City
Level
Eagan,
Minnesota
High-resolution
IKONOS satellite
data with
four multispectral
bands similar
to Landsat
TM bands
1-4 are ideal
for studying
small lakes.
To explore
the capabilities
of IKONOS
satellite
data for
lake water
quality assessment
and monitoring,
we acquired
an August
23, 2000
IKONOS image
for the City
of Eagan,
Minnesota.
Eagan has
375 small
lakes and
ponds larger
than one
acre, with
44-acre Thomas
Lake being
the largest.
To
map lake water
clarity for Eagan,
we first acquired
Secchi disk measurements
from 19 different
lakes in Eagan
that were collected
within three
days of the August
23, 2000 image. Next,
lake signatures
were extracted
from the image
to model lake
water clarity
for all the lakes
and ponds
in Eagan.
The
model
was developed
using
the band
1:3 ratio
and band
1 as the
independent
variables
and the
natural
log of
Secchi
measurements
as the
dependent
variable.
The relationship
between
the IKONOS
measurements
and the
Secchi
disk measurements
had an
R2 =
0.89 (an
R2 value
of 0 would
indicate
no relationship
and a
value
of 1 would
indicate
a perfect
relationship).
This R2 value
is very
similar
to the
results
using
Landsat
data
at the
metro
and state
scale. Click
on IKONOS
vs.
Secchi
Disk
Measurements
in the
right
column
to view
this
relationship.
Finally,
we created
a pixel
level
map of
the water
clarity
of the
small
lakes
and ponds
in Eagan. Click
on the
2001
Eagan
Lake
Water
Clarity
map in
the
right
column
to enlarge
the
map,
and
view
a close
up of
the southeast
corner.
The
use of
IKONOS
data (and
similar
data from
the QuickBird
satellite)
for
assessment
of water
clarity
for small
lakes
at a city
scale
is promising.
The high
spatial
resolution
of the
IKONOS
data enables
the assessment
of smaller
lakes
and ponds
than the
Landsat
30-meter
resolution
allows.
Only 14
of Eagan’s
375 ponds
and lakes
were included
in our
statewide
assessment,
while
IKONOS
data allows
for the
assessment
of all
of Eagan’s
small
lakes
and ponds.
IKONOS
data also
would be
useful
for detailed
city land
use/cover
and wetland
mapping.
These maps
could be
used to
assess
how land
use/cover
affects
water clarity.
The cost
of the
IKONOS data
would be
prohibitively
expensive
for regional
assessments,
but would
likely
be affordable
by many
cities.
At
this city
scale,
what can
influence
lake water
clarity?
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