Environmental Engineering Reference
In-Depth Information
varies among sensors due to their specific advantages. The majority of studies have
taken advantages of the moderate spatial resolution and long-term continuity of
AVHRR data to investigate the influence of climate change and disaster on terrestrial
ecosystems. More recent and much better calibrated sensor MODIS has additional
spectral bands besides maintain the visible and near-infrared wavelengths which are
important for phenological studies. The EVI based on multiple MOIDS bands has
been successfully used to assess environmental effects on phenological patterns.
However, the coarse scale of AVHRR and MODIS measurements render ground
validations difficult. The 30-m Landsat spatial resolution offers an appropriate scale
to bridge the ground-based observations and satellite-derived phenological metrics.
Other sensors although was not primarily designed for vegetation applications, its
multiple optical bands have broadened their application to vegetation phenology,
such as MERIS and SeaWiFS.
Despite the achievement obtained from satellite observations of vegetation
seasonal cycle, efforts to validate the accuracy of satellite-derived vegetation
phenology have had a low success rate. It is a big challenge to compare the two
sources (satellite and ground) of phenological data more effectively. Partially, this
is a scale problem. The satellite-derived vegetation phenology is based on pixel
level, while the ground records usually measure phenology at individual species
level. How to integrate the species-level phenology to pixel level is key issue
in validating satellite-derived vegetation phenology. In the further, more detailed
information of ground records should be collected, such as the area of field plots,
the composition, and the structure in vegetation community. The information
together with phenophases of individual species could be integrated to reflect the
canopy phenology and compared the results with satellite-derived phenology.
There is also a strong need to investigate the relationship between growing season
length and the concentration of atmospheric carbon dioxide. Increased knowledge
about the net ecosystem exchange of carbon dioxide between forest and atmosphere
would lead to regulate seasonal and interannual fluctuations of carbon uptake.
References
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