Geography Reference
In-Depth Information
These analyses were used to determine 56 categories
of land cover including crop type. Classification of agri-
cultural land cover was augmented with information
from aerial photographs, US Department of Agriculture
(USDA) farm records, county farm statistics, and ground
truthing (Enright et al., 2002, Berger and Bolte 2004),
creating LULC maps used for model projections of trends
in natural resource abundance and distribution.
crop compliance program. They were not georeferenced
nor subjected to strict photogrammetric requirements,
yet proved very useful for the identification of crop types
in 1992. Each of 369 slides was scanned into a tif format at
300 dpi, then imported to Imagine 8.3 and georeferenced
to the Landsat TM imagery with a minimum of nine
ground control points and an acceptable RMS error of
10 m. The slides were then mosaiced into 34 separate
study areas, intentionally distributed throughout all nine
counties in the basin, and across all land cover types.
To train the photo interpretation of the FSA slides, five
study areas were interpreted for each property tract which
participates in the FSA crop compliance program. Our
interpretations were then compared to the crop reports
filed by the farmers for the study year, which yielded
a photographic interpretation error of less than 12%.
Over 1100 polygons within the FSA study areas were
interpreted for 56 different land use/land cover codes.
This data set was then divided by class and geographic
location into testing and training data sets.
The interpretation of individual plots was sometimes
aided by inspection of ancillary GIS coverages, includ-
ing the Environmental Protection Agency Pudding River
riparian assessment, U. S. Fish & Wildlife Service National
Wetlands Inventory, U. S. Geological Survey Willamette
River Basin pesticide study, Oregon Department of Fish
and Wildlife Ecological Application Laboratory natural
vegetation inventory, county zoning and taxlot cover-
ages, The Nature Conservancy Willamette River basin
wetlands inventory and valley field visit database. In addi-
tion, inspection of the Landsat TM imagery was used to
determine greenness curves throughout the 1992 grow-
ing season. Where possible, field visits were conducted
during 1998 to examine land use types that may have
remained consistent over the six-year interval since the
photographs were acquired (Oetter et al., 2001).
An external review of the land cover classification con-
cluded that aggregated land use/land cover classes derived
from the Landsat TM data 'will likely yield correlation
results comparable to more costly photo-interpreted data
for certain aggregated LCLU classes and spatial domains
(e.g., riparian zones). Forest, woody, woody
12.2.1 Groundtruthing
The ground reference data used to complete this study
came
primarily
from
aerial
photographs
and
digital
orthophotographs, especially:
1988 & 1990 Color 1:12000 U. S. government aerial
photographs of U.S. Forest Service (USFS) and Bureau
of Land Management (BLM) lands
1988 Color Infrared 1:60000 U. S. government 1988
National
High-Altitude
Program
photographs
(NHAP)
1993 Color 1:24000 Western Aerial Corporation (WAC)
aerial photographs of Willamette basin
1992 Color 35 mm UUSDA Farm Service Agency (FSA)
aerial slide photographs
1994-95 Black & White Spencer Gross digital orthopho-
tographs
of
the
Willamette
river
and
its
major
tributaries
1996 Color digital orthophotograhs of metropolitan Port-
land, Oregon area
The USFS and BLM photographs were used to ref-
erence land cover conditions in the forested uplands of
the basin. The NHAP images were used solely to iden-
tify a small number of testing polygons for the barren
(lava) and permanent snow cover classifications. The
colour digital orthophotograph set, taken from a six
mi
2
area near Tigard, Oregon was used to reference the
urban land cover classification. The Spencer Gross digi-
tal orthophotographs were used for cross-reference and
spot-checking of forest, urban, and agricultural cover
types. The 1993 WAC aerial photographs were used to
reference forest cover conditions in and along the valley
floor. Two hundred and eighty-four forest cover polygons
were interpreted for percent canopy closure of conifer
and hardwood tree species, particular to oak, orchard,
or Christmas trees where discernable. This data set was
divided into training and testing sets and used to reference
the valley floor forest classification.
The majority of the non-forest portion of the basin was
referenced using the Farm Service Agency 35 mm slides.
These data are acquired annually by the FSA for their
grass/forb,
and agriculture classes appear strongly correlated across a
broad range of lateral and longitudinal scales, suggesting
that they may be good candidates for future model con-
sideration. The built-up class variable was not as strongly
correlated, but may have utility at the largest riparian
band (150 m) or watershed levels' (Lattin and Peniston,
1999). Accuracies of spectral classification of land cover
+
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