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

3

Carbon distribution

• Depends on:

− Height on the stem

− Distance to pith

• Related to:

− Specific gravity

Solution: use taper → diameter along stem

4

( , )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

5

Ultra wide - angle lenses

Fisheye lens

o Hemispherical lenses

Strong distortion

6

Study area

7

Field - Normal lenses

8

Field– hemispherical photo

9

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

12

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0 5 10 15 20

Sp

ecif

ic G

ravit

y

Height [m]

( , )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

14

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

16

Taper

17

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 stem

18

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-3D

Time – Field 30 min 10 min 2 min

Time – Office 0 min 15 min 25 - 120 min

Time - Total 30 min 25 min ½ hour–2 hours

Precision

Height / diam. 1 mm 0.1 mm–10mm 0.1 mm

Accuracy

Height / diam. 0 mm 10 - 40 mm 1 - 5 mm

Price $500+trees (paperwork)

$1,500(little training)

$10,000(significant training)

measurement

error distrib.

None Weibull unsignificant

21

Normal-3D

2 min

25 - 120 min

½ hour–2 hours

0.1 mm

1 - 5 mm

$10,000(significant training)

unsignificant

22