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Attitudes oscillation affects SAR imaging same with the track
oscillation. In this paper, every TerraSAR-X image
photographic time on the orbit is 8 seconds, and the original
attitude value and the calculated attitude value based doppler 0
value within this time were extracted. Plot the attitude change
curve within photographic time for a scene image as Figure (6)
shows. Among them, the left diagram for the roll angle sketch
map, and the right picture for yaw angle sketch map. In sketch
map, the variation curves represent the original measured values,
smooth curves for the motion-compensated reference value.
3
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S ü 2 4 8 8 40 2 B
Time(sec) Time(sec)
Figure 6 sketch map for attitude measured value and
compensation value
(2) Stereo positioning test with same side-looking direction
images
Tests through select different numbers of ground points as
control point, the number separate is 0, 1(No.1), 4(No.2-No.5),
9(No.1-No.9) and l5(uniform distribution), at the same time,
the remaining points are taken as check points for stereo
positioning accuracy test. Transform the adjustment value and
measured value of ground points to Gauss projection coordinate
system, and calculate the error based the adjustment value and
measured value, then compute the plane and height accuracy for
control points and check points .
For comparison, we based the R-D model and with the satellite
orbit one order linear refined model parameters as orientation
parameters, the speed change value calculated according to the
position vector of the time derivative, as formula (11).
V = P/dt+dP/dt=V, +dV (11)
The equation (9) was instead by error equation that established
base Doppler condition, and re-establish the stereo positioning
model based on R-D model and experiment. Table (1) statistics
of R-Cp model and R-D model for stereo positioning accuracy,
include the plane and elevation accuracy for control points and
check points, and the plane and elevation coordinate maximum
error of checkpoint.
(3)Stereo positioning test with opposite side-looking
direction images
In this test, we also select different numbers of control point to
experiment, there are 1 GCP (No.1), 2 GCPs (No.2, 5), 5 GCPs
(Nol-5) and 11 GCPs (LOOCV assess precision method,
(Brovelli M, et al, 2006)), and take the R-Cp model as the
foundation for stereo positioning test, then get the plane and
elevation precision for control points and check points, and the
maximum error, statistics in Table (2).
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
Table 1 stereo positioning accuracy statistics with same side-
looking direction images
Ntunber vf GCPs 0 1 2 3 9 15
GCPs iom 0,5 23 6.2 16 175
nig 0.8 1.9 33 4.3 4.6
CPs mp 298 | 127 | 111 104 9.1 89
Ground | R-Cp my 132183 177 158 | 53 [51
Points — [model | Max. | Vp | 427 | 194 | 185 | 18.0 | 165 | 162
Precision Errors | Vy | 234 150 | 133 99 | 96 | 90
And GCPs | mp 06 [26 164 130 lua
Error Bi 10 120 137 145 [49
CPs imp 297 | 12.6 | £1 | 165, 95. 192
n R-D mu 1132 | 83 77 58 $4 2
model | Max 1 Vp E425 | 192 1 184 | 1&2 ] 16,7 : 165
Errors | Vg 233 [149 | 132 199 197 191
Table 2. stereo positioning accuracy statistics with reverse
side looking direction images
Number of GCPs 0 1 2 S 11
RMSE | GCPs P 08 L33 161 6.7
and (RMSE) | H 09 |27 3.8 4.0
Error CPs P | 17.9 | 10.3 | 99 | 88 8.4
(m) (RMSE) | H | 29.2 | 61 |55 |4.7 | 45
Max P 1336 172 |161 |] 140 |] 133
Errors H | 359 112. ] 9.3 90.3 9.]
3.3 Test analysis
(1) The attitude value calculated with O Doppler conditions
show that the referenced attitude of SAR imaging has been
compensated, attitude compensation is also part of the SAR
imaging motion compensation. TerraSAR-X compensating
referenced attitude and the actual measured value is very close,
but the attitude shock has been eliminated.
(2) With the compensated attitude as initial value, the
positioning result used R-Cp model is close to R-D model.
TerraSAR-X compensating referenced attitude is in the vicinity
of the measured attitude, when adjustment can take the middle
values or mean values of measurement as the value of attitude,
it only has a smaller system error with the actual motion
compensation referenced value. In the case of one or more
control point, it would be easily to eliminate.
(3) In the absence of the ground control points, the plane
accuracy of TerraSAR-X image with same and opposite
direction observation separately are 29.8 m and 17.9 m, the
elevation precision are 13.2 m and 29.2 m, the result show that
location accuracy differences of this two kinds methods are
significant. In the condition of few amount ground control
points, the two kinds of images stereo positioning precision are
improved significantly, with the number of the control points
increased, plane and elevation precision are also improved.
(4) Along with the control points increased, the accuracy
improved rate of the opposite side-looking direction images is
less than the improved rate of same looking direction images,
