KOMPSAT-5 (Korea Multi-Purpose Satellite-5) / Arirang-5
KOMPSAT-5 is part of the Korean National Development Plan of MEST (Ministry of Education, Science and Technology) which started in 2005. The project is being developed and managed by KARI (Korea Aerospace Research Institute). The primary mission objective is to develop, launch and operate an Earth observation SAR (Synthetic Aperture Radar) satellite system to provide imagery for geographic information applications and to monitor environmental disasters. 1) 2) 3)
KOMPSAT-5 is also referred to as the GOLDEN mission:
- GIS: Acquisition of independent high resolution SAR images
- Ocean & Land Management : Survey of natural resources
- Disaster & ENvironment Monitoring : Surveillance of large scale disasters and its countermeasure.
Figure 1: Overview of KOMPSAT-5 applications scenario (image credit: KARI)
In March 2006, KARI signed a contract with Thales Alenia Space of Italy, TAS-I (formerly Alcatel Alenia Space), to provide an X-band SAR payload system for multi-mode observations, including the data link subsystem for gathering the data transmitted by the radar, archiving them and subsequently transmitting them to the ground station. In addition, the company will also provide the ground SAR image processor as well as the calibration algorithms and equipments. 4) 5)
Figure 2: Artist's view of the deployed KOMPSAT-5 spacecraft (image credit: TAS-I)
The KOMPSAT-5 spacecraft bus design, development and integration is being led by KARI. The private companies such as Korea Aerospace Industries, Korean Air, Hanwha, Doowon Heavy Industries, and SI (Satrec Initiative), which have already participated in the former Korean satellite programs, are involvied in the development of the KOMPSAT-5 spacecraft. Based on the experience of the previous programs, core technologies for satellite bus were enhanced during the development of KOMPSAT-5. 6)
The KOMPSAT-5 spacecraft bus is of modular design and of KOMPSAT-2 heritage. The bus allows parallel integration of equipment. The bus subsystems consists of the SMS (Structure and Mechanisms Subsystem), the TCS (Thermal Control Subsystem), EPS (Electrical Power Subsystem), AOCS (Attitude and Orbit Control Subsystem), PS (Propulsion Subsystem), TC&RS (Telemetry Command and Ranging Subsystem), and FSW (Flight Software). The spacecraft has a launch mass of ~1400 kg, the design life is 5 years.
Figure 3: Key design features of the KOMPSAT-5 spacecraft (image credit: KARI)
EPS (Electric Power Subsystem): EPS consists of three major components, the solar array, the battery, and the PCDU (Power Control and Distribution Unit).
- The solar array consists of two wings, each comprising four solar panels supported by a boom and attached to SADA (Solar Array Drive Assembly). The SADA rotates the wings and electrically connects their solar cell circuit, via junction box, through slip rings to the main bus. The SADE (Solar Array Drive Electronics) control the drives for sun tracking. The solar panels are populated with silicon solar cells electrically connected into strings. The spacecraft generates an average on-orbit power of 1.4 kW (EOL).
- The battery consists of 13 cells with 4 parallel Li-ion cells, cell bypass circuitry, and monitoring electronics. The battery has a capacity of 97 Ah (EOL)
- The PCDU perform the following major functions: It protects the battery from overcharging by the active control of the solar array generated power and it distributes the unregulated (+50 V) and the regulated electrical power (+28 V) to the bus and payload units via the controlled unit load switch. The PCDU also provides the secondary power for the TDE (Torque Drive Electronics) and TAM (Three Axis Magnetometer).
Figure 4: Schematic view of the EPS functional diagram (image credit: KARI)
RF communications: The TC&RS data are transmitted in S-band (4 kbit/s), while the payload data are downlinked in X-band at 310 Mbit/s.
Launch: The KOMPSAT-5 (Arirang-5) spacecraft was launched on August 22, 2013 on a Dnepr-1 launch vehicle of ISC Kosmotras from the Dombarovsky Launch Site, Yasny, Russia. The launch was executed by the Russian Strategic Rocket Forces of the Russian Ministry of Defense with the support of the Russian and Ukrainian companies, which are part of the ISC Kosmotras industrial team. 7) 8) 9) 10)
This marked the first flight of the Dnepr-1 launcher since August 2011. Dnepr-1 launches had been suspended in 2011 by the Russian Defense Ministry based on the financial aspects of the program. Subsequently, in May 2013, it was decided by the Russian and Ukrainian governments to undertake the two launches.
- The first launch took place on 22 August 2013 and placed the Korean Arirang-5/KOMPSAT-5 satellite into orbit.
- The second launch (Nov. 2013) will place a cluster of small satellites into orbit with DubaiSat-2 of EIAST (Dubai) and STSat-3 of KARI (Korea) as the primary payloads.
Orbit: Sun-synchronous circular dawn-dusk frozen orbit, mean altitude = 550 km, inclination = 97.6º, nodal period = 95.78 minutes (15 1/28 orbits/day), LTAN (Local Time on Ascending Node) = 6 hours, the repeat cycle is 28 days. 11) 12)
Figure 5: System architecture of the KOMPSAT-5 mission (image credit: KARI) 13)
• Dec. 19, 2013: KARI released SAR images acquired for calibration purposes. During the early operation and calibration phase, all of the satellites functions have been verified and the satellite is now under payload calibration. The released images are acquired for the verification of payload performance. 14) 15)
- The KOMPSAT-5 CAL/VAL team will complete the calibration of the radar instrument and optimizing the data processing chain by the end of February 2014. After completion of calibration, KOMPSAT-5 will be operated to provide products for various applications such as security and defense, image interpretation, mapping, land and natural resource management, environmental monitoring, disaster monitoring and more. Commercial data from KOMPSAT-5 can be expected to be available from the second quarter of 2014.
• The KOMPSAT-5 spacecraft made contact with a ground station in the Asian country early Friday (Aug. 23, 2013), confirming its successful deployment into its target orbit, officials in Yasny said. 16)
Beacon signals from the satellite were initially picked up by the Troll Satellite Station in Antarctica, 32 minutes following the launch, partly indicating the satellite's successful deployment into its orbit. 17)
Sensor complement: (COSI, AOPOD)
COSI (Corea SAR Instrument):
COSI is a multi-mode X-band instrument provided by TAS-I (Thales Alenia Space-Italy) as prime contractor (Ref. 2). The primary objective of the COSI assembly is to provide high resolution SAR imagery in various modes at an incidence angle of 45º (Ref. 1):
- High resolution SAR mode imagery: 1 m (also known as spot SAR mode)
- Standard SAR mode imagery: 3 m (stripmap mode)
- Wide swath SAR mode imagery: 20 m (ScanSAR mode).
The COSI payload consists of the SSS (SAR Sensor Subsystem) and the DLS (Data Link Subsystem). The SSS operates in X-band and is equipped with an active phased array antenna with electronic scanning capabilities in the azimuth and elevation planes. The DLS is in charge of source data storage (and ancillary data) and transmission to the ground segment.
Table 1: Performance parameters of the COSI assembly
Table 2: Observvation mode and resolution
The incidence angle range of the steerable beam is from 20-45º nominally so that the ground coverage will be, when measured from nadir, covers a potential coverage region from 185-490 km (305 km wide) for the nominal support, and 490-675 km (185 km wide) for extended beam steering (Figure 6).
Thanks to the wider coverage of up to 490 km width in a single orbit than the 95-km distance between adjacent passes (at equator), a ground target can be imaged several times with multiple incidence angles, which is required for radargrammetric configuration.
In addition, the agile KOMPSAT-5 spacecraft has a body pointing capability in cross-track which offers a left or right-looking observation capability. This feature is of great importance for event monitoring - doubling in effect the FOR (Field of Regard). 19)
CalVal (Calibration and Validation) of COSI: The first SAR mission of Korea requires special attention for successful mission operations support. The CalVal activities include relative and absolute radiometric calibration and pointing calibration. The mission uses DT (Distributed Targets) and PT (Point Targets). COSI employs a total of 50 radar beams, 19 beams are being used for the HR (High Resolution) mode, while 31 beams support the standard imaging mode. In the WS (Wide Swath) mode, a combination of 19 beams of the standard mode are being used.
On the basis of the antenna model, all modes supported will be validated in the IOT (In-Orbit Test) phase. The DT and PT imagery of the various test sites will represent the key inputs for the CalVal activities. 20) 21)
KARI selected fixed ground CalVal sites in the Mongolia steppe region for the positioning of CRs (Corner Reflectors). These CalVal sites will be used periodically by the COSI instrument during the KOMPSAT-5 mission life time (5 years). The CalVal sites were selected due to their characteristics: flat area, no man-made structures, and low backscattering coefficient.
- Each trihedral CR (Corner Reflector) has a high RCS (Radar Cross Section) value, enough to have more than 30 dB SCR (Signal-to-Clutter Ratio).
- The position of all CRs is designed in order that all ST & HR beams can access at least one CR.
Figure 7: Basic Concept for constructing KOMPSAT-5 calibration site (image credit: KARI)
Figure 8: Location of KOMPSAT-5 CR Site in Mongolia (image credit: KARI)
AOPOD (Atmosphere Occultation and Precision Orbit Determination):
AOPOD is a secondary payload consisting of IGOR, a spaceborne dual frequency GPS receiver and the LRRA (Laser Retro Reflector Array). The objective is to provide data for POD (Precision Orbit Determination) and GPS radio occultation measurements. KASI (Korea Astronomy and Space Science Institute) is in-charge of the development of the hardware and software for this system. 22) 23) 24)
The IGOR (Integrated GPS Occultation Receiver) of BRE (Broad Reach Engineering), Tempe, AZ, USA has been selected. The IGOR instrument, of BlackJack heritage, is customized to include a MIL-STD-1553B bus and two SSR (Solid State Recorders), each of 128 MByte. The IGOR instrument includes two RO antennas and two POD (Precision Orbit Determination) antennas. 25)
- IGOR instrument mass: 4.2 kg; size: 21.8 cm x 24.0 cm x 14.4 cm
- Peak power consumption: 25 W
- Tracking signals: L1 (1575.42 MHz) and L2 (1227.60 MHz)
- Tracking channels: 48 (4 antenna inputs)
- Sampling rate: 0.1 Hz and 50 Hz sampling; (0.1 Hz for POD support, 50 Hz for occultation science)
Figure 9: Illustration of the IGOR instrument (image credit: BRE, KARI)
As shown in Figure 10, IGOR consists following parts: the RF receiving part to receive 4 RF signals, the digital part where the GPS signals are digitalized, the data storage device part consisting of a 128 MB SSR (Solid State Recorder), the 1553B interface part for the MIL-STD-1553B communication with the spacecraft, and the ground test interface part for the ground test and RS-422 communication.
In particular, all the parts except the RF receiving part are duplexed to secure the receiver stability. In the case of KOMPSAT-5, a total of 4 filter/preamp assemblies are installed in between the RF input port and the antenna in order to reduce the signal interference caused by the SAR signal. Two POD antennas and two occultation antennas are connected to the four RF input ports of the IGOR receiver.
Figure 10: Integrated GPS occultation receiver interface diagram (image credit: BRE, KARI)
The GPS signals received by the GPS antenna are stored in the SSR, the data storage device part, through the RF receiving part and the digital part. Since the capacity of the SSR data storage device is limited, the data is overwritten from the initial storage space of the SSR if the capacity of the received GPS data exceeds the SSR capacity. The current storage address of the raw data can be known through the telemetry. The GPS raw data stored in this way is transferred to the mass memory of KOMPSAT-5 and then transferred to and stored in the data storage server of the ground data center. The stored GPS raw data is transferred to the data processing server which processes the data to the RINEX (Receiver Independent Exchange) format, the standard GPS data format, and store it.
The GPS data processed in the ground data center can be used in various studies of the atmosphere and ionosphere including determination of satellite orbit and estimation of the temperature and pressure, vapor distribution and electron density in the atmosphere. The function of the IGOR is to provide the POD data for the determination of the precise satellite orbit and the GPS radio occultation data for scientific application research.
Figure 11: GPS antenna configuration of KOMPSAT-5 (image credit: KARI)
The LRRA (Laser Retro Reflector Array) was developed at GFZ (GeoForschungsZentrum) Potsdam, Germany; it is being used for POD validation of KOMPSAT-5. The LRRA has four corner cube prisms mounted in a compact frame.
Figure 12: Illustration of the LRRA (image credit: KARI)
The KGS (KOMPSAT-5 Ground Segment) is developed by ETRI (Electronics and Telecommunications Research Institute) and operated by KARI. It consists of the following elements:
• MCE (Mission Control Element). MCE monitors and controls the satellite and provides mission planning. Mission control provides also operational orbit determination/prediction and the POD (Precise Orbit Determination) function. 26)
• IRPE (Image Reception and Processing Element). 27)
• CVE (Calibration and Verification Element).
Overall, KGS provides the capability to receive, process, and distribute the KOMPSAT-5 payload data to satisfy the users of the KOMPSAT-5 mission.
The SAR data products of the mission will be globally distributed to the scientific and commercial user communities after completion of the commissioning phase (~ 6 months after launch). The products of the AOPOD will be used for weather forecasting by the national weather agency.
The ground segment for KOMPSAT-5 has a system ability to generate level products from raw data within an hour. In particular, this feature is important for event monitoring support.
Table 3: KOMPSAT-5 SAR standard products
The KOMPSAT-5 SAR basic products are subdivided into four types:
1) L1A product: The level L1A product is a SCS (Single-look Complex Slant) product which is focused in slant range-azimuth projection that is the natural acquisition projection of the sensor. The primary purpose of L1A is to focus the image by compressing all of the energy that is backscattered from each illuminated target in the scene and acquired from the SAR antenna. Actually, the targets in an SAR image are acquired coherently along a certain time, so they distribute their energy in various image cells with many super positions of more targets in the same cell. This constitutes the main difficulty of SAR processing. The L1A also includes the determination of the Doppler Centroid, which is the centre frequency of the azimuth spectrum recorded by the SAR.
2) L1B product: The focused images obtained from the preceding L1A stage are in a slant range-azimuth plane. The application of the SAR images needs a more “user-friendly” geometry. Therefore, the L1B processing stage generates a detected ground multi-look product which is obtained by detecting, multi-looking, and projecting the SCS data onto a grid regular in ground.
3) L1C product: The L1C product is a geocoded ellipsoid corrected product which is obtained by projecting the L1A product onto a regular grid in a uniform pre-selected cartographic reference system (WGS84). For each sensor acquisition mode, the L1C contains the focused data, which is detected geo-coded on the reference ellipsoid and represented in a uniform preselected cartographic presentation.
4) L1D product: The L1D processing stage aims to generate a geocoded terrain corrected product which is fully calibrated through the use of a terrain model, then detected, geolocated on a DEM (Digital Elevation Model), and represented in a uniform pre-selected cartographic projection. The image scene is located and accurately (x, y, z) rectified onto a map projection through the use of ground control points and DEM. The L1D processing is performed on L1B data, with the use of the DEM for map projection.
MCE (Mission Control Element): The MCE system provides satellite control capabilities that allow the operators to carry out the KOMPSAT-5 mission with mission planning, command generation and transmission, telemetry processing and monitoring, flight dynamics support, and satellite static simulation. The system provides the primary interface to KOMPSAT-5 and the capabilities required to operate the KOMPSAT-5.
The MCE has the following key functions: satellite monitoring and control, mission planning and scheduling, flight dynamics, as well as S-band telemetry, tracking, and command.
IRPE (Image Reception and Processing Element): The IRPE provides the capability for receiving and storing KOMPSAT-5 SAR collected data; interfacing with the MCE for supporting image collection planning; generating standard and value-added SAR imagery products; and distributing imagery products to users. The IRPE also provides the X-band reception interface to satellite.
The IRPE consists of seven subsystems (Figure 13):
• Antenna and RF equipment
• DIS (Data Ingestion Subsystem)
• DAS (Data Acquisition Subsystem)
• ICPS (Image Collection Planning Subsystem)
• WMS (Workflow Management Subsystem)
• DPS (Data Processing Subsystem)
• UIS (User Interface Subsystem).
Figure 13: Internal and external interfaces of IRPE (image credit: KARI)
CVE (Calibration and Verification Element): The objective of CVE is the calibration of the COSI payload and maintaining its long-term system performance. Hence, the CVE’s main goal is to model the relationship between geophysical parameters and measured backscattering coefficients.
The overall system calibration includes the following: internal/external calibration; compensation/correction of known system errors in amplitude and phase; georeferenced transformation of SAR image data to backscatter coefficients within an estimated error; development and procurement of calibration targets; and delivery of calibration information to be used during SAR product generation at the IRPE.
The CVE is comprised of the following elements:
• CVP (Calibration and Validation Processor)
• BCVP (Bus Calibration and Validation Processor)
• CVS ( Calibration and Validation System)
• ECS (External Calibration System).
The CVP calibrates the COSI payload in IOT (Initial Operational Test) phase and in the routine calibration phase. It also generates Antenna Lookup Table (LUT), calibration constant LUT, and azimuth cuts LUT from SAR Product, as well as L0 file received from IRPE. The CVP also evaluates the azimuth beam-pointing offset by estimating the Doppler center frequency; performing reports on calibration; and evaluating and reporting on image quality. The BCVP performs on-orbit calibration for spacecraft bus sensors and mechanical misalignment between the spacecraft bus reference axis and each sensor axis, and calibrates the antenna phase center of the dual frequency GPS receiver with respect to the KOMPSAT-5 satellite center of mass by comparison with precision orbit determination results using SLR. The CVS manages all data related to calibration activity and image quality evaluation, and is connected with the CVPs for the internal and external calibration through an ethernet environment. In addition, the CVS communicates with the IRPE and MCE in order to receive all data related to the calibration operation and to transfer all data required by the IRPE and MCE. The ECS is the facility comprising the calibration site, corner reflector, and extended target for supporting the operations foreseen for the calibration phase of payload IOT and routine SAR instrument calibration activities.
In November 2012, Satrec Initiative (SI) of Daejeon, Korea announced an agreement with KARI (Korea Aerospace Research Institute) for “Worldwide Marketing and Sales Representative of KOMPSAT-2, -3 and -5 Image data.” KARI assigned Satrec Initiative as the ‘worldwide exclusive representative’ for KOMPSAT imagery sales. 28)
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9) On May 23, 2013, the Korean Ministry of Science, ICT, and Future Planning (MSIP) announced that Korea's first SAR satellite, Kompsat-5 will be launched on August 22 from Yasny, Russia.
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19) Duk-jin Kim, Wooil M. Moon, Ji-Hwan Hwang, Youn-soo Kim, “Application of KOMPSAT-5 for Emergent Oil Spill Monitoring,” Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium) 2010, Honolulu, HI, USA, July 25-30, 2010
20) JaeMin Shin, JinHee Kim, “Field Test of KOMPSAT-5 Calibration Equipment,” Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium) 2010, Honolulu, HI, USA, July 25-30, 2010
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26) Yoola Hwang, Byoung-Sun Lee, Young-Rok Kim, Kyoung-Min Roh, Ok-Chul Jung, Haedong Kim, “GPS-Based Orbit Determination for KOMPSAT-5 Satellite,” ETRI (Electronics and Telecommunications Research Institute) Journal, Volume 33, Number 4, August 2011, pp. 487-496, URL: http://etrij.etri.re.kr/Cyber/servlet/GetFile?fileid=SPF-1312420426452
27) Myungjin Choi, Taeyoung Kim, Hee-Jin Bae, Yunyook Jang, Tae-Byeong Chae, Yong-Sik Chun, “The KOMPSAT-5 Image Reception and Processing Element,” Proceedings of IGARSS (International Geoscience and Remote Sensing Symposium), Vancouver, Canada, July 24-29, 2011
28) “Satrec Initiative Announces Agreement with Korea Aerospace Research Institute,” SI, Nov. 15, 2012, URL: http://www.satreci.com/eng/ds1_1.html?tno=100&db=pr_board&no=22
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.