Submergent
Aquatic Vegetation
Mapping
Lake
Minnetonka Area,
Hennepin County
QuickBird
imagery was acquired
on July 28, 2002
of the Lake Minnetonka
area. The lakes
include Christmas
Lake (655 ha)
in Hennepin County,
and West Auburn
(645 ha) Lake
in Scott County,
Minnesota. The
Minnesota Department
of Natural Resources
collected the
field data for
these three lakes.
For
this study the
field data specifically
targeted submerged
plants using
an echo sounder equipped
with a GPS unit.
The hydroacoustic
survey collected
data pertaining
to lake depth
and plant depth
at thousands of
points in the
shallower portions
of the lakes where
aquatic plants
were present but
not at the surface.
General point
survey data were
collected in areas
where the submerged
plants were topped
at the surface
or where there
were floating
or emergent plants.
We
followed similar
imagery processing
procedures for
the lakes south
of Lake Minnetonka
as with Swan Lake
emergent vegetation
mapping with the
exception of also
stratifying the
open water areas
before classification
of the submerged
and emergent/floating
aquatic plants.
See examples of
the resulting
maps to the right.
Preliminary
review of the
aquatic plant
assessments of
West Auburn and
Christmas lakes
indicates that
submerged plants
can be separated
from open water
areas and classified
to a plant top
depth of around
2 m. It also appears
that submerged
plants with more
dense growing
characteristics
like Eurasian
watermilfoil (an
exotic to Minnesota
lakes) can be
separated from
other submerged
plants that tend
to have less dense
growing characteristics.
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