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Accuracy Assessment Methods and
Results for Two Satellite Imagery
Derived Landcover and Landuse
Datasets
Raymond Crew - GIS Researcher and MS Candidate
Rick L. Day - Associate Professor Soil Science
Hanxing Pu - Penn State University
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Image based on photo by Peggy Greb, USDA ARS (Richard Lowrance in foreground)
Introduction
• Part of a study to inventory the riparian land
cover conditions for the Chesapeake Bay
watershed
• Highlighting accuracy assessment of a GIS
based riparian land cover inventory
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The Chesapeake
Bay Watershed
• Largest estuary in the US
• Watershed covers 178,000
km2 and contains 464,000
km of stream banks and
shorelines
• New York, Pennsylvania,
Maryland, Delaware,
Washington DC, West
Virginia and Virginia
• 15 million residents growing
to 18 million by 2020
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Chesapeake Bay Program Office
• Collaborative group coordinating efforts to
protect the ecological health of the
Chesapeake Bay. Formed in 1983.
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Chesapeake Bay Commission
U.S. Environmental Protection Agency
Maryland
Virginia
Pennsylvania
District of Columbia
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Chesapeake Executive Council
Directive on Riparian Buffers
• The Executive Council:
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Governors of Maryland, Pennsylvania, and Virginia
Mayor of DC
Administrator of the EPA
Chair of the Chesapeake Bay Commission
• Issued a directive in 1994 asking the Chesapeake
Bay Program Office to increase the focus on
riparian stewardship, especially riparian forest
buffers
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What are riparian buffers
• Riparian buffers are area of vegetated land
adjacent to streams, rivers, marshes or shorelines
forming a transition between the land and water
environments.
(Vellidis and Lowrance, 2004)
(Lowrance, Altier et. Al, 1995)
• Both forests and
wetlands are effective
buffers
(EPA, 2005)
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photo David J. Welsch USDA
Why buffers are important
• Reducing and Filtering Runoff
• settles out sediments, nutrients and pesticides
• increase infiltration rates
• root systems stabilizing stream-banks and reduce erosion
• Nutrient Uptake
• increases absorption of fertilizers and other pollutants by storing
bio-mass
• de-nitrification via soil bacteria
• Canopy and Shade
• moderate stream temperatures
• leaf canopy filtering dust from wind erosion
• Habitat and Habitat Corridors
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Study Objectives
1. Develop an improved automated inventory method
2. Conduct an inventory for two time periods
3. Validate method to determine reliability
4. Study differences in buffer conditions by stream
order
5. Study environmental pressures associated with landuse surrounding the riparian zones
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Automated Inventory
• Determine and collect the GIS datasets required for
inventory acquire datasets
• land-cover
• streams and water body polygons
• watershed divides
• Calculate the inventory using an automated method
• 100 and 300 foot buffers
• stream miles – single sided and dual sided buffers
• riparian miles
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Streams and Water Body Data
• Hybrid dataset
produced by the
USGS and
Chesapeake Bay
Program Office
• 1:24K Resolution
National
Hydrography
Dataset (Higher
Resolution NHD)
• 1:24K Reach files
produced by the
CBPO
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Land-cover Data
• Original plan:
• Have the Mid-Atlantic Regional Earth Science
Applications Center (RESAC) produce a year 1990
and 2000 dataset using the same methods and
type of imagery
• Unfortunately only a year 2000 dataset was
produced
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Land-cover Near Dulles Airport
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2000 Land-cover Data
• Based on three year 2000 satellite images
• 30 meter resolution
• 21 land-cover and use classes - 4 pertinent to this
study
• forest
• urban forest
• wetlands
• water
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Solution
• Use the best available land-cover data available for
the year 2000 and the year 1992
• 2000
• Use the RESAC landcover/landuse data
• 1992
• Use the Multi-Resolution Land Characteristics
(MRLC) landcover data. Commonly called the
NLCD
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1992 MRLC Land-cover Data
• 18 land-cover classes in the Chesapeake Bay
- 3 pertinent to this study
• forest
• wetland
• water
• based on primarily early 1990’s satellite images,
however, some imagery as old as 1985 was used
• 30 meter resolution
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Problems Using These Two Datasets
• Different Methods uses to derive land-cover
categories
• example: large differences between classification of open water
vs. wetlands
• No urban forest category in the NLCD as in the
RESAC
• unsure if urban forest will be classified as forest or as
something else
• NLCD based on a wider temporal range of images
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The Sampling Process
1.
Splits streams into 300’ (91.44 m) segments
2. Orients a transect perpendicular to each stream
segment at the center of the segment
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Algorithm Outputs
3.
Establishes sampling locations every 50 feet (15.24 m) along
the transect
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Collects the land-cover information
from the satellite imagery at each sample location
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Calculates buffer statistics for each watershed
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Forest
Forest or urban forest
Forest, urban forest, or wetlands
Forest, urban forest, wetlands or water
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Riparian Buffer Algorithm
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Stream Miles
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One or more sides buffered 100 feet or more
One or more sides buffered 300 feet or more
Both sides buffered 100 feet of more
Both sides buffered 300 feet or more
Riparian Miles
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Buffers of 100 feet or more
Buffers of 300 feet or more
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Statistics
by
State
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Statistics by Watershed
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Year 2000
Inventory
Percent of streams with
at least 100 feet of a
forested buffer
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Validation Study
• Need to validate automated inventory method versus a
traditional method to generate buffer inventories
• Must also test the reliability of land cover
classifications in riparian zones
• Must validate and changes shown between the 1992
and 2000 inventories
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Validation Study
• Generate a forest land cover inventory using air photo
interpretation
• Compare each air photo inventory to the same year
automated inventory
• Compare the air photo inventories to each other
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Validation Study
• Randomly selected 50
locations throughout
Chesapeake Bay Watershed
• Stratified to include all States
and physiographic regions
• Used Hawth’s Analysis Tools
2.1 for ArcGIS
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Acquire Air Photos
• Purchase overlapping stereo sets of two or three
photos from the National Aerial Photography Program
(NAPP)
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9” by 9” prints grayscale prints
1:40,000 scale
Flown every 5 to 7 years
Only $5 per print
• Two or three photos cover
¼ of the extent a standard
USGS topographic map
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Air Photos
• Purchase two sets of
photos, one centered near
2000 and the other near 1992
• Had to remove NY, no
photos available later than
1998
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Scanning Stereoscope
• Used a scanning & magnifying stereoscope
• All photos work by one
individual, Hanxing Pu
• His work compared for
quality to another tech,
Chihiro Mather
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Photo Work
• Coded every visible stream bank and waterbody
outline into four classes
Red: Forest buffer exceeding 300’
Blue: Forest buffer between 100’
and 300’
Black: Forest buffer less than 100’
Yellow: No buffer visible
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Digitizing
• Next digitize all the buffers see via air photo work
• Can only be accomplished for those steams seen on
the air photos and those in the digital data
• Any stream missing from one of the two sets is not
compared
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Digitizing
• Removed the
automated method
results from the
datasets to prevent
any bias
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Results
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Thanks to:
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Dr. Anne Hairston-Strang – Maryland DNR Forest Service
J. Michael Foreman - Virginia Department of Forestry
Gene Odato - PA Bureau of Forestry
Sally Claggett - Chesapeake Bay Program Coordinator
Peter Claggett - Chesapeake Bay Program Office - USGS Land
Data Manager
• Dr. David Mortensen – Associate Professor of Weed Ecology
• Dr. Doug Miller – Assistant Professor of Geography
• Dr. Gary Petersen - Distinguished Prof of Soil Science
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