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6: REMOTE SENSING 125

porous and have more available ground water, altitude photography is available (1:120,000
producing lines of more vigorous vegetation. to 1:60,000) then this may also be examined.
Target areas are selected from the above studies
and, in conjunction with literature reviews, it
Lineament is then possible to select areas for detailed
photogeological studies.
This is a word used in photogeology to de-
scribe any line on an aerial photograph that Aerial photographs are mainly used by
is structurally controlled by joints, fractures, various ordnance surveys for the production
faults, mineral veins, lithological horizons, of topographic maps using photogrammetry.
rock boundaries, etc. These have already been Photogrammetry is described in detail by
discussed above, e.g. streams, gullies, lines of Allum (1966). Some additional uses of aerial
vegetation, etc. It is important to differentiate photography are regional geological mapping
these from fence lines, roads, rails, etc. (1:36,000–1:70,000), detailed geological map-
ping (1:5000–1:20,000), civil engineering for
road sites, dam sites, etc., open pit management
6.4.7 Interpretation for monthly calculations of volumes extracted
during mining, soil mapping, land use and
By using the elements of aerial photograph land cover mapping, agricultural applications,
interpretation described above we identify forestry applications, water resources applica-
landforms, man-made lines versus photogeo- tions (e.g. irrigation, pollution, power, drinking
logical lineaments, vegetation, rock outcrop water, and flood damage), manufacturing and
boundaries, rock types, and rock structures recreation, urban and regional planning, wet-
(folds, faults, fractures). Once identified, the land mapping, wildlife ecology, archaeology,
geological units and structure are transferred and environmental impact assessment.
on to a topographical base map.
Most near-surface mineral deposits in acces-
sible regions have been discovered. Emphasis 6.5 SUMMARY
is now on remote regions or deep-seated
deposits. The advantages of using imagery In remote sensing we are concerned with the
in remote, inaccessible regions are obvious. collection of information about an area with-
Much information about potential areas with out being in contact with it, and this can be
deep-seated mineralisation can be provided by achieved using satellites or aeroplanes carrying
interpretation of surface features, e.g. possible electronic scanners or sensors or photographic
deep-seated faults and/or fractures which may and TV cameras.
have been pathways for rising mineralizing Some satellite systems producing data use-
solutions. ful for mineral exploration include NASA’s
Aerial photographs are normally taken be- Landsat and Terra (ASTER) and the French
tween mid-morning and mid-afternoon when SPOT. Each has its advantages (section 6.3).
the sun is high and shadows have a minimal The first Landsat satellite was launched in
effect. Low sun angle photographs contain 1972 and SPOT 1 in 1986. Satellites are solar
shadow areas which, in areas of low relief, can powered and transmit data to their home
reveal subtle relief and textural patterns not station in digital form which enables the geo-
normally visible in high sun elevation photo- logist to manipulate, combine, and compare
graphs. There are disadvantages in using low this data with geological, geochemical, and
sun angles, especially in high relief areas, geophysical data which has itself been ex-
where loss of detail in shadow and rapid light pressed as digital images. Satellite imagery is
change conditions occur very early and very used in structural investigations, in hydro-
late in the day. geology, to provide basic geological maps, to
Most exploration studies involve multi- detect hydrothermal alteration, and to produce
image interpretation. Often satellite images maps of regional and local fracture patterns
are examined first (at scales from 1:1M, up that may have controlled mineralisation or
to 1:250,000) for the regional view. If high hydrocarbon accumulation.