| 2004
Small
"vation
Earth
COMPARISON OF INFORMATION CONTENTS OF HIGH RESOLUTION SPACE
IMAGES
H. Topan*, G. Büyüksalih*, K. Jacobsen **
* Karaelmas University Zonguldak, Turkey
** University of Hannover, Germany
htopan@karaelmas.edu.tr, gbuyuksalih@yahoo.com, Jacobsen@ipi.uni-hannover de
WGIV/7
KEY WORDS: high resolution, satellite, mapping, information, analysis
ABSTRACT:
The information contents of high resolution space images, usable for mapping, are not only depending upon the image resolution
that means in case of digital data, depending upon the pixel size in the object space. Important is also the contrast, the spectral range,
radiometric resolution and colour beside the atmospheric condition and the object contrast.
From the area of Zonguldak, Turkey different space images are available like taken by IKONOS, KVR-1000, SPOT 5, IRS-1C,
TK350, ASTER, Landsat TM, JERS and SRTM X-band. Of course the information content is mainly depending upon the pixel size
on the ground, but this is still quite different for the RADAR images taken by JERS and SRTM. The object identification in these
images disturbed by speckle cannot be compared with optical images having the same pixel size. There is a rule of thumb for the
relation of the pixel size to the possible map scale, but it cannot be used for ground pixels with a size exceeding 5m because this is
leading to a loss of important information which must be available also in small scale maps. The limited radiometric resolution of
IRS-1C images is still a disadvantage, especially in dark and shadow areas. The KVR-1000 available with 1.4m pixel size cannot be
compared directly with the information contents which should be included with this resolution. The colour information of IKONOS
supports the object identification, so the 4m ground pixel size includes a higher information contents like a panchromatic image with
the same resolution and the object identification is quite easier. With IKONOS pan sharpened images maps up to a scale 1 : 7000
can be created.
1. INTRODUCTION the map scale — that means for a map 1 : 50 000 a pixel size on
the ground of 2.5m up to 5m is required. But the pixel size is
The generation of topographic maps by means of space or aerial not the only criteria for the quality of the images; also the
images requires a sufficient relation between the pixel size on contrast (modulation transfer function) is important like the
the ground and the map scale. Even if today maps are available spectral range and colour information. This may also dependent
in a GIS with their national coordinates, the information upon the situation of the atmosphere and the sun elevation. In
contents and level of generalisation corresponds to a printing addition the area may be different — we may have some wide
scale. The required semantic information is depending upon the roads and large buildings like for example in the USA or in
map scale. So for example individual living houses are not Saudi Arabia or we may have small and bending roads without
shown in a map 1 : 50 000, only the general structure of the pavement. Also the specified information contents for the maps
area is presented in such a scale. Of course this is different for a may be different — for example in Switzerland we do have a lot
scale 1: 2000 where also the extensions of a building are of details in the maps, in the USA the maps are quite more
available. Under usual conditions there is no problem with the general. So there is still a range within the relation map scale to
mapping accuracy based on space images, the real limitation is pixel size on the ground.
coming from the information contents, that means, which object
can be identified during interpretation. Here we still do have the 2. GROUND PIXEL SIZE
difference between detection and interpretation of the object.
We may detect a line, but we may have problems with the The nominal pixel size of the different space sensors is only one
interpretation if the line is just a separation between agricultural indicator for the information contents. For example
fields or if this is a path or even road. For military mapping panchromatic IKONOS images are delivered as projections to a
(STANAG 3769) we do have the differentiation between plane with constant elevation with a fixed ground pixel size of
detection, recognition, identification and technical analysis Im independent upon the incidence angle. For an incidence
where identification always includes details about the situation angle of 45° the area covered by a physical pixel size is 1.15m
of the object not shown in civilian topographic maps. The x 1.62m. Of course the information contents of an image taken
required pixel size according to STANAG 3769 does not take with 45? incidence angle is not the same like for a nadir view.
care about the characteristics of the used image and cannot be a Also the sensor quality has to be respected. The effective pixel
rule for civilian mapping. A rule of thumb for the relation of the size can be determined by an edge analysis. At a location in the
pixel size and the map scale is 0.05 up to 0.1mm pixel size in image with a sudden change of the grey value in the object
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