Abstract
The Method for DEM generation using JERS1 OPS stereo data was developed. JERS1 satellite was launched by NASDA in 1992. The ground resolution of OPS data is about 18m on the cross track and about 24m on the along track. Also the OPS is able to perform stereoscopic observation from the same orbit with 0.3 B/H ratio.
DEM were generated the following method. (1) The orientation elements were determined without GCP. (2) DEM were by automatically stereo matching. (3) DEM were adjusted using a few GCP.
The Accuracy of DEM was 32.1m on the test site. Therefore, the generated DEM has the potentiality of drawing 1:200,000 scale topographic map.
1. Introduction
The Japanese Earth Resources Satellite-1 (JERS1) that was development by the National Space Development Agency of Japan (NASDA) and Ministry of International Trade and Industry (MITI) was carried on a Synthetic Aperture Radar (SAR) and an Optical Sensor (OPS).
The OPS is passive linear array sensor that measures in the visible, near infrared, and short wave infrared. Each spectral band has a 4096 elements linear CCD. The band wave length shows in Table 1.
Table 1 Observation band
| Band |
Wave Length
(mm) |
| 1 |
0.52 - 0.60 |
| 2 |
0.63 - 0.69 |
| 3 |
0.76 - 0.86 |
| 4 |
0.76 - 0.86 |
| 5 |
1.60 - 1.71 |
| 6 |
2.01 - 2.12 |
| 7 |
2.13 - 2.25 |
| 8 |
2.27 -
2.40 |
The Visible and Near Infrared Radiometer (VNIR) can produce stereoscopic images using band3 and band4 which looks 15.3 degrees forward in the orbit plane. It means that Base and height ratio (B/H) is 0.3
The swath width is about 75km and the ground resolution is about 18.3m on the cross track and about 24.2m on the along track.
This stereoscopic system has the advantage of the stereo matching as compared with the side looking observation system. Because the stereoscopic images is observed almost same time. Therefore it is expected that mismatching points are decreased.
The purpose of this study is to develop the method of DEM generation without orientation using the GCPs. Because it is difficult to get many GCPs in our target area where isn't prepared to the topographic map and the DEM generation also can't be automatically calculated by using GCPs. Automatic generation was given priority over accuracy of DEM.
2. Method of DEM generation
2.1 Orientation Elements
The Satellite's orbit and orientation elements were calculated from ephemeris data to be recorded in CCT without the GCPs.
The satellite's orbit are recorded to the following approximate of degree three.
X = a0 + a1 t + a2 t2 + a3 t3
Y = b0 + b1 t + b2 t2 + b3 t3
Z = c0 + c1 t + c2 t2 + c3 t3
where :
X,Y,Z: the location of satellite in the earth fixed coordinate system
Xaxis is from centre of the earth to the equator through meridian zero.
Zaxis is along the earth's spin axis.
Y axis is the orthogonal axis on XZ plane by a right hand coordinate system.
a
n , b
n , c
n : coefficient
t : progressing time from a standard time
and the satellite's orbit are recorded to the following approximate Fourier series.
where :
q : yaw, roll, pitch angle.
a
n , b
n : coefficient
T : approximate width on the time (32 sec)
t : progressing time from a standard time
When the setellite's orientation on the image coordinate is calculated, t is defined as the function of image line number.
t = F(L)
where :
L : line number on the image
t : the progressing time on the L line.
The geometry of observation by a linear array sensor is shown in Fig. 1. There kind of coordinate system were defined as the earth fixed coordinate system, the satellite orbit coordinate system and the satellite fixed coordinate system.
Figure 1 Geometry of Observation
The earth fixed coordinate system is defined that the origin is the center of the earth,
X
e axis is from center of the earth to the equator through meridian zero,
Z
e axis is along the earth's spin axis and Ye axis is the orthogonal axis on
X
eZ
e plane by a right hand coordinate system.
The satellite orbit coordinate system is defined that the origin is the center of the satellite,
X
s axis is the flying direction,
Z
s axis is the nadir direction and
Y
s axis is the orthogonal axis on
X
sZ
s plane a right hand coordinate system.
This coordinate is calculated from the location and velocity of satellite. The satellite fixed coordinate system is defined as the local attitude on the satellite orbit coordinate system. This coordinate is recorded as the ancillary data in the CCT.
The relationship of the each coordinate system are shown the follows.
Where :
(X
E,Y
E, Z
E) : the target point on the ground in the earth fixed coordinate.
(X
0,Y
0, Z
0) : the satellite location in the earth fixed coordinate.
(X
1,Y
1, Z
1) : the target point on the ground in the satellite fixed coordinate.
(X
2,Y
2, Z
2) : the target point on the ground in the satellite fixed coordinate with view angle
R (K
0,
j0,
w0) : The rotation matrix from the earth fixed coordinate to the satellite orbit coordinate.
R (K
1,
j1,
w1) : The rotation matrix from the satellite orbit coordinate to the satellite fixed coordinate.
q : the observation angle,
q=0 (nadir view)
q=15.33 degree (forward view)
As the center of projection, the target point in the image and the target point on the ground are alignment, the following equation are satisfied from satisfied from collinear condition.
Where :
f : the sensor focus ( = 2153mm )
Further; the relationship of the sensor coordinate and the image coordinate shows the following equation.
Where :
x y : the location of the target point in the sensor coordinate
x is the constant zero, because the sensor is a linear array sensor.
P, L : the number of the target point in the image coordinate
N : the number of the CCD sensor ( = 4096 )
D : an interval of a CCD sensor ( = 7 mm)
