Full text: Remote sensing for resources development and environmental management (Volume 1)

Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede /August 1986 
Image optimization versus classification - An application oriented 
comparison of different methods by use of Thematic Mapper data 
Hermann Kaufmann & Berthold Pfeiffer 
Institut für Photogrammetrie und Topographie, Universität Karlsruhe, FR Germany 
ABSTRACT: Image optimization and classification procedures are comparatively analyzed and discussed relative 
to their possibilities and limitations for distinct applications. To meet the objectives LANDSAT Thematic 
Mapper, data of two test-sites in different climatic areas (Saudi-Arabia and Southwest-Germany) have been 
For optimized presentation of TM-imagery, a basic concept was developed through which structural as well as 
spectral image contents can be enhanced within one product. By choice of bands and processing parameters the 
concept can be modified and fitted to various applications. Supervised and unsupervised classification methods 
are applied to separate surface phenomena by use of original-, enhanced-, and preprocessed data. Comparative 
evaluations have shown, that both methods give best results using not more than three information bands for 
one evaluation step. By qualitative and quantitative analysis it could be demonstrated, that classifying with 
original, enhanced or preprocessed components leads to the same results. For geologic applications in arid 
areas a standard band combination could be defined, which offers optimized conditions for rock discrimination 
and possibilities for separating diagnostic features. Concerning landuse applications, the various spectral 
behaviours of different surface phenomena, cannot be meaningfully represented within one product. The lack of 
structural information on classification results however could be removed by special merging techniques under 
use of image optimization products. 
Keywords: Image optimization, classification, Thematic Mapper, comparison of methods. 
In the past years a great variety and amount of remo 
tely sensed data has been offered from operational 
sensors. Forthcoming systems, characterized by ad 
vanced technologies with possibilities of multiband 
and stereorecordings are already launched. For data 
evaluation, different methods for enhancement and 
display are applied. 
This paper compares the advantages and disadvan 
tages of image optimization and classification me 
thods for several tasks with regard to distinct 
climates. Besides this optimal, transferable results 
for operational processing and meaningful combina 
tions of both methods can be demonstrated. 
To meet the objectives, two test-sites of different 
climatic character were selected (Fig. 1a, b). One 
is located in the Rhine-graben area and shows the 
city of Karlsruhe in its center. The second area is 
situated in SW-Saudi Arabia at the border to S.- 
Jemen and characterized by manifold lithological 
and structural varieties. 
2.1 Image Optimization 
Image optimization or enhancement is one method app 
lied to digitally recorded od digitized data. By 
employing various techniques, image contents already 
present in the raw data are made visible for the use 
of interpreters. In general, enhancement algorithms 
can be divided into two major groups. One group is 
especially used to enhance or suppress structural 
information. Such filtering techniques offer a wide 
range of applications e.g. for structural geology. 
The second group is best suited to enhance spectral 
image contents of multiband recordings. Ratio- and 
principle component transformations are applied to 
two ore more bands of multispectral information of 
the same target area, to emphasize spectral diffe 
rences, whereby structural (albedo-information) is 
simultaniously suppressed. 
Common color composites represent to a certain 
degree a combination of enhanced structural and 
spectral information based on contrast stretch of 
each single band used for coding. However, if high- 
pass filtering is applied and added to the data, 
spectral variations (saturation) decrease. On the 
other hand, color composites calculated by use of 
Pc's or ratioproducts show a bad signal to noise ratio, 
which makes delineation of textural patterns, or 
subtle structural features, inpracticable. 
Considering that image products calculated by 
enhancement techniques are used to support geo 
scientists in planning, execution and completion of 
field work, requirements for basic concepts became 
obvious. Such a concept has to include the choice of 
bands and algorithms used. It is a matter of fact, 
that not all information given by a seven band sen 
sor (e.g. TM) can be presented in one single product. 
But contrary to vegetated areas, where more than 
a three band combination is needed to utilize the 
full spectrum of applications, experiences with 
many arid areas have shown, that a combination of 
TM-bands 1,4,7, covers most requirements for rock 
discrimination. This additionally includes the 
possibility to map hydrothermally altered areas 
through the presence of diagnostic absorption 
bands for Fe^+ and clay minerals (Kahle et a 1,1982). 
The'image enhancement now follows a concept which 
was developed to satisfy the needs of geologists 
for lithological and structural data evaluation. 
In particular 
- data should be processed in a way, which can be 
understood and interpreted by different user 
- both structural and spectral (lithological) in 
formation should be emphasized and well diffe 
- only those algorithms should be used, which do 
not reduce the signal to noise ratio.

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