Thermal roof inspections are a critical application in the construction and maintenance industries, and the DJI Mavic 3 Thermal (M3T) drone provides an excellent solution for capturing radiometric thermal data. This guide provides the technical considerations and best practices for setting up, flying, and processing data for a successful thermal roof inspection using the M3T and DroneDeploy.
Step 1: Pre-flight setup and preparation
Proper equipment configuration and setup are essential to capturing high-quality thermal data.
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Check Equipment:
- Fully charge both the DJI Mavic 3 Thermal drone and the controller.
- Ensure the drone’s thermal camera (640x512 resolution) is functioning correctly.
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Thermal Camera Calibration:
- Adjust the emissivity based on typical roof materials. For example, set the emissivity to 0.95 for concrete or asphalt roofing materials.
- Set the temperature range to suit the inspection. A typical range for roof inspections is -20°C to 60°C to capture temperature variations such as hot spots from sun exposure or cool spots due to leaks or poor insulation.
- Choose a color palette that enhances the contrast of temperature differences. The Ironbow palette works well for roof inspections, as it highlights temperature variations in easy-to-interpret gradients.
Step 2: Planning flight path in DroneDeploy
Carefully plan the flight in DroneDeploy to ensure complete coverage of the roof area.
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Flight Path and Overlap:
- Set the flight path based on the building’s roof layout and structure.
- In DroneDeploy, set the front and side overlap to 70–80% to ensure comprehensive thermal imaging of the roof. This redundancy helps avoid missing thermal data and minimizes gaps in coverage.
- Ensure the flight path covers the entire roof, including high-interest areas like vents, skylights, chimneys, or HVAC units, which may show temperature differences.
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Ground Sampling Distance (GSD) and Image Resolution:
- Aim for a lower GSD by flying at altitudes between 50 to 80 meters for precise thermal resolution.
- The lower altitude provides better thermal detail of the roof's surface, which is especially useful for detecting small leaks or insulation issues.
- The closer you fly to the roof (without violating safety regulations), the better the GSD, resulting in higher image resolution for identifying fine details in temperature patterns.
Step 3: Flight execution and data capture
- Flight Altitude: For detailed roof inspections, set the flight altitude between 50 to 120 meters (164 to 394 feet). Lower altitudes (closer to 50 meters) provide better thermal resolution and more detailed images, but you may need to fly slower. Higher altitudes are helpful for quickly covering large areas but at the cost of resolution.
- Thermal Data Consistency: Use the side-by-side comparison tool in DroneDeploy to compare a thermal map of your location to a regular photo map to better understand what might be causing a hot or cold spot.
- Enable Both Sensors: Ensure you enable both Infrared and Visible options before initiating the flight plan.
- Environmental Factors to Avoid: Avoid flying in weather with wind speeds over 12 mph, humidity over 50%, or any precipitation.
Step 4: Data upload and processing
After the flight, upload the collected thermal and visual data to DroneDeploy for processing.
- Upload Data: Upload the thermal and corresponding visible RGB images to the DroneDeploy platform together. The platform uses the high-resolution RGB images to assist with geo-referencing and rendering the thermal map, automatically generating accurate orthomosaics and 3D models.
- Processing Time: Processing time varies depending on the amount of data captured and the size of the roof area. Ensure you have sufficient time for processing before conducting the analysis.
Step 5: Data analysis and reporting
Analyze the processed maps to identify roof defects and generate a comprehensive report.
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Thermal Analysis:
- Examine the thermal map for anomalies. Look for areas of distinct temperature variation, such as cold spots that may indicate water intrusion and moisture damage, or hot spots that may show poor insulation or electrical issues.
- Use the thermal color palette and temperature range settings to highlight anomalies.
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Defect Identification and Annotation:
- Use DroneDeploy's annotation tools to mark the locations of all identified defects (e.g., potential leaks, insulation gaps, drainage issues).
- Add detailed notes and capture screenshots of these areas for the final report.
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Export Thermal Map:
- Export the thermal orthomosaic in GeoTIFF format for GIS analysis or PDF for easy client presentation.
- The GeoTIFF is useful for further detailed analysis, while PDF reports summarize findings for clients.
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Report Generation:
- Generate a detailed report that includes the high-resolution thermal and visible orthomosaics, 3D models, and PDF exports with annotations.
- The report should summarize findings, including the location, type, and severity of each identified defect. This report is critical for communicating the inspection results to clients or maintenance teams.
Limitations/Considerations
- Environmental Factors: Thermal analysis is challenging if you fly too soon after a rain shower, especially if there is standing water hiding a problem. Wait at least 24 hours to a week after it rains to gain insight into drainage/leakage.
- Flight Speed: If you are performing a thermal inspection with the M3T, limit the flight speed to less than 10 mph (~ 4.4 m/s) to minimize image blur and incorrect image readings from the thermal sensor.
- Flight Time and Battery Life: Roof inspections can take time, so plan for sufficient battery life and have extra batteries on hand.
- Multiple Flight Passes: For large or complex roofs, consider making multiple passes over the roof to ensure comprehensive coverage, especially if you suspect certain areas need more detailed analysis.
- Adjust Camera Focus: Ensure the thermal camera’s focus is always sharp. If necessary, you can manually adjust the focus during the flight.
Additional information about thermal mapping:
Calibrating the M3T Thermal Camera in the DJI Pilot App
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