KOMPSAT-EOC SENSOR MODEL ANALYSIS
Kiin BANG and Prof. Woosug CHO, Korea
Key words: KOMPSAT, Sensor Model, Collinearity
Equation.
Abstract
In recent years, many countries have been giving special interest
on space program, especially multipurpose high resolution and
hyperspectral satellite. As one of national space programs in Korea,
the first Multi-Purpose Satellite 1 (KOMPSAT-1) was launched on
December 1999 and carried out its own mission. The EOC
(Electro-Optical Camera) is the primary payload for KOMPSAT-1. The
main mission of EOC is to provide the stereo images for the production
of topographic maps of Korean territory. An essential element in
capturing geospatial information through satellite imagery is to
establish accurate sensor model. There have been so many researches on
satellite camera model. In general, camera model for satellite imagery
could be categorized into three groups: physical, semi-physical and
mathematical models. The semi-physical model could be collinearity
model or extended collinearity model. In this study, we developed ten
different sensor models for KOMPSAT-EOC and applied to stereopair for
analyzing their behaviors. The satellite sensor models, which were
extended from collinearity condition equations, were developed and
then the behavior of each sensor model was investigated. The satellite
sensor models were represented by the six exterior orientation
parameters in 1st, 2nd and 3rd order function of satellite image
scanline. Among them, the rotational angle parameters such as w(omega)
and f(phi) correlated highly with positional parameters could be
assigned to constant values. For the experiments, two different
stereopairs of KOMPSAT-EOC satellite images exposed to the similar
area in different pass were used.
1. INTRODUCTION
Geographic Information System (GIS) enables the integration of
diverse types of natural and man-made features such as mountain,
river, road and building, and corresponding nonspatial attribute data.
In this context, National Geographic Information System (NGIS) which
makes possible the consistency and standardization of various
geographic data and avoidance of overlapped investment for
implementation, is recognized as one of the most fundamental
infrastructures planned and developed by central government in Korea.
At the end of the 20th century, the advanced nations have already
applied GIS to various fields such as urban management, disaster and
facility management, and environmental management. In the same
context, Korean Government has initiated a full-scale implementation
of NGIS master plan in 1995. The NGIS master plan can be categorized
mainly into the generation of spatial database for national geospatial
framework data, establishment of data standardization, assistance of
GIS-related technical improvement and development of infrastructure
for utilization and application of NGIS. Under the scope of NGIS, the
GIS data compilation work in various sectors is successfully making
headway.
In addition, Korean government supports Korea Space Program where
Korea Aerospace Research Institute (KARI) has developed KOMPSAT-1 that
was launched on December 1999. The EOC (Electro-Optical Camera) is the
primary payload for KOMPSAT-1. The main mission of EOC is to provide
the stereo images for the production of topographic maps of Korean
territory.
An essential element in capturing geospatial information through
satellite imagery is to establish accurate sensor model. There have
been so many researches on satellite camera model. In general, camera
model for satellite imagery could be categorized into three groups:
physical, semi-physical and mathematical models. The semi-physical
model could be collinearity model or extended collinearity model. In
this study, we developed ten different sensor models for KOMPSAT-EOC
and applied to stereopair for analyzing their behaviors. The satellite
sensor models extended from collinearity condition equations were
developed and then the behavior of each sensor model was investigated.
The satellite sensor models were represented by the six exterior
orientation parameters in 1st, 2nd and 3rd order function of satellite
image scanline. Among them, the rotational angle parameters such as
ω (omega) and Φ (phi) correlated highly with positional
parameters could be assigned to constant values. For the experiments,
two different stereopairs of KOMPSAT-EOC satellite images exposed to
the similar area in different passes were used.
2. KOREA MULTI-PURPOSE SATELLITE 1 (KOMPSAT-1)
Under Korea National Space Program, Korea Aerospace Research
Institute (KARI) has developed and launched KOMPSAT-1 in December
1999. The KOMPSAT-1 satellite is a small satellite with the mass of
500kg to be operated at the sunsynchronous orbit which has 98 minutes
orbit period, 28 days repeating ground track, 10:50 AM ascending orbit
crossing time, and 98.13 degrees inclination at the altitude of 685km.
The lifetime of KOMASAT-1 is expected to be over 3 years.
KOMPSAT-1 includes three instruments such as Electro-Optical Camera
(EOC), Ocean Scanning Multispectral Imager (OSMI), and Space Physics
Sensor (SPS) for the mission of cartography, worldwide ocean
observation, and space environmental monitoring, respectively (Paik
1998).
2.1 Electro-optical Camera (EOC)
Figure 1 shows the EOC operational concept of image collection. The
primary mission of EOC is to provide images for the production of
cartographic maps and digital elevation models of the Korea peninsula.
EOC collects panchromatic images with the ground sample distance (GSD)
of 6.6m and the swath width of 17km at nadir through the visible band
of 510~730nm. EOC scans the ground track of 800km altitude orbit with
pushbroom and body pointing method.
The EOC has the function of programmable gain and offset to take
the various conditions of ground reflected radiation into account. For
EOC mission, S-band communication link is used to transmit command
from the ground station and receive the State of Health (SOH) data of
EOC. The EOC transmits the image data to ground station via X-band
channel.
The EOC collects image for 2 minutes per 98 minutes orbit cycle,
which covers about 800 km along ground track. The EOC imagery can be
transmitted to Korean Ground Station in real time during Korean
peninsular observation or be stored in the Solid State Recorder(SSR)
of PDTS beyond the Korean Ground Station receiving area. The stored
image data can be transmitted when the data reception connection is
available later.
As shown in Figure 1, the EOC collects stereo images of target area
from opposite sides on different passes by roll-tilting of spacecraft,
then ground station can make DTM with stereo images. It is possible to
collect image data 39 times in the daytime per 28 days revisit cycle
by roll-tilting of up to ±45 degree. For cartographic mapping, up to
30 degree roll-tilting is used. Korean Ground station can obtain EOC
images 20 times out of 39 times in this sense.
Figure 1. EOC Operational Concept
3. SENSOR MODEL
The sensor models developed in this study are extended from
collinearity equation. It is well known that each scanline's center of
pushbroom satellite image keeps changing while image is being
captured. The attitude of each scanline is continuously changing as
well. Conclusively, each scanline has its own 6 of exterior
orientation parameters, which can't be solved without having a priori
information.
In general, we establish a continuous function for exterior
orientation parameters in terms of exposure time or scanline. The
satellite sensor models developed in this study were represented by
the six exterior orientation parameters in 1st, 2nd and 3rd order
function of satellite image scanline. Among them, the rotational angle
parameters such as w (omega) and f (phi) correlated highly with
positional parameters could be assigned to constant values. The ten
different sensor models for KOMPSAT-EOC are as follows:
4. EXPERIMENTS AND RESULTS
To assess the behavior of each sensor model, two different
stereopairs of KOMPSAT-EOC satellite images were used in the
experiments. Ground control and check points were selected and
measured in both stereopairs using Intergraph ImageStation. Those
ground and check points for two different stereopairs are well
distributed over both two stereopairs. Once ground and check points
were captured, these points were surveyed by precise DGPS technique
and then transformed into Korean TM coordinate system. The first
stereopair depicts Nonsan area, which is shown in Figure 2. Its
characteristics are listed in Table 1. The second stereo pair
represents hilly and developed urban area of Pusan. The second
stereopair is shown in Figure 3. Its characteristics for second
stereopair are listed in Table 2.
Figure 2. Nonsan stereopair (Left and Right Images)
Table 1. Characteristics of Nonsan Stereopair
Figure 3. Pusan stereopair (Left and Right Images)
Table 2. Characteristics of Pusan Stereopair
There are 17 control points and 8 check points, 18 control points
and 8 check points used for Nonsan and Pusan stereospair,
respectively.
Figure 4. Results of each sensor model for Nonsan
images
Figure 5. Results of each sensor model for Pusan
images
The investigation on behavior of each sensor model has been
performed in two ways. First, each sensor model was applied to each
KOMPSAT-EOC image. The behavior of each sensor model was analyzed with
respect to RMSE of check points. Secondly, each sensor model was
applied to each KOMPSAT-EOC stereopair. Again, the behavior of each
sensor model was analyzed with respect to RMSE of check points.
The Figure 4 and 5 show the results of each sensor model applied to
each KOMPSAT-EOC image. It was found in both Nonsan and Pusan images
that the FIRST-KAPPA and SECOND-KAPPA sensor model did not perform
well in terms of accuracy and computing time. The other sensor models
except those two models did provide the accuracy in acceptance level
for capturing geospatial information.
Figure 6. Results of each sensor model for the
Nonsan stereopair
Figure 7. Results of each sensor model for the
Pusan stereopair
The Figure 6 and 7 show the results of each sensor model applied to
each KOMPSAT-EOC stereopair, which are similar to those of each sensor
model to each satellite image.
5. CONCLUSION
This paper shows the behaviors of 10 different sensor models
extended from the collinearity equations applied to KOMPSAT-EOC
satellite images and stereopairs, respectively. Most of sensor models
except FIRST-KAPPA and SECOND-KAPPA sensor models perform provide
relatively good positional accuracy.
Conclusively, the FIRST-ZERO and FIRST-FIRST sensor models are
stable and accurate comparing the other sensor models. The positional
accuracy did fall into less than 1 pixel for both sensor models, which
shows the feasibility of generating topographic maps using KOMPSAT-EOC
satellite images.
For cartographic purpose, the sensor model for KOMPSAT-EOC should
be investigated in greater depth. In addition, the possibly identified
features and feasible topographic map scale should be further studied.
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CONTACT
Kiin Bang, Graduate Course
Inha University, Department of Geoinformatic Engineering
253 Yonghyun Dong, Nam Gu
Inchon
KOREA
Tel. + 82 32 863 8712
Assistant Professor Woosug Cho
Inha University, Department of Civil Engineering
253 Yonghyun Dong, Nam Gu
Inchon
KOREA
Tel. + 82 32 860 7571
Fax + 82 32 873 7560
E-mail: wcho@inha.ac.kr
13 April 2001
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