Georeferencing Oblique Aerial Wildfire Photographs: An Untapped Source of Fire Behaviour Data
- Develop an efficient, systematic, repeatable procedure to determine the geographic coordinates of wildfire features captured in oblique photographs.
- Demonstrate the use of the procedure to obtain estimates of wildfire spread rates and validate fire behaviour models, using the FBP System models as an example.
2. Materials and Methods
2.1. Monoplotting Process
2.2. Study Area, Image Selection and Data Compilation
2.3. Georeferencing Oblique Aerial Wildfire Images Using MPT
2.4. Headfire Position Interpretation and Rate of Spread Calculation
3.1. Fire Front Locations and Accuracy Assessment
3.2. Fire Spread Distance and Rate Estimates
4.1. Factors Affecting MPT Accuracy
4.2. Recommendations for Future Research and Application
- When selecting wildfire images for monoplotting, the fire front position must be visible or at least interpretable with a high degree of confidence and the visible landscape and resolution of the images must permit precise location of at least five GCPs. Monoplotting to determine the position of fire features will be most successful in heterogeneous landscapes. Accuracy may be higher in mountainous terrain.
- The accuracy of georeferencing increases with the resolution of the available orthophotos and DEM as well as the distance from camera to ground and camera settings, which influence the pixel resolution. The monoplotting method will be more accurate in regions where orthophotos of half meter resolution and an underlying DEM of at least 25 m resolution are available (for very irregular terrain a DEM with higher resolution is recommended).
- Images captured from close distance to the fire and at a lower elevation allow for more precise location of GCPs. However, this also reduces the field of view and may restrict the number of GCPs. We recommend a distance range between 650 and 2500 m, and an elevation range of 350 to 1050 m to yield angles of incidence from about −30 to −50° and a good field of view and perspective of the fire front. Ideally, the view of the flaming front is unobscured by the smoke plume, although it is not always possible. Bird dog aircraft attached to air tanker groups are often in this airspace and can provide a good platform for acquiring wildfire spread imagery.
- Care must be taken in locating fire fronts in oblique photos with regard to the depth of visible flame, the shape of the fire front, the location of the smoke plume base and direction of smoke spread; this requires some training and experience. Complex fire spread patterns, particularly when fuels or terrain are highly heterogeneous or spotting is a significant factor, may be georeferenced using monoplotting, but will be much more difficult to relate to the fire environment. Such considerations are beyond the scope of this article.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
|BCWS||British Columbia Wildfire Service|
|DEM||Digital Elevation Model|
|FBP||Canadian Fire Behaviour Prediction System|
|FFMC||Fine Fuel Moisture Code|
|FWI||Canadian Forest Fire Weather Index System|
|GCP||Ground Control Point|
|GIS||Geographic Information System|
|HROS||Head Fire Rate of Spread|
|ISI||Initial Spread Index|
|LST||Local Standard Time|
|MPT||WSL Monoplotting Tool|
|PATC||Provincial Air Tanker Centre|
|HSD||Geodesic Head Fire Spread Distance|
|VRI||Vegetation Resource Inventory|
Appendix A. Summary of Canadian Fire Behaviour Prediction System Calculations
|Site #||FFMC||Wind Speed|
|Wind Observation (LST)||Distance (km)||Slope, Azimuth||ISIsw||BUI||Fuel Type||HROSp|
|1||89.0||14.5||1500||23||<5%||7.7||57||C-2, C-3 a||5.8|
|3||93.6 c||1.8 d||1900||9||<5%||7.9||--||O-1b||22.0|
|4||94.0||7.7 e||1500||46||32%, 215 e||10.0||94||C-7 (O-1b) e||3.1|
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|Pixels||px||d||Distance from user defined image GCP (p) coordinates to MPT calculated image point (p’) coordinates given in pixels|
|Angle||°||α(r, r’)||The angle between the two light rays (r, r’)|
|Radius||m||R||Distance from MPT calculated ground point (P”) to user defined ground GCP (P)|
|World 3D||m||D||Distance from MPT calculated ground point (P’) to the user defined ground GCP (P)|
|World 2D||m||D2d||Projection of the World 3D error (D) on the horizontal plane|
|Site Number||Landscape Features||Vegetation Type|
|1||Flat riparian landscape, open areas with shrubs, patchy forest||Engelmann spruce—Subalpine fir forest|
|2||Flat landscape, two building structures, open areas with shrubs, forest and agricultural areas||Ponderosa Pine—Douglas-fir|
|3||Moderately sloped landscape, open grass field with lone standing trees||Interior grassland, cured|
|4||Steeply sloped landscape, two buildings, patchy forested sections with lone standing trees||Grassland—Ponderosa pine forest transition|
|5||A: Moderately sloped landscape, many buildings, sports fields, forested areas|
B: Moderately sloped landscape, two buildings, densely forested with open disturbance patches
|Closed Douglas-fir forest|
|Image #||Aerial Image Time Stamp||Mean Angle Error (°)||3D Error (m) Min.||3D Error (m) Max.||3D Error (m) Mean|
|Mean or Extreme||NA||0.008||0.033||2.030||0.533|
|Image #||Approx. Distance to Fire Front (m)||Elevation above Ground Level (m)||Angle of Incidence (°)||Azimuth (°)|
|Site #||Fire Year||Fire Spread Distance (m)||Burning Period (min)||Max Total 3D Error (m)||Max HROS Error (%)||HROS|
|Fire Obs. #||FBP Fuel Type||HROSp|
|Difference (m·min−1)||Difference (%)|
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Hart, H.; Perrakis, D.D.B.; Taylor, S.W.; Bone, C.; Bozzini, C. Georeferencing Oblique Aerial Wildfire Photographs: An Untapped Source of Fire Behaviour Data. Fire 2021, 4, 81. https://doi.org/10.3390/fire4040081
Hart H, Perrakis DDB, Taylor SW, Bone C, Bozzini C. Georeferencing Oblique Aerial Wildfire Photographs: An Untapped Source of Fire Behaviour Data. Fire. 2021; 4(4):81. https://doi.org/10.3390/fire4040081Chicago/Turabian Style
Hart, Henry, Daniel D. B. Perrakis, Stephen W. Taylor, Christopher Bone, and Claudio Bozzini. 2021. "Georeferencing Oblique Aerial Wildfire Photographs: An Untapped Source of Fire Behaviour Data" Fire 4, no. 4: 81. https://doi.org/10.3390/fire4040081