[HOT] landslides and imagery

john o'l ol.john.el at gmail.com
Sun May 10 00:49:07 UTC 2015


I've been focusing on landslides and have located several score that appear
recent.  Of these, a few are pre-quake and appear relatively stable, some
are pre-quake but appear reactivated and many appear to have been
associated with the quake and/or aftershocks. I've mapped several dozen of
these so far. In my next email, I'll cover why you won't find them in
osm... yet. For this one, I'd like to stick to post quake imagery and some
of its quirks.

There is an inhabited hillside that had numerous landslides, some predate
the quake, but most are presumably related. So far I've mapped about half
of them, those that are largest or appear to threaten buildings and
pathways. There is Digital Globe imagery available from May 3 and May 8. It
looks like QGIS easily operates with more than one coordinate system at a
time. The center of a large boulder in the May 3 imagery (Longitude,
Latitude; WGS84 EPSG:3857 x,y) is at
85.85659,27.83609;9557511.789,3228324.329, in the May 8 imagery it is at
85.85669,27.83656;9557522.728,3228382.865. Mind you, this is not a
complaint, rather it is a concrete example of the variability with this
recent imagery.

A more extreme example is a slide that appeared to be partially blocking a
stream in the May 3 imagery 85.90258,27.87818;9562631.312,3233623.303; --
it was completely obscured by a hillside in the May 8 imagery (probably
taken from a more northerly or northwesterly vantage point.)

Downslope (westward) from a likely reactivated slide located at
85.81987,27.90810;9553423.739,3237391.771  is a remote area that appears
very hard hit.  The May 8th imagery is mostly clouds, but the May 3rd
imagery shows a blue rooftop at 85.80644,27.90818;9551929.301,3237402.414,
it looks like there are several large boulders in the immediate area and
there is not much left to tell there were more than 20 buildings nearby.
While the boulders may have contributed, at the moment I think it is
probable that the shaking itself was mostly responsible for the extreme
level of destruction.

One advantage of different acquisition angles is that some features may be
discernible on slopes that don't ordinarily show up very well.

Question to the HOT folks -- is there a way to specify the date of DG
imagery we access through the proxy server?, Some of the May 8 imagery is
starting to come up over the May 3 imagery without me telling it to.

Best regards,

John
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