Terrain Model

Good evening from Yangon!  Geophysics has really hit the ground running over this project.  Compared to some of the themes of this investigation, geophysics requires relatively little support and/or permitting; all that the geophysics crew needs is a few gallons of water, and myself, Roger Clark and Andy Merritt can get on with some solid days’ work.  All in all, I’m really enjoying working in Myanmar: it’s frustrating at times that we have to wait for permits but, in the humid conditions, I can’t help but think that maybe it’s us in the west who wrongly demand immediate action!

And, speaking of conditions… During the 2004 survey, I was here during the monsoon season, when there was rain like I’ve never experienced since; the field area was a swamp and, whilst it was humid, it wasn’t too hot.  Now, in January, it’s both hot and humid – the dry ground makes for much better survey conditions, but the downside is that the humidity really saps your strength.  The team member who feels this most keenly is Andy; an important task of ours is to build a digital terrain model of the site and, to this end, Andy has been walking around armed with a Trimble differential GPS system.  I might complain about the heat, but I really have no right since Andy notched up a 17 km walkabout a few days back!

The terrain model is really important for the conflict archaeologists, as topographic lumps-and-bumps over the site can be strong indicators of something buried – whether this is a buried Spitfire, or an important piece of the historical jigsaw puzzle at the site.  However, characterising the causative feature of a topographic bump requires sampling the actual subsurface of the ground, as well as its surface.  While Andy gets on with the long march, Roger and I work on extending the coverage of the 2004 EM-34 (our electromagnetic survey apparatus) grid.  However, a direct comparison of the 2004 and 2013 EM responses proves difficult, given the different seasons in which the two datasets were acquired – the earlier dataset during the monsoon, the later in the dry season.  Nonetheless, we’ve observed another interesting anomaly that may correspond to a track that once cut through the airport site, potentially the road on which veteran soldier Stanley Coombe was standing when he saw crates at the base.  More on this in a moment! 

My least favourite bit of geophysical kit is the electrical resistivity tomography – essentially a large voltmeter for the ground.  What makes it so unpalatable is that 48 electrodes must be hammered into the bone-dry soil at each survey location – and my hands are now well-and-truly blistered…!  As much as I’d like to put the resistivity gear to one side, it is providing some interesting and useful data, potentially relating to former areas of airport infrastructure.  Confirming this through trenching should allow the conflict archaeologists to understand precisely the layout of the site.

Tomorrow, we’re looking to tie-down the position of the former track using a Geonics G-858 magnetometer.  A number of archaeological features are typically associated with disturbances to the Earth’s magnetic field, and we can detect and map these.  The G-858 has a higher resolution than the EM-34 hence, guided by the electromagnetic dataset, we will be able to accurately pin down a likely dig-site to find the track.  I’m the ‘designated driver’ of the magnetometer survey, so I’m about to feel Andy’s pain: like GPS, magnetometry surveys require a lot of walking up-and-down the site… wish me luck!

To wrap up, then, here are some of the vital statistics of our geophysical work so far performed in 2013…

• EM-34… Total area covered: an area of 110 x 100 m.
• ERT… Total profile length 445 m.
• Differential GPS… Total are covered 450 x 100 m.
• Magnetometer… about 100 m, but that’s just a test-line!

Archaeological digs will be targeted off the back of these results, so do look out for references to the geophysics in Andy’s future posts!