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/3: WAVEFORM LIDAR FOR REMOTE SENSING]

Document type:: Multivolume work

Structure type:: Chapter

Chapter

Title:: EXPLORING WEAK AND OVERLAPPED RETURNS OF A LIDAR WAVEFORM WITH A WAVELET-BASED ECHO DETECTOR C. K. Wang

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 Distance: 5 ns Distance: 6 ns = DN ® OO Soooo 2-05 oO ooo oe percentage of successful detection (%) en eo percentage of successful detection (76) 2 3 2 3 4 Ratio (A2 / A1) Ratio (A2 / A1) . 2 echo ; Echo with: 5 ns À Se Echo with: 5 ns Distance: 5 ns |Bilimore than 2 echo Distance: 6 ns (a) Zero-crossing (b) Distance: 5 ns Distance: 6 ns 1 2 3 4 5 1 2 3 4 Ratio (A2 / A1) Ralio (A2 / A1) à M2 echo i Echo with: 5 ns |Ezi1 echo Echo with: 5 ns Distance: Sns Mimorethan2echo) | Distance: 6 ns (c) Wavelet-based (d) percentage of successful detection (%) percentage of successful detection (%) Figure 8. Results of overlapped echo detection under variant relative ratio cases. CR2: blue, MR2: green, RR2: red, (a)(b) (b) verasetessitig (Nd) wavelet-tased Figure 9. (a) the study area, (b) the point clouds colored by 35 Real waveiprm data test elevation in the rectangle area of (a). Figure 9 shows the study area where tall and shrubs plants grow irregularly. The real waveform data is captured by Leica ALS60 Waveforms = Wavelet-based system. We chose the waveform data in the rectangle area detector shown in Figure 9 (a). The objective of this test is to see if the wavelet-based detector can effectively detect the weak and overlapped echoes so that the number of points increases obviously. Export point Remove echoes xport points where 3.5.1 Set up: The results of simulated experiments can be SNR, 4, « 16 dB used as reference to set up the strategy of detecting echoes in : s real waveform data. From section 3.3.2 the wavelet-based Figure 10. Flow chart ofthe wavelet-based detection method detector can confidently detect the echoes if the SNR value of an echo is greater than 16. Therefore a threshold is set as a condition to remove the uncertain echoes which may be incorrectly detected due to the noises. To obtain the SNR value of each echo, the noises in the waveform needs to be estimated. Fortunately that there only exists noises in some interval of each waveform, the noises can be therefore easily estimated using these waveform sections without target echo information. Figure 10 shows the procedure of the wavelet-based echo detection method applied to a real waveform dataset. 3.5.2 Results: The total number of waveforms is 459708 and the number of points provided by the instrument is 499997. Based on the wavelet-based detector, the number of detected points is 590074. It means that the detector increasingly found 1896 more of the original number of echoes. This result shows that the ability of the proposed detector in finding weak and overlapped returns from waveforms. Figure 11 shows a side view of a selected profile drawn by the system points and the points extracted by (b) our method respectively. One can see that the ground and the trees can be better described by the point clouds extracted by our methods. Figure 11. The side view of a selected profile. (a) points provided from the instrument, (b) points extracted from waveforms using the wavelet-based detector. The arrows show some of the extra-points detected by our method. 833

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