Abstract
The purpose of this study was to optimize a composite method for the Geostationary Ocean Color Imager (GOCI), which is the first geostationary ocean color sensor in the world. Before interpreting the sensitivity of each composite with ground measurements, we evaluated the accuracy of bidirectional reflectance distribution function (BRDF) performance by comparing modeled surface reflectance from BRDF simulation with GOCI-measured surface reflectance according to composite period. The root mean square error values for modeled and measured surface reflectance showed reasonable accuracy for all of composite days since each BRDF composite period includes at least seven cloud-free angular sampling for all BRDF performances. Also, GOCI-BRDF-adjusted NDVIs with four different composite periods were compared with field-observation NDVI and we interpreted the sensitivity of temporal crop dynamics of GOCI-BRDF-adjusted NDVIs. The results showed that vegetation index seasonal profiles appeared similar to vegetation growth curves in both field observations from crop scans and GOCI normalized difference vegetation index (NDVI) data. Finally, we showed that a 12-day composite period was optimal in terms of BRDF simulation accuracy, surface coverage, and real-time sensitivity.
Highlights
Terrestrial products such as surface albedo and vegetation index play an important role in soil moisture and energy balance and are critical for understanding the boundary layer energy mechanism between the atmosphere and land surface [1, 2]
Surface vegetation conditions and dynamics in terrestrial products [3] have mostly been constructed from optical satellites such as the Advanced Very High Resolution Radiometer (AVHRR) [4], ModerateResolution Imaging Spectroradiometer (MODIS) [4,5,6], SPOT/VEGETATION [7], METEOSAT Second Generation (MSG) [8], Geostationary Operational Environmental Satellite (GOES) [9], and Medium Resolution Imaging Spectrometer (MERIS) [10]
We ran our simulations using various composite periods and compared the normalized difference vegetation index (NDVI) profile derived from Geostationary Ocean Color Imager (GOCI) using four composite periods with field-observation NDVI
Summary
Terrestrial products such as surface albedo and vegetation index play an important role in soil moisture and energy balance and are critical for understanding the boundary layer energy mechanism between the atmosphere and land surface [1, 2]. A typical MODIS among polar-orbiting satellites performs BRDF modeling using a 16-day composite period to provide a suitable tradeoff between the availability of sufficient angular sampling observations and the temporal stability of the surface [16, 17]. The most commonly used 16-day composite for BRDF modeling in geostationary satellites [20, 25] shows reduced sensitivity to crop dynamics over selected rice paddy areas relative to real-time conditions. Yeom and Kim [21], when comparing in situ Normalized Distribution Vegetation Index (NDVI) with GOCI-BRDF-adjusted NDVI, showed that the BRDF-adjusted NDVI profile was shifted relative to the in situ profile These adjusted vegetation profiles are less sensitive to real-time change due to the composite period used for the BRDF model [21]. It is critical to optimize the BRDF composite method for sensitivity to vegetation profiles, with a choice-adaptive composite period
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