How Thermal Imaging is Used in GIS

Like an x-ray for temperature, thermal imaging has many applications both on and around the Earth. For many of us, our first exposure to thermal imagery was likely in a science class where you got to play around with looking at a rainbow depiction of your face or hand. However, thermal imaging is a lot more than just pretty colors. It’s a tool that we can use to monitor the Earth’s surface and gain incredible insight into various anomalies, processes, and resources. 

First used by the military to surveil areas of interest, thermal imaging has become commercially available over the last few decades, making it an ever-growing area of technology in the GIS space. Classified under remote sensing, what the USGS defines as the process of detecting and monitoring the physical characteristics of an area by measuring its reflected and emitted radiation at a distance, thermal imaging can offer more precise details about what’s on or in the Earth than its counterparts. 

Thermal Imaging vs. Heat Maps

Before diving too far into the technology and uses of thermal imaging, it should be made clear that thermal imaging in GIS does not necessarily produce heat maps. While both use temperature-related language, their applications are distinct. 

Thermal imaging is used in GIS to detect objects or surfaces that are physically emitting heat. By using an infrared sensor, the variations in heat emitted from different surfaces can be contrasted with one another to see what’s hotter and what’s colder. Using this information paired with other spatial data can help analysts better understand the relationship between the objects detected or with temperature itself. 

When someone is speaking about a heat map, they’re typically not referring to anything temperature related. A heat map is a data visualization method of displaying where figurative “hot spots” exist in terms of the data being analyzed. A hot spot in this case refers to where there is a lot of something in a specific location. For example, a city may be a hot spot for people because of population density.

Generally speaking, a thermal image used in GIS will look like a miscolored, but realistically shaped photo while a heat map will look like a typical map with clean gradients of changing color.

How Thermal Imaging of the Earth Works

Like all objects, the Earth emits energy from its surface. While regular imagery and photographs of the Earth are captured using the visible light spectrum (0.4μm to 0.7μm), thermal imaging relies on mid-long infrared waves that are 8 μm to 15 μm. Heat impacts the emission of infrared radiation making it possible to see objects on Earth through their “heat signature” contrasted against the Earth’s surface. 

Using a thermal imager, also known as a thermal camera, small temperature differences can be assessed utilizing the differences in these wavelengths. The collected data from these sensors or cameras are then put together to create an image that depicts different objects based on their temperature differences. Thermal imagers and sensors are typically used on satellites orbiting Earth, but can also be placed on drones or other UAVs to create thermal images of specific regions of interest.

One of the major strengths of thermal sensing for imagery is that infrared radiation is not dependent on ambient light. This means data can be sensed and collected at any time, not just when the sun is illuminating an area. Additionally, infrared radiation can penetrate through smoke, fog, and haze which would typically obscure imagery taken using the visible light spectrum. 

Use Cases of Thermal Imagery in GIS

Heat Islands

A heat island is an urban area that is significantly warmer than its greener and wilder surrounding areas as a result of absorbing and trapping heat. This is a result of having a high density of human activities where buildings, pavement, and traffic are all highly concentrated. 

The phenomenon of heat islands is particularly important for monitoring health and safety. With more and more cities experiencing extreme heat due to climate change, heat islands can be particularly challenging to live in for those who have respiratory difficulties, are older, or work outside in these conditions. Through thermal imaging, heat islands and how they change in terms of area and temperature can easily be monitored.  

Animal Ecology

Tracking the whereabouts and habits of wildlife is a highly complicated task without the help of technology. While thermal imaging is commonly used in static locations to detect animals in a single spot, using thermal imaging on an aerial device can help monitor movement more accurately. 

Thermal imaging of animal movement with drones or UAVs is a relatively inexpensive way to develop an understanding of what area various animal species occupy. Paired with other data and knowledge about the environment, the relationship between a species and its surroundings can be analyzed with GIS. 

Geothermal Activity

Around the world, we are searching for ways to replace fossil fuels with renewable sources. Geothermal energy is an extremely promising way of doing this. However, finding where geothermal energy exists for use isn’t always easy. After all, it’s an energy source that lives beneath the ground and can’t be seen directly. 

Detecting geothermal activity via thermal imaging has been a promising way of exploring where potential may exist as an alternative to drilling which can be expensive and detrimental. The creation of geothermal potential maps is a more complicated thermal imaging process than others but has been showing promise and optimization for many years.  

Precision Agriculture 

Precision agriculture is a way of combining temporal and spatial data along with other agricultural production knowledge to make optimal decisions. Monitoring the surface temperature of crops via thermal imaging is extremely important as temperature directly impacts the potential of crops and their growth. 

Drones and UAVs that carry thermal sensors can collect this data which can be overlaid with additional plant data to understand what changes may be required for successful crops. 

Accessing Thermal Imaging for GIS

Thermal imagery data can be accessed and downloaded from the U.S. Geological Survey for free. Since 1972, the USGS has been launching satellites with the intent of capturing imagery for earth observation, and their technology has become increasingly more capable over the years.

Thermal infrared wavelengths were not sensed and recorded until the Thematic Mapper was introduced on Landsat 4 in 1982. Since then thermal infrared wavelengths have been captured on each satellite mission with Landsat 8 and 9 carrying a thermal infrared sensor (TIRS) instead of the Thematic Mapper. 

Satellites Landsat 8 and Landsat 9 both record thermal infrared wavelengths under bands 10 and 11. If using data from Landsat 4, 5, or 7, thermal infrared wavelengths are recorded under band 6. 

FAQ’s About thermal imaging