October to early November right after the corn is harvested. In
contrast, for the single-cropping system (mainly peanuts), the
growing period normally lasts from early May to late October, and
the land would be left fallow after peanut harvest until next May.
Forest in our study area starts to grow from late March and leaves
start to fall in late November. Given their special spectral
signatures, barren lands and water bodies could be easily
delineated from the Landsat and HJ1A images during the period
from early July to late September when trees and crops are
growing.
To better capture the variations in spectral signatures of
different land-use/land-cover categories in our study area, multitemporal
Landsat and HJ1A images were obtained. One image
acquired during late October to early November was used to
distinguish the crop lands from other land-use/land-cover categories.
The second image acquired in early March to early May in the
next year was used to identify the single-cropping lands (which are
left fallow during this period) from double-cropping lands with
growing crops at this time. Another image acquired in late May to
late September was also used to better identify the two types of
cropping system. In total, 24 images were acquired for the periods
1999–2002 and 2010–2012 in this study. The Landsat images were
used to extract land-use/land-cover categories for 2000 and HJ1A
images for 2010.