A new "hera" in
hyperspectral
imaging cameras
The novel Fourier Transform-based HERA hyperspectral imaging cameras are designed to provide an exceptional light throughput, resolution, and ease of use.
Novel Fourier Transform-based hyperspectral imaging cameras enabling low light applications.
HERA IPERSPETTRALE is the novel hyperspectral camera commercialized by NIREOS. Thanks to the employed Fourier transform approach and to its 1-cm clear aperture, the camera is specifically designed to provide an exceptional throughput and sensitivity, making it the ideal device for low-light applications, such as cultural heritage, biology, and vegetation studies.
What is Hyperspectral Imaging?
Hyperspectral imaging (HSI) is a powerful analytical technique based on spectroscopy, with the aim of measuring the light spectrum at each point of an image.
While the human eye has only three colour receptors, for blue, green, and red light, HSI measures the continuous spectrum of the light as a function of the wavelength λ for each pixel of the scene at coordinates (x, y) with fine spectral resolution. The HSI data is thus a three-dimensional data cube, as a function of x, y and λ. This extensive informative content is processed by algorithms that enable the extraction of quantitative parameters related to the physicochemical properties of the imaged objects, as well as the clustering into different components, useful for the analysis of congested scenes.
In recent years, HSI has been applied to a large variety of applications, ranging from medical and biological imaging, from agriculture to archaeology and conservation science.
Approaches to hyperspectral imaging
Recently, HSI has been implemented in a wide variety of methods:
The most straightforward approaches are snapshot HSI systems, which employ a matrix of bandpass filters on the surface of the detector, and spectral HSI systems, which use a tuneable spectral filter (or a filter wheel) in front of a monochrome camera. The main drawback of these techniques is represented by the acquisition of a limited and discrete number of bands.
To measure continuous spectra, a common method is spatial scanning HSI, which combines a dispersive spectrometer with a raster-scanning approach, either in point-scanning (whiskbroom) or line-scanning (push-broom) modes. This technique is widely applied in industrial quality-control monitoring processes. However, its main limitation is related to the high losses caused by the entrance slit of the spectrometer.
An alternative HSI method to measure continuous spectra combines a monochrome imaging sensor with an interferometer. In this approach, known as Fourier transform (FT) imaging spectroscopy, the light of interest is split into two collinear delayed replicas, whose interference pattern is measured by a detector as a function of their relative delay.
The Fourier transform of the resulting interferogram yields the continuous intensity spectrum of the light. The FT approach has prominent advantages over dispersive techniques, namely (i) the multiplex or Fellgett’s advantage, (ii) the étendue or Jacquinot’s advantage,(iii) the Connes’ advantage, and (iv) a variable spectral resolution, which can be adjusted at will by varying the maximum scan delay of the interferometer via software, without affecting the throughput of the device.
HERA IPERSPETTRALE's working principle
HERA IPERSPETTRALE is based on a Fourier transform (FT) approach and employs a patented common-path birefringent interferometer (CPI, a modified version of the GEMINI Interferometer) in combination with an objective and a bidimensional sensor. The novel CPI guarantees remarkable accuracy, reproducibility, and stability, and it overcomes the limitations of other prism-based imagers, providing negligible chromatic dispersion and small geometrical separation between the interfering replicas, leading to high degree of coherence at each pixel and a strong interference modulation. All these features enable the camera to provide high quality spectra.
The three-dimensional HSI data-cube is measured in the time-domain, by recording multiple monochrome images acquired at different positions of the CPI. Finally, FTs at all the pixels of the image provide the hyperspectral data-cube.
As a result of an FT, the spectrum at each pixel is a continuous curve, so the number of bands is virtually unlimited, and it is not defined by the hardware. HERA IPERSPETTRALE is available in the “VNIR” (400-1000 nm), “SWIR” (900-1700 nm), “eSWIR” (1200-2200 nm) and “VIS-SWIR” (400-1700 nm) ranges.
As shown in the picture, the camera works with a staring approach, and it can be mounted on a tripod or coupled to a commercial microscope, to easily measure static samples, without the need of additional equipment or moving parts. This feature, combined with the remarkable sensitivity, makes the device particularly suitable for scientific experiments or characterization of samples in R&D departments, in all those applications where the signals are weak (e.g. fluorescence hyperspectral imaging) or it is not possible to employ powerful illumination lamps that would damage the sample (e.g. biology, cultural heritage, vegetation etc.).
Main applications
Discover the HERA Hyperspectral Cameras
