The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part BI. Beijing 2008
The direct sensor model calculates the orbital parameters
directly by using the position vector. Based on the collinearity
condition, an image point corresponds to ground point using the
employment of the orientation parameters, which are expressed
as o function of the sampling time.
This ephemeris information through the KOMPSAT-2 POD
system and the produced POD(Precision Orbit Data).
The calculation of ground coordinates on an arbitrary image
coordinate (u,v) is
The RFM is a generalized sensor model that uses a pair of
rations of two polynomials to approximate the condition
equation.
2.1 DIRECT SENSOR MODEL
The direct sensor model of KOMPSAT-2 MSC is realized on
the co-linearity condition. The spacecraft perspective center,
image point and the corresponding ground point are assumed to
be on one straight line using six basic coordinate systems. The
origin of sensor coordinate system is considering coincided
with the origin of the spacecraft which is located at the
spacecraft center of mass.
The Figure 1 gives a description of basic sensor model of
KOMPSAT-2.
v Nj
Interior
Exterior orientât!
Figure 1. Direct sensor modelling for KOMPSAT-2 geometric
calibration and validation
In from image coordinate system to sensor coordinate system,
the main cal/val parameters consist of focal length, distortion
which one is the LOD distortion the other is LOS distortion.
After those distortion corrected using by GCP(Ground Control
Point)/ICP(lmage Control Point) with under 0.3 pixel accuracy
and bundle adjustment, KOMPSAT-2 image data are provided
to users. The cal/val items of from sensor coordinate system to
body coordinate system compute to correct occurring
misalignment come from between star tracker sensor and MSC.
The Orbit Coordinate System as translation body coordinate
System, the produced rotation angle of roll, pitch and yaw
rotate and transfer the coordinate system from star tracker and
gyro sensor of KOMPSAT-2. The measured attitude data are
recorrected by the KPADS (KOMPAST-2 Precision Attitude
Determination Subsystem). Earth-Centered Earth-Fixed
Coordinate System(ECEF) is transfer from orbit coordinate
system to ECEF as coordinate system, using satellite position
and velocity vectors of the satellite measured from GPS sensors
of KOMPSAT-2. The measured from GPS of the KOMPSAT-2
satellite system, the satellite of position, velocity and time
information are transferred to the OBC, after this, that
information is transferred to ground station through the S-band.
x-x s ~
X
Y-Y s
= V. m ecef • M° rbit • M Body •
K m Orbit iV1 Body m Sensor
y
Z-Z s
z
where,
MSf • fr° m or b't coordinate system to ECEF
Meody : from body coordinate system to orbit coordinate
system
M Tl, ■ ft™ sensor coordinate system to body coordinate
system
[x, y, z] T : Scan line coordinate
[X s , Y S ,Z S ] T : Satellite position from ephemeris data
[X, Y, Z] T : Ground coordinate
k : scale factor
2.2 RFM
The RPC for the KOMPSAT-2 MSC sensor is generated from
the resulted KOMPSAT-2 direct sensor model using the RFM.
The RPC generation in KOMPSAT-2 IRPE system consists of 4
main parts as shown in Figure 2.
Figure 2. KOMPSAT-2 RPC generation workflow
The model uses a pair of rations of two polynomials, as shown
in equation 2.
PKX n J n ,Z n ) p3(X n ,Y n ,Z n )
p2(X n ,Y n ,Z n ) " p4(X n ,Y n ,Z n )
where,
r n , c n : the normalized row and column index of pixels in image.
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