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change-detection is directly conditioned by the geometric
rectification. Rectification of an image requires accurate and
homogenously distributed ground control points.
Elevation difference in Bucharest area is about 30 m. Points
displacement on the images caused by the simple rectification to
a reference plane can be improved using a digital elevation
model (DEM), changing the image to the geometry of a map-
product. The digital elevation model is generated from aerial
photographs 1:5,000 scaled, acquired in 1994. The height of the
reference plane level is not available for images. A deviation of
the reference plane from the correct value is causing an error in
points location. Together with the remaining deviation of the
sensor orientation this can be determined by means of control
points. To perform the rectification process, affine
transformation method was used and the image was resampled
by using nearest neighbor method. Geometric corrections
applied to photos and satellite images have been based on thirty
ground control points, distributed around the area and even
outside the site, easily identifiable and time-invariant. Ground
control points have been identified both in aerial photographs
and in IKONOS image.
The high resolution space sensors have a small view angle,
allowing the replacement of the perspective geometry in the
CCD-line by a three dimensional affine transformation. This
model can be improved by some corrections for a sufficient use
of the perspective geometry in the CCD-line direction.
Like the RPCs based on control points, the orientation
information of the sensor is not used and the control points
must be located and outside around the mapping area
(Jacobsen, K., 2008).
Based on 20 control points the full accuracy potential of
IKONOS image can be reached, with an RMS error of 2.8399m.
Figure 2. IKONOS color composite image of study area
Multispectral images allow different color combination, through
which are selectively pointed out study objects. In most cases a
very expressive standard false color composite is realized if a
combination between channels: blue, green and red.
Examining channels histograms for satellite images can be seen
that only a small part of sensor range is covered. As a result a
contrast enhancement is needed. For linear contrast
enhancement with point’s saturation, are used low values of
enhancement (2.5-3.5%) with purpose of optimal use of
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
unsupervised classification. It allows a preferential
enhancement of the areas covered with vegetation versus the
built urban areas or uncovered soils.
The nonlinear contrast enhancement offered better results
(histogram equalization) by enhancing the contrast for the
densest domain of reflectance values from the original image.
There also been used Laplace filters techniques for directional
and nondirectional edge enhancement (used for linear details -
streets, great building, paths in parks). Digital processing has
been done with Idrisi Andes GIS software.
3.3 CORONA image processing
In the past few years, it has been possible to obtain high-
resolution imagery for official and local users. New imaging
systems which have higher resolution and accuracy are on the
way coming in use within next few years. However, using high-
resolution imagery was not the case of recent years.
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Figure 3. Corona data block format
Nearly 50 years ago, in August 1960, USA succeeded in
starting a satellite mission called CORONA. It was the first spy
satellite system of USA. This program went through many
developments during its lifetime until 1972, but all images were
classified until 1995 (Lillesand, Kiefer, Chipman, 2003). The
spatial resolutions of these photographs are nominally
comparable to current high-resolution commercial satellite
imagery (IKONOS, QuickBird). This historical image records
enable investigation into urban land cover changes.
Corona’s cameras are referred to by the designator “KH” (from
KeyHole). Fairchild manufactured the first two cameras, KH-1
and KH-2 that were flown on five successful missions from
1960 to 1961. Other Corona cameras included KH-3 (operated
from 1961-1962), KH-4 (1962-1963), KH-4A (1963-1969) and
KH-4B (1967-1972), all designed, revised and manufactured by
Itek. On the majority of the 95 successful Corona missions, the
KH-4, KH-4A and KH-4B cameras have been used. These three
cameras are very similar. The film format is 5.54 cm x 75.70
cm. The film base is polyester and the film load capacity of KH-
4A and KH-4B is 32,000', allowing a mission life of up to 19
days. In longer missions, the film would be ejected twice
