Electromagnetic surveying - An Introduction to Geophysical Exploration - page 230

ground geophysical surveys over an area of the
Canadian Shield. The airborne EM survey used a
quadrature system with measurements of phase
angle taken at 2300 and 400 Hz. The ground tilt-
angle EM survey was undertaken with a vertical-
loop system using a local transmitter. Interpret
and comment upon these results. Figure 9.29 can
be used to estimate the product of conductivity
and conductor thickness from the airborne data.
6. Which geophysical methods are particularly
suitable for archaeological applications?

4. Figure 9.27 shows various ground geophysi-
cal measurements taken over volcanic terrain in
Bahia, Brazil. The EM survey was conducted with
a system using horizontal, coplanar coils 100 m
apart and a frequency of 444 Hz. The time-
domain IP survey used a double-dipole array
with a basic electrode separation of 25 m. Inter-
pret these data as fully as possible. What further
information would be necessary before an ex-
ploratory borehole were sunk?
5. Figure 9.28 shows the results of airborne and

Keller, G.V. & Frischnecht, F.C. (1966) Electrical Methods in
Geophysical Prospecting . Pergamon, Oxford.
Milsom, J. (1989) Field Geophysics . Open University Press, Milton
Keynes.
Parasnis, D.S. (1973) Mining Geophysics . Elsevier, Amsterdam.
Parasnis, D.S. (1996) Principles of Applied Geophysics , 5th edn.
Chapman & Hall, London.
Pedley, H.M., Hill, I. & Brasington, J. (2000) Three dimensional
modelling of a Holocene tufa system in the Lathkill Valley, N.
Derbyshire, using ground penetrating radar. Sedimentology , 47 ,
721-37.
Reynolds, J.M. (1997) An Introduction to Applied and Environmental
Geophysics .Wiley, Chichester.
Telford, W.M., Geldart, L.P. & Sheriff, R.E. (1990) Applied
Geophysics , 2nd edn. Cambridge University Press, Cambridge.
Wait, J.R. (1982) Geo-Electromagnetism .Academic Press, NewYork.

Further reading

Boissonas, E. & Leonardon, E.G. (1948) Geophysical exploration
by telluric currents with special reference to a survey of the
Haynesville Salt Dome, Wood County, Texas. Geophysics , 13 ,
387-403.
Cagniard, L. (1953) Basic theory of the magnetotelluric method of
geophysical prospecting. Geophysics , 18 , 605-35.
Davis, J.L. & Annan, A.P. (1989) Ground-penetrating radar for
high-resolution mapping of soil and rock stratigraphy. Geophys.
Prosp. , 37 , 531-51.
Dobrin, M.B. & Savit, C.H. (1988) Introduction to Geophysical
Prospecting , 4th edn. McGraw-Hill, NewYork.
Jewell, T.R. & Ward, S.H. (1963) The influence of conductivity
inhomogeneities upon audiofrequency magnetic fields.
Geophysics , 28 , 201-21.