Airborne laser scanner survey around the APLIS07 icecamp
H. Skourup and R. Forsberg, Danish National Space Center, hsk@space.dtu.dk,
rf@space.dtu.dk
In connection with DAMOCLES field work 2007 the Danish National Space Center
(DNSC) contributed with an extensive airborne survey in the area around APLIS07
icecamp on April 12, 2007. The main task was to collect high resolution laser scanner
data in order to estimate the sea ice freeboard. The DNSC laser scanner system provides
ice height data at a resolution of approx. 1 m in a 250 m wide swath. The flight tracks
were chosen to be coincident to other ongoing sea ice activities in order to compare the
results, giving deeper insight into various measurement methods and sea ice processes.
In Figure 1 (left) all the flight tracks are mapped. An approximate 100 km long track was
flown parallel to an ICESat track, and an approximate 70 km long line was flown
coincident to earlier flown AWI helicopter borne EM-bird thickness measurements. The
GPS icedrift information available at the flight epoch was used for waypoint definition.
The small red inner box is shown in details in upper right corner of Fig. 1. It shows the
flight tracks of a detailed mow-the-lawn pattern to survey the icefloe at which the
icecamp was located and the adjacent runway area. An area of approx. 5 x 2 km was
covered, centerede on the APLIS camp. The spacing between the lines were narrower
than the width of the laser scanner, and thus the entire area should be fully covered.
1
ICESat
ICESat
ICESat
EM-bird
AUV
1
7
6
5
2
3
4
146 W
Figure 1 Left: Flight tracks from the DNSC airborne laser scanner survey around the APLIS07 icecamp.
Right upper figure: a blow up of the mow-the-lawn pattern (small red box). Right lower figure: blow up of the
AUV subsurvey (large red box).
Finally the large red outer box, shown in details in the lower right figure, maps the survey
pattern corresponding to track lines (1-6) surveyed by a British nuclear submarine, which
maps the sea ice from below by upward looking sonar (ULS). The return flight line no. 7
represents a survey line measured by EM.
The laser scanner data from the survey has not yet been processed. The final product will
be delivered as freeboard maps with a horizontal resolution ~1x1m. For an example see
Figure 2. The width of the laser scanner is approximately the same as the flight altitude
(~250 m), and the vertical precision are primarily determined by the errors of the GPS
solutions in the order of decimeters, due to the long baselines. There is in total 3 scanner
files (each ~200 Mb) each representing 1hr of data, and also scanner data flying into
camp from Inuvik, Canada, on April 12, and leaving for Sachs Harbour, Canada, on April
13.
The flight tracks extracted from the
GPS-slaved onboard inertial
navigation system (INS) are
available. The files are:
102b_mtl.coo Mow-the-lawn
102b_auv.coo AUV subgrid
102b_ice.coo EM and ICESat
The data files are in ASCII format
with 4 columns, representing the
time (UT) in decimal hours, latitude
and longitude in decimal degrees
(WGS84), and the flight altitude in
metres.
Figure 2 An example of lidar swath (of width ~250 m) sea
ice freeboards. Units in metres.
Figure 3 From left: Reference GPS at APLIS flag at apron site, Kenn Borek Twin-Otter with lidar system on
a cold morning, and the icecamp seen from above.