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Thereafter. haze correction was done. i.e.
xssArc 77 X883 - 19 ; (x3-$-19)
Eventually, we ended up with three radiometncally
corrected images: xsslrc, xss2ro and xss3rc. These 3
bands were used to create the colour-composite image
for conventional classification purpose but after
geometric correction.
3.1.1.2 Geometric correction.
a) Panoramic distortion is negligible because the ratio of
swath end element to nadir element is equal to 1.0013.
b) Earth rotation is considerable because the ratio of the
shift across the swath to the swath width is equal to
0.050.
3.1.2 Train sampling
Eight classes were chosen to cover different land use to
this area, as shown in table 2. Therefore, by choosing
representative or prototype pixels from each of the
desired sets of classes, these pixels are said to form
training data. Training sets were established using the
established (existing) ground truth map from a colour
composite image on the ILWIS software. The training
samples for a given class should lie in a common region
enclosed by a boarder line or an edge. Unfortunately,
our area of interest did not have clear defined
boundaries to discriminate properly between different
land covers due to composition of parcels of variable
uses and outstanding height difference. Relief
displacement has blurred the image to the extent that
even edge enhancement does not help much to
distinguish the parcels.
Class Name Class Number
Forest 1
Orchard 2
Urban Area 3
Wasteland 4
Wasteland 5
Horticulture 6
Grass Field 7
Shrub 8
fable2- Spectral classes of data
3.1.3 Error analysis
At the completion of conventional classification it is
necessary to assess the accuracy of the results obtained.
This was done by selecting a sample of pixels(test
sampling) from remaining parcels and checking their
labels against classes determined from training sampling,
or crossing the two together to determine the accuracy.
These results are expressed in a tabular form, often
referred to as a confusion or error matrix.
Confusion matrix is shown in figure 2.
537
1 2 3 4 5 6 7 8 unci ACC
! 3 9 f 9 0 9 D 1 8 0.97
2182 0 0 0 0 0 0 0 0 0.00
340 0 68 1 7 2 0 0 0 0.87
4 | 51 0 0 0 0 0 0 30 0 0.00
510 0 9 3 1 0 25 0 0 0.03
610 1 0 4 0 0 0 0 0 0.00
710 0 0 0 8 0 9 0 0 0.00
8 | 16 0 0 0 0 0 0 1 Ü 0.06
REL | 0.18 0 0.88 0 0.06 0 0 0.03
average accuracy x 24.08 *
average reliability - 14.42 %
overall accuracy m 29.82 %
figure2- Confusion matrix of Maximum
Likelihood classifier
3.2 Creation of DEM and its applications
In satellite images there is some amount of relief
displacement and because of very high flying height
and moving projection center, relief displacement across
image lines is assumed to be very small and negligible
but for pixels along the lines is not too small and it can
be computed and removed.
In order to give corrections to all the pixels, the image
observations are modified by introducing artificial errors
(corresponding to relief displacement), errors that will be
corrected while later resampling the whole image. This is
the same as if the observations were made on a plane or
flat ground. Therefore we need a DEM of area to remove
relief displacement and obviously this DEM should be
georeferenced, so we only need an affine transformation
to remove relief displacement:
inb si a en T inser
Having DEM , with help of some software we can first
match our image to the DEM and then remove
displacements of all pixels. The program CTPTODTM
matches image to DEM and corrects the control points
for relief and its usage is:
CTPTODTM xtie outcoe pat dtm 5.6 -351 150
xtie: Name of our control points file
5.6: Looking angle.
-351: Beginning column.
150: Height reference.
The other program which name is GCD removes relief
displacements. The DEM should be georeferenced and
we match the images to the DEM with control points; It
means that we have matched the image to the ground
and after this step the program will read heights of
points from DEM and it applies relief displacement for
all pixels. We will also have a list of control points with
their heights and their displacements. It should also be
noted that relief displacement should be output driven.
Another application of DEM is to use it in creation of
orthophoto and to do so we should patch the DEM with
the program DTMPAT.
To create a DEM one can use SPOT PAN images (left
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996