Processing Thermal Imagery

Introduction:

The definition of light that comes to the minds of most people is typically only limited to the visible spectrum. However, using thermal sensors, it is possible to record heat emitted as light. Thermal imagery has numerous applications, including locating of poorly insulated areas on rooftops, and mineral identification. By using a thermal sensor, your data capturing capabilities truly enter a whole new world (Figure 1).

Figure 1: An average reaction upon realizing the capabilities of thermal UAS imagery.

Methods:

The thermal camera captures images using the Portable Network Graphics (PNG) lossless compression. PNG is a fantastic method for recording raster data, however, Pix4D doesn't allow for PNG files to be entered as inputs, so it was necessary to convert the images from PNG into the TIFF file format. After the images were converted they were processed using Pix4D, generating a DSM and an orthomosaic.

Results:

The thermal imagery facilitated the creation of temperature maps, which allowed for the identification of specific features (Figure 2). The imagery was captured in the afternoon, which allowed the ground and vegetation to warm up. Water has higher thermal inertia than ground and vegetation, so water-covered areas appear dark blue.

Figure 2: The output Mosaic of the thermal imagery.

Figure 3: The pond and stream are visible in dark blue in the center of the image.

As water flowed from the pond, it traveled through a concrete culvert below to a lower pond. The culvert caused the surface temperature to drop, and it is easily visible in the bottom center of figure 3. Note how the concrete on the southern end appears warmer because it had been in direct sun (Figures 3, 4).

Figure 4: The culvert from the NE. 

Conclusion:

There are numerous untapped possible uses for thermal imaging, and this has been only one of them. In the future, I will pursue these additional uses.