Multi-channel Camera Research Articles

Spectral Recalibration for In-Flight Broadband Sensor Using Man-Made Ground Targets

Accurate spectral calibration of the in-flight sensors is crucial for processing and exploration of remotely sensed data. This paper developed a strategy to make spectral recalibration (i.e., spectral response function, central wavelength, and bandwidth) for in-flight broadband sensor using a device-responsivity-decomposition model with a priori knowledge and an optimization algorithm. Sensitivity analysis indicates that an accurate result requires the targets to be observed under a dry and clear atmospheric condition (column water vapor <; 2 g/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and visibility > 23 km) and no more than 5% error is included in the measured data. The new strategy was used to retrieve the spectral parameters along with radiometric calibration coefficients for a multichannel camera onboard an unmanned aerial vehicle from simultaneously remotely sensed and ground measured data sets over 19 (15 color-scaled and four gray-scaled) man-made surface targets, and the retrieved results were validated with a similar data set over another four man-made targets. It demonstrated that the camera's spectral parameters were accurately retrieved and an error less than 3.5 W/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /μm/sr was brought to the channel radiance.

Large-scale particle tracking velocimetry with multi-channel CCD cameras

This paper presents a large-scale particle tracking velocimetry (LSPTV) system for measuring surface velocity in vast unsteady flows. The system consists of a flexible number of one-computer-six- camera working units connected via local network or the internet. Multiple zero-tilting cameras are used to increases the field of view with minimum perspective distortions. External synchronization of video outputs of all cameras facilitates uninterrupted image acquisition within the system. Effectiveness and efficiency of the multi-channel LSPTV are enhanced by optimizing illumination, flow seeding, image acquisition and correction, tracer identification, particle matching, and post-processing. The capacity of the LSPTV was demonstrated in the measurement of physical model flows for the Three Gorges Project.

Development of an inspection system for planar steel surface using multispectral photometric stereo

We address the methodology and hardware design for detecting defects on a steel surface. The goal of this work is to develop a surface inspection system for defects with three-dimensional (3-D) characteristics on planar steel surface using multispectral photometric stereo technique. First, the reflections of multispectral illuminations from a steel surface are captured by a multi-channel camera system. Then, a 3-D reconstructed surface profile is extracted from estimated gradient fields. The developed system is applied to real steel specimens and the experimental results show that it can reliably detect tiny defects on the surface.

A pepper-pot emittance meter for low-energy heavy-ion beams

A novel emittance meter has been developed to measure the four-dimensional, transverse phase-space distribution of a low-energy ion beam using the pepper-pot technique. A characteristic feature of this instrument is that the pepper-pot plate, which has a linear array of holes in the vertical direction, is scanned horizontally through the ion beam. This has the advantage that the emittance can also be measured at locations along the beam line where the beam has a large horizontal divergence. A set of multi-channel plates, scintillation screen, and ccd camera is used as a position-sensitive ion detector allowing a large range of beam intensities that can be handled. This paper describes the design, construction, and operation of the instrument as well as the data analysis used to reconstruct the four-dimensional phase-space distribution of an ion beam. Measurements on a 15 keV He(+) beam are used as an example.

Compact infrared cryogenic wafer-level camera: design and experimental validation

We present a compact infrared cryogenic multichannel camera with a wide field of view equal to 120°. By merging the optics with the detector, the concept is compatible with both cryogenic constraints and wafer-level fabrication. The design strategy of such a camera is described, as well as its fabrication and integration process. Its characterization has been carried out in terms of the modulation transfer function and the noise equivalent temperature difference (NETD). The optical system is limited by the diffraction. By cooling the optics, we achieve a very low NETD equal to 15 mK compared with traditional infrared cameras. A postprocessing algorithm that aims at reconstructing a well-sampled image from the set of undersampled raw subimages produced by the camera is proposed and validated on experimental images.

Free-standing subwavelength metallic gratings for snapshot multispectral imaging

A mosaic of ten spectral filters has been fabricated in a single 20 mm2 membrane drilled by nanoslits and coated by a gold layer. The nanostructured core-shell gratings exhibit 70% average maximum transmission efficiency in 15% aperture area, which represents a fivefold enhancement compared to the geometrical transmission. This mosaic of bandpass filters regularly spaced in the 3–5 μm wavelength range is used to demonstrate real-time spectral imaging in a multichannel camera.

A novel ultra-high speed camera for digital image processing applications

Multi-channel gated-intensified cameras are commonly used for capturing images at ultra-high frame rates. The use of image intensifiers reduces the image resolution and increases the error in applications requiring high-quality images, such as digital image correlation. We report the development of a new type of non-intensified multi-channel camera system that permits recording of image sequences at ultra-high frame rates at the native resolution afforded by the imaging optics and the cameras used. This camera system is based upon the concept of using a sequence of short-duration light pulses of different wavelengths for illumination and using wavelength selective elements in the imaging system to route each particular wavelength of light to a particular camera. As such, the duration of the light pulses controls the exposure time and the timing of the light pulses controls the interframe time. A prototype camera system built according to this concept comprises four dual-frame cameras synchronized with four dual-cavity pulsed lasers producing 5 ns pulses in four different wavelengths. The prototype is capable of recording four-frame full-resolution image sequences at frame rates up to 200 MHz and eight-frame image sequences at frame rates up to 8 MHz. This system is built around a stereo microscope to capture stereoscopic image sequences usable for 3D digital image correlation. The camera system is used for imaging the chip–workpiece interface area during high speed machining, and the images are used to map the strain rate in the primary shear zone.

Measurement of transient deformations using digital image correlation method and high-speed photography: application to dynamic fracture

The digital image correlation method is extended to the study of transient deformations such as the one associated with a rapid growth of cracks in materials. A newly introduced rotating mirror type, multichannel digital high-speed camera is used in the investigation. Details of calibrating the imaging system are first described, and the methodology to estimate and correct inherent misalignments in the optical channels are outlined. A series of benchmark experiments are used to determined the accuracy of the measured displacements. A 2%-6% pixel accuracy in displacement measurements is achieved. Subsequently, the method is used to study crack growth in edge cracked beams subjected to impact loading. Decorated speckle patterns in the crack tip vicinity at rates of 225,000 frames per second are registered. Two sets of images are recorded, one before the impact and another after the impact. Using the image correlation algorithms developed for this work, the entire crack tip deformation history, from the time of impact to complete fracture, is mapped. The crack opening displacements are then analyzed to obtain the history of failure characterization parameter, namely, the dynamic stress intensity factor. The measurements are independently verified successfully by a complementary numerical analysis of the problem.

Improving the Speckle Noise Attenuation of Simultaneous Spectral Differential Imaging with a Focal Plane Holographic Diffuser

Direct exoplanet detection is limited by speckle noise in the point spread function (PSF) of the central star. This noise can be reduced by subtracting PSF images obtained simultaneously in adjacent narrow spectral bands using a multi-channel camera (MCC), but only to a limit imposed by differential optical aberrations in the MCC. To alleviate this problem, we suggest the introduction of a holographic diffuser at the focal plane of the MCC to convert the PSF image into an incoherent illumination scene that is then re-imaged with the MCC. The re-imaging is equivalent to a convolution of the scene with the PSF of each spectral channel of the camera. Optical aberrations in the MCC affect only the convolution kernel of each channel and not the PSF globally, resulting in better correlated images. We report laboratory measurements with a dual channel prototype (1.575 micron and 1.625 micron) to validate this approach. A speckle noise suppression factor of 12-14 was achieved, an improvement by a factor ~5 over that obtained without the holographic diffuser. Simulations of realistic exoplanet populations for three representative target samples show that the increase in speckle noise attenuation achieved in the laboratory would roughly double the number of planets that could be detected with current adaptive optics systems on 8-m telescopes.

Application of a fast electrical pulse in gated multichannel plate camera

An eight-frame gated microchannel plate (MCP) camera and a gating electrical pulse are described in this article. The gating electrical pulse is obtained by first generating a high voltage fast step pulse using avalanche transistors in Marx bank configuration, and then shaping it using avalanche diodes. The high voltage fast step pulse is about 200 ps in fall time and 4 kV in amplitude. The gating pulse wave form with width of 160 ps and amplitude of 2.5 kV is achieved. Each frame photocathode coated with gold on the MCP is part of a 12 Omega transmission line with open circuit end driven by the gating electrical pulse. The camera is tested by illuminating its photocathode with ultraviolet laser pulses, 266 nm in wavelength, which shows exposure time as short as 120 ps.

Optimization of apertures and collimators for multi-channel plasma diagnostics

Aperture, pin-hole and collimator detection systems are often used in plasma diagnostics, for example, in soft x-ray detection and bolometer systems. In this article the simultaneous optimization of viewing-beam overlap and light yield is considered in multi-channel aperture and collimator systems for two-dimensional (2D) tomography. This article briefly highlights the relation between beamwidth overlap and spatial aliasing in tomography, and how aliasing can be avoided in theory and in practice. Three-dimensional (3D) single-channel aperture and collimator systems can be approximated by a combination of two planar systems if the aperture is rectangular. Three ways to optimize beamwidth overlap and light yield for planar aperture and collimator systems are considered in detail: overlap of the angular étendue at the full width at half maximum (FWHM), overlap of the geometric function at the FWHM a certain distance from the aperture, and arbitrary overlap for a given maximum beamwidth. The combination of 2D effects from all three optimization methods were used in the design of 3D apertures for a new multi-channel bolometer camera on the Joint European Torus tokamak. The resulting apertures are complex, but the new camera has several advantages over previous cameras.

A self-calibrating, multichannel streak camera for inertial confinement fusion applications

Self-calibrating, multichannel UV streak cameras have been designed, and six units have been deployed on the OMEGA laser system. These instruments acquire 12 channels simultaneously on a low-noise, charge-coupled-device camera in single-shot operation. The instruments can discern temporal features out to a bandwidth of 11 GHz, and the peak signal-to-noise ratio in each channel is 200:1. The unique feature of this system is the self-calibration ability built into it. The geometric distortions, flat field, and sweep speed of each channel can be measured and adjusted on a routine basis. By maintaining a strick regime of weekly calibrations, accurate power-balance measurements on the OMEGA laser can be obtained. These cameras represent a cost-effective solution for power balancing the OMEGA laser system.

On the potential of the imaging atmospheric Cherenkov technique for study of the mass composition of primary cosmic radiation in the energy region above 30 TeV

The technique of imaging atmospheric Cherenkov telescopes (IACTs) has proved to be an effective tool to register cosmic γ-rays in the very high energy region. The high detection rate of the IACT technique and its capability to reconstruct accurately the air shower parameters make it attractive to use this technique for the study of the mass composition of cosmic rays (CRs). In this article we suggest a new approach to study the CR mass composition in the energy region from 30 TeV/nucleus up to the “knee” region, i.e. up to a few PeV/nucleus, using an array of imaging telescopes of a special architecture. This array consists of telescopes with a relatively small mirror size (∼10 m 2) separated from each other by large distances (∼500 m) and equipped by multi-channel cameras with a modest pixel size (0.3–0.5°) and a sufficiently large viewing angle (6–7°). Compared to traditional IACT systems (like HEGRA, HESS or VERITAS) the IACT array considered in this study could provide a very large detection area (several km 2 or more). At the same time, it allows an accurate measurement of the energy of CR-induced air showers (the energy resolution ranges within 25–35%) and an effective separation of air showers created by different nuclei. Particularly, it is possible to enrich air showers belonging to the nucleus group assigned for selection up to ∼90% purity at a detection efficiency of 15–20% of such showers.

Sustained fully non-inductive scenarios using pressure and current profile control with ECCD

The ECW system on Tokamak à configuration variable (TCV) allows the study of a wide range of poloidal and toroidal launch angles. Both electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) experiments have been performed to demonstrate the modification of the electron temperature and current profiles. In particular a multi-channel hard X-ray camera (on loan from Cadarache) clearly shows the generation of a high energy electron tail, which increases with increasing toroidal launch angle. Using a scenario with three 0.5 MW gyrotrons providing on-axis co-current drive (CO-CD), we have obtained full current replacement of 150 kA. However, this leads to very peaked profiles which are MHD unstable and the discharge disrupts. By careful distribution of the power deposition and current source profiles over the minor radius, we have obtained steady-state scenarios up to 124 kA with T e0 ≈3.5 keV and n ̄ e =10 19 m −3. These scenarios are sustained for 1.9 s, that is, more than 900 confinement times and more than ten current redistribution times. Therefore, both the pressure and current profiles are sustained by the 1.5 MW of ECCD power. By lowering the feedback plasma current demand, the ohmic transformer is recharged; this provides a very good diagnostic of the total non-inductive current driven in these scenarios.

Spectral imaging by a multichannel camera

The <i>Journal of Electronic Imaging</i> (JEI), copublished bimonthly with the Society for Imaging Science and Technology, publishes peer-reviewed papers that cover research and applications in all areas of electronic imaging science and technology.

An imaging spectrometer operating in the visible near infrared for the study of planetary surfaces

This paper summarizes the capabilities, performances, and technical solutions of the Visible and Near InfraRed (VNIR) imaging spectrometer designed for remote sensing of planetary surfaces from a satellite platform. The VNIR consists of a multichannel camera with a spectral range 0.35 < λ < 1.05 μm which acquires data in 288 spectral channels with a spectral resolution of 24.3 A ° . The instantaneous field of view of the instrument is 0.4× 0.4 mrad. The simultaneous acquisition of both spatial and spectral data provides a powerful means for invest- igating the mineralogical and chemical composition of surfaces of solar system objects. The paper also reports some results from the first campaign of ground-based telescopic observations intended to test the instrument.

The effective technique of the charged particles background discrimination in the atmospheric Cherenkov light detectors

It is shown that parameters of flashes, detected by multichannel image cameras of Cherenkov detectors with closed lids are close to those of Cherenkov flashes initiated by VHE gamma-quanta in the Earth atmosphere. Even after application of criteria for gamma-like events selection a considerable part of those flashes may be misclassified and accepted as gammas. Since the flashes of this kind are detected also during normal measurements with the opened lids of image cameras it just increases the background and, as a consequence, decreases the detector sensitivity even when one uses an anticoincidence scintillator shield around the camera (its efficiency is about 75 %). The use of detectors consisting of two (or more) sections no less than 20–30 m apart permits us to avoid the detection of both muon and local charged particles flashes in the course of observations.

Los Alamos pinhole camera (LAPC): A new flexible x-ray pinhole camera

We have recently designed, built, and fielded a versatile, multichannel x-ray pinhole camera. The Los Alamos pinhole camera was designed to fit into any 6 in. manipulator (SIM) which is a standardized target chamber diagnostic tube. There are currently compatible SIMs available at the Trident, Omega, and NOVA laser systems. The camera uses nine pinholes in a 3×3 array to produce images at the film plane. The film housing is designed to hold multiple sheets of stacked x-ray film which also uses a dark slide to protect the film before exposure. Magnifications of 12, 8, 4, and 2X are selected by slip-on nose cones, which support pinholes, collimators, and blast shields. Individual channel filtering is provided by a 3×3 filter pack containing nine separate filter sub packs. Spatial resolution is limited by the pinhole diffraction limit and field of view is dependent on magnification and filter pack diameter.

On the optimization of multichannel cameras for imaging atmospheric Cherenkov telescopes

The optimization of the pixel size and of the field of view of the multichannel cameras of imaging atmospheric Cherenkov gamma -ray telescopes is discussed using the minimum distortion of the Cherenkov light images as a basic criterion. The parameters defining the shape of the Cherenkov image in the second-moment approach can already be properly determined using a pixel size approximately=0.25 degrees . The orientation of the image is more sensitive to the pixel size; thus, the optimal determination of orientation parameters requires a reduction of the pixel size to approximately=0.15 degrees . For observations of point gamma -ray sources the field of view of the imaging camera should not be significantly less than 4 degrees . To study moderately extended sources and sources whose positions are only known within approximately=1 degrees (like many EGRET gamma -ray sources) a camera with field of view >or=5 degrees is required.

On the optimal characteristics of the multichannel imaging camera for TeV gamma ray observations

The detection efficiency of atmospheric Cerenkov flashes as a function of the camera parameters was studied in order to determine the optimal camera parameters for the discovery of VHE gamma ray point sources. Simulations of the detection process and calculation of the flash parameters are used. It is shown that the optimal value of the camera angular diameter is in the range 3.1 degrees -3.7 degrees and the optimal pixel size is from 0.2 degrees to 0.3 degrees . In these cases the number of photomultipliers ranges from 61 to 127 for a camera with a hexagonal window. The computations are made for the case when any two channels generate a logical signal, i.e. at least two pulses are higher than the threshold. Note that the photocathode current fluctuation caused by the night sky radiation is very important for the calculations because it is the major factor which determines the lower limit for the pixel size. Calculations neglecting fluctuations caused by the night sky lead to an incorrect conclusion: the smaller the pixel size, the better are the images, i.e. they are close to real ones (unlimited resolution camera).