Protostar Labs

Shortwave infrared (SWIR) in machine vision imaging and other technologies – Part 1

This blog series explores the fundamentals and diverse applications of Short-Wave Infrared (SWIR) imaging, highlighting its critical role in industries such as agriculture, food production, pharmaceuticals, electronics, and space exploration, where it enables advanced material analysis, quality control, and remote sensing by leveraging unique spectral characteristics invisible to the human eye.

This blog story series covers the fundamentals and applications of the infrared spectrum which is common in many aspects of industry, science research, medicine, and public life. Short-wave infrared (SWIR) spectrum ranging from 1 μm to 2.7 μm is fundamental in several key technologies that surround us, and drive innovations. It is found in many forms and applications, but many do not refer to it as the SWIR, such as the largest world network – the fiber optic communication technology (e.g. 1300 nm, 1550 nm), many advanced medical imaging modalities (optical coherence tomography-OCT, diffuse optical tomography-DOT, photoacoustic imaging-PAI) or medical procedures (endoscopy, laser-assisted surgery, photothermal therapy). The most advanced deep-space laser communication system is being built also in SWIR in 1.5 μm for much increase in bandwidth and transmission speed from satellites, space stations, or spacecraft. LIDAR technology in traffic vehicles is also based on the SWIR waveband. And the list can go on…

1. Wide spectra of key-technologies and applications in the SWIR spectral domain

In this blog series, we will focus on the imaging applications in the SWIR wavelength spectrum of light using illumination in that particular band (natural from the Sun and space, or artificial light from halogen, LED, etc.), and a camera with semiconductor technology that can react to that light. SWIR imaging technology is not novel, its roots can be traced back to military applications in World War II, but the technological evolution over the years has made SWIR technology accessible and cost-efficient for vision experts in many imaging applications.

So, why is SWIR imaging important, and how does it compare to visual light spectrum (VIS) imaging (human vision from 400 nm to 700 nm)? The fundamental is the same as in VIS, the interaction of light (reflection, absorption) with matter is perceived with a camera, and as we see different colors, SWIR will produce contrast between materials. The difference is that the matter observed has different spectral characteristics in the SWIR range, which are not present in the visible spectrum. For example, a very common spectral characteristic of water is a very high light absorption in part of the SWIR band (1450 nm, 1950 nm). Imaging a scene with water content (e.g. lakes, drops on the surface, humid materials, etc) produces pictures with high contrast with water content being very dark in comparison to other materials. A lot of remote sensing applications rely on imaging in the SWIR band, and here we will cover some of them briefly. Next, we will explain many “on the ground” SWIR imaging applications, to help readers visualize as many possibilities of the SWIR applications in imaging.

2. Visualization of strong visible light reflection from water surface for visible light spectrum, and weak reflection (high absorption) of infrared spectrum (strong absorption around 1450nm, 1950nm and 2500nm) 

When talking about land monitoring, gas analysis, search for water, etc, many past and future space programs incorporated infrared imaging from space as part of other imaging technologies, for extraterrestrial imaging of the composition of planets, stars, and asteroids, or for detecting radiation from distant stars. Water content, gas, or atmospheric analysis plays a vital role in understanding the space dynamics, characteristics, and origin of matter and life itself.

Agricultural remote sensing relies in great part on SWIR imaging for crop and soil health monitoring, forest health monitoring, moisture evaluation, and so on. There are important vegetation indexes calculated, for example, NDMI (Normalized Difference Moisture Index, (NIR-SWIR)/(NIR+SWIR)) which helps describe the water stress level in crops. SWIR technology can also be integrated into farming vehicles to aid farmers in crop health monitoring or weed detection with elimination with special laser systems.

3. SWIR image of the greater county of city Osijek from Sentinel 2

The food industry with the machine vision on the production lines, benefits greatly from SWIR technology in terms of quality monitoring and sorting. There are many examples of quality control like apple bruising detection invisible in VIS, and contaminants detection in rice, coffee beans, and raisins, which can be life-threatening (stones, plastics, brick powder, etc.). Small pollutants such as plastics, metals, or even some types of bacteria can be detected in real-time on the production lines of meat or dairy products.

4. Apple bruising visible on SWIR at 1300nm
5. Note the higher contrast in SWIR between rice and contaminants

After the production comes the packaging of products. Many types of plastic materials used in packaging are translucent in the SWIR band which enables applications in packaging control such as fill level inspection, contaminants detection, or incorrect product detection. It can be applied with plastic bottles, boxes, blisters for pills, or any other plastic container. The pharmaceutical industry can benefit from SWIR also in the multispectral sense, where products can be visualized through packaging, and categorized with respect to multispectral response (faulty pill blister placement detection). There are promising scientific research projects involving different bacteria detection, also in the SWIR band.

6. Plastic bag with candies, and a white PET bottle filled with water

Liquid detection or classification can be done in SWIR through plastic, glass packaging, or on-surface detection (drops, spill). Different types of oils have specific spectral responses, so a multispectral imaging system with a combination of optical filters or illumination control in SWIR can be used to distinguish between liquids, even if they are stirred together.

7. SWIR water droplets on a glass surface at 1550nm

Electronics manufacturing can benefit from the detection of undesirable liquids, as very small drops are easily found with high contrast on the surface of electronic boards. One other SWIR advantage is the transparency of the silicon, so there are many quality control applications of the inspection of the wafer, where electronic parts can be examined for imperfections, weak bonding, etc, during or after production.

8. Arduino board, RFID keychain, and Protostar RFID card backlight vision with SWIR

The second part of the SWIR blog series will cover non-production imaging applications (public transport monitoring, safety, defense, etc.). We hope you now have a much clearer vision of the possibilities for SWIR imaging, and perhaps find use cases for your production or services. Don’t hesitate to contact us for any imaging questions.

Author: Marko Šprem, PhD, research scientist and photonics technologies expert.

His experience covers SWIR imaging, multispectral imaging, fluorescence microscopy, fiber optic communications, and sensors. You are welcome to contact Marko about any imaging applications via our Contacts page.

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