要旨
The goal of this study is the post-launch
validation of MODIS IGBP Land Cover Product for the
Mediterranean landscape. Southern Portugal, mostly a
Mediterranean ecosystem due to climate and geomorphology, is
characterized by large homogeneous patches. For this reason, it
was chosen as the most promising region where global products
could be used. The most recent 2002 MODIS Land Cover data set
was used. The selection of the test sites was conducted through a
method supported by Landsat5-TM images, to derive
homogeneous patches. Moreover, field test sites accommodated
the guidelines from the System for Terrestrial Ecosystem
Parameterization (STEP) document. Confusion matrix results in
an overall accuracy of about 36% and a kappa statistic of 0.09.
Croplands, which constitute the majority of the study area, is the
most well classified feature, with an accuracy of 77%, although
the MODIS classifies it largely by excess. The evergreen
broadleaf forest is the most confused theme, with several land
cover classes – evergreen needleaf forest, mixed forest, woody
savannas, savannas and closed shrublands - classified as such.
However, there isn’t any classified evergreen broadleaf forest
pixel. Therefore, it seems that there is a consistent
misclassification of broadleaf evergreen forest. We strongly
believe that the reason for the misclassification of the
Mediterranean landscape relies in its weak representation within
the training sites framework. MODIS land cover maps, produced
by processing the 32-day database using decision tree and
artificial neural network classification algorithms, are greatly
dependent on the core sites data. Therefore, the classification of
Mediterranean likely landscapes could never occur properly.
Adding Mediterranean ecosystem like training sites could greatly
improve the results. This study shows how careful the adoption of
global products to regional studies should be. The validation of
the MODIS IGBP Land Cover Product for Mediterranean
landscape revealed that more regional work should be taken into
account during the production of global products in order to reflect this biome.
