Abstract
Abstract. The spatiotemporal influences of climatic factors and atmospheric aerosol on vegetative phenological cycles of the Korean Peninsula was analysed based on four major forest types. High temporal-resolution satellite data can overcome limitations of ground-based phenological studies with reasonable spatial resolution. Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation index (VI) (MOD13Q1 and MYD13Q1) and aerosol (MOD04_D3) data were downloaded from the USGS Earth Observation and Science (EROS) Data Center and NASA Goddard Space Flight Center. Harmonic analysis was used to describe and compare the periodic phenomena of the vegetative phenology and atmospheric aerosol optical thickness (AOT). The method transforms complex timeseries to a sum of various sinusoidal functions, or harmonics. Each harmonic curve, or term (or Fourier series), from time-series data us defined by a unique amplitude and a phase, indicating the half of the height and the peak time of a curve. Therefore, the mean, phase, and amplitude of harmonic terms of the data provided the temporal relationships between AOT and VI time series. The phenological characteristics of evergreen forest, deciduous forest, and grassland were similar to each other, but the inter-annual VI amplitude of mixed forest was differentiated from the other forest types. Overall, forests with high VI amplitude reached their maximum greenness earlier, and the phase of VI, or the peak time of greenness, was significantly influenced by air temperature. AOT time-series showed strong seasonal and inter-annual variations. Generally, aerosol concentrations were peaked during late spring and early summer. However, inter-annual AOT variations did not have significant relationships with those of VI. Weak relationships between inter-annual AOT and VI variations indicate that the impacts of aerosols on vegetation growth may be limited for the temporal scale investigated in the region.
Highlights
Surface greenness dynamics are associated with the patterns of primary productivity and atmospheric carbon exchange rates on a broad scale (Field et al 1995; Running et al 2004; Potter et al 2007)
The objective of this study is to determine the spatiotemporal influences of climatic factors and atmospheric aerosol on phenological cycles of the Korea Peninsular on a regional scale
The Moderate Resolution Imaging Spectroradiometer (MODIS), a hyperspectral earthobserving satellite sensor operated by the National Aeronautics and Space Administration (NASA), provides daily satellite coverage, and its vegetation indices (VI) data products are designed to provide consistent vegetation conditions with spatial resolution ranging from 250 m to 1 km (Justice et al, 1998)
Summary
Surface greenness dynamics are associated with the patterns of primary productivity and atmospheric carbon exchange rates on a broad scale (Field et al 1995; Running et al 2004; Potter et al 2007). Vegetation responses to climate change appear strong in Northeast Asia, where diverse forest types and tree species in the region are considered as important carbon sinks. The objective of this study is to determine the spatiotemporal influences of climatic factors and atmospheric aerosol on phenological cycles of the Korea Peninsular on a regional scale. High temporal-resolution satellite data can overcome limitations of ground-based phenological studies with reasonable spatial resolution. One set of biophysical variables formulated from remote sensing data is vegetation indices (VI) These indices are defined as dimensionless, radiometric measures that have strong correlations with biophysical parameters of green vegetation, including leaf area index (LAI). This study was conducted to determine the spatiotemporal influences of climatic factors and atmospheric aerosols on vegetation phonological cycles in the Korea Peninsula on a regional scale using high-temporal satellite data
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