Abstract
In recent years, Korea has sustained consistent access to remote sensed data by launching Korea Multi-Purpose Satellite-3A (KOMPSAT-3A, K3A)—an updated version of the high-resolution KOMPSAT series. This KOMPSAT-3A required calibration and validation (Cal/Val) before and after its launch to enable proper functional characterization and to maintain the veracity of data collected. The Korea Aerospace Research Institute (KARI) executed the initial prelaunch calibration in the laboratory and we performed the Cal/Val of KOMPSAT-3A during the Launch and Early Operation Phase (LEOP) in the field. Two suitable sites in Korea and Mongolia with stable weather, almost uniform terrain, and near Lambertian diffusion, provided the necessary tarp reflectance to calculate the absolute radiometric calibration coefficients. The surface reflectance was determined using 12 and four well-calibrated reference reflectance tarps employing the FieldSpec® 3(Analytical Spectral Devices Inc., Boulder, CO, USA) Spectroradiometer. Subsequently, the top of atmosphere (TOA) radiance was estimated using radiative transfer code (RTC) software based on the Atmospheric and Topographic Correction (ATCOR). In addition, cross calibration was simultaneously performed at the Libya-4 pseudo invariant calibration site (PICS) for KOMPSAT-3A TOA radiance, using the spectral band adjustment factor (SBAF) compensated Landsat 8 reflectance and the Second Simulation of Satellite Signal in the Solar Spectrum (6S) to compute cross calibration coefficients. The results of the KOMPSAT-3A absolute calibration coefficient show that the R2 values were over 0.99, implying a significant correlation for almost all bands between the TOA radiance and the KOMPSAT-3A spectral band response at both campaign sites. However, this study reveals a difference of less than 5% calibration gains for all bands compared to the prelaunch values, while the cross calibration gain is below 5% in visible bands and above 5% in the near infrared band. An effort to optimize the reliability of the absolute calibration coefficients resorted to the rigorous quantification of uncertainties amongst atmospheric conditions, the digital number (DN), the reflectance tarp, the bidirectional reflectance distribution function (BRDF), and ozone levels. Therefore, we presumed that the total uncertainty was 4.27%, which conforms to some published results.
Highlights
Korea Multi-Purpose Satellite (KOMPSAT) is the name of the satellite series that was developed to satisfy the rapidly increasing demand for high-resolution satellite images due to economic development.Sensors 2020, 20, 2564; doi:10.3390/s20092564 www.mdpi.com/journal/sensorsThe Korean government successfully launched a new satellite, named Korea Multi-Purpose Satellite-3A (KOMPSAT-3A), on 26 March 2015
Absolute calibration using a vicarious approach is conducted under the assumption that the digital number (DN) of the satellite sensor is linear to the top of atmosphere (TOA) radiance
This paper examines the laboratory-based prelaunch calibration conducted by Korea Aerospace Research Institute (KARI), together with the post-launch absolute calibration and cross calibration executed by a tag team of KARI and Pukyong National University (PKNU) scientists during the Launch and Early Operation Phase (LEOP)
Summary
Korea Multi-Purpose Satellite (KOMPSAT) is the name of the satellite series that was developed to satisfy the rapidly increasing demand for high-resolution satellite images due to economic development.Sensors 2020, 20, 2564; doi:10.3390/s20092564 www.mdpi.com/journal/sensorsThe Korean government successfully launched a new satellite, named Korea Multi-Purpose Satellite-3A (KOMPSAT-3A), on 26 March 2015. The Korea Aerospace Research Institute (KARI) performed calibration and validation (Cal/Val) to enable an appropriate radiometric quality in the Launch and. This Cal/Val comprised geometry (position), spatial (resolution), and radiometric (energy) elements. During the absolute calibration coefficient process, the DN is converted into radiance. We performed this exercise using onboard calibration sources, which are considered to be well-established [2]. Post-launch calibration using onboard calibration systems is necessary, and sensors are continually monitored to identify issues and maintain data quality. The image quality is managed by absolute calibration using a vicarious approach with calibration devices installed in the sensor or by measuring the site surface reflectance [3]. Absolute calibration using a vicarious approach is conducted under the assumption that the DN of the satellite sensor is linear to the top of atmosphere (TOA) radiance
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