Page 121 - Introduction to Mineral Exploration

104 M.K.G. WHATELEY
6

Remote Sensing

Michael K.G. Whateley

6.1 INTRODUCTION 6.1.1 Data collection

Geologists have been using aerial photo- Remote sensing is the collection of informa-
graphy to help their exploration efforts for tion about an object or area without being in
decades. Since the advent of satellite imagery physical contact with it. Data gathering sys-
with the launch of the first earth resources tems used in remote sensing are:
satellite (Landsat 1) in 1972, exploration geolo- 1 photographs obtained from manned space
gists are increasingly involved in interpreting flights or airborne cameras, and
digital images (computerized data) of the ter- 2 electronic scanners or sensors such as multi-
rain. Recent technological advances now pro- spectral scanners in satellites or aeroplanes and
vide high resolution multispectral satellite and TV cameras, all of which record data digitally.
airborne digital data. More recently, geologists Most people are familiar with the weather
involved in research and commercial explora- satellite data shown on national and regional
tion have been seeking out the more elusive television. For most geologists and other earth
potential mineral deposits, e.g. those hidden scientists, multispectral imagery is synonym-
by vegetation or by Quaternary cover. Usu- ous with NASA’s Landsat series. It is images
ally geochemical, geophysical and other map from these satellites that are most readily
data are available. It is now possible to express available to exploration geologists and they
these map data as digital images, allowing the are discussed below. The use of imagery and
geologist to manipulate and combine them digital data from multispectral sources such
using digital image processing software, such as NASA’s flagship satellite, Terra, or commer-
as Erdas Imagine, ERMapper TNT MIPS, and cial satellites such as QuickBird and Ikonos,
geographical information systems (GIS). These are becoming more widespread. Remote sens-
latter techniques are discussed in detail in ing data gathering systems are divided into
section 9.2. two fundamental types, i.e. those with passive
As image interpretation and photogeology or active sensors.
are commonly used in exploration programs
today, it is the intention in this chapter to Passive sensors
describe a typical satellite system and explain
how the digital images can be processed, inter- These sensors gather data using available
preted, and used in an exploration program to reflected or transmitted parts of the electro-
select targets. More detailed photogeological magnetic (EM) spectrum, i.e. they rely on solar
studies using aerial photographs or high resolu- illumination of the ground or natural thermal
tion satellite images are then carried out on the radiation for their source of energy respect-
target areas. ively. Some examples are: