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 The
data that we received from Claire Beany came in an unprocessed
format and had to be pieced together. Consequently data had to
be resaved without an extension and Header files had to be created for
each before they can be opened in ER Mapper.
The first step was to
determine which of the thirty-eight Alberta DEM
files corresponded to the study area and the order and locations of each
piece. As the file names were
named after 1:50,000 UTM maps of Canada, these problems were quickly
solved, drastically reducing the number of files from thirty eight to nine. The
selected DEM pieces were then processed into the same format.
Each had a range of elevation values that had to be manually
adjusted so that every image had the same minimum and maximum values and
the same contrast stretch.
In ER Mapper, each image was positioned according to the header file
information and adjusted by a few rows and columns to try and create a
perfectly matched and seamless DEM cover. Results
were not entirely successful. More
formatting was needed to keep the data unchanged and to correct the
obvious gaps between the upper six DEM pieces.
The six unaltered images that were placed above 50°N
had to be resampled to the same parameters as the lower three DEM’s
below 50°N
(2401 pixels by 1201
lines) in order to have the images properly align.
This method was chosen over resampling the three lower DEM’s,
where half the data that made up these images would be lost in the
procedure. The DEM’s were
then all repositioned to create a completed DEM
image of the study area.
The final image is much better and with hill shading, the
topography of the region is very clear.
Once the DEM was complete, the data was converted into a Geotiff (correct
settings) and imported into Idrisi32 for our analysis.
The DEM was then subject to a Pit removal analysis to remove any
topographic depressions –
or cells that are surrounded by neighboring cells of higher elevations –
that may affect the drainage patterns (Burrough, P.A, 1998).
A Runoff analysis function was also done to produce a drainage
network. The module Reclass,
in Idrisi 32 was the final touch that produced the drainage
network.
See
Cartographic Model for DEM Processing
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