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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004
2.1 Correction of Sat./GLI Alignment
At first, the geometric accuracy just after the launch was
evaluated by utilizing the GCP data set. As an example, the
case of ch.23 (250m channel) is shown in Figure 4. The errors
in the along-track (line) direction are proportional to pixel
number, while those in the cross-track (pixel) direction are
almost same. Such error pattern is very similar to that of the
case of attitude error, where the linearly changed line errors are
induced by pitch and yaw error, and the pixel errors are by roll
error. Among the parameters related with the view vector, only
the alignment of the GLI sensor against the satellite (denoted as
‘Sat/GLI alignment’) has the same effect on the image as the
attitude. The components of the alignments are denoted as (a, p,
y) which correspond to roll, pitch , yaw angle, respectively.
By the Tailor’s expansion of the collinearity equations with
unknown parameters, the observation equations are written as
follows.
: : — = 0
s 54m 0f Oy (5)
where F °. F ° |= initial approximation
X y ,
(v. oY, )= residuals
12 |
gi
x
o
S
28
=
©
©
3
0 1276 2552 3828 5104
pixel
—1 49 *
cross track
0 1276 2552 3828 5104
pixel
Figure 4 Geometric Accuracy just after Launch
(ch.23, mirror_A)
0 1276 2552 3828 5104
2000 \
4000
a
an
6000 -
\ i N
\ E
\
— : 5 pixels
Figure 5 Example of Error Pattern of the Product just
after Launch (ch.23, mirror A)
The orientations were tried using the various GCP data sets;
different resolution data, different scan mirror side, etc. As the
result, the residuals from mirror A and B could not be treated as
the same. The extracted alignments from the GCP sets of 250m
channel and those of lkm channel could not be treated as the
same. Table 4 shows the corrected alignments from the GCP
sets of mirror A with different resolution as well as the values
of pre-flight test (PFT). The result from the mirror A of GCP
sets of 250m channel data is adopted.
res. GCP a ß Y
PFT 0.02583 -0.00819 0.02083
250m Ql 0.078145 0.115873 0.075058
1km Kl 0.121208 0.098561 0.074197
Table 4 Corrected Sat/GLI Alignment (deg.)
2.3 Modification of Detector Address
The corrected values of the Sat/GLI alignment are installed to
the EOC processing system. The GCP data sets (Q2 and K2) are
made with the new system. The geometric accuracy of the
products by the new system is evaluated with the data sets. The
mean values of the errors are shown in Figure 6. They vary with
channel number.
For the correction of the dependency of errors on channel
number, the addresses of detectors on the focal plane are
modified. The examples of correction values for modification
are shown in Table 5.
Ch.20 Ch23 Ch.29
250m Q2 [580 | -0.12 | -0.76 | 0.12 | 0.04 | 0.20
Ch.19 Ch.24 Ch34
Ikm | K2 [7930 | -9.10 | 0.16 |.0.04 | 0.00 | -0.04
Table 5 Modified Address (Am, An) (partial)
