Finally, we collected field data and aerial photographs to assist
land use/cover classification and thematic accuracy assessment.We
conducted two extensive field surveys across the entire study area
in December 2010 and May 2011. The field itineraries were
designed according to our knowledge about the study area and a
preliminary examination of the satellite images. During the field
trips, we recorded geographic positions and land use/cover types at
each predefined sample location with a Trimble GPS receiver. In
addition, two sets of color infrared aerial photographs were
collected and used as the reference data: (1) USGS aerial photographs
at a scale of 1:40,000 derived from National Aerial
Photography Program (NAPP) taken in January 2000; and (2) USDA
aerial photographs with 1 m spatial resolution derived from National
Agriculture Imagery Program (NAIP) acquired in August and
September of 2010. These datasets were mainly used to assist
thematic accuracy assessment.