Details of a multispectral imaging radiometer specially designed to retrieve fire characteristics from a nanosatellite platform are presented. The instrument consists of an assembly of three cameras providing co-registered midwave infrared, longwave infrared, and visible image data. Preliminary evaluation of the instrument budgets showed approximately a mass of 12 kg, an envelope of 220×240×200 mm3, and an average power consumption of 13 W. A method was devised to stagger two linear arrays of 512×3 VOx microbolometers in each infrared detector assembly. Investigation of the first completed detector assemblies showed an alignment accuracy better than 10% of pixel pitch and a response uniformity achieved across 92% of the pixels. Effects of the thermal environment seen by the pixels were evaluated to optimize the radiometric packaging design. It was found that the resulting thermal stability of the arrays, combined with the available electronic dynamic range, allows acquisition of targets with temperatures as high as 750 K with the desired accuracy and without saturation. The detector assemblies were able to withstand extreme environments with vibration up to 14 grms and temperatures from 218 to 333 K. Exposing the assembly’s window and bandpass filter to proton and Co-60 gamma radiation with successive dose of 10 krad and 100 Gy resulted in no adverse effect on their transmittance characteristics. Performance characteristics of the assembled midwave and longwave infrared telescopes were consistent with modeling predictions. Results of the point spread function measurement supported the conclusion that the lenses alignment had been achieved within mechanical tolerances for both telescopes.
This paper reviews recent developments in customized packaged bolometers at INO with an emphasis on their applications. The evolution of INOs bolometer packages is also presented. Fully packaged focal plane arrays of broadband microbolometers with expanded absorbing range are shown, for applications in spectroscopic and THz imaging. This paper also reports on the development of customized packaged bolometer focal plane arrays (FPAs) for space applications such as a multispectral imaging radiometer for fire diagnosis, a far infrared radiometer for in-situ measurements of ice clouds and a net flux radiometer for Mars exploration.
Subwavelength imaging has recently seen increased interest in multiple fields. There are various applications and distinct contexts for performing subwavelength imaging. The technological ways to proceed as well as the benefits obtained are as various as the applications foreseen. To benefit from subwavelength imaging a way around standard imaging procedure is often required.
INO is also involved in this activity mainly for the infrared and the THz wavebands. In the infrared band a detector with 17 um pixel pitch, larger than the pixel, was used in conjunction with a microscanning device to oversample the image at a pitch much smaller than the wavelength. In this case the pixel size is in the order of the wavelength but the sampling is at subwavelength level. In the THz band a 35 um pixel pitch is used at wavelength ranging from 70 um to 1,063 mm to perform imaging through various objects. In this case, the pixel itself is smaller than the wavelength.
Subwavelength imaging is not without its challenges, though. For instance, while the use of ultra-fast optics provides better definition, their design becomes more challenging as the models used are at their very limits. Questions about information content of images can be raised as well. New research avenues are being investigated to help address the challenges of subwavelength imaging with the goal of achieving higher imaging system performance. This paper discusses aspects to be considered, review some results obtained and identify some of the key issues to be further addressed.
The fast growing consumer electronics market of connected and wearable devices is driving a wealth of new applications. Personal capability for detecting and monitoring substances part of our everyday life (food, cosmetics, drugs, etc.) by spectroscopic means will soon become a reality as a number of new miniature spectrometers are being reported. These devices mostly operate in the visible and near infrared spectral region due to the readily available lowcost detectors in these spectral regions. However, enhanced selectivity is achievable in the molecular fingerprint spectral region (7-20 μm), allowing for applications that would be difficult or impossible at lower spectral wavelengths. To this end, a compact, portable, Long-Wave Infrared (LWIR) hyperspectral imager was developed. It is based on INO’s MICROXCAM-384 camera featuring a 384 x 288 pixel, 35 μm pitch uncooled bolometric broadband Focal Plane Array (FPA) and Fraunhofer ENAS’ 2 mm x 2 mm aperture MEMS tunable Fabry-Pérot Interferometer (FPI). The INO’s broadband FPA exhibits a Noise Equivalent Temperature Difference (NETD) lower than 25 mK (for the 8-12 μm range at 300 K, 50 fps and f/1) and a flat spectral response from 3 to 14 μm. The footprint of the hyperspectral imager is 7 cm x 8 cm x 10 cm excluding the source. The spectral resolution varies from 55 to 220 nm depending on the type of FPI used. The Noise Equivalent Spectral Radiance (NESR) is 430 mW/(m2 .sr.μm) at 9 μm. Using this hyperspectral imager, spectra of various substances including polymers were recorded in the transmission, reflection and transflectance configurations. A good agreement was found with spectra obtained by applying the FPI transfer function to spectra recorded with a commercial FTIR spectrometer. The LWIR configuration of the imaging spectrometer will be described and test results presented.
This paper reports on the development of a fully packaged focal plane array of broadband microbolometers. The detector makes use of a gold black thin film to expand its absorption range from 3 to 14 μm. A low temperature packaging process was developed to minimize sintering of the gold black absorber during vacuum sealing of the bolometer array package. The gold black absorber was also laser trimmed to prevent lateral diffusion of heat and promote a better MTF. The resulting FPAs show a NETD lower than 25 mK at a frame rate of 50 Hz
Spaceborne assessment of fire characteristics relies on radiance measurement of fire pixels and non-fire pixels mainly in the midwave infrared (MWIR). Because ambient temperature non-fire pixels have low thermal emission in this spectral range, it remains a challenge to retrieve fire characteristics with the desired accuracy. This paper reports on uncooled microbolometers specially designed with low noise equivalent power (NEP) to enable fire diagnosis at MWIR wavelengths. Each microbolometer forming a 512x3 format array includes a Wheatstone bridge of one active, one blind, and two thermally shunted pixels followed by its own signal chain. Design analyses suggest the conditions for achieving the best NEP performance are: (i) the active, blind, and one shunt pixel have equal electrical resistances while the other shunt pixel has a larger resistance; (ii) the temperature difference between the active pixel and heat sink corresponds to about one-third the heat sink temperature; and (iii) the active and blind pixels have low thermal mass and conductance. Hardwired devices having different structural layouts were prepared for the validation of physical parameters and performance so that the suitable designs could be identified. After this, focal planes of 512x3 microbolometers were fabricated on readout electronics to allow further performance evaluation and development of staggered 1017x3 format arrays for a planned mission. The active pixel designs on the fabricated arrays exhibit a MWIR absorptance as high as 0.83 through implementation of a Salisbury screen absorber, a thermal conductance of ~ 67 nW/K, and a response time shorter than 10 ms. Their responsivities are found to be in good agreement with predictions of the design analysis. The effectiveness of an Al shield platform erected above the blind pixel was investigated, showing that certain designs are capable of attenuating the incident power by up to 24 times. Under optimal operating conditions an NEP of ~ 64 pW was derived from measurements in the spectral range of 3.4-4.2 um, which was corroborated by the probing results obtained on the on-wafer focal plane arrays. When using these arrays with an F/1 telescope to retrieve scenes of 400 K from low Earth orbits, a noise equivalent temperature difference of ~ 320 mK can be achieved.
The ability of millimeter waves (1-10 mm, or 30-300 GHz) to penetrate through dense materials, such as leather, wool, wood and gyprock, and to also transmit over long distances due to low atmospheric absorption, makes them ideal for numerous applications, such as body scanning, building inspection and seeing in degraded visual environments. Current drawbacks of millimeter wave imaging systems are they use single detector or linear arrays that require scanning or the two dimensional arrays are bulky, often consisting of rather large antenna-couple focal plane arrays (FPAs). Previous work from INO has demonstrated the capability of its compact lightweight camera, based on a 384 x 288 microbolometer pixel FPA with custom optics for active video-rate imaging at wavelengths of 118 μm (2.54 THz), 432 μm (0.69 THz), 663 μm (0.45 THz), and 750 μm (0.4 THz). Most of the work focused on transmission imaging, as a first step, but some preliminary demonstrations of reflection imaging at these were also reported. In addition, previous work also showed that the broadband FPA remains sensitive to wavelengths at least up to 3.2 mm (94 GHz). The work presented here demonstrates the ability of the INO terahertz camera for reflection imaging at millimeter wavelengths. Snapshots taken at video rates of objects show the excellent quality of the images. In addition, a description of the imaging system that includes the terahertz camera and different millimeter sources is provided.
A software application, SIST, has been developed for the simulation of the video at the output of a thermal imager. The approach offers a more suitable representation than current identification (ID) range predictors do: the end user can
evaluate the adequacy of a virtual camera as if he was using it in real operating conditions. In particular, the ambiguity in the interpretation of ID range is cancelled. The application also allows for a cost-efficient determination of the optimal design of an imager and of its subsystems without over- or under-specification: the performances are known early in the development cycle, for targets, scene and environmental conditions of interest. The simulated image is also a powerful method for testing processing algorithms. Finally, the display, which can be a severe system limitation, is also fully
considered in the system by the use of real hardware components. The application consists in Matlabtm routines that
simulate the effect of the subsystems atmosphere, optical lens, detector, and image processing algorithms. Calls to
MODTRAN® for the atmosphere modeling and to Zemax for the optical modeling have been implemented. The realism of the simulation depends on the adequacy of the input scene for the application and on the accuracy of the subsystem
parameters. For high accuracy results, measured imager characteristics such as noise can be used with SIST instead of
less accurate models. The ID ranges of potential imagers were assessed for various targets, backgrounds and atmospheric conditions. The optimal specifications for an optical design were determined by varying the Seidel aberration coefficients to find the worst MTF that still respects the desired ID range.
The detection of concealed weapons in crowd situations is a critical need and solutions are being sought after by security agencies at the federal, state and municipal levels. Millimeter waves have been evaluated for these kinds of applications, but the currently available technologies are typically too large and bulky to allow for widespread deployment. Alternatively soft X-rays have been considered but safety issues hinder their acceptance. Terahertz technology is ideally suited for such an application as it has the ability to see through clothing, and offers higher resolution than in the millimeter band, also being more compact. THz photons have lower energy than infrared and do not show the ionizing properties of X-ray radiation. The longer Terahertz waves penetrate deeper into various materials then their visible and infrared counterparts. Though the wavelength is longer it has been shown that high resolution in a small form factor can be obtained in the THz wavebands thanks to the use of small pixel pitch detectors. In this paper, a case study for the use of a compact THz camera for active see-through imaging at stand-off distances is presented. More specifically, the cases of seeing through packages and clothing are analyzed in the perspective of concealed weapons detection. The paper starts with a review of the characteristics of a high resolution THz camera exhibiting small pixel size and large field-of-view. Some laboratory results of concealed object imaging along with details of a concept for live surveillance using a compact see-through imaging system are reviewed.
A turn-key semi-automated test system was constructed to perform on-wafer testing of microbolometer arrays. The
system allows for testing of several performance characteristics of ROIC-fabricated microbolometer arrays including
NETD, SiTF, ROIC functionality, noise and matrix operability, both before and after microbolometer fabrication. The
system accepts wafers up to 8 inches in diameter and performs automated wafer die mapping using a microscope
camera. Once wafer mapping is completed, a custom-designed quick insertion 8-12 μm AR-coated Germanium viewport
is placed and the chamber is pumped down to below 10-5 Torr, allowing for the evaluation of package-level focal plane
array (FPA) performance. The probe card is electrically connected to an INO IRXCAM camera core, a versatile system
that can be adapted to many types of ROICs using custom-built interface printed circuit boards (PCBs). We currently
have the capability for testing 384x288, 35 μm pixel size and 160x120, 52 μm pixel size FPAs. For accurate NETD
measurements, the system is designed to provide an F/1 view of two rail-mounted blackbodies seen through the
Germanium window by the die under test. A master control computer automates the alignment of the probe card to the
dies, the positioning of the blackbodies, FPA image frame acquisition using IRXCAM, as well as data analysis and
storage. Radiometric measurement precision has been validated by packaging dies measured by the automated probing
system and re-measuring the SiTF and Noise using INO’s pre-existing benchtop system.
Current state-of-the-art pixel dimensions for both visible and long-wave infrared (LWIR) imagers are approaching the wavelength of measurement. It is expected that technological advances will continue and that sub-wavelength pixels for these wavebands will become a reality. In light of the diffraction limit, scientists and engineers in the visible and infrared domains have now begun pose the question as to whether it is worth having a focal plane array (FPA) with pixel dimensions smaller than the imaging wavelength. Meanwhile, in the terahertz domain, FPAs have already been fabricated and cameras designed around them with sub-wavelength pixels. INO has developed THz cameras with 160x120 pixels with pixel pitch of 52 μm and with 388 x 284 pixels with pixel pitch of 35 μm. The THz wavelength range is from 40 μm to 1000 μm and thus the focal plane array has pixel dimensions below that of the imaging wavelength. This paper discusses experimental results of diffraction limit investigation using sub-wavelength pixel THz cameras.
Conventional guidelines and approximations useful in macro-scale system design can become invalidated when applied
to the smaller scales. An illustration of this is when camera pixel size becomes smaller than the diffraction-limited
resolution of the incident light. It is sometimes believed that there is no benefit in having a pixel width smaller than the
resolving limit defined by the Raleigh criterion, 1.22 λ F/#. Though this rarely occurs in today's imaging technology,
terahertz (THz) imaging is one emerging area where the pixel dimensions can be made smaller than the imaging
wavelength. With terahertz camera technology, we are able to achieve sub-wavelength pixel sampling pitch, and
therefore capable of directly measuring if there are image quality benefits to be derived from sub-wavelength sampling.
Interest in terahertz imaging is high due to potential uses in security applications because of the greater penetration depth
of terahertz radiation compared to the infrared and the visible. This paper discusses the modification by INO of its
infrared MEMS microbolometer detector technology toward a THz imaging platform yielding a sub-wavelength pixel
THz camera. Images obtained with this camera are reviewed in this paper. Measurements were also obtained using
microscanning to increase sampling resolution. Parameters such as imaging resolution and sampling are addressed. A
comparison is also made with results obtained with an 8-12 μm band camera having a pixel pitch close to the diffractionlimit.
Infrared and terahertz are two imaging technologies that differ fundamentally in numerous aspects. Infrared imaging is
an efficient passive technology whereas terahertz technology is an active technology requiring some kind of illumination
to be efficient. What's more, the detectors are also different and yield differences in the fundamental physics when
integrated in a complete system. One of these differences lies in the size of the detectors. Infrared detectors are typically
larger than the infrared wavelengths whereas terahertz detectors are typically smaller than the wavelength of
illumination. This results in different constraints when designing these systems, constraints that are imposed by the
resolution capabilities of the system.
In the past INO has developed an infrared imaging camera core of 1024×768 pixels and tested some microscanning
devices to improve its sampling frequency and ultimately its resolution. INO has also engineered detectors and camera
cores specifically designed for active terahertz imaging with smaller dimensions (160×120 pixels). In this paper the
evaluation of the resolution capabilities of a terahertz imager at the pixel level is performed. The resolution capabilities
for the THz are evaluated in the sub-wavelength range, which is not actually possible in the infrared wavebands. Based
on this evaluation, the comparison between the resolution limits of infrared detectors and the terahertz detectors at the
pixel level is performed highlighting the differences between the wavebands and their impact on system design.
In various military, space and civilian infrared applications, there is an important need for fast prototyping. For example,
detectors with small pitch compared to the diffraction limited spot radius are now available and their specificities must
be studied to optimize the design of the next imaging systems. At the very heart stands a requirement for flexible camera
modules that provide a multitude of output formats as well as fast adaptability. Based on this concept, INO has
developed an advanced compact camera module IRXCAM that can provide both raw data as well as fully processed
images under a variety of outputs: NTSC, DVI, VGA, GigE and Camera Link. This tool can be used to perform a rapid
demonstration of concept for a specific application. IRXCAM now supports the bolometric detectors INO IRM160A
(160 x 120 52 μm pitch pixels, LWIR and THz), Ulis 04 17 1 (640 x 480 25 μpitch pixels, LWIR) and Ulis 05 25 1
(1024 x 768 17 μm pitch pixels).
Reduction of the pixel pitch is a way to improve the compromise between the spatial resolution and the dimensions of an
imaging system, mainly by reducing the required optical focal length with constant numerical aperture. Microscanning is
another way that provides excellent results in terms of spatial resolution for pixel pitches as small as 25 μm in the LWIR
range for F/1 optics. Microscanning also preserves the field of view without increasing the number of pixels of the
detector. Finally, microscanning is an efficient way to reduce the aliasing effect of a non unity filling factor, a parameter
that becomes increasingly important for small pixels. This paper presents the IRXCAM-1024 camera module, its
performances, and its use for microscanning with 17 μm pitch pixels and commercial F/1 and F/0.86 refractive optical
lenses.
The SciSat-1 mission is a dedicated Canadian science satellite that will investigate processes that control the distribution of ozone in the stratosphere. The SciSat-1 satellite consists of primarily two science instruments; an Atmospheric Chemistry Experiment (ACE) high-resolution Fourier-transform spectrometer (FTS) and an ultraviolet-visible-near-infrared spectrograph. These instruments will primarily function in occultation mode; however, during the dark portion of the orbit the Earth will pass between the sun and the satellite. This configuration will give rise to the opportunity of acquiring some nadir-view FTIR spectra of the Earth. Since the ACE FTS was designed to view a hot source (i.e., the Sun) at high resolution using a single scan, it is necessary to determine if the FTS will provide nadir spectra of the relatively cold atmosphere and surface with a sufficient signal-to-noise ratio. Methane, ozone and carbon monoxide gases were used in the cell for the purpose of determining the measurement characteristics of the ACE FTS instrument for a low-intensity source. These measurements were compared with data obtained from the Interferometric Monitor for Greenhouse (IMG) gases onboard the ADEOS satellite. The results show that the ACE FTS should be able to measure the abundant trace gases in the atmosphere with sufficient signal-to-noise ratio.
The SciSat-1 satellite will primarily function in occultation mode; however, during the dark portion of the orbit the Earth will pass between the sun and the satellite. This configuration will give rise to the opportunity of acquiring some nadir-view FTIR spectra of the Earth. Since the ACE FTS was designed to view a hot source (i.e., the Sun) at high resolution using a single scan, it is necessary to determine if the FTS will provide nadir spectra of the relatively cold atmosphere and surface with a sufficient signal-to-noise ratio. Hence, preliminary tests were performed on the ACE FTS instrument using a background source that provided a radiative contrast of about 100 K with the gas in a cell, thereby approximately simulating the atmospheric temperature conditions of the Earth. Methane, ozone and carbon monoxide gases were used in the cell for the purpose of determining the measurement characteristics of the ACE FTS instrument with respect to the nadir radiation emanating from the planet’s surface and atmosphere over most of the thermal infrared region. The signal-to-noise ratio from the laboratory test measurements is used to estimate the error on column measurements of carbon monoxide and other gases.
A novel and simple technique is described for the calibration of satellite instruments for the measurement of atmospheric ozone. Ozone is generated in a gas cell and spectral measurements of the ozone absorption are measured with a standard Fourier-transform spectrometer (FTS) in order to determine the amount of ozone in the cell. The satellite instrument then views the cell using an appropriate illumination source. In this presentation the preliminary results from the ozone calibration procedure are presented for the ACE FTS and MAESTRO instruments to show how consistently both instruments measure ozone. The thermal infrared band of ozone at 4.7 microns was used to provide the calibration of the ACE interferometer, whereas the Chappuis band at 600 nm was used to characterize the response of the MAESTRO instrument. The ozone transmission spectra that were derived from the ACE FTS and MAESTRO spectrograph measurements were found to be in good agreement with the simulated spectra of known amounts of ozone from a radiative transfer model. All of the results yielded column ozone amounts that were within 10% of each other. These calibration measurements were taken at the University of Toronto in March 2003, before the expected launch date of the SciSat-1 satellite in August 2003.
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