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three-line CCD camera in China supported by the National
High-Resolution Earth Observation System program. The key
components of the GFXJ camera include the optical imag-
ing system, large-capacity memory unit, operation display
system, pilot and navigation system, and gyro stabilization
platform Leica PAV80. The optical imaging system integrates
the lens system and the Leica POS/AV 610 system together. The
Leica POS/AV 610 system includes the inertial measurement
unit (IMU) unit, the Global Navigation Satellite System (GNSS)/
IMU recoding and processing unit and the GNSS antenna,
which records the camera shooting position and attitude
parameter synchronously during flight. The IMU unit and the
GNSS receiver and processing unit are rigidly connected to the
camera lens system. The positioning accuracy of Applanix
POS/AV 610 system is 0.05–0.30 m. The angular accuracy is
0.0025 degrees for pitch and roll angles, and 0.0050 degrees
for kappa angles. The large-capacity memory is mainly used
to store the acquired image and GNSS/IMU data, the operation
display system is mainly used to provide an interface for
human-computer interaction, and the navigation display sys-
tem is used to plan the navigation route. The Leica PAV80 plat-
form provides angle compensation in three axes during flight.
The lens system, large-capacity memory unit, and operation
display system are self-developed in China. The GFXJ camera
uses the three-line array push-broom imaging mode. The same
ground target is imaged three times in forward, nadir and
backward views during aerial photography. The camera pro-
vides three panchromatic images with different view angles
and four-band multispectral (red, green, blue, near-infrared)
images. The nominal viewing angles of the forward, nadir and
backward CCD lines are 21, 0, and 27 degrees, respectively. For
panchromatic images, each imaging CCD line array consists
of 32 756 detectors, and the entire CCD array is an integrated
body instead of multichip splicing. This array is currently
the largest single CCD line array with the most detectors. The
pixel size is 5 µm, and the camera focal length is 130 mm.
The nominal viewing angle of the multispectral CCD line
is 13.5 degrees. The radiometric resolution is 16-bit. The
image line sampling rate is from 540 to 1080 Hz. The imaging
spectrum for a panchromatic image is 465–680 nm, and those
of the multispectral bands are 608–662 nm (red), 533–587 nm
(green), 428–492 nm (blue), and 703–757 nm (near infrared).
Figure 1 shows the GFXJ camera and the gyro stabilization
platform Leica PAV80. An imaging principle sketch is outlined
in Figure 2. The global positioning system (GPS) sampling fre-
quency is 200 Hz, and the IMU sampling frequency is 1000 Hz.
Compared with the POS/AV 510, Applanix uses a GNSS signal
receiver instead of a GPS receiver to simultaneously receive
and process satellite signals such as GPS, GLObal NAvigation
Satellite System (GLONASS), and Beidou (BSD ). The POS/AV 610
system mainly comprises an IMU, GNSS receiver, computer
system, and data postprocessing software POSPac. The POSPac
postprocessing software provides optimal navigation data by
filtering the original GNSS and IMU data by combining the base
station receiver data. The POSPac postprocessing software can
only provide GNSS/IMU observations, and the GFXJ calibration
and triangulation work is realized by self-developed software.
Compared with the ADS40 camera, the GFXJ has a longer
focal length, a larger CCD line size and a wider ground cover-
age range. To improve the positioning accuracy and meet
the requirements of 1:1000 scale topographic mapping, it is
necessary to carry out the aerial triangulation (AT) process on
the image. To further enhance the direct geopositioning (DG)
accuracy of the GFXJ camera and alleviate its dependence on
ground control points during triangulation, the inherent sys-
tematic error sources of the camera need to be calibrated. The
systematic error sources that lower the stereoscopic mapping
accuracy of airborne three-line CCD cameras and cause geomet-
ric deformation can be categorized into two parts: one is the
GNSS antenna center offset (GNSS lever arms) and IMU boresight
misalignment, and the other is the distortion errors of the cam-
era lens and CCDs (Tempelmann 2000; Hinsken 2002; Kocaman
2006, 2008; Casella 2008a, 2008b; Fuchs 2010).
In this paper, a deep study is carried out on GNSS lever
arms and IMU boresight misalignment calibration and the
camera lens and CCD line distortion calibration of the GFXJ.
First, geometric models for GNSS lever arms and IMU boresight
misalignment are established, and corresponding calibration
models are put forward. Then, a piecewise self-calibration
model based on the CCD viewing angle is designed for the
GFXJ lens and CCD line distortion. Subsequently, an iterative
two-step calibration scheme is designed for actual calibration.
Figure 1. GFXJ camera and the gyro stabilization platform.
Figure 2. Imaging principle sketch of the GFXJ .
644 September 2019 PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING