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A firefighter from Missouri submitted the following question:
Jonathan: We recently got into a discussion about how we could use a thermal imager to find people lost outside. We talked about everything from an open field, to a forest, to a corn field. But when we started adding in rain, snow, hot days and cold nights, things got more complicated. How can we use the TI to find lost kids, and what sort of restrictions will we have?
First, keep in mind that search and rescue operations are a mainstay of thermal imager (TI) usage. Normally, firefighters think of search and rescue in terms of pulling people from house fires. However, there are a number of times when the fire service is called upon to locate people lost outside. The victim could be a child who wandered away from his Scout troop or an elderly Alzheimer's patient who has wandered from home.
Regardless of the exact circumstances, the general theory is the same. In poor-visibility, we can use the TI to detect the victim's heat. Even in pitch-black conditions, the victim's heat will still radiate out, giving us a chance to "see" it with the TI. Because the presence or absence of light does not affect the TI, it can be a great tool for locating lost individuals.
As with many TI applications, locating victims lost outdoors is not as simple as just scanning and finding the victim waving at you. One of the biggest challenges to using the TI is the blocking effect of foliage. It's rare that people become lost in open fields. It is much more common for them to be lost in woods, or even corn fields. The leaves and branches that prevent the victim from seeing his way back home also block the body heat of the victim.
In order to improve the effectiveness of your TI search, you may have to search an area from several different angles. When you examine an area from different positions, you reduce the likelihood that a plant or tree is blocking the victim's heat from reaching your TI. Sometimes, it may be helpful to search from an elevated position. This can be especially true with corn fields, as the foliage is oriented horizontally. The stalks and leaves block heat from the side, but corn has little foliage on top. As a result, an elevated view of a corn field could easily show a child lost in the rows.
Since the TI senses heat, it is important to remember the effects of weather on how the TI receives that heat. First, the TI will be much more helpful as a search aid when the ground temperature is significantly different than the victim's body heat. Note that it is ground temperature, not air temperature, which concerns us. The ground temperature may be affected by the air temperature and the sun, as well as any precipitation.
The thermal imager detects temperature differences. The greater the difference, the more clearly the objects are displayed on the imager. A human's surface temperature is about 90 degrees Fahrenheit, so the more the background temperature varies from that, the higher the chance of detection. If the background temperatures are close to 90 degrees, then detection will be more difficult. The effective range of the TI will also diminish.
Precipitation can cool the ground and surrounding foliage, but it can also cool the victim. Even though a person is generating heat, rain or snow can cool his clothing and reduce his heat signature. Active precipitation can also impact the total amount of heat entering the imager, creating poor images that make detection of the victim even more difficult. This effect can be magnified if a lot of snow or water builds up on the TI lens. Don't let bad weather stop you from using the TI; just be aware that it may impact the overall performance of the imager.
Search and rescue operations outdoors can be enhanced by using a thermal imager. The TI can be used any time normal vision is compromised. Keep in mind that trees, shrubs, tall grass, sheds and a number of other obstacles can block heat. When you are scanning an area with heat-blocking obstacles, you need to try scanning from several different angles to reduce the chance that the victim's heat is being blocked from your TI.