This study aims for producing high-quality true-color red-green-blue (RGB) imagery that is useful for interpreting various environmental phenomena, particularly for GK2A. Here we deal with an issue that general atmospheric correction methods for RGB imagery might be breakdown at high solar/viewing zenith angle of GK2A due to erroneous atmospheric path lengths. Additionally, there is another issue about the green band of GK2A of which centroid wavelength (510 nm) is different from that of natural green band (555 nm), resulting in the unrealistic RGB imagery. To overcome those weakness of the RGB imagery for GK2A, we apply the second simulation of the satellite signal in the solar spectrum radiative transfer model look-up table with improved information considering altitude of the reflective surface to reduce the exaggerated atmospheric correction, and a blending technique that mixed the true-color imagery before and after atmospheric correction which produced a naturally expressed true-color image. Consequently, the root mean square error decreased by 0.1–0.5 in accordance with the solar and view zenith angles. The green band signal was modified by combining it with a veggie band to form hybrid green which adjust centroid wavelength of approximately 550 nm. The original composite of true-color RGB imagery is dark; therefore, to brighten the imagery, histogram equalization is conducted to flatten the color distribution. High-temporal-resolution true-color imagery from the GK2A AMI have significant potential to provide scientists and forecasters as a tools to visualize the changing Earth and also expected to intuitively understand the atmospheric phenomenon to the general public.
<p>In ocean color remote sensing, the importance of developing and validating atmospheric correction and ocean bio-optical algorithms has been emphasized. However, if uncertainty remains in the fundamental procedure of converting the sensor signal to the top of the atmosphere (TOA) radiance, the errors will affects the overall reliability of the ocean satellite products.</p> <p>The purpose of this study is to monitor the gain parameters of two on-board GOCI-II calibration using Solar Diffuser (SD) and Diffuser Aging Monitoring Device (DAMD) and to improve the accuracy of ocean color sensors for radiometric calibration (RC) quality at the TOA level. Our results show that the SD gains parameter tends to decrease with seasonal periodicity in all bands, confirming sensor degradation and solar azimuth angle over time. In addition to the current RC model using only SD gain in the relationship between the sensor-observed digital counts and TOA radiance, we develop an azimuth angle correction model and a sensor degradation correction model. Verification will be performed by calculating the TOA radiation applied with an improved RC model around the Korean Peninsula. It will contribute to providing more stable GOCI-II ocean color products for short-term and long-term analysis.</p>
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