Why use Short Wave Infrared (SWIR)?
The SWIR (Short Wave InfraRed ) spectral region has evolved to become critical for many industrial, scientific, remote sensing and surveillance applications. Below we explain why SWIR has advantages over visible and thermal cameras for the following applications:
- SWIR Remote Sensing
- SWIR Microscopy
- SWIR Surveillance and Target Identification
- SWIR Laser Tracking
- Reflective and Hyperspectral SWIR Imaging
- Defect detection in industrial products by SWIR Imaging
Each object has its own spectral signature, which is also the basic principle of remote sensing. Today we have satellites with various sensors collecting data in visible light, Near Infrared (NIR), Thermal Infrared (TIR), Panchromatic and Shortwave Infrared (SWIR).
SWIR is immediate adjacent to NIR in electromagnetic spectrum and refers to non-visible light falling roughly between 900 and 2500 nanometers (nm) in wavelength.
SWIR Sensor vs. Visible Light Sensor for Remote Sensing
SWIR light is reflective in nature and bounce of objects much like visible light. But SWIR light is not visible to human eyes. As a result of reflective nature, SWIR light has shadow and contrast in its imagery (contrast depends upon the radiometric resolution of sensor). Unlike visible light imagery SWIR light image is not in color. This makes objects easily recognizable and yields one of the tactical advantages of the SWIR, namely, object or individual identification.
SWIR Sensor vs. Thermal Sensor:
Thermal sensors are another important type of sensor as they can see heat and so use for thermal mapping. Instead of measuring the temperature of the air (as weather station do), they capture the ground heat. Thermal sensor capture imagery of warm object against a cool background and they do not provide good resolution imagery. Whereas SWIR sensors can have high resolution and can actually identify what object is. They also pinpoint sites of active burning, detect hot spots and estimate of where the fire is burning the hottest, so that response efforts can be directed most efficiently.
SWIR Sensor vs. NIR Sensor:
Near Infrared sensor are extremely important for ecology because healthy plants reflect it – the water in their leaves scatters the wavelengths back into the sky. They can be used for vegetation monitoring, crop stress etc. By comparing it with other bands, we get indexes like NDVI, which let us measure plant health more precisely than if we only looked at visible greenness. But NIR sensor do not tell us about the geology, rocks etc.
SWIR sensors are particularly useful for telling wet earth from dry earth, and for geology: rocks and soils that look similar in other bands often have strong contrasts in SWIR. SWIR sensors discriminates moisture content of soil and vegetation and penetrates thin clouds.
Remote Sensing Applications of SWIR Sensors:
- Mineral exploration
- Wildfire response (can penetrate through smoke)
- Food security
- Urban feature identification (such as roofing and construction materials)
- Petroleum (e.g. an oil spill)
- Snow and Ice discrimination
Soil moisture estimation
Advantages of SWIR for Remote Sensing
Provide imagery in day and night
Can see penetrates thin clouds
SWIR sensors are small in size, hence lighter payload and can be mounted on UAV
Can see through the smoke
Atmospheric aerosols have lesser effect on SWIR bands.
SWIR for Surveillance and Target Identification
SWIR is used for surveillance and target identification and has four distinct advantages over visible and thermal sensors:
No Illumination Needed
SWIR cameras are extremely sensitive to light, with individual pixels of the focal plane array able to capture and detect single photons. When combined with a phenomenon called night sky radiance, which emits up to 700% more illumination than starlight and is comprised mainly of SWIR wavelengths, SWIR cameras are able to see objects with a high level of detail, even on moonless and starless nights.
See Through Fog & Haze
The longer wavelengths of the SWIR spectrum are able to penetrate fog, smoke and other atmospheric conditions. As a result, shortwave infrared cameras consistently provide superior images to their optical counterparts as they are able to see through these obstructions, making them particular useful in cities, marine and coastal protection.
Effective for Identification
Unlike thermal energy which is radiated, SWIR is a reflected energy like visible light, which makes it a viable technology for identification purposes, and the only such technology that can be effectively used at night without additional illumination. While images made from the SWIR wavelength are black and white, they have similar properties to visible light, such as reflection and contrast.
See Through Glass
Another advantage that SWIR has over thermal is its ability to see through glass. This not only allows SWIR cameras to look through most windows but also allows for more affordable glass lenses and housings to be used.
SWIR Advantages in Microscopy
SWIR microscopes are designed to image what cannot be seen and magnified with visible microscopes.
Many semiconductor materials are NOT transparent to visible light but are to SWIR backlight illumination. A good example is the high SWIR magnification of industrial semiconductor wafers:
We can configure SWIR microscopes to your specific requirements for field of view, magnification range, and illumination type (reflective, co-axial, or backlight transmissive)
SWIR Reflective and Hyperspectral Imaging
For many remote sensing, commercial, and scientific application, single and multi-color imagery is needed. Single wavelength SWIR reflective imaging is very easy to implement with a SWIR camera, fixed focal length lens, and bandpass filter. Multi-wavelength hyperspectral imagers require integrating the SWIR camera with a SWIR dispersive spectrometer.
Hyperspectral imaging, like other spectral imaging, collects and processes information from across the electromagnetic spectrum. The goal of hyperspectral imaging is to obtain the spectrum for each pixel in the image of a scene, with the purpose of finding objects, identifying materials, or detecting processes.
Whereas the human eye sees color of visible light in mostly three bands (red, green, and blue), SWIR spectral imaging divides the spectrum into many more SWIR bands. This technique of dividing images into bands can be extended beyond the visible. In hyperspectral imaging, the recorded spectra have fine wavelength resolution and cover the SWIR range of wavelengths.
Engineers build hyperspectral sensors and processing systems for applications in astronomy, agriculture, biomedical imaging, geosciences, physics, and surveillance. Hyperspectral sensors look at objects using a vast portion of the electromagnetic spectrum. Certain objects leave unique ‘fingerprints’ in the electromagnetic spectrum. Known as spectral signatures, these ‘fingerprints’ enable identification of the materials that make up a scanned object. For example, a spectral signature for oil helps geologists find new oil fields.
SWIR Laser Beam Profiling and Tracking
Many lasers for scientific and military applications lase in the SWIR region and SWIR cameras can easily track the location and power beam profile in real time. Our SWIR cameras are very well suited to these applications because of the SWIR sensor’s exceptional dynamic range, short exposure time, and fast frame rate.
640×512 InGaAs focal plane array camera for visible and SWIR imaging
Canada’s First Airborne SWIR Imaging Spectrometer
Understanding the visibility of blood on dark surfaces: A practical evaluation of visible light, NIR, and SWIR imaging
SWIR InGaAs focal plane arrays in France
Implementation of a novel low‐noise InGaAs detector enabling rapid near‐infrared multichannel Raman spectroscopy of pigmented biological samples
Spectral imaging of chemical compounds using multivariate optically enhanced filters integrated with InGaAs VGA cameras