Skrifennow

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Ebrenn y'n Nos - mis-Est 2015

Aug 12, 2015

This is a transcript of the second part of a series I am doing for Radyo An Gernewegva about the night sky and space exploration. There a few extra parts here that were removed as I shortened it for the podcast.

Ottomma an nessa rann a'm kevres a-dro dhe'n ebrenn nos ha nowodhow a-dhiworth an bys steronieth ha hwilans spas.

Dalleth mis-Est yw Lammas y'n kalendar keltek, dhe verkya hanter-fordh ynter Golowan ha'n kehysnos kynyav. An jydh y honan yw dy'kalann Est, mes yn hwir bos seythves mis-Est hanter an termyn yntra'n howlsav ha'n kehysnos yn poran.

Y'n ebrenn wosa hi dhe dewlhe, yma trihorn a sterennow splann. Hemm yw an 'Trihorn Hav', ow komprehendya an sterennow Vega y'n ranneves Lyra (daffar ilow kepar ha telyn), Deneb yn ranneves Cygnus (an Alargh), hag Altair yn Aqulia (an Er). Kynth yw an sterennow ma ogas dhe'n keth splannder heveladow y'n ebrenn, nyns yns i an keth splennyjyon yn spas, drefenn bos Altair sterenn ogas dhyn ni, 17 bloodh-wolow diworthyn, ha Deneb yw sterenn pell, moy ages 2000 bloodh-wolow diworthyn. Deneb yw sterenn kowr, gorgowr yn hwir, gans splennyjyon pur ughel, hanterkans milgweyth an howl. Mars yw an ebrenn tewl lowr, gweladow yn ta yw 'Fordh Sen Jamys' yn rannevesow Cygnus, Altair, ha Saggitarius avel kommol niwlek, mes yn gwirionedh yth yw milyow a sterennow pell yn disk agan galaksi.
An Trihorn Hav. Mappa ster gwrys gans Cartes du Ciel
Kresenn an galaksi yw yn ranneves Saggitarius mes nyns yw gweladow an gresenn y honan. Yma kommol gas ha doust y'gan galaksi, ha meur anedha ogas dhe'n kresenn. Dres henna nyns yw possybl dhe weles y'n tu na gans golow gweladow mes possybl yw y'n is-rudh, drefenn golow an par na dhe dhewana an kommol yn esya. Yma nebes sterennow a wra resek pur uskis ogas dhe gres an galaksi, ha dres henna ni a woer eus neppyth pur boos ena. Dell hevel, ny yll henna bos travyth marnas 'toll du'.
Yma kowas sterennow kodha yn mis-Est, henwys an Perseids. An gwella chons aga gweles vydh an 12ves bys dhe'n 14ves mis-Est. Ny vydh an loor y'n ebrenn ena, ytho y fydh gwel da anedha mar pydh an gewer da, bys dhe tri ugens anedha gweladow pub our, hag i a wra dos a-dhiworth tu an rannneves Perseus.
An planet Sadorn yw gweladow hwath, isel y'n soth y'n gorthugher, mes y hwra ev sedha a-varra yn termyn usi ow tos. Yn dalleth an mis y hwra sedha dhe unn eur myttin, ha dhe'n diweth unnek our nos.
Sterenn ow kodha Perseid a-ugh an "Pellweler Pur Vras" (VLT) yn Chili. Imaj diworth
ESO / S. Guisard yn 'Astronomy Now'.

Gans an loor yma kwartron diwettha dhodho 7ves mis-Est, loor nowydh 14ves mis-Est, an kynsa kwartron 22a mis-Est, ha loor leun arta vydh 29ves mis-Est.

An efanvos New Horizons a sewenas dresnija Pluton dhe'n 14ves mis-Gortheren ha studhya an planet ha'y loryow. Ev a welas rew dowr war enep Pluton, mes yn oor na, ogas dhe -235 C, an rew na yw moy kepar ha karrek es rew. Yma rew nitrojen, karbon monoksid ha methan a dhevera avel rewlivow.
Enep Pluton gans rewlivow nitrojen. Moy diworth gwiasva NASA New Horizons.

Yma nebes tollow skwatt war Pluton ha'y loor bras Charon, mes yma ranndiryow gwastas ha leven, gans enep yowynk yn istori system howlek, martesen saw kans milvil bloodh po le. Yn sur yma fenten tommder ena a wra teudhi an rew ha dres henna dasenebi an enep. Y hyll bos dowr linyel a-ji dhe Bluton.

   Gwydheo dresnija Pluton (simulatys) gans NASA



Yma nebes ayrgylgh tanow methan ha nitrojen, mes ha Pluton dhe bellhe diworth an howl, an gassow na dhe rewi war an enep.

Bagas steronydhyon a wrug diskudha planet a wra resek a-dro dhe sterenn arall, neb yw an moyha kehaval dhe'n norvys hwath diskudhys. An planet yw aswonnys avel Kepler-452b, gans gwradh a-dro dhe 1.6 kweth gwradh an norvys. Ev a resek a-dro dhe sterenn klass G, kepar hag an howl, hag a dhurya 385 dydh dhe dreyla a-dro y resegva. Possybl eus dowr linyel war enep an planet na, ha martesen chons bywnans. Nyns yw kler po an gronnedh poran, po gis an enep. An gronnedh yw ynter 3 ha 7 kweth gronnedh an norvys. An paper yn y gever o skrifys gans steronydh Jon Jenkins yn kynsa, hag onan an kesskriforyon yw Jason Rowe. (kevrenn http://arxiv.org/abs/1507.06723)
Gwel artek Kepler-452b (deghow) ha'n norvys (kledh). Diworth NASA/Ames/JPL-Caltech

Mars eus gwreydh kernewek dhedha, ny viens i an kynsa Kernow dhe dhiskudha planet. Den a Gernow John Couch Adams a wrug awrgrymya le planet Neptun kyns y vos gwelys y'n nownsegves kansblydhen.
Henn yw oll an mis ma, govenek a'm beus bos an gewer kler. Bys nessa prys.

A bit more on geomorphons, varying the 'inner search radius'

Aug 3, 2015

I had originally posted maps of DEMs of Cornwall and the Aberystwyth area of mid-Wales processed using Tomasz Stepinski et al.'s geomorphon method as descibed in the papers of: Stepinski+Jasiewicz 2011, Jasiewicz + Stepinski 2013.

Since then I have become aware of the 1 arcsecond SRTM data being available, so I have recalculated the geomorphons and here show the map of the same area of mid-Wales that the landcover assignment from my MSc was concerned with.

Using the search distance L=1500m, as did T. Stepinski in his geomorphon map of Poland (user guide), I varied the 'inner search radius' which determines the minimum distance the software looks, using 0, 2 and 4 cells. 1 cell is ~ 24m in the SRTM 1 arcsec data after conversion to OS grid reference coordinates.

Inner search radius 0m

In some of the flatter areas results are difficult to interpret. full-resolution image.

Inner search radius 2 cells (~50m)

Looking in Borth Bog, more of the area is shown as 'Flat' full-resolution image.

Inner search radius 4 cells (~100m)

As the inner search radius is expanded to 4 cells, most of the possibly spurious peaks in the flat area of Borth Bog disappear. full-resolution image.

I expect it would be interesting to combine it with the segmentation and classification with RSGISlib and to examine correlations between the landscape position of a location, and the land-cover.

Revisiting geomorphons - with 1 arcsecond SRTM data

Aug 2, 2015

I had originally posted maps of DEMs of Cornwall and the Aberystwyth area of mid-Wales processed using Tomasz Stepinski et al.'s geomorphon method.

Since then I have become aware of the 1 arcsecond SRTM data being available, so I have recalculated the geomorphons and present some maps of Cornwall here.

I've also become more aware of the various layer blending methods in QGIS which has allowed me to blend it with a hill-shaded topography layer.

In these maps, the search distance L = 1500m, flatness threshold 1 degree.

West Cornwall. Full resolution image.

SE Cornwall, Tamar valley and Dartmoor. Full-resolution image.

North Cornwall. Full-resolution image.

Minimum search radius

It is possible to specify an 'inner search radius' that ensures a minimum search radius for the geomorphons. In the maps below, using a minimum search radius of 2 cells (about 50m for this data), this makes the map look a little less noisy:

West Cornwall. Full resolution image.

SE Cornwall, Tamar valley and Dartmoor. Full-resolution image.

North Cornwall. Full-resolution image.

Showing elevation and slope on a map for cycling

Jul 30, 2015

A while ago, I was thinking about making a map that showed elevation and slope by colour-coding. It is often conventional to show elevation with contours, or by some sort of arbitrary colour palette.

Slope is shown on a map usually by contours being closely spaced, or by arrows shown along roads in some cases. Contours can sometimes obscure map features in some cases.

An alternative approach I have used to produce, is to colour-code both elevation and slope simultaneously in different colour channels.

In the cases below, I have used the blue band for elevation, and red for slope. Since I intended this as a map for cycling I have named the different scalings after professional cyclists.

Elevation shading colour codes elevations from 0-150m above sea level in the blue channel, and slope values from 0-10 degrees (up to 22.5%) in red. This map is optimised for lowland areas, however at higher elevations the direction of elevation change is no longer clearly shown on this map.
Elevation shading colour codes elevations from 50-400m above sea level in the blue channel, optimising the map to show elevations in the higher part of the range. Slope values are shaded from 0-10 degrees (up to 22.5%) in the red channel as earlier.

I give a few more examples of this using a different slope scaling and downloads of larger image files on my website.

The Lost Land of Lyonesse - update with high resolution bathymetry

Jul 27, 2015

I found high resolution bathymetric data available via the INSPIRE portal from UK Hydrographic Office.

So I thought it time to update my previous post on the lost land of Lyonesse, off the coast of Cornwall.

I was interested to find out what sea level the first people to inhabit Britain in a post-glacial climate around the Younger Dryas stadial (12 kyr BP) may have encountered.

The bathymetry from the above link comes in small sections and not all areas have ready gridded data so there is a background from the General Bathymetric Chart of the Oceans which has a resolution of 30 arcseconds (about 600m here) but resampled to 48m/pixel for a less pixellated look.

For this reason, and also to not worry about differential post-glacial rebound across the area, I have concentrated on West Cornwall. I have used the same assumptions of it as my previous post on the subject, that is the Shennan + Horton 2002 paper primarily also referring to the work of Kurt Lambeck.
I have assumed that sea level was 40m lower 12kyr BP,  30m lower 10kyr BP, 2m lower 8kyr BP, 16m lower 7kyr ago, 12m lower 6kyr ago, and 7m lower 5kyr ago.

I have taken no account of sediment deposition/erosion after marine transgression.

I have accidentally labelled Universal Transverse Mercator zone 30N coordinates rather than Ordnance survey grid coordinates,the units are however still in metres.

The elevation shading restarts from zero for the land, but incrementing in 20m steps rather than 2m. The first shaded colour on land is light green at 40-60m (12kyr ago).

Let me know what you think in the comments.

In legend Lyonesse is supposed to have connected Cornwall to Scilly. We see above that this is not likely to have been the case in a post-glacial climate since there is deep water of > 70m below present sea level between Land's End and Scilly. However substantial areas in Mount's Bay and north of St. Ives would have been dry land, up to about 8 kyr ago (sea level assumed to be 20m below present).
Unfortunately I don't currently have wide area gridded high-resolution bathymetry around Scilly. The inundation of the area between the currently inhabited islands occurred rather later than would be indicated by the labelling of this map, since this is known to have been dry land in historical times.


Close-up of area north of St. Ives and Hayle. A relatively large area of land would be been likely to have been submerged between about 9kyr and 7kyr ago.






The Cornish name for St. Michael's Mount, Karrek loos y'n koosmeans 'the grey rock in the woods'. At 5kyr ago, sea level is assumed to be 7m below present (i.e the pink land).



A bit of artistic licence, imagining vegetation colonising the lowlands, with the uplands still sparse at this stage (shortly after Younger Dryas 12-11yr ago)

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