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Land Use Change and Effects onWater Quality in the Lake Tahoe Basin:
Applications of GIS
Christian RaumannResearch and Technology Team
USGS Western Geographic Science Center, Menlo Park, California
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Project Background
3-year project funded by a Geographic ResearchApplication Prospectus Grant (now in second year)
Multi-agency collaboration:
• USGS Menlo Park: Principle investigators
• Desert Research Institute, Reno: Remote sensing specialist and geomorphologist
• USGS Water Resources, Carson City: GIS analyst and hydrologist
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Lake Tahoe Basin
• Located on the California-Nevada border in the central Sierra Nevada.
• Permanent population of 60,000 Transient population over 300,000 22 million visitors per year.
• Destination for snow sports, hiking, camping, gambling, water sports, and general tourism.
• Significant development during the past 70 years.
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Consequences of Growth
Land use change contributes to a highly disturbed ecosystem.
Increase in impervious surfaces: any material that prevents the infiltration of water into soil and thereby changing the flow dynamics, sedimentation load, and pollution profile of storm water runoff (roofs, roads, parking lots, sidewalks, etc.).
Major issue: Decrease in Lake Tahoe water quality (~1.5 feet/year) due to increased nutrient and pollutant loading.
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Pilot Study Area
Upper Truckee River andTrout Creek Watersheds
Develop methods and test hypothesis,then apply them to the entire basin.
Representative of all land use/land covertypes in the Tahoe Basin.
Contains the most developed area of theBasin: City of South Lake Tahoe.
Many agencies (TRPA, USFS), privatecompanies (Sierra Pacific), andcommunity groups (UTWFG) involvedin related projects.
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Currently Available Digital Data
Must have GIS data before performing analysis.
Much GIS data is available for the Tahoe Basin: elevation, orthophotography, soils, fire, wildlife, forestry…
…even land cover!
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2000 National Land Cover Data
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Data Collection
• High-resolution historical land cover and impervious cover (IC) data is unavailable, so a comprehensive data collection effort is necessary to produce data for analysis in a GIS.
• Case with many GIS projects: a need for specific data = time + $$$
Mapping historical land use change and increase in IC:• Derive land use data with IC estimates from historical
orthophotography using traditional interpretation techniques (labor intensive!).
• For present day coverage, derive land use and IC from IKONOS multispectral satellite imagery using remote sensing software employing semi-automated routines (T.Minor).
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What is Remote Sensing?
"...the science of acquiring, processing, and interpreting images, and related data, obtained from aircraft and satellites that record the interaction between matter and electromagnetic radiation." -- F.Sabins, 1997
OR MORE GENERALLY:
Collecting information about an objectwithout being in physical contact with it.
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Reflected/scattered/emitted energy can be measured using various kinds of remote sensing instruments.
Thankfully, many earth materials have very unique spectral signatures, almost like fingerprints.
Satellite Imagery
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Remote Sensing of Impervious Surfaces
IKONOS high-resolution multispectral imagery
• Collected by satellite that “scans” the earth rather
than using a camera to photograph it.
• 4 spectral bands:
visible RED, GREEN, and BLUE
plus NEAR INFRARED
• 4-meter ground pixel resolution.
• Current scene within pilot study area
is approximately 25 km2. Acquiring
entire basin coverage this summer.
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Satellite Imagery vs. Aerial Photography
2000 IKONOS ImageryFalse natural color composite,
bands 3-2-1 (RGB)
1987 Digital OrthophotoTrue natural color
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Cover Variety in the Tahoe Basin
Forest canopy cover and shadow is a major concern.
Commercial area around the “Y” intersectionLow canopy cover
Black Bart neighborhoodHigh-density canopy cover
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Step 1
Mask out areas in the IKONOS
scene known not to have any
impervious cover using other
data sources and visual
inspection.
Infrared false color composite,
bands 4-2-1.
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Step 2
Impervious cover layer generated using image classification processing techniques (PCA).
Impervious cover in red,natural cover in black.
However, forest canopy cover isstill an issue…
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Step 3
Looking through the trees:
Use logical operations to fill
gaps where forest canopy likely
covers IC.
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Road detected!
Canopy covering road Road detected
undercanopy shadow
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Final Impervious Cover Layer
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Accuracy Assessment
ImperviousCover
NaturalCover
RowTotal
ImperviousCover (96) 92 4 96
Natural Cover (74) 8 66 74
ColumnTotal 100 70 170
Overall Accuracy = 158/170 = 92.94%
In the field, 170 “random” points were surveyed using GPS.
Labeled points as “impervious cover” or “natural cover”, then comparedto corresponding points in IKONOS-derived IC layer.
IC Layer Points
Sur
veye
d P
oint
s
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Final Process for Deriving Impervious Cover Layer
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What’s Next?
Contact:[email protected]
(650) 329-5648
1. Derive IC for the entire pilot study area.
2. Compile historical land cover data using aerial photography.
3. Quantify change and analyze in a GIS.