Friday 19 August 2011

LBA Topographic Survey

The coarse grained topographic survey of the LBA field was conducted
using a laser level and laser distance finder. First 10 posts were
marked on the corner points and on the center of the field. The
distances between these posts were measured using a laser distance
finder. Several distances were also cross-checked with a tape
measure. The LBA field center point, one of the corner points, and a
reference point were also measured using a Sokkia precision GPS
device. The accuracy of the measured distances between the posts was
estimated to be +/- 10 cm. The accuracy of the GPS measurements has
not yet been estimated, but by comparison with tape measure distances,
it is expected to be approximately +/- 5 cm in longitude and latitude,
but significantly higher in altitude.

In addition to the 10 posts, we added a post that marks the
approximate location of the LBA field centerpoint, as the previous
center post was too close to the reindeer fence on the outer perimeter
of the KAIRA site. This was then measured using a precision GPS with a 1
hour integration time.

The local coordinates of the posts were then determined using
triangulation. We then used a string with 10 m marks to measure the
variation of ground level at approximately 10 m intervals on the
baselines between the edge posts. The measurement points are shown in the figure below.

Based on these results, the difference between the highest and lowest
point is approximately 220 cm. The ground is fairly even over the
whole field, and the altitude drop occurs evenly over the whole
field, with a slightly steeper descent approximately half-way down the
field. The topographic map of the LBA field is shown in the figure below.

Based on several test hole that were dug in the ground, the surface
layer of organic material is 5-20 cm thick. Underneat this, is a layer
of wet silt. This is a non-Newtonian fluid (very similar to a mixture
of corn starch and water), which is hard when forced, but liquid when
gentle pressure is applied. When dried up, the material is
powder-like and easilily blown away by the wind. It is difficult to
estimate what impact this has in terms of ground movement due to
permafrost, but most likely this is not a very stable soil-type.

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