AISA hyperspectral imagers have been utilized in airborne applications for various defense related Intelligence, Surveillance and Reconnaissance (ISR) applications. In expanding the utility and capabilities of hyperspectral imagers for defense related applications, the implementation in a ground scanning configuration for check-point and forensic purposes has been achieved. System specifications, design, and operational considerations for a fully automated, near real-time target detection capability are presented. The system utilizes modularized software architecture, combining C++ command, capture, calibration, and messaging functions with drop-in IDL exploitation module for detection algorithm and target set flexibility. Performance capability against known defense related targets of interest have been tested, verified, and are presented utilizing full 400-2450nm spectral range provided by combined AisaEAGLE and AisaHAWK hyperspectral imagers. Initial results are also described for a new extended InGaAs system, covering 585-1630nm to provide a similar capability for integrations which have size, weight, and power restrictions.
Several chemical compounds have their strongest spectral signatures in the thermal region. This paper presents three
push-broom thermal hyperspectral imagers. The first operates in MWIR (2.8-5 μm) with 35 nm spectral resolution. It
consists of uncooled imaging spectrograph and cryogenically cooled InSb camera, with spatial resolution of 320/640
pixels and image rate to 400 Hz. The second imager covers LWIR in 7.6-12 μm with 32 spectral bands. It employs an
uncooled microbolometer array and spectrograph. These imagers have been designed for chemical mapping in reflection
mode in industry and laboratory. An efficient line-illumination source has been developed, and it makes possible thermal
hyperspectral imaging in reflection with much higher signal and SNR than is obtained from room temperature emission.
Application demonstrations including sorting of dark plastics and mineralogical mapping of drill cores are presented.
The third imager utilizes a cryo-cooled MCT array with precisely temperature stabilized optics. The optics is not cooled,
but instrument radiation is suppressed by special filtering and corrected by BMC (Background-Monitoring-on-Chip)
method. The approach provides excellent sensitivity in an instrument which is portable and compact enough for
installation in UAVs. The imager has been verified in 7.6 to 12.3 μm to provide NESR of 18 mW/(m<sup>2</sup> sr μm) at 10 μm
for 300 K target with 100 spectral bands and 384 spatial samples. It results in SNR of higher than 500. The performance
makes possible various applications from gas detection to mineral exploration and vegetation surveys. Results from
outdoor and airborne experiments are shown.
Two long-wave infrared (LWIR) hyperspectral imagers have been under extensive development. The first one utilizes a
microbolometer focal plane array (FPA) and the second one is based on an Mercury Cadmium Telluride (MCT) FPA.
Both imagers employ a pushbroom imaging spectrograph with a transmission grating and on-axis optics. The main target
has been to develop high performance instruments with good image quality and compact size for various industrial and
remote sensing application requirements. A big challenge in realizing these goals without considerable cooling of the
whole instrument is to control the instrument radiation. The challenge is much bigger in a hyperspectral instrument than
in a broadband camera, because the optical signal from the target is spread spectrally, but the instrument radiation is not
dispersed. Without any suppression, the instrument radiation can overwhelm the radiation from the target even by 1000
The means to handle the instrument radiation in the MCT imager include precise instrument temperature stabilization
(but not cooling), efficient optical background suppression and the use of background-monitoring-on-chip (BMC)
method. This approach has made possible the implementation of a high performance, extremely compact spectral imager
in the 7.7 to 12.4 μm spectral range. The imager performance with 84 spectral bands and 384 spatial pixels has been
experimentally verified and an excellent NESR of 14 mW/(m<sup>2</sup>srμm) at 10 μm wavelength with a 300 K target has been
achieved. This results in SNR of more than 700.
The LWIR imager based on a microbolometer detector array, first time introduced in 2009, has been upgraded. The
sensitivity of the imager has improved drastically by a factor of 3 and SNR by about 15 %. It provides a rugged
hyperspectral camera for chemical imaging applications in reflection mode in laboratory and industry.
Current hyperspectral imagers are either bulky with good performance, or compact with only moderate performance.
This paper presents a new hyperspectral technology which overcomes this drawback, and makes it possible to integrate
extremely compact and high performance push-broom hyperspectral imagers for Unmanned Aerial Vehicles (UAV) and
other demanding applications. Hyperspectral imagers in VIS/NIR, SWIR, MWIR and LWIR spectral ranges have been
implemented. This paper presents the measured performance attributes for a VIS/NIR imager which covers 350 to 1000
nm with spectral resolution of 3 nm. The key innovation is a new imaging spectrograph design which employs both
transmissive and reflective optics in order to achieve high light throughput and large spatial image size in an extremely
compact format. High light throughput is created by numerical aperture of F/2.4 and high diffraction efficiency. Image
distortions are negligible, keystone being <2 um and smile 0.13 nm across the full focal plane image size of 24 mm
(spatially) x 6 m (spectrally). The spectrograph is integrated with an advanced camera which provides 1300 spatial pixels
and image rate of 160 Hz. A higher resolution version with 2000 spatial pixels will produce up to 100 images/s. The
camera achieves, with spectral binning, an outstanding signal-to-noise ratio of 800:1, orders of magnitude higher than
any current compact VIS/NIR imager. The imager weighs only 1.4 kg, including fore optics, imaging spectrograph with
shutter and camera, in a format optimized for installation in small payload compartments and gimbals. In addition to
laboratory characterization, results from a flight test mission are presented.
Performance studies and instrument designs for hyperspectral pushbroom imagers in thermal wavelength region are
introduced. The studies involve imaging systems based on both MCT and microbolometer detector. All the systems
employ pushbroom imaging spectrograph with transmission grating and on-axis optics. The aim of the work was to
design high performance instruments with good image quality and compact size for various application requirements.
A big challenge in realizing these goals without considerable cooling of the whole instrument is to control the instrument
radiation from all the surfaces of the instrument itself. This challenge is even bigger in hyperspectral instruments, where
the optical power from the target is spread spectrally over tens of pixels, but the instrument radiation is not dispersed.
Without any suppression, the instrument radiation can overwhelm the radiation from the target by 1000 times.
In the first imager design, BMC-technique (background monitoring on-chip), background suppression and temperature
stabilization have been combined with cryo-cooled MCT-detector. The performance of a very compact hyperspectral
imager with 84 spectral bands and 384 spatial samples has been studied and NESR of 18 mW/(m<sup>2</sup>srμm) at 10 μm
wavelength for 300 K target has been achieved. This leads to SNR of 580. These results are based on a simulation
The second version of the imager with an uncooled microbolometer detector and optics in ambient temperature aims at
imaging targets at higher temperatures or with illumination. Heater rods with ellipsoidal reflectors can be used to
illuminate the swath line of the hyperspectral imager on a target or sample, like drill core in mineralogical analysis.
Performance characteristics for microbolometer version have been experimentally verified.
This work studies visual quality control in ceramics industry. In tile manufacturing, it is important that in each set of tiles, every single tile looks similar. For example, the tiles should have similar color and texture. Our goal is to design a machine vision system that can estimate the sufficient similarity or same appearance to the human eye. Currently, the estimation is usually done by human vision. Differing from other approaches our aim is to use accurate spectral representation of color, and we are comparing spectral features to the RGB color features. A laboratory system for color measurement is built. Experimentations with five classes of brown tiles are presented. We use chromaticity RGB features and several spectral features for classification with the k-NN classifier and with a neural network, called Self-Organizing Map. We can classify many of the tiles but there are several problems that need further investigations: larger training and test sets are needed, illuminations effects must be studied further, and more suitable spectral features are needed with more sophisticated classifiers. It is also interesting to develop further the neural approach.
Imaging spectrometry has mainly been a research tool, employing laboratory spectrographs and scientific cameras. This paper describes an add-on imaging spectrography that provides a unique combination of high quality image in a small, rugged, industrial, easy-to-use component. The spectrograph is based on a prism/grating/prism dispersing element which provides straight optical axis, astigmatism free image and polarization independent throughput. A volume holographic transmission grating is used for high efficiency. The tubular optomechanical construction of the spectrography is stable and small, D30 X L110 mm with F/2.8 numerical aperture and 2/3 inch image size. Equipped with C-mounts, the spectrography plugs between lens and area camera, converting the camera to a spectral line imaging system. The spectrograph allows the utilization of rapidly developing monochrome camera techniques, like high speed digital cameras, smart cameras and CMOS sensors, in color and spectral analytical applications. It is the first component available for upgrading existing industrial monochrome vision systems with color/spectral capability without the need to change the basic platform hardware and software. The spectrograph brings the accuracy of spectral colorimetry to industrial vision and overcomes the complex calibration that is needed when an RGB color camera is applied to colorimetric applications. Other applications include NIR imaging, spectral microscopy, multichannel fiberoptics spectroscopy and remote sensing.
This paper presents an imaging spectrometer principle based on a novel prism-grating-prism (PGP) element as the dispersive component and advanced camera solutions for on-line applications. The PGP element uses a volume type holographic plane transmission grating made of dichromated gelatin (DCG). Currently, spectrographs have been realized for the 400 - 1050 nm region but the applicable spectral region of the PGP is 380 - 1800 nm. Spectral resolution is typically between 1.5 and 5 nm. The on-axis optical configuration and simple rugged tubular optomechanical construction of the spectrograph provide a good image quality and resistance to harsh environmental conditions. Spectrograph optics are designed to be interfaced to any standard CCD camera. Special camera structures and operating modes can be used for applications requiring on-line data interpretation and process control.
This paper describes two new spectroscopic techniques which are utilizing hybrid integrated optoelectronics particularly suitable for field and hand-held use. First, the LED module is based on a linear array of light emitting diodes and a fixed monochromator, and provides a solid-state electrically scanned source for pre-dispersive spectrometers. A prototype module operating from 810 to 1060 nm with resolution of 10 nm scans one spectrum in 19 ms and has a solid glass construction with dimensions of 4 X 4 X 7 cm. Potential applications include miniature, rugged and low cost instruments for transcutaneous blood and tissue spectroscopy in the near infrared (NIR) region.
Optical analysis techniques, infrared spectroscopy in the front end, are rapidly achieving new applications in process control. This progress is accelerated by the development of more rugged instrument constructions. This paper describes two analyzer techniques especially developed for use in demanding environments. First, the integrated multichannel detector techniques is suitable for applications where the measurement can be accomplished by using 2 to 4 wavelengths. This technique has been used to construct several compact, portable and battery-operated IR analyzers, and process analyzers which measure exactly simultaneously at each wavelength resulting in very high tolerance against rapid changes and flow of the process stream. Secondly, a miniaturized Fourier transform infrared (FTIR) spectrometer is being developed for use as an OEM module in specific process and laboratory instruments. Special attention has been paid to increase the resistance of FTIR technique to ambient vibrations. The module contains an integrated digital signal processing electronics for intelligent control of the spectrometer and for fast real time spectral data treatment. Application studies include on line measurement of the concentrations of diluted and colloidal organic detrimental substances, especially pitch components, in the circulating waters in paper machine wet end.
Paper coatings are porous structures of pigments, binder and air. This research aims at developing a model for the prediction of the bulk optical properties of coating from its structure and material characteristics. Two theoretical approaches have been studied and compared. In both cases the coating is treated as a structured layer consisting of individual scatterers in a medium, and the pores are regarded as scatters. In the first approach they are assumed to be independent. The second approach takes into account that due to their close position the pores are in fact correlated scatterers. The approximation used limits the consideration to pair correlation only. Comparison of the theories to reflectance measurements on polystyrene pigment coatings have uniform pore sizes in the range from 0.13 to 0.95 micrometers showed that for pore size parameters less than 5 the dependent scattering model provides a good prediction for the reflectance, but for larger pore size parameters the reflection behavior approaches that predicted by the independent scattering theory.
A compact and versatile 32-wavelength spectrometer module has been developed based on a linear LED array and a fixed grating monochromator. The design includes all the optical, mechanical, and optoelectronic parts in a size of approximately 4 x 4 x 7 cu cm. The wavelength bands are scanned electronically without any moving parts. All the optical parts have been assembled to form a cemented solid glass construction, which is mechanically and thermally stable and well protected against water condensation or dust. The developed source module can be easily modified and has obvious advantages for spectroscopic analyzers, especially in process and portable applications.
This paper discusses the requirements for a portable infrared analyzer and presents the design of a four wavelength NIR analyzer utilizing the integrated multichannel detector technique for wavelength separation and detection. This technique, together with an electrically modulated miniature tungsten filament source and surface mount electronics manufacturing, provides a compact, rugged handheld instrument construction without any moving parts. Improved accuracy and short stabilization time is achieved through a combination of thermoelectric temperature stabilization in the four channel detector and a calculated signal compensation for the residual temperature error. Parallel analog phase sensitive detection of the detector signal maximizes the S/N ratio and maintains the simultaneity of the measurement. All composition calculations are performed in a microcomputer built inside the analyzer. The weight of the prototype analyzer is about 1 kg and a NiCd battery pack provides capacity for hundreds of single measurements or about 3 hours of continuous operation. Two prototype instruments have been fabricated with optimized NIR wavelengths for the moisture measurement of milled fuel peat on production fields. The accuracy of digitized two-wavelength signal ratios were tested in the laboratory over time and against temperature. Full accuracy is achieved in 10 seconds after switch-on and the maximum short time peak-to-peak variation in the signal ratios is 0.2%. The errors due to temperature fluctuations in the range from +2 to +50 degree(s)C are between -0.4 to +0.6%. The instruments were calibrated using 102 samples of Finnish milled fuel peat. the cross-validation testing of calibration gave a standard deviation of 1.6% (moisture by weight) compared to the reference method. Other applications for the analyzer are being planned in wood processing and chemical industries as well as in agriculture.
This paper discusses the advantages that can be achieved by using integrated multichannel detectors instead of the traditional filter wheel construction in process analyzers and presents four accomplished applications. Integrated multichannel detectors include several parallel detector elements each equipped with a specific interference filter and a Peltier cooler in one hermetic package. Advantages gained by filter integration are good withstanding of ambient stresses and low price due to small size. Multichannel detectors enable the use of different chopper techniques and rugged miniature and highly reliable analyzer constructions. Furthermore multichannel detectors provide exactly simultaneous measurement at each wavelength. This minimizes noise caused by rapid variations in fast moving nonhomogeneous process streams. The first application described is a two wavelength water monitor designed for on-line measurement of water content in lubricating oils. It has to meet high temperatures and high relative humidities in production plant environments. The oil analyzer is an advanced instrument that continuously measures oil content of water effluents in marine and land based applications. The peat moisture meter is a rugged portable NIR instrument constructed without any moving parts. Finally a four-wavelength NIR reflectance instrument is described. In a pilot application in a wood grinding plant the instrument with fibre optics is used to achieve a true in-line moisture measurement of the pulp stream having a speed of 15 - 40 rn/s and temperature of 125 - 145 OC. 1.
The dependent scattering problem in dense attering media has been studied theoretically and experimentally for concentra- Lions up to 50 and for spherical scatters having the values ofka in the Mie scattering range. The agreement between theory and experiment is good. 1.