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1 BSMN 425: Imaging Geophysics Lecture Notes on 29th^ January, 2024
1. GPR: Typically, pulsed EM energy is generated at predetermined station locations along the length of the GPR profile. The travel times and amplitudes of reflected EM energy are usually recorded by a monostatic transmitter–receiver. The recorded travel time–amplitude information is normally used to generate a GPR profile (2-D time–amplitude image). These data can be transformed into a 2-D velocity–depth model. If external constraints are available, a geologic model can be generated. 2. Gravity
2 Gravimeters are designed to measure variations in the gravitational field of the Earth, and are typically used to generate 2-D or 3-D density–depth models of the subsurface. If external constraints are available, the density–depth models can be transformed into a geologic model.
3. Magnetics Magnetometers are designed to measure variations in the magnetic field of the Earth. These are usually caused by the presence of magnetically susceptible material of natural or human origin (typically magnetite or iron, respectively). In certain instances, magnetic data can be interpreted quantitatively, and transformed into constrained geologic models. More typically, however,
4 The following are key considerations when developing a geotechnical geophysics exploration program for engineering purposes: What are the physical properties of interest? Which geophysical methods respond to the physical properties of interest? • Which techniques can provide the required spatial resolution and target definition? Which geophysical tools can perform well under study-area conditions? Which techniques are most cost effective? Which techniques can provide complementary data? What nongeophysical control is required to constrain the interpretation of acquired geophysical data? Is the overall geophysical program cost-effective? If these considerations are not addressed, unsuitable geophysical data may be acquired, unnecessary expenditures may be incurred and undesirable time delays may be experienced.
