Correction of Distortions in
YG-12 High-Resolution Panchromatic Images
Yonghua Jiang, Guo Zhang, Deren Li, Xinming Tang, Wenchao Huang, and Litao Li
Abstract
Design deficiencies and hardware limitations cause a num-
ber of issues with the images acquired by Chinese satellites
launched before 2012, such as
YG-
12. The geometric quality of
the images recorded by
YG
-12 cannot match its high reso-
lution because of serious time-synchronization errors and
interior distortions. To improve the geometric quality of
YG
-12
images, this paper proposes a method of interior calibration
for the
YG
-12 panchromatic sensor. In addition, an innova-
tive method is proposed to eliminate time-synchronization
errors using parallel observations of the panchromatic sensor
onboard
YG
-12. The experimental results indicate the interior
parameters of the panchromatic sensor are determined with
an accuracy of better than 0.32 pixels, and seamless mosaic
images can be obtained after the elimination of distortions.
Furthermore, the positioning accuracy with relatively few
ground control points is shown to be better than 1.5 pixels.
Introduction
The high-resolution YaoGan-Weixing 12 (
YG
-12) satellite was
launched by China in November, 2011, and is located in a 500
km
. It is intended for scientific experiments,
land surveys, crop yield assessments, and disaster monitoring
(Barbosa, 2011).
YG
-12 can acquire panchromatic images with
a resolution of 1 m using a pushbroom camera, whose focal
plane is briefly illustrated in Figure 1. Detailed camera infor-
mation is provided in Table 1.
The positioning accuracy of
YG
-12 using ground control
points (
GCP
s) is known to be very poor due to large distor-
tions, and this seriously restricts the satellite’s applications.
As an example, Figure 2 shows the positioning errors after
using sufficient
GCP
s to compensate for systematic orbit and
attitude errors, with the image line (representing scanning
time) on the horizontal axis and residual errors on the vertical
axis. Obviously, the residual errors vary randomly with scan-
ning time, so increasing the number of
GCP
s will not improve
the geometric accuracy. The reasons for such large distortions
in
YG
-12 panchromatic images are as follows: (a) The time
system is not unified onboard
YG
-12. Therefore, time-synchro-
nization errors exist because of delays between the time of
orbit data, attitude data, and scanning time. The magnitude
of the error was found to be several ms (for comparison, the
average integral time of the panchromatic sensor is about 0.13
ms); (b) The panchromatic sensor of
YG
-12 was designed as a
large-distortion optical system, meaning that high-order dis-
tortions exist in panchromatic images without precise interior
calibration; and (c) there may be some large random errors in
the measurements of orbit and attitude data.
While scanning in orbit,
YG
-12 uses a single-frequency
GPS
system to measure the satellite position and velocity relative
to the
WGS
84 coordinate system with accuracies of 10 m and
Yonghua Jiang, Guo Zhang, Deren Li, Wenchao Huang, and
Litao Li are with the State Key Laboratory of Information
Engineering in Surveying, Mapping and Remote Sensing
(LIESMARS), Wuhan University. 129 Luoyu Road, Wuhan,
430079, P.R. China (
).
Xinming Tang is with the Satellite Surveying and Mapping
Application Center (SASMAC), National Administration of-
Surveying, Mapping and Geoinformation. 28 Lianhuachi West
Road, Haidian District, Beijing, 100830, P.R. China.
Photogrammetric Engineering & Remote Sensing
Vol. 81, No. 1, January 2015, pp. 25–36.
0099-1112/15/811–25
© 2014 American Society for Photogrammetry
and Remote Sensing
doi: 10.14358/PERS.81.1.25
Figure 1.
ccd
array placement of panchromatic sensor.
T
able
1. D
etailed
P
ayload
I
nformation
for
yg
-12
Payload Information
Spectral range
0.5 – 0.8 μm
Ground sample distance 1 m
Focal length
5 m
CCD array information 3072 pixels × 4 CCDs × 0.00001 m
Field of view (FOV)
1.4°
Agility
32°
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
January 2015
25
