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"The
Use of Digital Elevation Models (DEMs) In Managing Natural Habitats In The
South Coast Wilderness"
Terry Lumati
Undergraduate Students
Mentor: Suzanne Wechsler
California State University Long Beach
ABSTRACT:
Geographic Information Systems (GIS) are an effective technology used to
evaluate natural resources. GIS can construct models of vegetation habitat
that rely on existing or readily obtainable information such as remotely
sensed images, soil surveys, topographic maps and digital elevation models
(DEMs). DEMs represent surface elevation in a GIS. DEMs are used to
represent terrain. Topographic parameters such as slope and aspect are
computed directly from the DEM. Slope and aspects are important indicators
of vegetation habitat preference. DEMs contain errors. The nature and
extent of these errors are unknown and require further investigation.
There are many ways to compute slope and aspect from a DEM in a GIS.
This research investigated the accuracy of two GIS algorithms that derive
slope and aspect from grid DEMs and how elevation error manifests in these
derived data. Centroids (geographic center of a grid cell) of a portion of
the USGS Laguna Beach 10m DEM were collected using a Trimble proXRS GPS
unit. These ground truth locations were used to compute field measurements
of slope and aspect and were compared with GIS derived values. Results
indicate that there is a statistically significant difference between the
DEM and GPS elevations. This error propagated to slope. There was no
statistically significant difference found between slope algorithms. DEM
error does not appear to influence aspect calculations. These results are
important for understanding the limitations associated with the use of a
DEM for vegetation analysis and hydrologic modeling.
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