ENGINEERING GEOLOGY/Geophysics 483 Table List of techniques commonly used in engineering geophysics Technique Passsive/active Physical property used Source/signal Magnetics Microgravity Continuous wave and time domain electromagnetics Resistivity imaging/sounding Induced polarization Passive Passive Active/passive Magnetic susceptibility Density Electrical conductivity/resistivity Active Active Earth’s magnetic field Earth’s gravitational field Radio frequency electromagnetics (Hz/kHz band) DC electrical (20 20 30 30 15 >10 30 8 15 3.5 1500 1500 4000 6000 6500 7000 3500 4500 1100 2000 2500 2300 2300 2500 2000 4000 160 600 >2000 methodology can be designed to meet the survey objectives Once acquired, geophysical data needs to be processed and interpreted to provide meaningful information to the engineer Data analysis plays a vital role in the successful application of engineering geophysics and is just as important as the selection of the survey method, survey design, and the practical skills needed to collect good data A key aspect of processing geophysical data ready for interpretation is the recognition and removal or separation of effects unrelated to the target being investigated As an example, consider raw data collected during a microgravity survey These data incorporate significant effects, such as the elevation of the site relative to sea-level, change in the Earth’s radius with latitude, tides, local topography, and density of intervening materials, in addition to any