Geometric Calibration for the Aerial Line
Scanning Camera GFXJ
Tao Wang, Yan Zhang, Yongsheng Zhang, Gangwu Jiang, Zhenghao Zhang, Ying Yu, and Lijun Dou
Abstract
The Gao Fen Xiang Ji (
GFXJ
) is the first Chinese self−devel-
oped airborne three−line array charge-coupled devices (
CCD
)
camera and is designed to meet 8 cm ground sample distance
(GSD), 0.5 m planimetry accuracy, and 0.28 m elevation ac-
curacy for ground three-dimensional (3D) points at a flight
height of 2000 m. These values also meet the 1:1000 scale
mapping requirements in China. However, the original direct
geopositioning accuracy of the
GFXJ
is approximately 4 m in
the planimetry direction and 6 m in the elevation direction.
To meet the ground 3D point accuracy requirements and
improve the direct geopositioning accuracy of the
GFXJ
, this
paper carries out a deep investigation on the
GFXJ
geometric
calibration. This geometric calibration includes two main
parts: the Global Navigation Satellite System (
GNSS
) lever
arms and inertial measurement unit (
IMU
) boresight misalign-
ment calibration, and the camera lens and
CCD
line distortion
calibration. First, a brief introduction is given on the imag-
ing properties of the
GFXJ
camera. Then, the
GNSS
lever arms
and
IMU
boresight misalignment calibration models are built
for the
GFXJ
camera. Next, a piecewise self-calibration model
based on the
CCD
viewing angle is established for the
GFXJ
lens
and
CCD
line distortion calibration. Subsequently, an iterative
two-step calibration scheme is proposed for the geometric
calibration. Finally, experiments were implemented using
multiple flight blocks obtained in the Songshan remote sens-
ing comprehensive field and the Hegang area of Heilongji-
ang Province. Through calibration experiments, geometric
calibration values were obtained for the
GNSS
lever arms and
IMU
boresight misalignment. Reliable
CAM
files were indepen-
dently generated for the forward, nadir, and backward line
arrays. The experiments showed that the proposed
GNSS
lever
arms and
IMU
boresight misalignment calibration models and
the piecewise self-calibration model had good applicability
and effectiveness for the
GFXJ
camera. The proposed two-step
calibration scheme can significantly enhance the geometric
positioning accuracy of the
GFXJ
camera. The original direct
geopositioning accuracy of the
GFXJ
is approximately 4 m in
the planimetry direction and 6 m in the elevation direction.
Using the
GNSS
lever arms and the
IMU
boresight misalignment
calibration values and the
CAM
files, the positioning accuracy
of the
GFXJ
camera can fulfill the 3D point accuracy require-
ments and the 1:1000 mapping accuracy requirements at a
2000 m flight height after aerial triangulation with only sever-
al ground control points. The planimetry accuracy is approxi-
mately 0.2 m, and the elevation accuracy is less than 0.28 m.
In addition, the calibration models and calibration scheme
established in this paper can provide a reference for calibra-
tion studies on other airborne linear array
CCD
cameras.
Introduction
The three-line array charge-coupled device (
CCD
) scanning
camera can obtain stereoscopic images and efficiently realize
topographic mapping (Hofmann 1984, 1993) as well as Digital
Elevation Model generation. In the aerial remote sensing (
RS
)
field, the Switzerland Leica Geosystems’
ADS40
camera is a
typical three-line array
CCD
camera. Several publications have
given a detailed description of the
ADS40
camera’s structure
and properties and introduced the principles and workflow of
the corresponding software
SOCET SET® LH
system (Leica 2006;
Hinsken 2002; Sandau 2000, 2003; Börner 2001; Tempel-
mann 2000). In the European Spatial Data Research (
EuroSDR
)
project, multiple empirical sensor test flights were made with
the Leica Geosystems
ADS40
, Integraph/ZI-Imaging
DMC
, and
Microsoft/Vexcel Imaging
UCD
cameras. The empirical results
clearly showed the importance of additional self-calibration
during processing, which was necessary in all cases to obtain
maximum geometric accuracy (Cramer 2006a, 2006b, 2007,
2008, 2009a; Kocaman 2006, 2008). Another set of empiri-
cal test flights were flown at the Pavia Test Site, located in
northern Italy, and major findings were obtained on the rela-
tionship between flying height and
ADS40
geometric accuracy
(Casella 2007a, 2007b; Kocaman 2007a, 2007b, 2008).
Concerning the second-generation
ADS40
, Tempelmann
and Hinsken (2007) summarized the optical and mechani-
cal properties of the new sensor and presented its geometric
parameters and model. Subsequent studies analyzed its preci-
sion (Casella 2008a, 2008b; Saks 2008; Fuchs 2010; Gonza-
lez 2013). In China, empirical test flights were flown in the
Songshan remote sensing comprehensive test field (Tu 2010)
and processed by both the Leica system and self-developed
software (Wang 2012a, 2012b, 2012c). These works produced
similar results to those of the first-generation
ADS40
in that
external precision results varied from values lower than the
Ground Sampling Distance (
GSD
) to those above it. The Ger-
man Society of Photogrammetry, Remote Sensing, and Geo-
information (
DGPF
) project “Digital Airborne Camera Evalua-
tion” reported results from diverse research groups on various
large format aerial digital cameras and the second-generation
ADS40
(Cramer 2009b, 2010; Jacobsen 2010).
In addition, many scholars have conducted in-depth
research on the similar three-line scanner
STARIMAGER
developed by the Japanese
STATLABO
Corporation of and the
University of Tokyo, and performed extensive experiments on
its radiometric and geometric properties (Gruen 2002, 2003;
Kocaman 2003, 2005, 2006, 2008; Chen 2003, 2007).
All of these research results have accumulated valuable
experience for the development and geometric processing
of the China domestic airborne three-line
CCD
camera Gao
Fen Xiang Ji (
GFXJ
). The
GFXJ
is the first airborne large-field
Tao Wang, Yongsheng Zhang, Zhenghao Zhang, Ying Yu,
and Lijun Dou are with the Geospatial Infomration Institute,
Information Engineering University, Zhengzhou, Henan,
China, 450052.
Yan Zhang and Gangwu Jiang are with the Data and Object
Engineering Institute, Information Engineering University,
Henan, China, 450052
Photogrammetric Engineering & Remote Sensing
Vol. 85, No. 9, September 2019, pp. 643–658.
0099-1112/19/643–658
© 2019 American Society for Photogrammetry
and Remote Sensing
doi: 10.14358/PERS.85.9.643
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING
September 2019
643
