Symposium on Remote Sensing for Resources Development and Environmental Management/Enschede/August 1986 
© 1987Balkema, Rotterdam. ISBN 90 6191 674 7 
1009 
Remote sensing for non-renewable resources: Satellite and airborne 
multiband scanners for mineral exploration 
Alexander F.H. Goetz 
University of Colorado, Boulder, and Jet Propulsion Laboratory, Pasadena, Calif, USA 
ABSTRACT: The application of remote sensing techniques to mineral exploration involves the use of both spatial 
(morphological) as well as spectral information. This paper is directed toward a discussion of the uses of 
spectral image information and emphasizes the newest airborne and spaceborne sensor developments involving 
imaging spectrometers. 
1 INTRODUCTION 
Remote sensing has been applied to mineral 
exploration problems since the first aerial 
photographs became available. The advent of space 
imaging systems, beginning with Landsat-1 in 1972, 
provided a whole new perspective afforded by the 
synoptic view from orbit. In the early days of 
Landsat, image data were interpreted directly for 
spatial information much as had been done with aerial 
photographs. Mineral exploration relies heavily on 
structural interpretation (Gold 1980). For the 
interpretation of structural and geomorphological 
features, high spatial resolution as well as stereo 
coverage is desired. The most widely available data 
at higher spatial resolutions come from the Landsat-4 
and -5 Thematic Mapper (Slater 1980) and SPOT which 
provides stereo coverage (Chevrel et al. 1981). 
With the application of computer image enhancement 
techniques, multispectral data could be used to map 
spectrally different units and, in particular, iron 
oxide anomalies. During the mid-1970s, it was 
recognized that broader spectral coverage and higher 
spectral resolution was necessary to derive 
meaningful mineralogical information. This 
realization brought about the development of high 
spectral resolution systems, both profilers and 
imagers, to derive surface compositional information 
with direct application to mineral exploration. 
2 BASIS FOR SPECTRAL MEASUREMENTS 
Incoming solar radiation is either scattered from the 
Earth's surface or absorbed and re-emitted in the 
thermal portion of the spectrum. The process of 
scattering and absorption takes place in the 
uppermost layers of the surface, in fact, in the 
upper millimeters. Thus, scattering is a function of 
the geometric properties of the surface, including 
particle size and aspect, and the absorption 
coefficient. The absorption coefficients are a 
function of wavelength and are brought about by 
various physical phenomena such as intermolecular 
vibrations and electronic transitions in atoms bound 
in the crystal lattices. Re-emission of energy as a 
function of wavelength is dependent upon the 
temperature of the surface material and again its 
physical properties such as particle size and 
composition. Therefore, by spectral remote sensing 
it is possible to derive information about the 
physical properties and composition of the surface 
cover. 
The spectral reflectance of minerals in the visible 
and solar reflected infrared is the result of five 
different phenomena as shown in Figure 1. 
The three most important processes contributing to 
the spectral reflectance of common materials are the 
electronic processes of charge transfer and crystal 
feld effects, and the vibrational processes (Hunt 
1977) . The Fe-0 charge transfer takes place in the 
blue and ultraviolet portion of the spectrum and, 
since iron is ubiquitous, practically all minerals 
and soils have rising reflectances toward longer 
wavelength in the visible portion of the spectrum. 
Electronic transitions in the d-shell electron of 
the transition elements embedded in the crystal field 
create absorption features in the visible and near 
infrared. Again, the most commonly occurring 
features are related to iron in both the Fe^ + and 
Fe^ + state. 
Vibrational processes yield the greatest number of 
sharp and unique spectral absorption features, mainly 
in the region 2-2.5 Jim. Overtone bending/stretching 
vibrations for H2O, OH, AlOH, MgOH, and CO3 produce 
unique features for identification of the most common 
surface materials and weathering products. Figure 2 
shows representative spectra of common minerals in 
the 2-2.5 Jim region. 
Some common rock forming minerals such as quartz ana 
feldspar do not have diagnostic absorption features 
in the solar reflected infrared. For silicates the 
fundamental Si-0 stretching vibrations occur near 9 
Jim (Hunt and Salisbury 1974) . The region around the 
fundamental vibration creates a metallic-like 
reflectance or reststrahlen band, and, therefore, an 
emittance minimum, the position of which is 
diagnostic for the silicate mineral. Figure 3 shows 
a compilation of emittance spectra ranging from 
acidic high-quartz rock such as granites to 
quartz-free, olivine-bearing rocks such as dunite 
(Lyon 1965). 
The fundamental stretching vibration frequency 
depends on the degree of interlocking or 
oxygen-sharing among the SiC>4 tetrahedra in the 
crystal lattice. The greater the degree of 
interlocking, the shorter the wavelength of the 
reststrahlen band. Recently, a multispectral scanner 
for the 8-12 Jim region has been constructed to allow 
spectral imaging in this wavelength region (Kahle and 
Goetz 1983) . 
The variation in spectral reflectance among 
different types of vegetation short of 2.5 Jim is much 
less pronounced than for minerals. The leaf 
reflectance is controlled in the visible to 0.7 Jim by 
the pigments in the leaves, in particular, 
chlorophyll which has strong absorptions in the blue 
and far red portion of the visible spectrum. These 
absorptions involve electronic transitions in the 
chlorophyll molecules centered around the magnesium 
component of the photoactive site. The blue 
absorption is also the result of electronic