Investigating Surface and Near-Surface Bushfire Fuel Attributes: A Comparison between Visual Assessments and Image-Based Point Clouds
<p>Location of the study area southeast of Melbourne, Australia, with the location and photos of study plots in Cardinia Reservoir (shaded blue).</p> "> Figure 2
<p>Diagram of transect and plot layout for image capture, showing the approximate location of samples (s1 to s9), and a photograph indicating frame set up.</p> "> Figure 3
<p>Example point clouds derived from the photosets captured in Plots 1, 2 and 3. (<b>a,b</b>) show a point cloud captured in Plot 1 with the Oppo phone, (<b>c</b>,<b>d</b>) show a point cloud captured in Plot 2 with the Motorola phone and (<b>e</b>,<b>f</b>) show a point cloud captured in Plot 3 with the Sony phone. Distance is measured from the plot centre, and height reflects estimated height above sea level.</p> "> Figure 4
<p>Boxplots of eight assessment teams’ estimates of surface and near-surface fuel attributes from visual assessments (dark grey), and image-based point clouds (light grey) across Plots 1, 2 and 3. Boxplots show the median and quartiles, minimum (lower whisker), maximum (upper whisker), with mean (red point) also shown. (<b>a</b>) surface percent cover, (<b>b</b>) surface litter depth, (<b>c</b>) near-surface percent cover, (<b>d</b>) near-surface percent dead, (<b>e</b>) OFHAG near-surface average height and point cloud mean maximum height, and (<b>f</b>) near-surface average height.</p> "> Figure 5
<p>Isochrones showing the spread of surface litter height (<span class="html-italic">y</span>-axis) and percent cover values (<span class="html-italic">x</span>-axis) and resulting surface fuel hazard score from visually assessed metrics (dashed outline) and point cloud metrics (solid outline) across Plots 1, 2 and 3.</p> ">
Abstract
:1. Introduction
- the variability between visual estimates of surface and near-surface fuel hazard and underpinning variables obtained by assessment teams using the OFHAG;
- the variability in metrics derived from image-based point clouds (Fuels3D method) with respect to cover and height of surface and near-surface fuels at both the plot and sample level, and derived surface fuel hazard rating;
- the agreement between metrics derived from the two methods; and
- the influence of differing smartphone models on metrics derived from image-based point clouds.
2. Materials and Methods
2.1. Study Area
2.2. Assessors and Visual Fuel Hazard Assessment
2.3. Image Capture
2.4. Standardised Image Capture and Smartphone Model Comparison
2.5. Image-Based Point Cloud Generation
2.6. Metric Derivation
2.7. Point Cloud Normalisation
2.8. Surface and Near-Surface Fuel Metrics
2.9. Fuel Load and Hazard Score Calculations
2.10. Analysis
3. Results
3.1. Point Cloud Properties
3.2. Consistency between Smartphone Models
3.3. Plot Level Variability between Assessment Teams
3.4. Sample Level Variability between Assessment Teams
3.5. Agreement between the Two Methods
3.6. Fuel Hazard Scores
4. Discussion
Implications for Management
5. Conclusions
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Brand and Model | Screen Size and Resolution | Available Aperture | Sensor Size | Camera Megapixels |
---|---|---|---|---|
Sony Xperia Z1 compact | 4.3′′ | f/2.0 | 1/2.3′′ | 20.7 |
720 × 1280 pixels | ||||
Motorola Moto G (3rd Gen) | 5′′ | f/2.0 | 1/3.06′′ | 13 |
720 × 1280 pixels | ||||
Oppo F1 | 5′′ | f/2.2 | 1/4′′ | 13 |
720 × 1280 pixels |
Variable | Mean (s.e.) | CV (%) | ||||
---|---|---|---|---|---|---|
Motorola | Oppo | Sony | Motorola | Oppo | Sony | |
Surface % cover | 93.4 (1.7) | 96.5 (1.0) | 96.8 (0.8) | 9.2 | 5.5 | 4.1 |
Surface height (mm) | 12.9 (0.7) | 14.1 (0.6) | 14.4 (0.7) | 28.9 | 23.2 | 26.8 |
Near-surface % cover | 19.9 (2.3) | 26.9 (2.2) | 30.7 (3.0) | 60.4 | 43.0 | 51.0 |
Near-surface % dead | 65.6 (2.0) | 67.2 (2.0) | 66.7 (2.3) | 15.9 | 15.2 | 18.2 |
Near-surface mean maximum height (cm) | 10.8 (1.3) | 12.0 (1.2) | 10.1 (1.1) | 60.3 | 50.7 | 54.2 |
Near-surface mean height (cm) | 3.5 (0.4) | 3.0 (0.2) | 2.8 (0.1) | 55.7 | 30.8 | 27.1 |
Variable | Plot 1 | Plot 2 | Plot 3 | |||
---|---|---|---|---|---|---|
Mean (s.e.) | CV (%) | Mean (s.e.) | CV (%) | Mean (s.e.) | CV (%) | |
Surface fuel | ||||||
Litter depth (mm) | 18.6 (1.8) | 26.9 | 14.4 (1.8) | 34.5 | 22.5 (2.1) | 26.6 |
PC Litter depth (mm) | 15.1 (0.5) | 9.7 | 13.6 (0.5) | 9.5 | 17.1 (0.6) | 10.0 |
Litter cover (%) | 79.4 (2.3) | 7.7 | 68.1 (4.8) | 20.0 | 76.3 (4.0) | 14.8 |
PC Litter cover (%) | 96.7 (0.5) | 1.6 | 94.3 (0.7) | 2.2 | 96.6 (0.6) | 1.6 |
FHS | 2.5 (0.2) | 21.4 | 2.0 (0.0) | 0.0 | 2.8 (0.3) | 25.7 |
Near-surface fuel | ||||||
Cover (%) | 20.5 (3.6) | 50.3 | 21.1 (5.0) | 67.2 | 30.0 (7.5) | 70.7 |
PC Cover (%) | 26.4 (2.4) | 25.4 | 26.1 (2.0) | 21.9 | 41.1 (2.0) | 13.4 |
Height (cm) | 31.0 (5.7) | 51.7 | 29.5 (7.8) | 74.3 | 49.4 (7.2) | 41.4 |
PC mean max. height (cm) | 32.3 (3.5) | 30.6 | 22.9 (2.1) | 26.5 | 29.5 (2.5) | 24.2 |
PC mean height (cm) | 4.0 (0.3) | 21.9 | 3.8 (0.4) | 29.2 | 4.1 (0.2) | 14.3 |
Percentage dead | 31.8 (5.4) | 47.9 | 38.8 (9.0) | 65.4 | 46.1 (6.7) | 41.0 |
PC percentage dead | 53.3 (6.0) | 31.9 | 50.0 (3.1) | 17.4 | 52.5 (4.0) | 21.6 |
FHS | 2.0 (0.3) | 37.8 | 2.3 (0.2) | 20.6 | 2.3 (0.2) | 21.3 |
Variable | Plot 1 | Plot 2 | Plot 3 | |||
---|---|---|---|---|---|---|
Mean (s.e.) | CV (%) | Mean (s.e.) | CV (%) | Mean (s.e.) | CV (%) | |
Surface fuel | ||||||
Cover (%) | 96.3 (1.2) | 3.0 | 94.3 (1.1) | 3.3 | 96.1 (0.9) | 2.5 |
Height (mm) | 11.6 (0.7) | 15.3 | 11.9 (0.6) | 14.0 | 16.2 (1.1) | 18.3 |
Near-surface fuel | ||||||
Cover (%) | 13.0 (1.3) | 24.5 | 22.9 (2.0) | 25.2 | 31.4 (3.6) | 30.1 |
Cover dead (%) | 44.7 (3.5) | 19.3 | 63.3 (4.8) | 21.3 | 61.3 (4.3) | 18.7 |
Mean maximum height (cm) | 8.7 (0.6) | 16.2 | 10.8 (0.9) | 22.3 | 21.2 (4.9) | 61.5 |
Mean height (cm) | 2.6 (0.1) | 11.3 | 2.8 (0.2) | 19.7 | 3.5 (0.3) | 21.3 |
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Spits, C.; Wallace, L.; Reinke, K. Investigating Surface and Near-Surface Bushfire Fuel Attributes: A Comparison between Visual Assessments and Image-Based Point Clouds. Sensors 2017, 17, 910. https://doi.org/10.3390/s17040910
Spits C, Wallace L, Reinke K. Investigating Surface and Near-Surface Bushfire Fuel Attributes: A Comparison between Visual Assessments and Image-Based Point Clouds. Sensors. 2017; 17(4):910. https://doi.org/10.3390/s17040910
Chicago/Turabian StyleSpits, Christine, Luke Wallace, and Karin Reinke. 2017. "Investigating Surface and Near-Surface Bushfire Fuel Attributes: A Comparison between Visual Assessments and Image-Based Point Clouds" Sensors 17, no. 4: 910. https://doi.org/10.3390/s17040910