Skrifennow

My blog, imported from Blogger and converted using Jekyll.

An overview of glaciers in the mid-latitudes of Mars

Sep 2, 2014

The paper by Colin Souness et al. in 2012 (link) gave an inventory of Martian "Glacier-like forms"

Here is where they are found plotted on a layerstack of Mars Express HRSC DTM tiles, where red=nadir image, green = elevation, and blue = slope, falling back to MOLA topography in areas I don't have that tile because it didn't underlay any Souness GLFs. For MOLA I use aspect as a substitute for the image layer.

The Souness GLFs are numbered, but not all are plotted because QGIS automatically avoids plotting too many labels on top of each other.

The coordinates are Mars Equicylindrical, with a standard parallell of 40 degrees.

Northern Hemisphere (25 to 65N)




Southern Hemisphere (25 to 65 S)

 











Analysis of Crater Greg using LandSerf

Aug 28, 2014

I had some trouble with geomorphons, because I couldn't get the GRASS 7 extension to compile in Linux for unclear reasons, so I was limited to using the Windows version inside a virtual machine, and it decided to crash when presented with Mars data, although it was OK with Earth DTMs...

I have however been using LandSerf to generate curvature layers, and a feature classification, so here we are, for the well known (at least to Martian glaciologists) crater "Greg":

I hope you're not too confused by the use of transparency...

Units are in metres.

Some of the glaciers form a channel as they are constrained by topography, but not all channels are glaciers.....

Using longitudinal curvature calculated in LandSerf, showing negative curvature where a slope starts off steep and shallows as it goes down, which the Martian glaciers in Greg and elsewhere generally do, (Bryn Hubbard et al.):



Using RSGISLib to segment a layerstack consisting of nadir image, elevation, slope, aspect, and curvature layers:


Selecting all slopes above 15 degrees



Geomorphons of mid-Wales

Aug 24, 2014

Following the machine-vision based method of topographic analysis, "Geomorphons" by Stepinski and Jasiewicz, here's an example of the method applied to mid-Wales:

The authors argue that the method can make a useful analysis of topography at differing scales, in a better way than typical differential-geometry based methods do.

A close-up of the Aberystwyth area:

The method is available either as an extension to version 7 of the open-source GRASS GIS software, or, for small datasets, as an online interface.


After a number of hours, a wider search area can be made to match the scale of Stepinski and Jasiewicz's map of Poland in their paper , in which the authors used a DEM at 30m resolution at a search radius of 50 cells.



Hopefully I'll have something useful from this method applied to Mars in time to go in my dissertation....

Website: Space Informatics Lab - University of Cincinnati

Segmenting with LandSerf: Wales DEM

Aug 7, 2014

Using some more SRTM tiles, I will try segmenting the DEM of Wales, using the elevation, slope, aspect, and several curvature layers generated in LandSerf:


 Here is an example segmentation showing the mid-Wales area with RSGISlib with a minimum object size of 80 pixels (0.2sqkm):



Segmenting Topography with LandSerf and RSGISLib

Aug 3, 2014

As a training for segmenting Martian topography, I have done a little work on Earth.

Using the software LandSerf  by Prof. Jo Wood (the website www.landserf.org appears to be down at the moment), I created a number of derived topograhic layers from Shuttle Radar Topography mission data, i.e. slope, aspect, and plan, longitudinal,  cross-sectional, profile and mean curvature. I then layerstacked these files (taking the aspect in degrees from north-facing).


Using RSGISlib to segment these (using min 128px sized objects where a pixel is ~ 72m) I get results like this:

The curvature layers seem to enable it to segment along ridge and valley lines and it can sometimes be seen how the topography is orientated spatially.










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