John Milsom is the author of the first four editions of Field Geophysics. He has over 50 years’ experience in geophysics, with a focus on applied geophysics. He is also the author of The Hunt for Earth Gravity. Asger Eriksen, PhD, is the founder of Zetica Ltd., an environmental geophysics company specializing in ground penetrating radar, electrical resistivity imaging, seismic measurements, and electromagnetic profiling. Brian Barrett, PhD, has extensive experience in a wide range of shallow geophysical investigation techniques, including seismic refraction, seismic reflection, surface wave seismics, and seismic tomography.