Estimating Leaf Area Index from Airborne Laser Scanning in Pinus radiata Forests

191 Pages·2017·4.04 MB·English

Estimating Leaf Area Index from Airborne Laser Scanning
in Pinus radiata Forests

A thesis submitted in partial fulfilment of the requirements for the Degree of
Doctor of Philosophy in Forestry by Grant Dennis Pearse

School of Forestry
University of Canterbury
2017

for Simon

Contents
Background and Introduction ............................................................................ 1
1.1 Applications and measurement of leaf area index ..................................................... 1
1.2 Remote sensing for leaf area index ............................................................................ 3
1.3 Lidar and LAI ............................................................................................................. 4
1.4 Thesis context ............................................................................................................. 5
1.5 Thesis objectives and layout ...................................................................................... 5
Literature Review .............................................................................................. 7
2.1 Introduction ................................................................................................................ 7
2.2 LAI and site quality .................................................................................................... 8
Nutrient status and LAI ....................................................................................... 9
Impact of canopy conditions and development on LAI .................................... 10
Summary of factors affecting LAI .................................................................... 11
2.3 Measurement of LAI ................................................................................................ 12
Non-destructive direct measurement ................................................................. 12
Destructive model tree method ......................................................................... 12
Allometric techniques ....................................................................................... 13
Canopy light interaction .................................................................................... 14
Gap fraction by hemispherical photography ..................................................... 22
LI-COR LAI-2000 plant canopy analyser ......................................................... 27
A scattering correction model for LAI-2000 measurements ............................. 29
Summary ........................................................................................................... 33
2.4 LAI from spectral vegetation indices ....................................................................... 34
Vegetation indices related to LAI ..................................................................... 36
Summary ........................................................................................................... 39
2.5 LAI estimation from lidar ........................................................................................ 39
Terrestrial lidar and LAI ................................................................................... 41
Waveform terrestrial lidar ................................................................................. 43
Waveform satellite lidar .................................................................................... 45
Waveform airborne lidar ................................................................................... 46
Discrete lidar sensors and methods ................................................................... 48
Lidar campaigns for forestry ............................................................................. 50
2.6 Overview of approaches for ALS-LAI estimation ................................................... 52
Linking theory to lidar metrics .......................................................................... 53
Evaluating optimal lidar metrics and plot parameters ....................................... 57
Evaluating the impact of forest type on ALS-LAI models ............................... 58
Potential applications of ALS-LAI estimation in New Zealand forestry .......... 60
2.7 Conclusion ................................................................................................................ 61
2.8 Research questions ................................................................................................... 62
Instrument Validation ...................................................................................... 66
3.1 Abstract .................................................................................................................... 67
3.2 Introduction .............................................................................................................. 68
3.3 Materials and methods ............................................................................................. 70
The forest plots .................................................................................................. 70
Plot selection and layout ................................................................................... 71
Measurement of LAI with the LAI-2200C ....................................................... 71
Sky conditions during sampling ........................................................................ 73
Obtaining needle optical properties................................................................... 74
Collection of needle samples ............................................................................ 75
3.4 Measurement of needle spectra by spectroradiometer ............................................. 75
3.5 Analyses ................................................................................................................... 76
3.6 Results ...................................................................................................................... 78
Sky variability ................................................................................................... 78
Needle optical property scenarios ..................................................................... 78
Comparison of diffuse and clear sky LAI ......................................................... 80
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Bland-Altman contrasts ..................................................................................... 82
Differences in instrument error ......................................................................... 85
3.7 Discussion ................................................................................................................ 85
3.8 Conclusions .............................................................................................................. 88
3.9 Acknowledgements .................................................................................................. 89
Estimating LAI from Lidar ............................................................................. 90
4.1 Abstract .................................................................................................................... 91
4.2 Introduction .............................................................................................................. 92
Remote sensing of LAI ..................................................................................... 92
Development of ALS-LAI models .................................................................... 93
Study objectives ................................................................................................ 95
4.3 Materials ................................................................................................................... 95
The forest........................................................................................................... 95
Inventory and LAI plots .................................................................................... 96
LAI measurements ............................................................................................ 97
Lidar data........................................................................................................... 98
4.4 Methods .................................................................................................................... 99
Lidar metrics ..................................................................................................... 99
Plot parameters and lidar processing ............................................................... 110
Variable screening ........................................................................................... 110
Statistical methods to estimate LAI from lidar metrics................................... 111
4.5 Results .................................................................................................................... 116
Elastic net regression – fixed radius plots ....................................................... 116
Elastic net regression – variable radius plots .................................................. 120
Elastic net – variable importance .................................................................... 123
Random forests – fixed radius plots ................................................................ 126
Random forests – variable radius plots ........................................................... 129
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Random forests - variable importance ............................................................ 129
Semi-physical models ..................................................................................... 133
4.6 Discussion .............................................................................................................. 134
4.7 Conclusions ............................................................................................................ 140
4.8 Acknowledgements ................................................................................................ 140
Summary and Conclusions ............................................................................ 141
5.1 Acquiring field measurements of LAI ................................................................... 141
5.2 Estimating LAI from lidar ...................................................................................... 143
5.3 Operational implications ........................................................................................ 144
References ........................................................................................................................ 147

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List of Figures
Fig. 2.1................................................................................................................................ 18
Fig. 2.2................................................................................................................................ 19
Fig. 3.1................................................................................................................................ 78
Fig. 3.2................................................................................................................................ 79
Fig. 3.3................................................................................................................................ 81
Fig. 3.4................................................................................................................................ 82
Fig. 3.5................................................................................................................................ 84
Fig. 4.1................................................................................................................................ 96
Fig. 4.2.............................................................................................................................. 118
Fig. 4.3.............................................................................................................................. 119
Fig. 4.4.............................................................................................................................. 121
Fig. 4.5.............................................................................................................................. 122
Fig. 4.6.............................................................................................................................. 123
Fig. 4.7.............................................................................................................................. 125
Fig. 4.8.............................................................................................................................. 126
Fig. 4.9.............................................................................................................................. 127
Fig. 4.10............................................................................................................................ 128
Fig. 4.11............................................................................................................................ 130
Fig. 4.12............................................................................................................................ 132
Fig. 4.13............................................................................................................................ 133

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List of Tables
Table 3.1. ............................................................................................................................ 72
Table 3.2. ............................................................................................................................ 74
Table 4.1. ............................................................................................................................ 97
Table 4.2. .......................................................................................................................... 100
Table 4.3. .......................................................................................................................... 101
Table 4.4. .......................................................................................................................... 105
Table 4.5. .......................................................................................................................... 109
Table 4.6. .......................................................................................................................... 124

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