Publication Date:
2020-02-17
Description:
Surface dynamics, such as subsidence and heave,
as a result of permafrost thawing and freezing is a
well-known phenomenon. Ground measurements are
indicating that such movements exist and first attempts
to use satellite data to detect these changes
on a larger scale have been undertaken. In particular
data from radar satellites have been used to generate
differential interferograms (D-InSAR) in order
to detect areas of movements. However there are
still many uncertainties and limitations related to
this method, such as the influence of vegetation and
microtopography on the radar signal.
Within the PermaSAR project a multi-source approach,
using TanDEM-X data, ground truth measurements
(subsidence stations and RTK GNSS), but
also highly precise terrestrial 3D LiDAR data shall
help to identify influences of the captured surface
characteristics on high-resolution D-InSAR. In a subsequent
working step the identified influences will be
quantified and a method developed in order to mask,
reduce, or even eliminate, these effects.
For the study, a region in Northwest Canada, 50 km
North of Inuvik has been chosen. The site, so-called
Trail Valley Creek, lies in the continuous permafrost
zone and the thickness of the permafrost is up to
370 m. The dominant vegetation in the basin are
open tundra areas consist mostly of grasses, lichens
and mosses. Research activities of the past reveal a
potential of subsidence due to permafrost thawing in
this region.
In 2015 two field campaigns in the region could
be realized: One in early June, after the freezing
period and one in late August at the end of the thawing
period. During the first campaign 8 automated
ground temperature loggers and manual 24 subsidence
stations were installed. Active layer thaw depth,
as well as subsidence was recorded at 12 sites manually.
During both campaigns the high-performance
terrestrial LiDAR system Riegl VZ-400 was used to
survey at two different sites (40 × 50 m) the microtopography
and vegetation in 3D. The used LiDAR has
full-waveform recording, with each single 3D measurement
having a range precision and accuracy of about
3-5 mm at 100 m. Both test sites have been scanned
with a point spacing of 3 mm at a distance of 10 m
from 7 different scan positions. Additionally the Leica
GNSS RTK GS10/GS15 system was used to get exact
information about ground height and coordinates of
certain features.
First results indicate
i) a very good co-registration of the LiDAR data
and RTK GNSS data of the two campaigns and
ii) a high correlation between the subsidence records
of the LiDAR data, the RTK GNSS records and
the subsidence stations.
The corresponding mean subsidence rates derived
from the three independent sources (LiDAR, GNSS
RTK and subsidence stations) range from -2.31 cm
(LiDAR) to -2.72 cm (subsidence station) (std. deviations
from 0.89 (LiDAR) to 1.01 (subsidence
station)). First analysis of subsidence using the
TanDEM-X data are shown and compared to our
multi-source ground truth measurements.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Conference
,
notRev
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