Impervious Surface Mapping using Multi-Resolution Imagery
Introduction
In the Chesapeake Bay Watershed population has been increasing rapidly since the end of World
War II. This growing population has put an increased strain on the
regions natural ecosystems through the expansion of urban
centers. The environmental damage from urbanization and the related
effects from non-point source pollution and increased water runoff have
been shown to have adverse effects on the Bay. The need for accurate
estimates of urban sprawl and man-made impervious surfaces at the local,
city, and regional levels are necessary to assess the environmental impacts
of the growing urban population on watershed quality. This need to
monitor urban expansion at various scales has led the Mid-Atlantic RESAC
to investigate the usefulness of multi-spectral and hyper-spectral imagery
in discerning man-made impervious surfaces. Take a tour of Paint Branch creek, a tributary of the Anacostia river, to
see the effect of impervious surfaces on stream channel erosion.
Methods
Previously urban
mapping efforts have included the use of historical maps, United States
Geological Survey (USGS)
topographic maps, aerial photography, and satellite imagery from the Landsat
Multi-Spectral Scanner (MSS) and Thematic Mapper (TM). Manual interpretation
of aerial photography and image classification techniques are common methodologies
used to discriminate between vegetated surfaces and the built environment.
While some of these methods were sucessful in delineating between urban
and non-urban land surfaces many of the techniques are labor intensive
and non-repeatable. The Mid-Atlantic RESAC efforts are focused on
the use of Geographic Information Systems (GIS), high-resolution multi-spectral
and hyper-spectral imagery from aircraft, as well as satellite-based imagery
from the Landsat series of satellites. We hope to develop methodologies
that can be automated and used in a variety of ecologically diverse regions.
High Resolution Imagery
Another aspect of our impervious surface
research efforts focuses on the use of high resolution aerial imagery collected
from two different sensors. The Airborne Data Aquisition and Registration
(ADAR) system flown by Positive
Systems Inc. is a four band TM-like sensor that is capable of collecting
submeter multispectral imagery and the Airborne Imaging Spectroradiometer
for Applications (AISA) system flown
by 3DI is a submeter tunable hyperspectral
instrument. Each system captures views of the land surface that complement
the Landsat TM imagery and extend the possibilities of impervious surface
mapping in spatially complex environments. For more information
on either the ADAR or AISA imagery aquired for the Mid-Atlantic RESAC see
the above links or visit the respective company's website.
Summary
The ultimate goal of our impervious surface
research effort is to evaluate the numerous methodologies used to map urbanization
and suburban sprawl. We hope to provide information about the application
of certain methodologies to specific study areas and to highlight the limitations
of certain types of data to the user community so that they can best utilize
avilable resources to fulfill their needs. The impacts of urbanization
on the environment can best be evaluated by identifying areas that are
in the most need of attention and to preserve those that are more pristine.
The Mid-Atlantic RESAC is collaborating with partners, including the
Nautilus RESAC to improve
public and community government awareness of the links between impervious
surfaces and water quality.
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