Skrifennow

My blog, imported from Blogger and converted using Jekyll.

The Green, Green, QGIS of Mars (Part 2)

Oct 20, 2015

Here is the southern mid-latitudes of Mars, in the same colour scheme as the previous post showing the northern mid-latitudes:

The lowest elevation area of Mars, the Hellas basin has areas of bright terrain which makes the colour scheme a little confusing. Download larger version.

The Green, Green, QGIS of Mars

Oct 20, 2015

There are many blog posts on the Internet and even scientific papers on the evils of the spectral/rainbow colour palette for continuously varying data.

The series of 6 by Robert Simmon on NASA's Earth Observatory website is particularly worth reading and references many interesting and potentially useful sources.

Incidentally while looking for that, I saw this Image of the Day of a landslide onto a glacier in the Yukon in Canada. I wonder how often they have landslides on Mars.

Thus, I now show you the north of Mars, with the elevation encoded in a single hue palette and again overlaid with "Hard Light" on the Mars Global Surveyor image mosaic.

This will not be perfect for a quantitative visualisation, since it is not possible to distinguish between intrinsically darker areas and areas that are low in elevation.

I choose the green colour, because it leaves red and blue free to plot the classifier function values for areas similar to glacier head and extents.

The various individual HRSC tiles also have the same kind of colour palette of DTM elevation scaled locally overlaid on the nadir image HRSC. Download a larger image of this here.

If there's a North there must be a South

Oct 20, 2015

See also previous post for the North.

Here is the southern hemisphere of Mars. Again, I have used the same equirectangular coordinates optimised for 40° latitude.

The Souness et al. glacier like forms (such as QGIS plots them at this scale) are marked and numbered.






Lots of planets have a North

Oct 19, 2015

Here is the North of Mars, showing the Mars Express High Resolution Stereo Camera tiles used in my MSc dissertation, colour-coded by elevation, but also with the output of the Bayesian classifier measuring the similarity to Colin Souness's glacial form.

This is possibly a bit too colourful and the classifier output isn't really useful at this scale. The segmented DTM has red indicating similarity to glacier 'head' areas, green for 'context' areas (9x area of extent) and blue for extents.

I use QGIS to blend the elevation with an underlying nadir image also from HRSC with "Hard Light". I am not sure whether the developers of QGIS intended the Red Dwarf reference.


The coordinates are in an equirectangular projection in metres optimised for a standard latitude of 40°.


The Lost land of Lyonesse revisited

Oct 13, 2015

In a previous post, I mentioned the work of Shennan and Horton (2002) about sea level change around Britain through the Holocene.

I showed a visualisation of the West Cornwall coastline as it may have been around 12,000 years before present.

After downloading further bathymetry via the UKHO INSPIRE portal, I present an updated version covering the whole area around Cornwall.

Much of this came as .csv point data, which I had to grid, and use the QGIS Concave Hull plugin from the Processing toolbox to restrict the interpolated grid to where there was data.

In some areas, there are gaps in what is currently available at high resolution so it falls back to low-resolution data.

Based on my reading off the graphs in Shennan and Horton, the sea level rise at this time should be similar across the area covered here:
 
Site Number Site Name Lat Long RSL 1kyr RSL 2kyr RSL 3kyr RSL 4kyr RSL 5kyr RSL 6kyr RSL 7kyr RSL 8kyr RSL 9kyr RSL 10kyr RSL 11 kyr RSL 12 kyr

42 Pembroke 51.8 -5.1 -0.8 -1.6 -2.4 -3.2 -4 -9.2 -14.4 -19.6 -24.8 -30 -35.2 -40.4
43 Glamorgan 51.5 -3.7 -2 -4 -6 -8 -10 -13.6 -17.2 -20.8 -24.4 -28 -31.6 -35.2
51 Devon 50.4 -3.5 -1 -2 -3 -4 -5 -10 -15 -20 -25 -30 -35 -40
52 Cornwall 50.2 -5.5 -1.4 -2.8 -4.2 -5.6 -7 -11.6 -16.2 -20.8 -25.4 -30 -34.6 -39.2



It is clear there were substantial areas of land that were disappearing in the millenia after the reoccupation of Britain after the last glacial maximum (with this map corresponding to the cold spell of the Younger Dryas).
In the period of time, between 12kyr BP and 8kyr BP sea level rose by 20m, which corresponds to half a metre every century.
Especially in the large expanses of gently sloping terrain off the north coast, it would be likely that coastal retreat would have been noticeable by people within a single lifetime.

A version speculating about woodland colonising the lowlands:

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