Impact of spatial scale for phenological indices derived from remotely
sensed data
Abstract
Land surface phenology (LSP) characterizes the vegetated land surface
and is practical to understand terrestrial environmentals at a global
scale. Regularly observed remotely sensed data such as Landsat, MODIS,
and AVHRR contributes to analyze LSP spatially. However, at least two
main challenges should be addressed such that (i) the spatial resolution
which attributes to the data source may significantly impact to LSP
estimation, and (ii) the estimated LSP may not represent the vegetated
land surface well due to the mixed land cover. Previous studies have
shown that the estimation of LSP from different data is not consistent
due to the spatial scale of data but yet fully linked with the mixed
land cover problem. Thus, in this study, we attempt to analyze the
impact of spatial scale issue to the estimated LSP in homogenous land
cover areas. We use freely available remotely sensed data with different
spatial resolution such as Landsat (30m), MODIS (250m, 500m, 1km), and
GIMMS3g (8km) and estimate phenological indices for each. As land cover
description differs among data products, land cover classes are
aggregated into 12 classes globally from major global land cover producs
(GLCC, GLC2000, and globcover), then spatially homogenuous land cover
are only picked up. Phenological indices such as the magnitude and the
peak of DOY are calculated by harmonic analysis to compare results among
different spatial scales. The variability of phenological indices is
explored according to the different spatial scale under the condition of
homogenuous land cover. It is expected to model such variability to
overcome the spatial scale impact and such characteristics depending on
the spatial scale should be taken into account when considering LSP from
satellite.