Geoscience Reference
In-Depth Information
Plate 18.2
(See color insert following page 114.) Results of a Spectral Angle Mapper (supervised) classifica-
tion, indicating likely areas of relatively homogeneous stands of Phragmites australis (solid blue)
and field-based ecological data. Black arrows show field-sampled patches of Phragmites . Areas
of mapped Phragmites are overlaid on a natural-color PROBE-1 image of Pointe Mouillee wetland
complex (August 29, 2001). Yellow ā€œPā€ indicates location of generally known areas of Phragmites,
as determined from 1999 aerial photographs.
The nominal spatial resolution associated with the ADAR data acquired at Pointe Mouillee was
ideal for viewing field GPS overlays and for ensuring the accuracy of coarser-resolution PROBE-
1 data. The ADAR data were also easily georeferenced using DOQQ image-based warping tech-
niques. However, these four-band data were limited in their usefulness for developing Phragmites
spectral signatures.
Field data from quadrat sampling was an essential part of effectively assessing the accuracy of
PROBE-1 Phragmites maps. The nominal 1-m spatial accuracy associated with field data collections
at vegetation sampling sites provided essential information to support the accuracy assessment at
Pointe Mouillee. The observed heterogeneity in Phragmites stands was likely the result of variability
within underlying vegetation, litter, and soil conditions, as evidenced by field data and PROBE-1
spectral variability within stands. The use of precision-located field data enabled the selection of
specific pixels within the imagery that contained the highest densities of Phragmites . Additionally,
the ground imagery data (i.e., video and digital still images) corresponding to individual quadrats
improved the decision-making processes for identifying which specific stand locations were dom-
inated by high-density plant assemblages.
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