IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002 
REMOTE SENSING: FROM QUALITATIVE TO QUANTITATIVE 
GEOLOGICAL STUDIES 
R. P. Gupta, 
Department of Earth Sciences, 
Indian Institute of Technology Roorkee, 
Roorkee, 247667, India 
E-mail - rpgesfes @iitr.ernet.in 
Commission VII, Working Group VII/3.3 
KEY WORDS: Quantitative studies, Mineralogical composition, Temperature estimation, Ground movements 
ABSTRACT: 
The qualitative methods of photo/image interpretation in geological sciences have been used for several decades. With the 
advancement in remote sensing technology, quantitative measurements on some of the geological problems/themes can be 
accomplished, and the same form the subject matter of this review article. 
For estimating mineralogical composition, the remote sensing techniques utilize spectral characteristics of minerals and mineral 
assemblages, and the methods of hyperspectral sensing, which allow generation of a near-continuous spectrum at each pixel, are 
used. Spectral unmixing analysis leads to generation of mineral maps. Further the thermal IR multispectral data can be used to 
create SiO,-content images. 
Another application of remote sensing is in the estimation of temperature of lava, coal fire etc. Such objects posses temperatures 
much higher then the background and emit blackbody radiation in accordance with the temperature. Remote sensors in the thermal 
IR and SWIR region are used for measuring intensity of thermally emitted radiation from hot sources (e.g. coal fires, volcanic 
events, lava flows etc.). Further the hot objects need not occupy the whole of the pixel; using dual band methods it is possible to 
compute sub-pixel area and temperature. Such information on temperature distribution and movement of lava flows and coal fires 
would hardly be available by any other technique. . 
A third important application is in the estimation of ground deformation related to earthquakes, volcanism, creeps etc. The synthetic 
radar interferometric techniques are used to generate DEMs, which allow determination of differences in the 3D location of objects. 
Using differential INSAR, movements of the order of some millimeters can be determined from space-borne SAR. These data have 
found a wide range of applications in geosciences — measuring earthquake-related fault displacements, aseismic creep, land 
subsidence, landslides, ice and glacier movements and volcano monitoring. 
1. INTRODUCTION reviews these techniques with examples, also mentioning their 
present limitations. 
Remote Sensing has evolved primarily from the techniques of 
photo-interpretation, which are mainly qualitative methods, 
utilizing the various elements of photo interpretation, viz., tone, 
‘texture, pattern, shape, size, shadow and association and the 
principle of convergence of evidence. The skill and experience 
of photo-interpreter is extremely important in deducing 
interpretation and drawing thematic information particularly for 
geologic features. In many remote sensing based geological 
studies, the techniques of photo interpretation are still the most 
valuable, and there is no intention to undermine its importance. 
However, with the advances in remote sensing technology, 
particularly during the last decade it is now possible to derive 
quantitative data on a number of geological aspects (Gupta 
2002). This was hitherto not possible. This article broadly 
S 
ite) and the geotechnical elements (drainage, landforms, soil 
and vegetation) have long been used to identify and map broad 
lithological units. 
Remote sensing based identification of specific mineral 
assemblages is based on the spectral characteristics of minerals. 
Figure 1 gives an overview of the important mineral-absorption 
469 
Thematically, the various remote sensing based quantitative 
geologic applications can be grouped under the following: 
1. Estimation of mineralogical composition. 
2. Estimation of temperature of lava, coal fire etc. 
3. Estimation of ground deformation related to earthquakes, 
volcanism, creeps etc. 
2. ESTIMATION OF MINERALOGICAL 
COMPOSITION 
One of the basic aims of all geological studies is to identify 
minerals and rocks and map their distribution in the field. 
Conventional methods involving the elements of aerial photo 
interpretation (tone, texture, pattern, shape, size, shadow and 
bands, occurring in the solar reflection region (SOR) and the 
thermal emission region (TIR). 
2.1 Solar Reflection Region 
2.1.1 Physical Principle: Detection of broad spectral features 
in the solar reflection region can be accomplished with coarser