Geoscience Reference
In-Depth Information
Review questions
.....................................................................................................
1.
What is the difference between absolute and relative measurements? What is a gradient measurement?
2.
Give a practical definition of noise in a geophysical context. Describe some common types of non-geological
environmental noise.
3.
A data series comprises 1001 evenly sampled data values spaced 10 m apart. (a) What is the longest wavelength
(lowest frequency) fully represented in the data series; (b) what is the shortest wavelength (highest frequency)
present; and (c) what would it be if the sampling interval were reduced to 1 m?
4.
What is levelling? Give examples of typical levelling artefacts.
5.
Describe how data values can be manipulated to create coloured pixel images on a computer screen.
6.
Describe techniques for separating the longer-wavelength regional field and shorter-wavelength local variations in a
data series.
7.
How can the strike extent and attitude of an anomaly source be estimated using a contour display of geophysical
data? How do changes in depth to the source affect the display?
8.
What is meant when a model is described as 1D, and as 2.5D?
9.
Explain equivalence and the phenomenon of non-uniqueness. How are they related?
10.
What is the difference between forward and inverse modelling? Describe the advantages and disadvantages of both.
FURTHER READING
Gupta, V.K. and Ramani, N., 1980. Some aspects of regional
-
residual separation of gravity anomalies in a Precambrian
terrain. Geophysics, 45, 1412
Oldenburg, D.W., Li, Y., Farquharson, C.G. et al. 1998. Applica-
tions of geophysical inversion in mineral exploration. The
Leading Edge, 17, 461
1426.
Good clear demonstration of the how and why of the creation
of a residual gravity map of greenstone terrain in the Super-
ior Province, Canada. The authors conclude that analytical
methods are inferior to manual graphical interpolation.
same data, show that interpolation based on the
-
465.
Oldenburg, D.W. and Pratt, D.A., 2007. Geophysical inversion
for mineral exploration: a decade of progress in theory and
practice. In Milkereit, B. (Ed.), Proceedings of Exploration
'
-
07: Fifth Decennial International Conference on Mineral
Exploration. Decennial Mineral Exploration Conferences,
61
finite-
element methods produces a similar result to the manual
methods.
Hamming,
99.
Phillips, N., Oldenburg, D., Chen, J., Li, Y. and Routh, P., 2001.
Cost effectiveness of geophysical inversion in mineral
exploration: Application at San Nichols. The Leading Edge,
20, 1351
-
R.W.,
1989. Digital
Filters.
Prentice-Hall
International.
This is an introductory text to the broad
1360.
These three papers discuss the philosophy of inverse modelling
and present examples of inversion of various types of geo-
physical data using mineral exploration examples.
Shermer, M., 2005. Science Friction: Where the Known Meets the
Unknown. Times Books.
This topic is not about geoscience but about scienti
c think-
ing and ideas in general, in particular how personal bias and
preconceptions can affect scientific judgements. Highly rec-
ommended as an interesting read and a warning about how
difficult being a good scientist actually is.
-
field of digital
signal
processing
and
provides
good
plain-language
explanations
of digital
sampling,
the Fourier
trans-
form, and digital
filtering, with only
the
essential
mathematics.
Meju, M.A., 1994. Geophysical Data Analysis: Understanding
Inverse Problem Theory and Practice. Society of Exploration
Geophysicists, Course Notes 6.
A very good description of geophysical inverse methods
requiring only a low level of mathematical expertise.
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