Here is another flight debrief from a flight of mine to help share observations and lessons learned.
Flight Time: 15 minutes
Provide a visual overview of the scene and determine what the FLIR camera could visualize.
What Went Well:
The following items were conducted without incident:
- It was a safe flight operation within normal limits.
- The FLIR footage obtained was extremely helpful and educational.
A truck carrying liquid cargo developed a leak of the cargo. A hazardous material response was initiated.
The event was a substantial learning opportunity. Our drone, Firebird 1, arrived on scene at 2115 and established a safe LZ at the end of the line of vehicles in the southbound lane. I had to travel north in the southbound side to the command location but both sides of the highway were closed and suitable to establish a LZ.
There are a number of FLIR palettes that are available for use. In this situation, I selected the rainbow HC palette since I find it to be easier to see more subtle changes in thermal energy.
Flight images captured were good examples of a wide variety of situations faced by the UAS in typical operations.
One of these issues is the reduction in human body heat signatures when the person is layered in clothes or gear. This demonstrates why humans may not always be detectable using FLIR isotherm settings for human body temperature.
In the image above you can see the difference in temperature from a firefighter in bunker gear and a helmet and of those people not in such gear.
Under cooler temperatures, I have been unable to find a thermal signature when the person is appropriately dressed for the cold weather. They simply emit little thermal energy and can easily blend into the background when the exterior thermal energy emitted is near the thermal signature of the outside of their protective clothing.
The FLIR camera and rainbow HC palette show the gradation in thermal emissions in a fashion that is much easier to visualize than just a more limited color palette. As you can see by the above image, there is an apparent change in thermal energy emissions from each vehicle. The FLIR camera is fairly sensitive to energy emission changes. As you can see below, just the water coming of the running vehicle air conditioning is easy to see given the right underlying material. In this case, it was warm asphalt.
In the rainbow HC palette, white is the highest thermal energy. You can see the scale below. Black is the lowest thermal energy.
Most vehicles show the warmest area on the hood to be on the driver side. Using the scale above and the images above you can see this clearly in the vehicle images.
If you compare the most commonly used palettes of white hot, black hot, and the one you most commonly see in a lot of advertising – fusion.
Understanding the scales and colors you be better able to understand the information observed from the thermal image below.
I was told handheld thermal imagers had detected a 5 degree difference between the leaking fluid and dry asphalt. While the UAS thermal camera can provide thermal interpretations of temperature, it can provide a wider view of a scene.
In the picture above you can see that the front of the vehicle appears to show a thermal signature associated with a running engine. The truck was confirmed to be still running.
There is some material that is surrounding both sides of the truck in red. The red area appears to be some sort of material that is easily distributed, like fluid or small loose flowable material since the pattern of the red areas appears to follow the contour of the terrain.
If this is the fluid reported to be leaking out of the truck then the passenger side of the truck would have a larger pool of material. It was lower than the drive side of the truck. The assumed leaking fluid was then running back behind the truck.
I do not know what the leaking fluid was or how it reacted to air or the road surface it was in contact with. What I can observe is the thermal emissions from the leaking fluid were able to be easily visualized so enough of a thermal difference existed.
The issue that was most puzzling about the incident was the shimmering image of high thermal emission that was seen under the tree to the left. The target appeared to move very slightly and appeared to have been partially obscured by the leaves on the tree.
The first interpretation was it appeared to possibly be a human target, not wearing protective gear and standing under the tree but slightly obstructed by leaves on the tree.
It is the similar sort of image you get as a person walks under a canopy of trees and you catch a glimpse of them through the leaf canopy.
The concern was since it was dark, a curious civilian had possibly wandered into the restricted area to see what going on.
Chief Barrett, Ladder 1, and Engine 1 were stuck up the smaller parallel roads leading to the neighborhood to the left. He was guided to the target, walked all around the target but could not observe anything. What was especially curious was no matter how he was directed, he never walked between the airborne UAS FLIR camera and the thermal target.
At the time I thought that he possibly missing the target or he was not walking around enough of the area.
Another similar hotspot can be seen on the lower entrance road but since it was located on a road the chances were it was more likely to be a manhole cover given its shape and location.
As you can see above, the firefighter in the PPE was a lower temperature than the hot target identified under the tree.
The mystery was not solved until the next day when I went back to closely look at the scene with the thermal camera.
I was unable to locate any structure or reason for why the hot spot was seen under the tree. I did find a warm junction box in the ground next to the light pole but it was clearly not under the tree.
It turned out that the human body thermal target hiding under the tree was, in fact, the very hot bulb in the light post next to the entrance drive.
Because the pole had a thermal signature that could not be observed, the hot target appeared to be below the tree and slightly behind it because of the angle of the UAS camera in the sky. The view from above and away of the light pole made it appear to be under and behind the tree.
The other object on the lower entrance drive that was at first assumed to be a sewer access cover was actually a second streetlight on another pole.
The issues surrounding the correct identification of these targets just highlights the difficulties a SAR UAS pilot can encounter in an urban or suburban setting. There are just a number of thermal emitting targets in these areas that can be hard to correctly identify.
What Could Have Gone Better:
- Command determined the UAS was not authorized to fly near the subject truck. All observations had to be collected at a distance. Being able to fly closer and shift the observing angles would have been very helpful.
- The UAS was not tasked with collecting documentation or actionable observations of the specific incident.
- There is still a hurdle to overcome when incorporating the UAS into Hazmat situations. In this case, the UAS was not dispatched at the time of the incident but called for approximately two hours later. It is completely understandable why this happens at this stage of the integration of the UAS into operations. Especially when it is a multi-agency operation as this one was.
Recommendations From Flight:
The thermal imaging issues with the streetlights is a lesson learned from this flight and that was a tremendous benefit. My only recommendation is the hope for command to call the UAS in early to incidents and allow it to provide actionable information to assist with the incident.
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