By Leia Michele Toovey-Exclusive to
Gold
Investing News
Remote sensing involves gathering data and information about the
physical "world" by detecting and measuring signals composed of
radiation, particles, and fields emanating from objects. This
data is collected without direct contact with the object and can
be used to identify and categorize objects of interest. Remote
sensing has a variety of applications. It is used in medical
applications, environmental applications- and in mineral
exploration. In terms of mineral exploration, remote sensing is a
rapidly advancing, and extremely valuable tool. It allows mineral
explorers to more accurately pin-point a resource at a reduced
cost. According to
Anglo-American
(LON:
AAL
), in terms of
diamond exploration
the average cost per 'traditional' kimberlite discovery is US $1
million per kimberlite. By using HyMap (
Hyperspectral Mapping
) the cost per kimberlite discovery drops down to around
US$300,000.Remote sensing is best used for the discovery of
high-value rare commodities such as diamonds and gold which are
becoming more and more difficult to locate. This is due to the
fact that remote sensing, in its simplest sense, can help narrow
down a search area. When used in gold exploration, remote sensing
is the science of acquiring, processing, and interpreting images
and related data acquired from aircraft and satellites. Remote
sensing utilizes a variety of sophisticated technology to record
the interaction between matter and electromagnetic energy. Remote
sensing images are used for mineral exploration in two
applications: (1) map geology and the faults and fractures that
localize ore deposits; (2) recognize hydrothermally altered rocks
by their spectral signatures.
The history of remote sensing
While remote sensing has been around since before World War II,
it has rapidly advanced in the past few years. In the beginning,
the primary use of remotely gathered data was comparative. If
gold was found in a particular area, aerial photos of that
particular area would be compared with aerial photos from other
locales to find places that had similar surface features hoping
they too would be covering a valuable gold deposit. Once
satellite imagery became commercially available, the same compare
and contrast was used with satellite images. To date, aerial
photography still is used as an exploration tool. Aerial
photographs are used to identify topographic surface features
which may imply the subsurface geology. Such telling surface
features as differential erosion, outcropping rock, drainage
patterns, and folds/faults can be identified. Faults fractures
and contacts often provide a conduit or depositional environment
for hydrothermal or magmatic fluids in regions of known
mineralization, and thus make excellent targets for further
investigation.The advent of multispectral imaging and thematic
mapping has allowed surface mapping to be performed remotely,
thereby enabling vast areas to be mapped in a short time at a
fraction of the cost of traditional geologic mapping. Different
scanning spectrums enabled researchers to begin cataloguing
various reflection and adsorption properties of soils, rock, and
vegetation. These spectra could be utilized to interpret actual
surface lithologies from remote images. Among the most valuable
data collected are the weathering and alteration products of
mineral deposits, especially clays. Clays and oxides can be
readily differentiated by the spectra utilized for remote
sensing. By correlating the alteration products to parent
materials, potentially valuable ores may by distinguished without
the need for extensive soil sampling programs. Today, there are a
variety remote sensing tools available to the exploration
geologist. By far, the greatest advancement in mineral
exploration has been the ability to synthesize various forms of
data. Known drilling results can be integrated with topographic
maps, air photos, structural maps, and ore grade data, greatly
increasing the accuracy and effectiveness of an exploration
program.
In-depth
Remote mineral data is collected from one of two ways- via
low-lying aircraft, or from satellites. Two main sensor types are
used in remote sensing, optical sensors and synthetic aperture (
SAR
) sensors. Optical sensors that measure the spectral data of
sunlight reflected from the Earth's surface, and (
SAR
) sensors sense electromagnetic data by transmitting microwaves
and receiving the back scatter waves from the Earth's
surface.Collecting the data in the field is the just the first
step in coming up with a product that is useful in exploration.
The next step is to translate the data into a form that is useful
for explorers. There are a variety of techniques and
manipulations that can be used, but one of the more useful, and
one of the first applied techniques I learned in school was image
classification. Remote Sensing makes use of spectral signatures.
For any given material, the amount of solar radiation that it
reflects, absorbs, transmits, or emits varies with wavelength.
When that amount coming from the material is plotted over a range
of wavelengths, the connected points produce a curve called the
material's spectral signature. All objects have a
unique spectral signature- and similar objects share a spectral
signature. Once you have identified the spectral signature of
that object- you can look for the same spectral signature on
other data sets to pin-point what could be, in fact, the same
object. This, of course, is an overly simplified explanation. To
determine an objects "spectral signature" the data must be
manipulated- in terms of remote sensing most of the manipulation
is accomplished by playing around with the spectral colour bands
in the imagea. We will go more in-depth into this
technology in part 2 of this feature, when we address
multi-spectral imagery.
Current remote sensing techniques
While this is a rapidly advancing field, currently, most
remote sensing is performed through the following technologies:
Landsat
, ASTER, Hyperspectral, Field Spectrometry and
Thermal Infrared
(TIR).
Introduction to Remote Sensing and Mineral
Exploration
originally posted on
goldinvestingnews.com