Environmental Engineering Reference
In-Depth Information
30 km north of the City of Milwaukee, WI, Grafton occupies a
geographical area of 65.4 km
2
, with more than 14 000 residents,
and approximate 5700 housing units according to Census 2000.
Land uses in this region include urban (e.g., commercial, res-
idential, transportation) and rural (e.g., agricultural, forestry).
Grafton has experienced a rapid growth in the last decades. In
fact, the population of Grafton has increased approximate 58%
from 1970 to 2000, and the number of housing units reached
about 5800 in 2000, doubled the total housing unit number
in 1970. For the study area, an IKONOS image (Fig. 17.1b)
acquired on 3 September 2002 was provided by the Ameri-
can Geographical Society Library (AGSL) in the University of
Wisconsin-Milwaukee. This IKONOS image was preprocessed
and the reflectance for each pixel was calculated from its dig-
ital number (DN) values under the guide of Space Imaging
technical documents (Peterson, 2001). In order to evaluate the
results of automatic impervious surface estimation, a color dig-
ital aerial photograph (Fig. 17.1c) for Grafton was also obtained
from the AGSL. This photograph was acquired in November
2002, with a spatial resolution about 2 ft (0.61 m). Both the
IKONOS image and aerial photograph were orthorectified and
re-projected to the UTM projection (zone 16, datum WGS84).
Moreover, a further georeference was implemented to reduce
geometry misregistration between the IKONOS image and the
aerial photograph.
17.3.3
Methodology
With the preprocessed IKONOS imagery, impervious surface
information was derived for the study area. In this chapter,
two popularly applied impervious surface estimation methods,
SMA and RT, have been examined. These two methods have
been successfully applied to medium-resolution remote sensing
imagery (e.g., Landsat TMand ETM
+
),butitisstillquestionable
whether they are suitable with the IKONOS imagery, which has a
much higher spatial resolution and less number of spectral bands
N
Village
Town
Grafton
Milwaukee
90
45
0
90
Kilometers
(a)
(b)
0 0.5 1
2
3
4
Kilometers
(c)
FIGURE 17.1
Grafton Village and Town, Ozaukee, Wisconsin (a) indicates the geographic location of Grafton in Wisconsin;
(b) shows the IKONOS imagery for Grafton obtained on September 3, 2002, and (c) illustrates the color aerial photograph
taken in November 2002.
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