Journal
REMOTE SENSING OF ENVIRONMENT
Volume 86, Issue 2, Pages 232-242Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/S0034-4257(03)00103-2
Keywords
onset of greenness; phenology; MODIS; mixed forest; climate; cross-validation
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A regional phenology model for detecting onset of vegetation greenness was developed using year 2001MODIS land products in temperate mixed forests in Korea. The model incorporates a digital elevation model (DEM), moderate resolution imaging spectroradiometer (MODIS) landcover and leaf area index (LAI) products, and climate data from weather-monitoring stations. MODIS-based onset of greenness varied spatially and showed significant correlation with air temperature (r = -0.70, p < 0.001). Our modeling methodology is to relate thermal summation calculated using the MODIS-based timing of onset with 30-year mean air temperature. Onset of greenness is expected to occur at values above the critical thermal summation threshold and is predicted to vary spatially. An algorithm for downscaling 8-day composite MODIS LAI product to a daily unit was introduced, and its predictability was validated using ground-measured onset of greenness. Two unknown parameters and the best regression were determined by iterative cross-validation. Minimal cross-validation errors between the predicted and MODIS-based timings of onset were found at a mean absolute error (MAE = 3.0 days) and bias (+ 1.6 days). The predicted onsets show good agreement with ground-measured onset of greenness (MAE = 2.5 days and bias = +2.5 days). This study demonstrates the utility of MODIS land products as tools for detecting spatial variability in phenology across climate gradients. (C) 2003 Elsevier Science Inc. All rights reserved.
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