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| Titel |
Mapping snow depth from manned aircraft on landscape scales at centimeter resolution using structure-from-motion photogrammetry |
| VerfasserIn |
M. Nolan, C. Larsen, M. Sturm |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 9, no. 4 ; Nr. 9, no. 4 (2015-08-05), S.1445-1463 |
| Datensatznummer |
250116827
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| Publikation (Nr.) |
 copernicus.org/tc-9-1445-2015.pdf |
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| Zusammenfassung |
| Airborne photogrammetry is undergoing a renaissance: lower-cost equipment,
more powerful software, and simplified methods have significantly lowered
the barriers to entry and now allow repeat mapping of cryospheric dynamics
at spatial resolutions and temporal frequencies that were previously too
expensive to consider. Here we apply these advancements to the measurement
of snow depth from manned aircraft. Our main airborne hardware consists of
a consumer-grade digital camera directly coupled to a dual-frequency GPS; no inertial motion unit (IMU) or on-board computer is required, such that
system hardware and software costs less than USD 30 000, exclusive of
aircraft. The photogrammetric processing is done using a
commercially available implementation of the structure from motion (SfM)
algorithm. The system is simple enough that it can be operated by the pilot
without additional assistance and the technique creates
directly georeferenced maps without ground control, further reducing overall
costs. To map snow depth, we made digital elevation models (DEMs) during
snow-free and snow-covered conditions, then subtracted these to create
difference DEMs (dDEMs). We assessed the accuracy (real-world geolocation)
and precision (repeatability) of our DEMs through comparisons to ground
control points and to time series of our own DEMs. We validated these
assessments through comparisons to DEMs made by airborne lidar and by a
similar photogrammetric system. We empirically determined that our DEMs have
a geolocation accuracy of ±30 cm and a repeatability of ±8 cm
(both 95 % confidence). We then validated our dDEMs against more than 6000
hand-probed snow depth measurements at 3 separate test areas in Alaska
covering a wide-variety of terrain and snow types. These areas ranged from
5 to 40 km2 and had ground sample distances of 6 to 20 cm. We found that
depths produced from the dDEMs matched probe depths with a 10 cm standard
deviation, and were statistically identical at 95 % confidence. Due to the
precision of this technique, other real changes on the ground such as frost
heave, vegetative compaction by snow, and even footprints become sources of
error in the measurement of thin snow packs (< 20 cm). The ability
to directly measure such small changes over entire landscapes eliminates the
need to extrapolate limited field measurements. The fact that this mapping
can be done at substantially lower costs than current methods may transform
the way we approach studying change in the cryosphere. |
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