Distribution of errors along stem in carbon estimation using hemispherical

photography

Bogdan Strimbu

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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

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