georeferencing accuracy of Data A, B, C, and D can meet the ac-
curacy demands of 1:1000 scale topographic mapping.
Conclusion
The innovation of this paper is to probe and study the
geometric calibration technology of the China domestic
airborne three-line
CCD
camera
GFXJ
, including the
GNSS
lever
arms and
IMU
boresight misalignment calibration and the APs
calibration. According to the specific imaging characteristics of
the
GFXJ
, the
GNSS
lever arms calibration model and
IMU
bore-
sight misalignment model are established for the
GFXJ
. A piece-
wise self-calibration model based on the
CCD
viewing angle is
established. Based on the empirical research work, a feasible
iterative two-step calibration scheme is proposed in detail.
The experimental results show that the calibration mod-
els proposed in this paper are correct and valid for the
GFXJ
camera. The original
DG
accuracy of the
GFXJ
is approximately
4 m in the planimetry direction and
direction. After calibration and
AT
, t
approximately 0.2 m, and the elevat
0.28 m. The calibration values of th
boresight misalignment and
CAM
fil
provided to subsequent users if the
GFXJ
,
GNSS
, and
IMU
instal-
lations remain unmoved. Additionally, the calibration meth-
ods proposed in this paper provide a reference for calibration
research on other aerial
CCD
cameras.
Through a series of experimental research and analysis, the
following conclusions can be drawn.
1. There is obvious systematic error in the
GFXJ
’s direct geore-
ferencing, and it is necessary to adopt the
AT
and calibra-
tion process.
2. The
GNSS
lever arms and
IMU
boresight misalignment
cause obvious systematic errors, which is the one main
geometric error source that must be calibrated. The
GNSS
lever arms and
IMU
boresight misalignment mainly affect
the planar geometric positioning accuracy.
3. The camera lens and
CCD
line array distortion mainly
affect the height accuracy of the
GFXJ
camera. The cali-
brated
CAM
files can effectively eliminate the inherent
distortion errors of the
GFXJ
, such as lens and
CCD
distor-
tions, and significantly improve the geometric positioning
accuracy in the height direction.
4. The two-step iterative calibration method proposed in this
paper is reliable and feasible. The calibration values of the
GNSS
lever arms and
IMU
boresight misalignment and
CAM
files are stable and consistent, and this method is available
for other flight data processing.
5. The
GFXJ
camera is the first airborne three-line
CCD
camera
in China. Through many flight experiments, it has been
verified that this camera has good stereo surveying and
mapping performance. After calibration, the
GFXJ
can meet
the 1:1000 scale topographic mapping requirements at
2000 m or even a slightly higher flight altitude.
On December 17, 2018, another flight was taken in Yangjiang,
Guangdong, China. The height altitude is 2000 m. In this
flight, no calibration work was done. The calibrated
CAM
files
obtained in this paper are taken for the
AT
process directly. 20
GCPs
are collected and used in
AT
process. The final accuracy
after
AT
process is 0.088m, 0.092m, and 0.176m at
X
,
Y
, and
Z
directions, respectively. From May 12, 2017 to December 17,
2018, it lasts one year and a half. The sensor structure keeps
unchanged during this period. And the
CAM
files obtained in
2017 are still suitable for the
AT
process of data on December
17, 2018. It validates that the
CAM
files generated in our paper
are very stable. The scheduled sensor recalibration time is
two years. Up to now, the calibrations
CAM
files still have
good suitability. In the future, if the
AT
accuracy deteriorates
greatly, recalibration work will be carried out.
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