Yongseung Kim

Absolute radiometric calibration of the KOMPSAT-2 multispectral camera using a reflectance-based method and empirical comparison with IKONOS and QuickBird images

Abstract. This paper presents absolute radiometric calibration coefficients (gains) that explain the relationship between the digital number (DN) and at-sensor radiance for the multispectral camera (MSC) on Korea’s first high-resolution satellite (KOMPSAT-2). Absolute radiometric calibration was performed using a reflectance-based method. In addition, the suitability of vicarious results from radiance- and reflectance-based validations was analyzed with reference to IKONOS and QuickBird images. The latter are spectrally similar to KOMPSAT-2 images and have been validated in a large number of studies. For all bands, the R 2 values of fitted lines for the gain ranged from 0.82 to 0.94, representing an improvement compared to previous findings for the KOMPSAT-2 MSC. To analyze the suitability of the vicarious results, same-pixel at-sensor radiances across different spectral bands were compared. In all bands, except the red band of QuickBird, the at-sensor radiances of KOMPSAT-2 MSC were highly correlated with those of IKONOS and QuickBird. In addition, same-pixel comparisons of reflectance across different spectral bands showed that the slopes of the least-squares lines for each band were similar to the results of the radiance comparison. The standard deviation among top of atmosphere (TOA) reflectances was within 0.019 for all bands. To calculate the tasseled cap transformation (TCT) coefficients for the KOMPSAT-2 MSC, an empirical method was applied using radiometric normalization. The results were similar to those obtained using the TCT coefficients for IKONOS and QuickBird in the brightness, greenness, and wetness components. The TCT images showed similar patterns. The absolute radiometric calibration coefficients presented here appear to be a good standard for maintaining the optical quality of the KOMPSAT-2 MSC, for which prelaunch, on-board, and vicarious calibration data are lacking.

An experimental study on the image-based atmospheric correction method for high resolution multispectral data

The atmospheric correction is prerequisite to derive both land and ocean surface properties from satellite remote sensing data. It also improves the satellite image quality and the performance of value-added image processing. The purpose of this study is to develop an image-based atmospheric correction method for the forthcoming Korea Multi-Purpose SATellite-2 (KOMPSAT-2) multi-spectral camera (MSC) data. For this purpose, we have first tested the several atmospheric correction models using the Landsat Enhanced Thermal Mapper Plus (ETM+) data that have quite similar spectral characteristics to the KOMPSAT-2 MSC data, and the in-situ measured surface reflectance data during the satellite overflight. Subsequently, we have applied the selected models to the IKONOS data with off-nadir viewing corrections because most passes of KOMPSAT-2 are subject to such viewing conditions. This presentation discusses the results of the above tests.

Observation of Crude Oil Spill Off the West Coast of Korea using TerraSAR-X, ENVISAT ASAR and ALOS PALSAR

On December 7th, 2007, more than 10,000 tons of crude oil from a tanker leaked into the Yellow Sea off the west coast of Korean Peninsula. Several SAR images including TerraSAR-X, ENVISAT ASAR, RADARSAT-1, ERS-2 SAR and ALOS PALSAR were acquired over the contaminated area from oil spill. Observed dark patches in SAR images, due to the presence of oil slicks, were extracted using adaptive thresholding methods, and then classified based on field information. The damping ratio, which is a ratio between slick-free and slick-covered sea surface, was analyzed by the SAR radar frequencies and wind condition. With the acquired SAR images in temporal resolutions, the movement of oil slicks was monitored and traced.

An experimental study on verification of the compact airborne imaging spectrometer system

The Compact Airborne Imaging Spectrometer System (CAISS) was designed and developed as the airborne hyperspectral imaging system. The mission of the CAISS is to provide full contiguous spectral information with high spatial resolution for advanced applications in the field of remote sensing. The CAISS has an ability to control the spectral and spatial configuration of the imaging instruments. In order to understand the mechanism of imaging spectrometer system and its characteristics, the several verification tests with the CAISS were conducted in the laboratory. Especially, the verification of camera system was performed with the integrating sphere and spectral lamps. In order to verify the spectral characteristics, four spectral binning (x1, x2, x4, and x8) were measured using each of the spectral lamps and the position of the peaks was compared to the reference data sheet of each spectral lamps. For all measurements, it was found that the spectral deviation was lower than the Full Width Half Maximum (FWHM) of the system for each of the spectral binning. Also several interface verification tests between the CAISS and the airplane were conducted on the ground. This paper presents the preliminary results of verification test in the camera system level and interface test with airplane on the ground.

Comparison of ocean color products between OSMI and SeaWiFS: preliminary results

Much effort has been made in the radiometric calibration of the ocean scanning multispectral imager (OSMI) since after the successful launch of KOMPSAT-1 in 1999. A series of calibration coefficients for OSMI detectors were obtained in collaboration with the NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary (SIMBIOS) project office. In this study, we compare the OSMI level-2 products (e.g., chlorophyll-a concentration) calculated from the NASA cross-calibration coefficients with the SeaWiFS counterparts. Sample study areas are some of diagonostic data sites recommended by the SIMBIOS working group. We will present the preliminary results of this comparative study.

Overview of KOMPSAT-1 data applications

Since the successful launch of KOrea Multi-Purpose SATellite-1 (KOMPSAT-1) on Dec. 21, 1999, the optical sensors of Electro-Optical Camera (EOC) and Ocean Scanning Multi-spectral Imager (OSMI) aboard KOMPSAT-1 have been observing the global land and ocean, respectively. KARI distributed the KOMPSAT-1 data to government agencies, government-supported research institutes and universities for public use. And Korea Aerospace Industries (KAI) undertook the data dissemination for commercial use. To promote the development of remote sensing technology using the KOMPSAT-1 data, KARI has been collaborating with three research groups, each representing land applications, marine applications, and meteorological applications. The studies of land application group demonstrated that the EOC data are useful in the area of mapping, surveillance, land cover mapping, land use analysis, and disaster monitoring. Although much effort has been made in the calibration and validation of OSMI data, they have been successfully used to monitor yellow dust, forest fire, red tide, and typhoon. The current sensor calibration efforts in collaboration with NASA are expected to bring more outcomes related to the ocean color research. The presentation will summarize the status of KOMPSAT-1 data applications and highlight some results obtained from the above research groups.

Correlation of cloud radiative forcing with clear-sky flux: Seasonal variations of longwave components

Variations of cloud radiative forcing (CRF) have been considered important in the analysis of cloud-climate interactions. As CRF is defined to be the difference between clear-sky and total fluxes, of some concern is the contribution of clear-sky flux variations to the observed CRF variations. This study investigates the relationship between longwave (LW) CRF and clear-sky LW flux (LW CS) variations using the Earth Radiation Budget Experiment (ERBE) monthly mean data for the period February 1985 through to January 1989. It is illustrated that positive correlations, which are especially strong in the Northern Hemisphere mid- to high-latitude continents, are found in the extratropics, whereas strong negative correlations dominate in the tropics. These latitudinal characteristics of correlations are shown to be linked to the strength of seasonal changes of LW CS relative to the LW CRF counterpart. Further analysis demonstrates that the seasonal changes of LW CRF in the tropics are significantly correlated with the corresponding changes of clouds, and those in the mid- to high latitudes are substantially influenced by the corresponding changes of surface and atmospheric temperatures.