OVERVIEW OF KOMPSAT-3A CALIBRATION AND VALIDATION

Transcription

1 OVERVIEW OF KOMPSAT-3A CALIBRATION AND VALIDATION DooChun Seo 1, GiByeong Hong 1, ChungGil Jin 1, DaeSoon Park 1, SukWon Ji 1 and DongHan Lee 1 1 KARI(Korea Aerospace Space Institute), 45, Eoeun-dong, Yuseong-gu, Daejeon , Korea dcivil@kari.re.kr KEY WORDS: KOMPSAT-3A, Calibration, Validation, EO, IR ABSTRACT: The KOMPSAT-3A was successfully launched on 25 March KOMPSAT-3A is a lightweight Earth observation satellite developed by the Korea Aerospace Research Institute KARI. It will operate at an altitude of 528 km in a sun-synchronous orbit for 4 years and monitor the Korean peninsula using a payload capable of submeter class resolution. The mission objectives of the KOMPSAT-3A are to provide continuous satellite Earth observation after KOMPSAT-2 and KOMPSAT-3 and to meet the nation's needs for high-resolution EO (Electro- Optical) images required for GIS (Geographical Information Systems) and other environmental, agricultural and oceanographic monitoring applications and provision of IR (Infrared) images for GIS application and for monitoring the forest fire, the volcanic activity, the waste heat pollution in lakes and rivers, the flood damage, the urban heat island. KOMPSAT-3A Cal/Val(Calibration and Validation) activities is consist of Phase I and Phase II. In Cal/Val Phase I, the Cal/Val has been done to characterize, calibrate and validate the requirements and the performance of KOMPSAT-3A. In Cal/Val Phase II, the image data restoration has been done for the final KOMPSAT-3A image data quality with the requirement. This research is to describe overview of KOMPSAT-3A according to Phase I and Phase II. 1. Introduction After KOMPSAT-3A launched at March , the Cal/Val for KOMPSAT-3A had been doing by Cal/Val team in KARI. The primary mission of KOMPSAT-3A is to provide 0.55 m Ground Sample Distance (GSD) panchromatic image, 2.2 m GSD multi-spectral image, and 5.5m GSD infrared image data for various applications. The main mission objectives of KOMPSAT-3A System are to provide continuation of satellite earth observation after KOMPSAT-2 and KOMPSAT-3 to meet national need firstly, provision of the high-resolution EO (Electro-Optical) images required for GIS establishment and the applications for environmental, agriculture and ocean monitoring, and provision of IR (Infrared) images for GIS application and for monitoring the forest fire, the volcanic activity, the waste heat pollution in lakes and rivers, the flood damage, the urban heat island Generally, because the present remote sensing satellite technique cannot satisfy user s requirements for image data quality directly, the Cal/Val for image data quality must be carried out after launch before distributing the imagery to the user. In the broad concept of Cal/Val, the Cal/Val of the remote sensing satellite can be divided into two parts if we recognize the technical gap between the satellite technique and the users requirements; Cal/Val to calibrate and validate the requirements of satellite (Cal/Val Phase I; CVP I), and Cal/Val and image data restoration to guarantee the image data quality for the user (Cal/Val Phase II; CVP II). The KOMPSAT-3A Cal/Val has been carried out with this concept. Before KOMPSAT-3A launched, KARI Cal/Val team had prepared and developed Cal/Val sites, equipment and Cal/Val code for KOMPSAT-3A in KARI s own way. After launch, we have been doing the Cal/Val work according to the KOMPSAT-3A Cal/Val procedure. After CVP I, the KOMPSAT-3A has been calibrated and validated by the Cal/Val team, and during CVP II, the processing system of the KOMPSAT-3A image data has been calibrating and validating with the result of CVP I and the result of Cal/Val in CVP II. 2. KOMPSAT-3A SYSTEM The KOMPSAT-3A system consists of space segment, ground segment, and launch service segment, and various external interfaces including additional ground stations to support image data reception or launch and early operations. The space segment is a satellite consists of the spacecraft bus and payload. The main payload of KOMPSAT-3A is AEISS-A (Advanced Earth Imaging Sensor System-A). The AEISS-A is a high spatial resolution imaging sensor which collects visible image data of the earth's sunlit surface. The AEISS-A is a push-broom scanned sensor which incorporates a single nadir looking telescope. The sensor is submerged and rigidly attached to the spacecraft and the optical bore-sight of the telescope is aligned with the spacecraft +Z direction (nadir). The AEISS-A collects panchromatic and multi-spectral images of the earth. At the nominal mission altitude with nadir attitude, the AEISS-A collects ground image with a ground sample distance of approximately 0.55 meter panchromatic, 2.2 meter multi-spectral data and 5.5meter IR data and swath width of greater than 13 km. The image telemetry data can be compressed on-board by ground command.

2 The Mission orbit of the KOMPSAT-3A is a sun-synchronous circular orbit with an altitude of 528 km. The Orbit inclination is 98.1 degrees and the eccentricity from 0 to The satellite operates with a nominal local time of ascending nodes of 13:30 AM +10/-15 min. Table 1. AEISS-A Specification System Attributes Design lifetime Ground Sample Distance Spectral Band Swath Width Duty Cycle Radiometric Resolution Requirement 4 years PAN: km (nadir) MS: km (nadir) IR: km (nadir) PAN: 450 ~ 900 nm MS1 (Blue): 450 ~ 520nm MS2 (Green): 520 ~ 600nm MS3 (Red): 630 ~ 690nm MS4 (NIR): 760 ~ 900nm IR : 3 ~ 5 um PAN: 13 nadir MS: 13 nadir 10% per orbit (50 minutes per day) 14 bits Figure 1. KOMPSAT-3A System Configuration

3 2. OVERVIEW OF KOMPSAT-3A CALIBRATION & VALIDATION 2.1 Cal/Val parameters & frame work The KOMPSAT-3A Cal/Val parameters are divided for 4 groups; Spatial, Radiometric, Geometric and IR Radiometric, and each group have several parameters according to its property. There are some interaction between each group; Focusing after AOCS on-orbit Cal., LOS/LOD after MTFC, etc. The Table 1 is Main activity of each KOMPSAT-3A Cal/Val Phase. Table 2. Main activity of each KOMPSAT-3A Cal/Val Phase Cal/Val Phase I Cal/Val Phase II Step After System IOT After Cal/Val Phase I Target Satellite, AEISS-A Satellite Data(Product) Activity Characterization, Calibration Validation Calibration Validation Requirement System Specification System Specification, System Performance Figure 2. KOMPSAT-3A Cal/Val frame work 2.3 Spatial Cal/Val The MTF(Modulation Transfer Function) is a technique for characterizing the spatial resolution of optical system. Therefore, the MTF of satellite cameras is the image quality parameters assessed during on-orbit operation. The main activity of spatial calibration is focus calibration. Before launch, on the ground, this KOMPSAT-3A focus mechanism is positioned on the best step measured in a vacuum. Nevertheless, possible shift during launch may upset this focusing so that the position of each mechanism has to be checked and calibrated.

4 Figure 3. Focusing mechanism position 2.4 Geometric Cal/Val The geometric calibration is consist of interior orientation on payload and exterior orientation on bus system. KOMPSAT-3A is done calibration activity focal length, ccd alignment and distortion using KOMPSAT-3A geometric calibration sites. After calibration, the performance geometric calibration is checked by location accuracy, length distortion and planimetric accuracy. Figure 4. After geometric calibration, Location accuracy. 2.5 Radiometric Cal/Val The aim of radiometric calibration is to correct images for relative inter-dectector sensitivities so that a uniform landscape gives a uniform image. This radiometric calibration activity is NUC (Non-Uniform Correction). NUC calibration is conducted using side-slither image and many acquisition to select cloud-free image from low radiance uniform area such as the night sea and deep space image to high radiance image likes cloud and south or north pole image.

5 Figure 5. After NUC, PAN uniformity Figure 6 Compare of before and after image uniformity characterization 4. Conclusion During KOMPSAT-3A Cal/Val Phase I & II, the Cal/Val for the KOMPSAT-3A satellite and AEISS-A had been finished. KOMPSAT-3A Cal/Val(Calibration and Validation) activities is consist of Phase I and Phase II. In Cal/Val Phase I, the Cal/Val has been done to characterize, calibrate and validate the requirements and the performance of KOMPSAT-3A. In Cal/Val Phase II, the image data restoration has been done for the final KOMPSAT-3A image data quality with the requirement. After Cal/Val phase II, the KOMPSAT-3A has gone in Normal operation phase and the general user may get the imagery of the KOMPSAT-3A just now. 5. Reference [1] Lee, D.H., etc., 2012, Focusing Calibration and Validation for KOMPSAT-3, International Symposium on Remote Sensing 2012, Incheon, Korea

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