Geoscience Reference
In-Depth Information
11
Recording
numerical data and
use of instruments
in the fi eld
11
Angela L. Coe
A wide range of geophysical instruments can be used to: detect
and characterize rock bodies that are not exposed; quantify
relative changes in rock composition; and measure ground
movements related to earthquakes and active volcanoes.
Instruments to collect data on subsurface geology include
magnetometers, gravity meters and geophones for seismic
surveys. Common instruments used to quantify the changing
composition of a rock include the portable gamma-ray
spectrometer and magnetic susceptibility meter. These
instruments are particularly useful on mudstone successions
and can be used as a proxy for changes in clay mineralogy
(gamma-ray spectrometer) and relative changes in the amount
of clay to carbonate (magnetic susceptibility meter).
All of these geophysical methods have the advantage that they
are non-destructive. The use of specifi c geophysical
instruments and more specialist techniques is beyond the scope
of this topic and instead the manufacturers' handbooks or more
specialist text books should be consulted. Here we provide a
brief overview of some of the instruments available and their
possible applications (Table 11.1) along with some general
notes on data collection.
11.1 Data collection
The built-in memory of many geophysical instruments makes
data collection fast and easy. However, given that weather
conditions and fi eld access can be challenging, the demands
put on any instrument are large. Therefore if the data will be
hard or too expensive to re-collect should it be lost, it is
essential either to back-up regularly to a separate device or to
make a hard copy in the fi eld. A separate record of the data
will also prevent it all being lost if the instrument is stolen, or
confi scated by Customs! In addition, if there is no way of
entering extra data into the device it will also be necessary to
