Map Info
This map shows various indexes generated for the Pangnirtung area.
Slope Index
Slope Index is a measure of how steep the land is. It is generated from a 2m Digital Elevation Map from
ArcticDEM and then downsampled to 10m. It's important to note
that the building heights are included in the DEM, this may cause some unusually high slope artifacts around existing buildings.
Each value is then categorized into 3 different bins as follows:
- Low: Slope under 11.3° or 20% grade.
- Medium: Slope between 11.3°/20% and 22.6°/40%
- High: Slope above 22.6°/40%
Wetness Index
Wetness Index is a measure of where water is likely to collect/flow based on topology. The Topographical Wetness Index (TWI) is
calculated and then binned into 3 categories.
It does not consider actual rainfall or snow melt, it is solely based off of the topography of the area. The
same 2m Digital Elevation Map as Slope Index is used, the result is then downsampled to 10m. The specfic
thresholds are selected manually and qualitatively, they may need to be adjusted for other locations in the future. The Wetness Index
does not take into account existing underground drainage (e.g culverts). The building heights are included in the original DEM,
this may result in some artifacts surrounding existing buildings that can be ignored.
- Low: TWI < 8. Water is unlikely to collect here.
- Medium: 8 < TWI < 9.5. Water may collect here, drainage should be considered.
- High: 9.5 < TWI. Water flows through here often, there's potentially an existing river/stream
already. Drainage will almost certainly be an issue here.
Permafrost Stability
Permafrost Stability is a measure of the stability of the permafrost in the area. It's based on an aggregate of
how much the ground sunk over the past 3 summers. Ground sinking over the course of the summer is usaully
caused by ice in the permafrost's active
layer melting, higher displacements indicate more ice melt and more unstable ground. To determine the
displacement over the summer, we take data from Sentinel-1, apply
a
DINSAR processing pipeline to get displacement over 12 day periods in the summer. Alaska Satelitte Facility tools are used to gather the data and for
some processing. We then use manually annotated points corresponding to bedrock outcroppings to apply a
correction to the data. After being corrected, we combine the 12 day displacements to get the
displacement over the summer months (specifically we use data from between June 1st and August 31st). Then
for each position in the index, we take the 80th percentile of the displacement in that location for the
previous 3 summers. The resulting map is at a 40m
scale. Lastly we take the resulting displacements and bin them into 3 categories:
- Low: displacement < 1cm. Ground is consistently stable.
- Medium: 1cm < displacement < 3cm. Ground shows some shifting, may cause some issues.
- High: 3cm < displacement. Ground shows significant shifting, will likely cause issues with
structures in these areas.
Buildings
Building footprints for Pangnirtung come from CS PALS.