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In-Flight Calibration Design
Published in Shen-En Qian, Hyperspectral Satellites and System Design, 2020
For absolute radiometric calibration the sun is used as a source of reference spectral irradiation and correct spectral composition. A sun-illuminated diffuser placed in front of the telescope reflects radiation entering the sun calibration port into the system aperture. Acting as a diffuse reflectance standard the full entrance pupil is simultaneously illuminated by the diffuser for all field points. Figure 9.3b illustrates the arrangement. The diffuser panel is mounted on a mechanism which allows it to be rotated in front of the telescope aperture for system calibration. Care is taken to keep residual specular reflections from the diffuser from entering the FOV of the telescope. The baffle design for the Sun calibration port is such that stray reflections on the panel are avoided. Spectralon has been selected as diffuser material since it has been demonstrated to be a stable standard of diffuse reflectance in a space environment. In the storage position of the mechanism the diffuser will be sheltered by a protection cover to prevent constant UV exposure causing premature degradation.
Applications of Nanocarbons for High-Efficiency Optical Absorbers and High-Performance Nanoelectromechanical Systems
Published in Sivashankar Krishnamoorthy, Krzysztof Iniewski, Nanomaterials, 2017
Anupama B. Kaul, Jaesung Lee, Philip X.-L. Feng
The optical measurements on the samples were conducted from λ ~ 350 to 2500 nm using a high-resolution, fiber-coupled, spectroradiometer (ASD Inc., Fieldspec Pro, Boulder Co) where a standard white light beam was focused at normal incidence to the sample, as shown by the schematic in the inset of Figure 10.2c. The bare fiber connector of the spectroradiometer was oriented at ~40° from the normal. Relative reflectance spectra were obtained by first white referencing the spectroradiometer to a 99.99% reflective spectralon panel. The reflected light intensity from the sample was then measured and the spectra were compared for samples synthesized under different growth conditions.
Hyperspectral Imaging of Diabetes Mellitus Skin Complications
Published in Andrey V. Dunaev, Valery V. Tuchin, Biomedical Photonics for Diabetes Research, 2023
Viktor V. Dremin, Evgenii A. Zherebtsov, Alexey P. Popov, Igor V. Meglinski, Alexander V. Bykov
A broadband illumination unit utilizing 50W halogen lamp was constructed, based on a fiber-optic ring illuminator (Edmund Optics, USA), providing a uniform distribution of light intensity in the camera focal plane with the average irradiance of 4.3 ± 0.5 mW/cm2 in the camera field of view (FOV) on the skin surface. The use of the ring illuminator made it possible to combine the axes of illumination and detection. The illumination ring and the camera were equipped with rotatable broadband linear polarizers fixed at the crossed position to reduce specular reflection from the measured object. A 3D model of the unit was implemented using CAD software and printed out with a 3D material printer. The measurement approach considered allows the capture of the reflected signal of the entire FOV at a certain waveband. The scanning is performed in the spectral domain. Generally, the constructed device is capable of recording spatially and spectrally resolved reflectance used for further ANN analysis. Thus, diffuse reflectance is recorded with a spectral step of 5 nm from an area of 8 × 8 cm2 at 1010 × 1010 pixels resolution by the CMOS sensor. Normalized spatially resolved tissue reflectance is calculated as a pointwise ratio of dark-noise-corrected light intensity reflected from the object to that reflected from the diffuse reflectance standard. A hypercube from the reflectance standard is recorded every time before the measurement of an object. Gray Spectralon (50% reflection, Labsphere, Inc., USA) is used as a calibration standard. Use of the gray standard allows us to avoid the possible oversaturation of the CMOS sensor matrix for white reflectance standard (100% reflection) at a fixed integration time.
Reflectance spectroscopy and ASTER mapping of aeolian dunes of Shaqra and Tharmada Provinces, Saudi Arabia: Field validation and laboratory confirmation
Published in International Journal of Image and Data Fusion, 2023
Yousef Salem, Habes Ghrefat, Rajendran Sankaran
In addition, the spectral reflectances of the different sand fractions are measured in the visible to shortwave infrared (VNIR-SWIR, 0.4–2.5 μm) regions of the electromagnetic spectrum using a GER3700 spectrometer in the laboratory to understand the spectral absorption of minerals of the dunes and map the dunes. The measurement is carried out keeping the instrument vertically above the samples. The samples are illuminated at an incident angle of 30° and reflectances are measured in a rectangular field of view of 1.5 by 7 cm. The GER3700 spectrometer measures 640 bands between 0.315 and 2.519 μm at the spectral sampling range from 0.0015 to 0.012 μm (Ghrefat et al. 2007). The spectral radiance (W/m2/sr/nm) of a Spectralon (calibration material) is used as a reference to measure the spectral radiance of samples. The reflectance of samples is calculated from the ratio of two spectral radiance that is by dividing the radiance of the Spectralon by the radiance of the measured target.
Accuracy of Hyperspectral Imaging Systems for Color and Lighting Research
Published in LEUKOS, 2023
Aiman Raza, Dominique Dumortier, Sophie Jost-Boissard, Coralie Cauwerts, Marie Dubail
The MacBeth ColorChecker Chart (MCC) also known as the X-Rite Munsell Color checker classic is a reference for color image processing (Berns 2001) and is often used for color rendering characterization (Royer and Wei 2017). The 24 patches of the MCC used to assess the accuracy of the HSI Systems represent 24 natural colors corresponding to skin tone, sky, flowers, primary colors, and a gray scale. To measure the reference spectra, a reference white standard called Spectralon (Gigahertz-Optik ref. BN-R986SQ2C) was included in the scene. Spectralon has the highest diffuse reflectance of a known material and is highly Lambertian in nature. The scene also contained 33 color samples from the Munsell Book of Color, which were added for another study and were not analyzed (in this article) to avoid redundancy in result analysis. A visual acuity chart (a chart with Landolts rings and tumbling E’s in the upper part, and a Rossano and Weiss-Inserm test in the lower part) was also placed in the scene to visually assess the sharpness of the images (without analysis). All the objects were placed in a white booth with walls of 0.81 reflectance factor (see Fig. 1).
Using colour, shape and radionuclide fingerprints to identify sources of sediment in an agricultural watershed in Atlantic Canada
Published in Canadian Water Resources Journal / Revue canadienne des ressources hydriques, 2018
Monica Boudreault, Alexander J. Koiter, David A. Lobb, Kui Liu, Glenn Benoy, Philip N. Owens, Serban Danielescu, Sheng Li
The colour of both source material and sediment samples was measured using spectral readings over a 350–2500-nm wavelength range using a spectroradiometer (ASD FieldSpec Pro, Analytical Spectral Device Inc., Boulder, CO, USA, at the University of Manitoba, Winnipeg, Canada). A 10-cm-diameter transparent plastic support was used to hold the sample that was smoothed with a straight edge in order to reduce shading. The Spectralon standard (white reference) was used to calibrate the spectroradiometer prior to each measurement. The samples were illuminated with a white light source (a 1000-W quartz halogen lamp mounted on a tripod at a distance of 10 cm), and a fibre optic cable was mounted 2 cm away and at an angle of 45° from the sample.