Environmental Engineering Reference
In-Depth Information
17.1
Introduction
Phenology, first introduced in 1853 by the Belgian botanist Charles Morren, is derived
from the Greek words phainos, meaning “to appear, to come into view,” and logos,
meaning “to study” (Haggerty and Mazer
2008
). The study of phenology ranges from
the leafing, maturating, and defoliating times of plants to the molting, mating, and
migration times of animals. Since this chapter focuses on the plant phenological
events, the animal phenological events are not within the scope. The plant phenologi-
cal events can be observed and measured at multiple levels, varying from individual
and population to community and biome. Information from each of these levels
provides fundamental knowledge about ecological interactions and process in nature.
Conventional phenological studies are carried out by biologists and ecologists through
botanical inventories. Such conventional approaches, which often include manual
sampling, can track fine details of the phenology process; however, they are time-
consuming and costly. A landscape-based approach using remote sensing techniques
provides an efficient way to observe phenology at large scales, which can complement
the site intensive information provided by conventional approaches. Plant phenology
observed from satellites at landscape scales is called vegetation phenology, also
referred as land surface phenology (Reed et al.
2009
).
The vegetation phenology at landscape scales which is comparable with climate
model-derived data (Botta et al.
2000
) is an important signal of climate change and
global environment variation. Global climate warming may advance the biological
spring and delay the arrival of biological winter. The earlier presence of green land
cover and the delay in leaf fall of deciduous canopies in turn alter the seasonal
climate through the effects of biogeochemical process and physical properties
(Pe˜uelas et al.
2009
). Accurate assessment of phenological events, therefore,
becomes increasingly vital for investigating vegetation-climate interactions.
Satellite-derived information has been demonstrated to be an important source for
detecting vegetation phenology. The advantages in high temporal frequency and large
spatial scales make satellite data increasingly prevalent in determining leaf onset and
offset dates (Botta et al.
2000
;Kangetal.
2003
; Zhang et al.
2003
), developing
phenological models (DeBeurs and Henebry
2005
; Kim andWang
2005
;St¨ckli et al.
2008
; White et al.
1997
; Zhang et al.
2004
;Zhouetal.
2003
), and quantifying effects
of phenological changes on local, regional, and global scale (Myneni et al.
1997
;
Peckham et al.
2008
;Schwartzetal.
2006
; White et al.
1999
,
2002
). This chapter
outlines the methods used to develop phenological metrics from satellite
measurements and the applications of satellite-derived vegetation phenology.
17.2 Method
Vegetation phenology derived from satellite measurements is distinct from the
individual plants or species phenology. The large view of satellite sensors captures
the canopy reflectance over the pixel size which ranges from high resolution as 30 by
30 m to coarse resolution as 8 by 8 km. The pixel-sized canopy reflectance is an
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