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Distribution of errors along stem in carbon estimation using hemispherical
photography
Bogdan Strimbu
1
Overview Taper and Hemispherical
Carbon estimation
Measurements
Error distribution along stem
Application – loblolly pine (P. taeda)2
Objective
Impact of measurements error in estimation of
carbon along stem WITHOUT cutting trees
Accuracy
Precision
Expedite
Equipment / software cost
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Carbon distribution• Depends on:
− Height on the stem− Distance to pith
• Related to:− Specific gravity
Solution: use taper → diameter along stem
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( , )Cerror f height diameter
Measurement Techniques
• Close range photogrammetry
1. Wide-angle lenses: angle of view 180°
2. Normal lenses: angle of view ~ 50°
• Cut trees
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Ultra wide - angle lenses
Fisheye lenso Hemispherical lenses
Strong distortion
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Study area
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Field - Normal lenses
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Field– hemispherical photo
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Field - Hemispherical photo
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Data - Ground
• Carbon – estimated thru specific gravity
− Linearly related
• Cookies – 2.5 m
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Specific gravity / Carbon content
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0 2 4 6 8 10 12 14 16 18 200.3
0.350.4
0.450.5
0.550.6
0.650.7
0.750.8
Height [m]
Spec
ific
Gra
vity
( , )SG f height diameter
• SG linearly related to height (R2=0.82)
• FOCUS: error in height
Data – Photo processing
• Hemispherical photography: − Equations & Custom software− Photo enhancement: super-resolution (PhotoAcute)
• Normal photos: Pix4D or Agisoft and Civil3D− Build 3D model− Calibrate model− Measure 3D object
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Normal photos
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Normal photos - Issues
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Hemispherical photos
• PhotoAcute – enhance from 12M to 50M
• Diameter• Height• Precision
• Time to measure• 10 min/tree - field• 15 min/tree - office
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Taper
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Taper Assessment
• 3D model
− Precision and Accuracy: ≤ 2 mm any height
• Hemispherical photo
− Precise: ≤ 5 mm bellow 5 m
− Biased: 10 – 40 mm
o Concentrated on higher sections of the stem
• Bias induced by human errors → identify stem18
Errors - Hemispherical photo
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Error distribution – Hemispherical photo
e ~ Weibull distributed20
( , )SGerror f height e diameter e
Summary
Item Cut Fisheye Normal-3DTime – Field 30 min 10 min 2 minTime – Office 0 min 15 min 25 - 120 minTime - Total 30 min 25 min ½ hour–2 hoursPrecisionHeight / diam. 1 mm 0.1 mm–10mm 0.1 mmAccuracyHeight / diam. 0 mm 10 - 40 mm 1 - 5 mmPrice $500+trees
(paperwork)$1,500
(little training)$10,000
(significant training)
measurement error distrib.
None Weibull unsignificant
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Normal-3D2 min
25 - 120 min½ hour–2 hours
0.1 mm
1 - 5 mm$10,000
(significant training)
unsignificant
22