As a child, I was aware that, at night, infrared vision would reveal monsters hiding in the bedroom closet only if they were warm-blooded. But everybody knows that your average bedroom monster is reptilian and cold-blooded.
An accidental Discovery
Infrared is a type of light that we cannot see with our eyes but can sometimes feel as heat on our skin. In the 1800s, the English astronomer William Herschel discovered infrared light. He came from a musical family, and his father was a professional musician, and he followed in his father’s footsteps from a young age.
He became fascinated by musical theory and began to study it. Fate had something else in store for him, as he will soon discover. He quickly became interested in other scientific fields. He wanted to look far into space, so he learned how to build a telescope. However, while studying the sun one day, he was faced with a major challenge: the glare of the sun was too dangerous for his eyes. As a result, he began wearing coloured glasses to block out sunlight. He noticed that the amount of heat passed through each colour filter varies. This prompted him to conduct another experiment in which he created a visible spectrum and measured the temperature of each color’s light. Surprisingly, the highest temperature was not from colour light, but from a point beyond red light where he couldn’t see any light. He discovered infrared light as a result.
Infrared Radiation Properties
Infrared radiation carries a large portion of the Sun’s energy to Earth. Infrared light is found in the electromagnetic spectrum between the visible and microwave bands. Infrared light has wavelengths that range from red to violet, just like visible light. The wavelength of “near infrared” light is closest to visible light, while “far infrared” light is closer to the microwave in the electromagnetic spectrum. Far infrared wavelengths are about the size of a pinhead, while near-infrared wavelengths are about the size of cells or are microscopic.
Thermal waves are far infrared waves. In other words, we are constantly exposed to infrared radiation in the form of heat. The heat we experience from sunlight is infrared. Infrared light is sometimes used to heat food. Shorter near-infrared waves are not at all hot, and you can’t even feel them. These shorter wavelengths are used by your television’s remote.
Given that heat or thermal radiation is the primary source of infrared radiation, any object with a temperature radiates in the infrared. Even very cold objects, such as ice cubes, emit infrared radiation. In addition, at 37°C, the human body emits infrared radiation with a wavelength of about 800 nm. When an object is not hot enough to emit visible light, it emits the majority of its energy in the infrared spectrum. Hot charcoal, for example, does not emit light, but it does emit infrared radiation, which we perceive as heat. The more heat an object emits, the more infrared radiation it emits.
Exploring the Universe
Humankind has always found space exploration to be a fascinating journey, allowing us to unravel the mysteries of the universe beyond our planet. We have seen tremendous advancements in space-based technology over the years, allowing us to study celestial objects and phenomena in previously unimaginable ways. “Infrared Sensing,” a powerful tool that has revolutionised our understanding of the cosmos, is one such technological marvel.
Infrared sensing is the detection and study of infrared radiation that exists outside of the visible spectrum of light. While our eyes can perceive only a small portion of the electromagnetic spectrum, from red to violet, infrared radiation has longer wavelengths and is therefore invisible to the human eye. It is, however, present all around us, emitted by objects that produce heat, such as stars, planets, and even our own bodies.
Although the concept of using infrared radiation for scientific purposes dates back to the 1800s, it was not until the mid-twentieth century that this technology made its way into space exploration. The development of infrared sensors and detectors paved the way for space-based observatories to peer into the universe from a new perspective, revealing captivating celestial phenomena that optical telescopes cannot see.
Why is Infrared Sensing from Space Important?
Space-based infrared sensing is critical for several reasons:
- Infrared radiation can easily pass through cosmic dust and gas clouds that frequently obscure visible light, providing us with clearer images of objects such as star-forming regions, galaxies, and even the centre of our Milky Way.
- Infrared telescopes can detect cool and dim objects such as brown dwarfs, planets, and other celestial bodies that are difficult to observe using visible light. This has resulted in significant discoveries in the field of exoplanet research, broadening our understanding of planets outside our solar system.
- Stellar Birth and Death: Astronomers can study stellar nurseries, where new stars are born, using infrared observations. It also aids in the observation of dying stars such as supernovae and red giants, which emit a large portion of their energy in the infrared spectrum.
- Understanding the Early Universe: As the universe expanded, light from distant objects shifted to longer wavelengths, often beyond the visible range. Astronomers can investigate the early universe’s conditions and the formation of galaxies by studying redshifted light with infrared telescopes.
- Infrared radiation can penetrate the dense gas and dust that surrounds black holes, allowing scientists to study the behavior of matter that falls into these enigmatic objects as well as the intense gravitational forces at work.
Infrared Observatories in Space
Through infrared sensing, several space-based observatories have helped advance our understanding of the universe. Among the notable ones are:
Spitzer Space Telescope: The Spitzer Space Telescope, launched in 2003, was the first infrared telescope to orbit the sun. It shed new light on the formation of stars and planets, the evolution of galaxies, and the properties of distant celestial objects.
Herschel Space Observatory: From 2009 to 2013, the Herschel Space Observatory was the world’s largest infrared telescope. It enabled astronomers to study the cold universe with unprecedented sensitivity, observing dust clouds and star-forming regions.
JWST (James Webb Space Telescope): The James Webb Space Telescope (JWST) is the largest space telescope, made to conduct infrared astronomy. Its high-resolution and high-sensitivity instruments allow it to view objects too old, distant, or faint for the Hubble Space Telescope. This enables investigations across many fields of astronomy and cosmology, such as observation of the first stars, the formation of the first galaxies, and detailed atmospheric characterization of potentially habitable exoplanets.
Application:
Characterizing the spectral features of ground formations, Environmental mapping.
Weather and climate monitoring from on-board satellites.
Observing cold stellar objects in deep space.
Planetary Exploration and capturing of detailed images and spectroscopic data across the visible, UV, NIR and infrared (IR) spectrum.
The IR sensitivity is not only used for space exploration, but also used for earth exploration using the earth satellites for:
- Climate and weather monitoring.
- Volcanic Activity and wildfire detection.
- Crop Health Monitoring.
Crop Health Monitoring:
A critical role of infrared sensing in agriculture is monitoring the health of crops. The different characteristics (like the near-infrared or short infrared waves, etc.) of infrared waves are used differently to monitor the vegetation or soil quality. Recent advances in this technology have allowed farmers to observe their fields and make timely crop management decisions. Crop identification using remote sensing also helps identify crops affected by conditions related to weather, pests, etc.
Volcanic Activity and wildfire detection:
Volcanic activity is always accompanied by the transfer of heat from the earth’s crust. The heat is used to measure the volcanic activity with the help of MODIS (Moderate Resolution Imaging Spectroradiometer) data and provides the near-real time data.
Using the MODIS data and VIIRS data (Visible Infrared Imaging Radiometer Suite), the wildfire data which consists of area to which the wildfire is covered, the major area, the area to be covered can be detected from the gathered data.
Climate and weather monitoring:
With the use of various cloud features, infrared thermal imaging technology is one of the most effective ways to monitor meteorological variables such as clouds, precipitation, and wind direction. By measuring the distribution of surface temperatures of various objects and their corresponding infrared radiation, the temperature of the earth’s surface may be measured. This gives meteorologists important knowledge regarding the distribution of air temperatures, variations in surface temperatures, and ocean surface temperatures.
The Future of Space-Based Infrared Sensing
As technology advances, the future of infrared sensing from space appears bright. Future missions, such as the JWST, will undoubtedly make exciting discoveries, pushing the boundaries of our understanding of the universe. JWST will include the capability to perform mid-infrared transit spectroscopy of exoplanets and to directly image young massive exoplanets.
Combining with other spectral bands:
The future of imaging technology involves merging infrared sensors with other spectral bands such as visible light and UV radiation. Furthermore, if combined with the infrared observations with data from other wavelengths like radio, X-ray, and gamma-ray will provide a comprehensive and multi-dimensional understanding of celestial objects and phenomena. This method covers a greater variety of wavelengths, providing more in-depth insights into complicated events across several domains like healthcare, environment monitoring, etc.
Infrared sensing via space-based technology has transformed our understanding of the universe. Astronomers have gained unique insights into hidden cosmic wonders by harnessing the power of infrared radiation, shedding light on the birth and death of stars, the formation of galaxies, and the existence of planets beyond our solar system. We can look forward to a future filled with amazing discoveries that will continue to inspire and awe us with the wonders of the universe as we eagerly await the next generation of space-based infrared observatories.
Near infrared detectors with high sensitivity in the spectral region of 900 nm to 2.5 um (and maybe greater) are critical for the spectral characterization of exoplanets and identification of possible biosignatures. Future exo-earth missions (HabEx, LUVOIR) will consider infrared spectroscopy capabilities to detect hydrocarbons such as methane (1.00 um, 1.69 um, and 2.32 um).
The Space Domain Awareness (SDA) mission can be optimized to detect Resident Space Objects (RSOs). It is done by checking the reflected and thermally emitted IR of the planets or anything in space, which can be used in missions to observe in poor illumination scenarios and improves sensitivity.
Future Scope as per industry usage
- Miniaturization: Miniaturizing and integrating of infrared sensors into compact, portable devices to make instruments lightweight and more affordable.
- Enhanced Resolution and Sensitivity: Innovations in sensor design, optics, and image processing algorithms are enabling thermal cameras to capture more details and detect subtle temperature differences with unprecedented accuracy.
- Integration of AI and ML: AI-powered thermal cameras can automate the detection, categorization, and analysis of thermal abnormalities in real time, allowing for speedier decision-making and increased situational awareness.
- Uncovering Invisible Worlds: Thermal cameras collect and visualize infrared radiation generated by objects and creatures, resulting in vivid pictures that depict temperature changes across surfaces. This skill has proven helpful across a wide range of businesses, including healthcare, construction, law enforcement, and animal protection.
