# Full text: Proceedings of the Symposium on Global and Environmental Monitoring (Part 1)

```X
y
0
f•tan( 0 )
(5)
Here is introduced an example of' the results. The geometric
correction of thermal infrared Image of VIMR (band 3) was done with
18 GCPs and resampled into the pixel size of 20” in latitude and 30
In longitude. Photo. 2 shows the surface temperature distribution
of the east part of Japan. The image is represented by color level
slicing.
4. Geometric Correction of SEASAT SAR Imagery with DTM
A radar imagery over mountainous areas has geometric distor
tions owing to topographic effects since it is acquired at the big
off-nadir angle and processed on the assumption that the ground
surface is plane. Especially the distortion on the range direction
is very big and cannot be ignored. The study on correction of these
distortions of SEASAT SAR using elevation data has been carried out
It is assumed that the earth is globe and the swath area of
radar is plane as shown in Fig. 3. Topographic effects are examined
on the reference plane B-C which is defined by the intersection B
between the earth surface and the beginning point of swath and by
the intersection C between the earth surface and the main axis of
fan beam. The reference plane of uncorrected imagery is supposed to
be the plane B-E which is normal to the vertical line from sensor
and contains point B. The relation between corrected image coordi
nate (u,v) and uncorrected one (u’,v') is expressed as below, where
u and u’ is on the range direction and v and v' is on the azimuth
direction. Let the origin of coordinate to be ( 0 ) in (u,v) and
( 0' ) in (u',v’), respectively.
r 2 = t*+ s 2 = ( T - z ) 2 + u 2
= ( H + m ) 2 + u ' ‘
v = v '
(6)
where
r : slant range
T : distance from sensor to plane B-C
H : altitude of sensor
z : ground height above plane B-C
s : position on plane B-C corresponding to u’ on plane B-E
m : difference between distance from sensor to plane B-E
and altitude of sensor ( H )
The ground height (z) is prepared on a geographic coordinate
system(x.y). The transformation functions between (u,v) and ( x,y )
is determined as polynomials by GCPs as below.
u = f ( x, y ) (7)
v = g ( x, y )
The several polynomials of different; order have been examined with
35 GCPs. The results indicated that the range direction (f) could
be sufficiently expressed by a binomial and the azimuth direction
(g) could be by a monomial with accuracy of less than one pixel.
Photo. 3 shows one of the results, which covers Pasadena area
803
```

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