhole
Physical Parameter measured - Vector component of gravity field
Source of Anomaly - Density contrast
Depth of Investigation - All
- Magnetic Survey Method
Survey Application - Airborne, ground, downhole
Physical Parameter measured - Vector component of total magnetic field
Source of Anomaly - Magnetic susceptibility and or remnant magnetisation contrast
Depth of Investigation - All
- Radiometric Survey Method
Survey Application - Airborne, ground, downhole
Physical Parameter measured - Count rate and Energy level of recieved gamma ray photons
Source of Anomaly - K, Th and U contrast
Depth of Investigation - Upper 25 cm
- Electromagnetics Survey Method - many variations available
Survey Application - Airborne, ground, downhole
Physical Parameter measured - Dependent on method; Vector component of magnetic field (B Field), time derivative of magnetic field (dB/dt), ratio of received to applied electric and magnetic fields, total magnetic field
Source of Anomaly - Lateral or vertical changes in Earth conductivity. Requires a target with a high absolute conductivity.
Depth of Investigation - Highly dependent on frequency. Shallow (VLF - 10m, controlled source – 300m), intermediate (AMT – 1km), deep (MT-10km)
- MagnetoMetric Resistivity Survey Method
Survey Application - Ground and downhole
Physical Parameter measured - Vector Component of Magnetic field
Source of Anomaly - Lateral or vertical changes in Earth conductivity. Only requires a target with a conductivity contrast rather than one with a high absolute conductivity.
Depth of Investigation - A few hundred metres
- Sub-Audio Magnetic Survey Method
Survey Application - Ground
Physical Parameter measured - Total Magnetic Intensity (TMI), Total Field MagnetoMetric Resistivity (TFMMR)
Source of Anomaly - Relative conductor
Depth of Investigation - 50m
