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| Titel |
Multi-temporal UAV-borne LiDAR point clouds for vegetation analysis – a case study |
| VerfasserIn |
Gottfried Mandlburger, Martin Wieser, Markus Hollaus, Martin Pfennigbauer, Ursula Riegl |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127191
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| Publikation (Nr.) |
 EGU/EGU2016-7036.pdf |
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| Zusammenfassung |
| In the recent past the introduction of compact and lightweight LiDAR (Light Detection
And Ranging) sensors together with progress in UAV (Unmanned Aerial Vehicle)
technology allowed the integration of laser scanners on remotely piloted multicopter,
helicopter-type and even fixed-wing platforms. The multi-target capabilities of
state-of-the-art time-of-flight full-waveform laser sensors operated from low flying
UAV-platforms has enabled capturing of the entire 3D structure of semi-transparent
objects like deciduous forests under leaf-off conditions in unprecedented density
and completeness. For such environments it has already been demonstrated that
UAV-borne laser scanning combines the advantages of terrestrial laser scanning
(high point density, short range) and airborne laser scanning (bird’s eye perspective,
homogeneous point distribution). Especially the oblique looking capabilities of
scanners with a large field of view (>180∘) enable capturing of vegetation from
different sides resulting in a constantly high point density also in the sub canopy
domain.
Whereas the findings stated above were drawn based on a case study carried out in
February 2015 with the Riegl VUX-1UAV laser scanner system mounted on a Riegl RiCopter
octocopter UAV-platform over an alluvial forest at the Pielach River (Lower Austria), the site
was captured a second time with the same sensor system and mission parameters at the end of
the vegetation period on October 28th, 2015. The main goal of this experiment
was to assess the impact of the late autumn foliage on the achievable 3D point
density. Especially the entire understory vegetation and certain tree species (e.g.
willow) were still in full leaf whereas the bigger trees (poplar) where already partly
defoliated.
The comparison revealed that, although both campaigns featured virtually the same laser
shot count, the ground point density dropped from 517 points/m2 in February (leaf-off) to
267 points/m2 end of October (leaf-on). The decrease of ca. 50% is compensated
by an increase in the upper canopy area (>20 m a.g.l.; Feb: 348 points/m2, Oct:
757 points/m2, increase rate: 118%). The greater leaf area in October results in
more laser echoes from the canopy but the density decrease on the ground is not
entirely attributed to shadowing from the upper canopy as the point distribution is
nearly constant in the medium (10-20 m) and lower (0-10 m) sub-canopy area.
The lower density on the ground is rather caused by a densely foliated shrub layer
(0.15-3 m; Feb: 178 points/m2, Oct: 259 points/m2, increase rate: 46%). A sharp
ground point density drop could be observed in areas covered by an invasive weed
species (Fallopia japonica) which keeps its extremely dense foliage till late in the
year.
In summary, the preliminary point density study has shown the potential of UAV-borne,
multi-temporal LiDAR for characterization of seasonal vegetation changes in deciduous
environments. It is remarkable that even under leaf-on conditions a very high terrain point
density is achievable. Except for the dense shrub layer, the case study has shown a
similar 3D point distribution in the sub-canopy area for leaf-off and leaf-on data
acquisition. |
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