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Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Structural information of the landscape as ground truth
for the interpretation of satellite imagery
M.Antrop
State University of Ghent, Belgium
ABSTRACT : The possibilities for a detailed and accurate land use interpretation using satellite imagery,
depend for a great part upon the landscape structure. The selection of the training sites for image classifi
cation should follow a stratified scheme based upon a landscape classification which uses structural indica
tors. An analysis is made of the landscapes of Flanders based upon such indicators. An estimation of the
occurence of pure pixels (TM size) for different landscape components and types is given, as well as the
compactness of the field shapes and their orientation in relation to the pixel size and scan direction.
RESUME : Les possibilités pour une interprétation détaillée et accurate de l'utilisation du sol sur des
images satellites, dépendent en grande partie de la structure du paysage même. Les sites pour l'élaboration
des clefs d'interprétation devrait être sélectionnés à partir d'une classification du paysage, basée sur
des indicateurs structurels. Un exemple d'une pareille analyse est donné pour les paysages de Flandre.
Un estimation est faite de la nroportion des pixels purs (TM) pour différentes composantes du paysage, ainsi
qu'une analyse de la forme et de l'orientation des champs en relations avec la taille du pixel et la direction
du balavage.
1. INTRODUCTION
It is a basic knowledge in classical airphoto-inter
pretation that an interpretation key has a restricted
validity. It remains valid and guarantees a tested
accuracy for a given application only for one set
of photographs (with a constant scale, emulsion and
season) and for one reoion which can be considered
as homogenous with resnect to geographical and eco
logical relations. Large study areas show a great
environmental diversity and there it becomes neces
sary to differentiate the interpretation key on the
basis of the geographical structure of the terrain
observed. A first and fast assessment of this can be
achieved by a photomorphic image analysis, which ma
kes a holistic approach of the landscape information
contained in the image. In fact, it can be conside
red as a natural way of an unsupervised visual image
classification.
The influence of the geographical diversity of the
environment on the interpretation of an image beco
mes even more important for orbital remote sensing
because very vast regions are observed. Consequente-
ly, the decree of detail and the accuracy by which
thematic information can be extracted from satellite
imagery - and thus the economic rentability -,
does not depend only upon the characteristics of
the remote system used. From the technical point of
view, spatial, spectral and temporal resolution of
the system can still be improved, as well as tech
niques for image processing and enhancement. From
the methodological point of view, the interpretaion
accuracy depends upon the selection of the training
areas, the classifier used and how successfelthe
extrapolation of this local knowledge can be achie
ved for the whole area of interest. Crucial for this
are the variations of the spatial, spectral and
temporal characteristics of the terrain itself.
As F.Henderson (1980) put it very clearly : the
omnipotent role of the environment.
In most parts of Western Europe, we have to deal
with complex and fine structured landscapes, charac
terized by important human pressures. Even the power
ful ground resolution of second generation sensors as
TM of Landsat and HRV of SPOT, remain rather coarse
for thematic inventorization and is, for small areas,
still not competitive to classical ground methods.
Therefore, a geographical landscape classification
may be helpful to give a regional and structural ba
sis for a stratified samp! ing of the training areas
and a more intelligent extrapoation of the results
obtained there.
2. BASIC CONCEPTS
Landscapes should be considered as holistic phenomena
which continuously change on the 3 dimensional space
of the earths surface. They reflect the efforts made
by man through history to adapt, shape and organize
the natural environment to its cultural needs.
Consequentely, landscapes do not vary by the natural
conditions of the environment alone, but also by
cultural zones. Generally spoken, cultural factors
determine more the regional variation then the na
tural ones in areas with a high human pressure
(high population density, high technological level
and a long history).
Landscape studies make the distinction between
landscape elements, components and structures.
This is mainly based upon their spatial and topolo
gical characteristics. Each of them is described
using attributes which can have different levels of
measurement. Landscape elements are discrete objects
(houses, single trees, fields, etc.) of relative
small size and consequentely they are characterized
by high spatial frequencies. Landscape components
(relief, microclimate, etc...) change continuously
and gradually through space. They may remain almost
constant within some areas which can be small or
large and which are called landfacets according the
already classical system of landclassification
(Howard J. 5 Mitchell C., 1980 ; Webster R. &
Beckett P., 1970 ; Mabbutt J., 1968). Their spatial
frequency is lower then for landscape elements, but
may vary a lot. Landscape structures (fieldpatterns,
road networks, relief- and dratnagepatterns, etc.)
are spatial arrangements of landscape elements and
landfacets and can be described by typological
parameters as density, connectivity, orientation ,
and so'on.On small scale maps, zones wth a similar
and a constant structure are delineated by immate
rial boundaries to form the high order landunits in
the hierarchical landclassification systems (landsy-
stem, -region, -province and -division) .
