XXII ISPRS Congress 2012: Technical Commission VII

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Multivolume work

Persistent identifier:: 1663813779

Title:: XXII ISPRS Congress 2012

Sub title:: Melbourne, Australia, 25 August-1 September 2012

Year of publication:: 2013

Place of publication:: Red Hook, NY

Publisher of the original:: Curran Associates, Inc.

Identifier (digital):: 1663813779

Language:: English

Additional Notes:: Kongress-Thema: Imaging a sustainable future

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Document type:: Multivolume work

Volume

Persistent identifier:: 1663821976

Title:: Technical Commission VII

Scope:: 546 Seiten

Year of publication:: 2013

Place of publication:: Red Hook, NY

Publisher of the original:: Curran Associates, Inc.

Identifier (digital):: 1663821976

Illustration:: Illustrationen, Diagramme

Signature of the source:: ZS 312(39,B7)

Language:: English

Additional Notes:: Erscheinungsdatum des Originals ist ermittelt.; Literaturangaben

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Corporations:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Adapter:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Founder of work:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Other corporate:: International Society for Photogrammetry and Remote Sensing, Congress, 22., 2012, Melbourne; International Society for Photogrammetry and Remote Sensing

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2019

Document type:: Volume

Collection:: Earth sciences

Chapter

Title:: [VII/7, III/2, V/1, V/3, ICWG V/I: LOW-COST UAVS (UVSS) AND MOBILE MAPPING SYSTEMS]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: ASSESSING THE FEASIBILITY OF UAV-BASED LIDAR FOR HIGH RESOLUTION FOREST CHANGE DETECTION L. O. Wallace, A. Lucieer and C. S. Watson

Document type:: Multivolume work

Structure type:: Chapter

International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B7, 2012 XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia AT ors vum. e 9 ss nse n c ^ $ $e ; = S E CMS. rs as m a. ; © aee iN cd * o E rs ud : " s atc € zl in o uw € © Gl 27 o x Aet. = o d = S4, x 22e . < S 45 sf c 9 wu. 8 Oo ir ps N 221 7; J S AT ga a e << 0: i ; 5 10 15 20 Across Track Distance (m) Figure 7. a) Top view and b) profile plot of a strip of a point cloud demonstrating the shadowing effect which increases as scan angle increases. flying height is a significant attenuation of the number of returns received from the upper part of the canopy. It is evident that in- creased above ground flying heights result in a decreased return intensity from the top of the canopy which becomes insufficient to trigger a return at flying heights greater than 50 m. As the Ibeo LUX scanner has a working range of 200 m, the signal attenua- tion is most likely due to a combination of the canopy structure (i.e. small surface areas to trigger a return), the reflectance prop- erties of the vegetation, the footprint size as well as the triggering mechanism of the Ibeo LUX laser scanner. Artefacts of this at- tenuation are still evident at flying heights below 50 m . To deter- mine if this small amount of attenuation effects the measurement of forest metrics, or if attenuation is occurring in all point clouds, comparison with field measurements of tree height and canopy properties (width and volume) is required. Previous studies that have focused on the effect of point density on the measurement of forest structure have suggested that in- creased point densities result in an improved accuracy at the tree level (Disney et al., 2010; Lovell et al., 2005). It has also been shown that increased point density has no significant effect on metrics derived at the stand or plot level (Tesfamichael et al., 2010). In this study we found that decreased point density re- duced the number of returns from the upper part of tree crowns. This is in line with the findings of Disney et al. (2010) and Lovell et al. (2005). However, it is also highly evident that a reduction in point density is not contributing to the attenuation of crown returns in the point clouds generated at higher flying heights. For point densities between 30 and 70 point per m at the plot level all statistics were reliably derived. Furthermore, the collection of high density data, from a UAV platform, over a plot sized area does not incur a significantly higher cost. As such point density should not be a controlling factor in the design of a survey for multi-temporal studies. The poor quality data collected from the higher altitudes (higher than 50 m), limited the ability to resolve the effects of scan angle and footprint size within this study. Morsdorf et al. (2006) high- lighted that increases in scan angle result in a reduction in canopy penetration due the distance the beam has to travel through the canopy and a reduction. This was also observed in the UAV gen- erated point clouds as the shadowing effect shown in Figure 7 resulted in parts of the plot not being observed. These areas pri- marily consisted of the lower parts of canopy and some ground areas. This suggests that narrow scan angle ranges should be used 503 where possible. No effect due to footprint size was observed in the data analysed. However, as previously discussed, it is highly likely that large footprint sizes are contributing to the attenuation of canopy returns with flying height. Based on these results several recommendations for this specific UAV- LiDAR system and for UAV-borne LiDAR systems in gen- eral can be made. Primarily, this study shows that both flying heights above 50 m and the use of high scan angles should be avoided where possible. Although a different miniaturised laser scanner may perform better at higher altitudes, the potential for the use of UAVS is seen to be most beneficial at the plot level. As individual plots can be surveyed at flying heights below 50 m within a single flight, this recommendation holds for all UAV surveys at this scale. Furthermore, the spatial accuracy of the generated point clouds suggests the fusion of forward and back- ward transects is a feasible option to further restrict the scan an- gles used within lower altitude flights. In the case of this study, a 12.62 m radius circular plot is the primary area of interest. To completely cover this area a flying height of 20 mabove the tree height, would theoretically allow the entire plot to be covered with a maximum scan angle of 17.5 °. Whereas this could be reduced to 12 °if the point clouds collected from forward and re- verse transects were used to generate a single point cloud, while insuring 50% overlap. This study has shown that with correctly chosen flying condi- tions, statistics which have been shown to be related to key for- est metrics can be derived with high repeatability from UAV- borne LiDAR systems. This suggests that any changes in for- est structure, such as a loss of biomass due to disease or prun- ing, should be observable from multi-temporal surveys. One of the primary advantages of a UAV-system is an ability to fly on- demand. Therefore, the UAV can be used to assess a number of the dynamics which are important in modern forestry manage- ment. For example, an assessment of biomass loss due to disease could be tracked through time. Another advantage of UAV sys- tems is their ability to generate very high resolution datasets. Al- though it has not been a focus of this study, the measurement of forest structure at the tree level is highly feasible with this platform and requires further investigation. Such analysis could aid studies into carbon modelling and the calibration of full scale data. Furthermore, the use of return intensity as an indicator of forest structure is becoming an important tool in forestry man- agement (Garcia et al., 2010). The use of a UAV-borne scanners limits the range and atmospheric effects in the measurement of intensity. This suggest that UAV-borne intensity metrics could be more accurate than similar full scale metrics. In conclusion, the mapping of forest structure using the TerraLuma UAV-borne LiDAR system has been demonstrated to be feasible at the plot level. There are a number of potential uses for UAV- borne LiDAR within forest management some of which will be the focus of the research with this system. However, the next stage of this research will focus on the comparison and calibra- tion of the tree level metrics with ground inventory data. References Disney, M., Kalogirou, V., Lewis, P., Prieto-Blanco, a., Han- cock, S. and Pfeifer, M., 2010. Simulating the impact of discrete-return lidar system and survey characteristics over young conifer and broadleaf forests. Remote Sens. Environ. 114(7), pp. 1546-1560. Donoghue, D., Watt, P., Cox, N. and Wilson, J., 2007. Remote sensing of species mixtures in conifer plantations using Li- DAR height and intensity data. Remote Sens. Environ. 110(4), pp. 509-522.

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