Polyspectral imaging (multispectral and hyperspectral) basically consists of taking images using a reduced part of the wavelength spectrum that the sensor can detect. This is achieved by filtering the incident light so that only the band of interest is allowed to pass. In this way, only one image is obtained, but the process can be repeated for different spectral ranges. Some cameras make use of technologies that allow taking images of different regions of the spectrum simultaneously, or quasi-simultaneously. We will thus obtain the response of the evaluated object against the different colors (spectral ranges). Let's say that each image is the result only of each of the "colors" that the object reflects.
The analysis of the different images will provide very valuable information on the state or properties of the object.
Depending on the technology used, more or fewer spectral bands can be identified. Nobody agrees, but it seems accepted that:
- multispectral cameras or imaging systems: up to 10 bands
- hyperspectral cameras or imaging systems: more than 10 bands
Nireos-HERA hyperspectral technology
Based on Fourier-transform (FT) spectroscopy, a technique that uses interference of light rather than dispersion to measure spectra. Light is split in two collinear time-delayed replicas, whose interference pattern is measured by a detector as a function of their delay. The FT of the resulting interferogram yields the continuous-intensity spectrum of the waveform. FT spectrometers have prominent advantages over dispersive ones:
(i) higher signal-to-noise ratio in a readout-noise-dominated regime (multiplex or Fellgett’s advantage)
(ii) higher throughput and increased system étendue, due to the absence of slits (Jacquinot’s advantage)
(iii) higher wavelength accuracy (Connes’ advantage)
Moreover, FT spectrometers provides a flexible spectral resolution, which is adjusted (via software) at will by varying the maximum scan delay and does not affect the throughput of the device.
Furthermore, our interferometer is ultra-stable and completely insensitive to external vibrations. Unlike a Michelson or a Mach–Zehnder interferometers, our device does not separate the two replicas in space (which would cause mechanical instabilities) but in polarization. To this purpose, it makes use of birefringence. In this class of materials, vertically and horizontally polarized light experience a different index of refraction, and thus it propagates with different speed. It is possible to vary the delay between the two replicas by changing the insertion of a birefringent wedge, thus continuously varying the material thickness.
Our patented passive common-path interferometer inherently features an extremely high delay stability and reproducibility (better than 1 attosecond, i.e. approx. a thousandth of the wavelength). For this reason, it can be used without any active control or position tracking even in harsh environments such as industries in the presence of vibrations.
In this vídeo you can learn more on FT technology and how the Gemini inteferometer works.
Silios multispectral technology
Color Shades(R) technology is a unique manufacturing technique developed by Silios Technologies to produce multispectral pixelated filters.
Made by hybridizing a customized Bayer-type matrix on a commercial CMOS or InGaAs sensor, the Silios multispectral cameras allow the spectrum to be extracted at each point of the image.
The sensor is divided into "n" zones and on each of them a type of spectral filter is applied to all its pixels. In this way, each zone records the image corresponding to a color, to a spectral band.
In this way, all the spectral images are achieved at the same time, and the Silios cameras are therefore real snapshot.
An added advantage of Silios technology is the low resonance level of its filters (low Q factor). This implies:
- low sensitivity to the angle of incidence of light: only slight spectral band changes with angles up to 15°. Other technologies that also distribute the sensor, on the other hand, accept only very small fields of view (FoV) that force the use of very large focal length lenses.
- high sensitivity, thanks to high integrated transmission
Typical applications of polyspectral imaging cameras and systems are:
- vegetation: species classification and identification, NDVI, plant health and water stress study
- water: analysis and contaminants; wetland monitoring
- land, crops and agriculture: analysis of components, nutrients or fertilizers
- detection and study of fires
- agri-food industry: food, beverages; sorting and packaging
- materials, mining, petrochemical
- archeology and art
- biomedicine and biosciences; microscopy
- health: study of tissues, diseases, wounds
- pharmaceutical industry
- identification of surfaces and coatings
- recycling and waste management
- forensic science
- identification of counterfeits
- remote sensing
- machine vision in general
- aerial, field, laboratory, industrial or R&D applications in general
Iberoptics can offer you a wide range of multispectral and hyperspectral cameras:
- VIS-NIR (VNIR): 400 - 1000nm
- Multispectral (Silios)
- Hyperspectral (Nireos)
- SWIR: 900 - 1700 / 900-2500nm
- Multispectral (Silios)
- Hyperspectral 900-1700nm (Nireos)
- Hyperspectral 900-2300nm (Nireos)