Thermal photography:
History and modern applications
Thermal photography, also called thermal imaging or thermography, is an imaging technique that uses infrared radiation emitted by objects to create an image based on surface temperature. Unlike traditional photography which captures visible light, thermal photography captures infrared, which allows temperature variations to be visualized day and night. How did the discovery of infrared radiation give rise to such revolutionary technology?
History and evolution of thermal technology
The history of thermal technology dates back centuries, but significant advances in modern thermography have occurred in recent decades. We can note moments that marked the history of thermal technology.
In 1800, the discovery of infrared radiation was attributed to Sir William Herschel. He conducted experiments using prisms to study the distribution of light
Using an optical prism, he split the white light from the sun and directed it toward a thermometer whose receptacle had been darkened. He observes a constant increase in temperatures from violet to red, passing through the various hues of the rainbow. The color red turns out to be the warmest, and he identifies that near it, in an area beyond red, a region even warmer than all the others existed. Unable to discern it visually, he opted for the name "infrared" (from the Latin "infra" meaning "lower", therefore below red). This pioneering experiment marks the first demonstration that heat could be transmitted without emitting visible radiation.
(1738-1822)
Advances in thermal imaging technology have significantly increased the performance and versatility of the technology. Modern thermal cameras offer higher resolution, capable of capturing finer details and improving the overall quality of thermal images. The growing adoption of uncooled thermal cameras eliminates the need for expensive cooling systems, making them more affordable and portable. The miniaturization of electronic components has also played a crucial role in reducing the size of thermal cameras, making them easier to integrate into portable devices such as smartphones and drones.
Some thermal cameras now offer extended dynamic range, capturing scenes of objects with significant temperature differences while preserving detail. The integration of multispectral imaging technology further enriches the data, allowing thermal and visible information to be captured simultaneously, improving understanding of the captured scene.
(Using a thermal camera in public transport)
These advances make it possible to integrate thermal cameras into complex systems such as automated surveillance solutions, drones, night vision systems and medical equipment. As a result, the application fields of thermal imaging technology have diversified, covering security, medicine, industry, scientific research, environmental monitoring and other fields, demonstrating the innovation potential of this technology in multiple areas.
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In the 2000s, thermal sensors became more sensitive; they offer more precise detection of temperature variations. This improvement provides better performance in varied environmental conditions. From 2010, artificial intelligence began to be integrated into thermal cameras. This made it easier to share and process information in real time. Let’s take the example of automated anomaly analysis. Thermal camera connected to AI systems is used to automatically analyze thermal images to identify anomalies or complex patterns in industrial or security environments.
Practical applications of thermal imaging today
Thermal imaging offers a diversity of practical applications across different sectors.
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Defense sector
In the 1950s to 1960s, thermography found military applications during wars to detect enemy movements at night. The development of thermal cameras for military and research applications then continued over the decades and the first civilian applications emerged especially in scientific research and in the detection of energy leaks in industry.
(Military thermography)
II. Medical sector
Infrared thermography, a non-invasive technique, has proven to be a remarkable tool in the medical field, which has made it possible to detect breast cancer in women. Infrared thermography uses special cameras that capture infrared radiation emitted from the skin's surface to measure the body's heat emissions. The cameras then generate thermal images that represent the temperature distribution on the body surface. Cancer cells tend to be more metabolically active than surrounding tissues, often leading to increased vascularity around the affected area. Infrared thermography can therefore detect these temperature variations even before structural abnormalities are visible by other medical imaging methods, such as mammography.
(Thermography as a breast cancer screening tool)
Nowadays, artificial intelligence analyzes thermal images to detect people with elevated temperatures. It is a quick way to detect fever in densely populated places. This process is part of efforts to control the spread of infectious diseases particularly in densely populated environments. The analysis of thermal images relies on the use of infrared sensors which capture heat emissions coming from the human body. These sensors convert this information into thermal images, creating a visual representation of body temperature variations. AI then intervenes in the process using sophisticated machine learning algorithms.(Article link on Machine Learning, Deep Learning and Neural Networks)
​These algorithms are trained to recognize thermal patterns associated with elevated body temperatures. The AI model can be trained to distinguish normal heat signatures from those indicating a potential fever.
(Fever detection in public places)
III) Marine and environmental sciences sector
​Thermal imaging makes it possible to detect the presence of marine mammals such as whales by detecting the heat they emit on the water surface. Using thermal cameras on board ships or drones, researchers can detect the heat emitted by mammals on the water surface. This technology makes it possible to observe the behavior, movements and migration patterns of marine animals, thereby helping to conserve and understand marine ecosystems.
IV) Industrial sector
Thermal cameras became smaller, lighter, and more affordable from 1970 to 1980. Its use became widespread in areas such as building inspection. Indeed, the ability to visualize temperature variations considerably facilitates the detection of thermal leaks, insulation problems and other structural defects. These devices have become essential for building engineers.
(Checking insulation defects using infrared thermography)
Racing teams can use thermal cameras to monitor tire temperatures in real time during races to optimize tire performance and durability. This allows racing teams to adjust their strategies in real time to optimize tire performance while minimizing the risk of overheating. This allows resources to be used more efficiently and improves competitiveness.
(Temperature control of tires and vehicle components)
V) General public sector
From 1990 to 2020, technological progress continues with the integration of uncooled sensors, improving the portability of thermal cameras. The miniaturization of thermal cameras is becoming a reality, making the technology more portable and accessible. Thermal sensors are therefore integrated into consumer devices such as smartphones. Thermal camera accessories and modules have been developed to connect to smartphones
(Source: camerathermique.eu)
​Athletic trainers use thermal imaging to evaluate athlete performance. By monitoring body heat distribution during exercise, trainers can identify areas of muscle stress and assess the body's response to physical exertion. This information is valuable for optimizing training programs, preventing overuse injuries and maximizing athlete performance. The application can be extended to a variety of sports, from endurance sports like running to team sports like soccer.
(Screenshot from a Buzzfeed video on the thermal activity of the human body. — BUZZFEED)
In conclusion, thermal imaging technology has come a long way since the discovery of infrared radiation by Sir William Herschel in 1800. In recent decades, technological advancements have promoted the development of thermal imaging technology, it allowing it to play an important role in various fields.
In a future article we will talk about the operation of modern thermal cameras which use advanced sensors such as micro bolometers to accurately detect temperature changes. The integration of artificial intelligence opens up new perspectives and facilitates the automated analysis of thermal images.
