GEO DATA

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The Map Data of BRDF-Adjusted Surface Reflectance from GOCI Geostationary Satellite Imagery over Korean Peninsula: Jong-Min Yeom; GEO DATA. 2021;3(4):66-70. Published online December 31, 2021; DOI: https://doi.org/10.22761/DJ2021.3.4.006

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Abstract PDF: In this study, the spatial maps of the BRDF (Bidirectional Reflectance Distribution Function) adjusted surface reflectance (SR) were estimated by using the Geostationary Ocean Color Imager (GOCI) mounted on the Communication, Ocean and Meteorological Satellite (COMS) over the Korean Peninsula. The BRDF-Adjusted surface Reflectance (BAR) is a more effective indicator that not only quantitatively identifies the growth characteristics of vegetation, but also corrects the bidirectional error in the time series observation characteristics, because the surface reflectance is changed according to the solar altitude during the daytime period. Therefore, this BAR products have high data utilization in various fields such as agriculture, environment, land surface information, and atmosphere. In this study, BRDF-adjusted surface reflectance maps were calculated for the Korean peninsula from April 2011 to December 2012 with hourly temporal resolution from 9 a.m. to 4 p.m. For the BAR surface reflectance, the spatial observation range is from latitude 34° N to 39 °N and longitude 125 ° E to 130 ° E, and the spatial resolution is 500 m. The semi-empirical BRDF model was used to calculate the BRDF-adjusted surface reflectance, and the radiometric characteristics of surface reflectance were decomposed into isotropic scattering, geometric scattering, and volumetric scattering. For this model simulation, at least 7 clear pixels are required to fit BRDF model. In this study, unlike the Nadir BRDF-Adjusted surface Reflectance (NBAR) calculation method which was calculated from the existing polar orbiting satellites, semi-empirical BRDF modeling was performed with a value fixed to the satellite viewing angle for each pixel since geostationary satellites of GOCI are difficult to observe in the nadir direction unlike polar satellites. It is more effective to perform BRDF correction by fixing them at the viewing angle in the case of GOCI geostationary satellite.

Hyperspectral Irradiance Data for a Comparison and an Analysis of Optical Satellite Spectral Observation: Based on Seogwipo Forest Flux Tower: Hongtak Lee, JongMin Yeom; GEO DATA. 2019;1(1):7-12. Published online December 30, 2019; DOI: https://doi.org/10.22761/DJ2019.01.01.002

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Abstract PDF: Comparison with ground-truth data is essential for developing and applying remote sensing algorithm towards the Earth surface. Unfortunately, major sources of domestic ground-truth data are depending on fieldcampaign with limited period because of insufficient all-time observation facilities within a domestic region. Korea Aerospace Research Institute, KARI, is planning to construct and operate surface observation tower to provide remote sensing infrastructure. This study was conducted as a pilot program of the observation tower construction and targeted to observe surface reflectance. The observation was made for about 21 months from May 2017. Two hyper-spectroradiometers were installed on top of a forest flux tower at Mt. Halla to measure hyperspectral up/down-welling irradiance, and surface reflectance was derived simply from their ratio. The derived surface reflectance was compared to surface reflectance values estimated from LANDSAT8 VNIR images, and the two surface reflectances coincided while showing effectiveness of the derived surface reflectance. The data acquired from this study would be able to provide background information for the expected surface observation tower, as well as actual ground-truth data for remote sensing application upon Mt. Halla area.

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