Impervious
Surface Mapping
Satellite-based
Approach to Impervious Surface Mapping
Defining the relationship
between aerial photograph measurements of impervious
surface area (ISA) and spectral-radiometric responses
of Landsat satellite data was key
to determining whether satellite imagery would be a good candidate
for creating maps of ISA for the TCMA.
To do so, analysts performed
two tasks. First, they delineated areas on aerial photographs
that represented varying degrees of ISA.
Sample area delineated over aerial photograph
used to calculate varying degrees of ISA for model calibration
and evaluation. The
degree of ISA refers to the percent imperviousness in a given
area. The higher the percentage, the greater the environmental
impact. A term such as “degraded,” “impacted” or “protected” is
often assigned to percentages to describe the impact of ISA
on one or more natural resources.
.
Second, Landsat image data
were converted to “greenness” - a
variable that is strongly related to the amount
of green
vegetation (and therefore, is inversely related
to the amount
of ISA).
To confirm that Landsat can
be used to accurately classify the percent ISA, the Landsat
estimates were compared to measurements made from aerial
photographs.
Comparison
of aerial photograph measurements and Landsat estimates
of percent impervious surface area.
The results indicate that
there is a strong relationship between aerial photograph
measurements and satellite-derived estimates. With
these results, analysts successfully created maps of
ISA for
TCMA in Minnesota,
and also larger scale maps of cities within the TCMA
that are experiencing a significant amount of growth.
Each map details land cover and the percent of ISA for
urban/developed land.  
Maps of impervious
surface area in the Twin Cities Metropolitan Area (left)
and in the City of
Woodbury, Minnesota (above). Each map depicts land cover
and the percent of impervious surface area. The percentage
of impervious surface area is depicted as a continuous
variable, ranging
from 0 to 100% imperviousness based on greenness. Areas
shaded in black have the highest percentage of imperviousness
(low greenness), while areas shaded in white have the lowest
percentage of imperviousness (high greenness). These maps
were created using Landsat TM imagery from the year 2000,
calibrated from aerial photograph measurements.
The
Value of an Integrated Approach >> |
