KEYWORDS: Black bodies, Sensors, Temperature metrology, Hyperspectral imaging, Body temperature, Sulfur, Infrared radiation, Infrared imaging, Head, Gas cells
Defence Research and Development Canada, through a Canadian government innovation support program, has tested the Telops Hyper-Cam Airborne Mini (HCAM) thermal infrared hyperspectral imager to assess its performances, including its Noise Equivalent Spectral Radiance (NESR), its radiometric accuracy and its ability to detect gas-phase targets both in laboratory and in flight. The results are compared to those obtained with the Telops Hyper-Cam LW system.
High resolution broad-band imagery in the visible and infrared bands provides valuable detection capabilities based on
target shapes and temperatures. However, the spectral resolution provided by a hyperspectral imager adds a spectral
dimension to the measurements, which leads to an additional means of detecting and identifying targets based on their
spectral signature.
The Telops Hyper-Cam sensor is an interferometer-based imaging system that enables the spatial and spectral analysis of
targets using a single sensor. It is based on the Fourier-transform technology, which yields high spectral resolution and
enables a high accuracy radiometric calibration. It provides datacubes of up to 320×256 pixels at spectral resolutions as
fine as 0.25 cm-1. The LWIR version covers the 8.0 to 11.8 μm spectral range. The Hyper-Cam has been recently
integrated and flown on a novel airborne gyro-stabilized platform inside a fixed-wing aircraft.
The new platform, more compact and more advanced than its predecessor, is described in this paper. The first results of
target detection and identification are also presented.
Persistent surveillance and collection of airborne intelligence, surveillance and reconnaissance information is critical in today’s warfare against terrorism. High resolution imagery in visible and infrared bands provides valuable detection capabilities based on target shapes and temperatures. However, the spectral resolution provided by a hyperspectral imager adds a spectral dimension to the measurements, leading to additional tools for detection and identification of targets, based on their spectral signature. The Telops Hyper-Cam sensor is an interferometer-based imaging system that enables the spatial and spectral analysis of targets using a single sensor. It is based on the Fourier-transform technology yielding high spectral resolution and enabling high accuracy radiometric calibration. It provides datacubes of up to 320×256 pixels at spectral resolutions as fine as 0.25 cm-1. The LWIR version covers the 8.0 to 11.8 μm spectral range. The Hyper-Cam has been recently used for the first time in two compact airborne platforms: a bellymounted gyro-stabilized platform and a gyro-stabilized gimbal ball. Both platforms are described in this paper, and successful results of high-altitude detection and identification of targets, including industrial plumes, and chemical spills are presented.
Persistent surveillance and collection of airborne intelligence, surveillance and reconnaissance information
is critical in today's warfare against terrorism. High resolution imagery in visible and infrared bands
provides valuable detection capabilities based on target shapes and temperatures. However, the spectral
resolution provided by a hyperspectral imager adds a spectral dimension to the measurements, leading to
additional tools for detection and identification of targets, based on their spectral signature. The Telops
Hyper-Cam sensor is an interferometer-based imaging system that enables the spatial and spectral analysis
of targets using a single sensor. It is based on the Fourier-transform technology yielding high spectral
resolution and enabling high accuracy radiometric calibration. It provides datacubes of up to 320×256
pixels at spectral resolutions as fine as 0.25 cm-1. The LWIR version covers the 8.0 to 11.8 μm spectral
range. The Hyper-Cam has been recently used for the first time in two compact airborne platforms: a belly-mounted
gyro-stabilized platform and a gyro-stabilized gimbal ball. Both platforms are described in this
paper, and successful results of high-altitude detection and identification of targets, including industrial
plumes, and chemical spills are presented.
Algorithms have been developed to support quantitative analysis of a gas plume using down-looking airborne
hyperspectral long-wave infrared (LWIR) imagery. The resulting gas quantification "GQ" tool estimates the quantity of
one or more gases at each pixel, and estimates uncertainty based on factors such as atmospheric transmittance,
background clutter, and plume temperature contrast. GQ uses gas-insensitive segmentation algorithms to classify the
background very precisely so that it can infer gas quantities from the differences between plume-bearing pixels and
similar non-plume pixels. It also includes MODTRAN-based algorithms to iteratively assess various profiles of air
temperature, water vapour, and ozone, and select the one that implies smooth emissivity curves for the (unknown)
materials on the ground. GQ then uses a generalized least-squares (GLS) algorithm to simultaneously estimate the most
likely mixture of background (terrain) material and foreground plume gases. Cross-linking of plume temperature to the
estimated gas quantity is very non-linear, so the GLS solution was iteratively assessed over a range of plume
temperatures to find the best fit to the observed spectrum. Quantification errors due to local variations in the camera-topixel
distance were suppressed using a subspace projection operator.
Lacking detailed depth-maps for real plumes, the GQ algorithm was tested on synthetic scenes generated by the Digital
Imaging and Remote Sensing Image Generation (DIRSIG) software. Initial results showed pixel-by-pixel gas
quantification errors of less than 15% for a Freon 134a plume.
Airborne hyperspectral ground mapping is being used in an ever-increasing extent for numerous
applications in the military, geology and environmental fields. The different regions of the
electromagnetic spectrum help produce information of differing nature. The visible, near-infrared and
short-wave infrared radiation (400 nm to 2.5 μm) has been mostly used to analyze reflected solar light,
while the mid-wave (3 to 5 μm) and long-wave (8 to 12 μm or thermal) infrared senses the self-emission
of molecules directly, enabling the acquisition of data during night time.
The Telops Hyper-Cam is a rugged and compact infrared hyperspectral imager based on the Fourier-transform
technology. It has been used on the ground in several field campaigns, including the
demonstration of standoff chemical agent detection. More recently, the Hyper-Cam has been integrated
into an airplane to provide airborne measurement capabilities. The technology offers fine spectral
resolution (up to 0.25 cm-1) and high accuracy radiometric calibration (better than 1 degree Celsius).
Furthermore, the spectral resolution, spatial resolution, swath width, integration time and sensitivity are
all flexible parameters that can be selected and optimized to best address the specific objectives of each
mission.
The system performance and a few measurements have been presented in previous publications. This
paper focuses on analyzing additional measurements in which detection of fertilizer and Freon gas has
been demonstrated.
The MR-CATSI combines the latest ABB Bomem MR spectro-radiometer technology and software with
the concepts used in the design of the ABB and DRDC CATSI instrument twelve years ago.
This instrument is a Fourier transform spectro-radiometer with dual input beams. It is a passive, stand-off
sensor. One input port can be directed to the area to be interrogated while the other input beam can be
pointed at the background. The instrument automatically measures the difference of spectral radiance
between the target and the background, hence achieving a suppression of the background signal. The
resulting measurement is the unique spectral signature of the target.
The system includes a software module to control the instrument and the acquisition parameters, a module
for the radiometric calibration and a module to perform the identification and quantification, in real time, of
various gases.
Overview of the design and results from field trials will be presented. This includes recent measurements
of a number of gas plumes.
Hyperspectral ground mapping is being used in an ever-increasing extent for numerous applications in the military,
geology and environmental fields. The different regions of the electromagnetic spectrum help produce information of
differing nature. The visible, near-infrared and short-wave infrared radiation (400 nm to 2.5 μm) has been mostly used to
analyze reflected solar light, while the mid-wave (3 to 5 μm) and long-wave (8 to 12 μm or thermal) infrared senses the
self-emission of molecules directly, enabling the acquisition of data during night time.
Push-broom dispersive sensors have been typically used for airborne hyperspectral mapping. However, extending the
spectral range towards the mid-wave and long-wave infrared brings performance limitations due to the self emission of
the sensor itself. The Fourier-transform spectrometer technology has been extensively used in the infrared spectral range
due to its high transmittance as well as throughput and multiplex advantages, thereby reducing the sensor self-emission
problem.
Telops has developed the Hyper-Cam, a rugged and compact infrared hyperspectral imager. The Hyper-Cam is based on
the Fourier-transform technology yielding high spectral resolution and enabling high accuracy radiometric calibration. It
provides passive signature measurement capability, with up to 320x256 pixels at spectral resolutions of up to 0.25 cm-1.
The Hyper-Cam has been used on the ground in several field campaigns, including the demonstration of standoff
chemical agent detection. More recently, the Hyper-Cam has been integrated into an airplane to provide airborne
measurement capabilities. A special pointing module was designed to compensate for airplane attitude and forward
motion. To our knowledge, the Hyper-Cam is the first commercial airborne hyperspectral imaging sensor based on
Fourier-transform infrared technology. The first airborne measurements and some preliminary performance criteria for
the Hyper-Cam are presented in this paper.
Hyperspectral ground mapping is being used in an ever-increasing extent for numerous applications in the military,
geology and environmental fields. The different regions of the electromagnetic spectrum help produce information of
differing nature. The visible, near-infrared and short-wave infrared radiation (400 nm to 2.5 μm) has been mostly used to
analyze reflected solar light, while the mid-wave (3 to 5 μm) and long-wave (8 to 12 μm or thermal) infrared senses the
self-emission of molecules directly, enabling the acquisition of data during night time.
Push-broom dispersive sensors have been typically used for airborne hyperspectral mapping. However, extending the
spectral range towards the mid-wave and long-wave infrared brings performance limitations due to the self emission of
the sensor itself. The Fourier-transform spectrometer technology has been extensively used in the infrared spectral range
due to its high transmittance as well as throughput and multiplex advantages, thereby reducing the sensor self-emission
problem.
Telops has developed the Hyper-Cam, a rugged and compact infrared hyperspectral imager. The Hyper-Cam is based on
the Fourier-transform technology yielding high spectral resolution and enabling high accuracy radiometric calibration. It
provides passive signature measurement capability, with up to 320x256 pixels at spectral resolutions of up to 0.25 cm-1.
The Hyper-Cam has been used on the ground in several field campaigns, including the demonstration of standoff
chemical agent detection. More recently, the Hyper-Cam has been integrated into an airplane to provide airborne
measurement capabilities. A special pointing module was designed to compensate for airplane attitude and forward
motion. To our knowledge, the Hyper-Cam is the first commercial airborne hyperspectral imaging sensor based on
Fourier-transform infrared technology. The first airborne measurements and some preliminary performance criteria for
the Hyper-Cam are presented in this paper.
Defence Research and Development Canada (DRDC) - Valcartier is currently developing a ruggedized passive standoff
sensor for the detection of chemical warfare agents (CWAs) based on differential Fourier-transform infrared (FTIR)
radiometry. This system is referred to as the Compact ATmospheric Sounding Interferometer (CATSI) Engineering
Development Model (EDM). The CATSI EDM sensor is based on the use of a double-beam FTIR spectrometer that is
optimized for optical subtraction. A description of the customized sensor is given along with a discussion on the
detection and identification approaches that have been developed. Preliminary results of validation from a number of
laboratory measurements and open-air trials are analyzed to establish the capability of detection and identification of
various toxic and non-toxic chemical vapor plumes. These results clearly demonstrate the capability of the passive
differential radiometric approach for the standoff detection and identification of chemical vapors at distances up to a few
kilometers from the sensor.
A selection of field trial results on the passive standoff detection by differential FTIR radiometry with the CATSI sensor is presented. This selection covers the seven-year development period (1998-2004) of the CATSI project. The results obtained with the CATSI instrument at two major field trials in Kansas (1998) and Nevada (2001) have shown the successful passive standoff detection of a number of chemical vapors at short and medium ranges of 100 m and 1.5 km, respectively. In particular, the detection method has been used at short range (100m) to map the column amounts of a methanol plume with an estimated uncertainty of the order of 15 - 30%. At medium range (1.5 km), the measurement technique has been successfully used to detect and identify low, medium and high concentrations of vapor mixtures of DMMP and SF6 but appears to have limited quantification capabilities in its original form. At long range, CATSI has successfully measured SF6 gas amounts at the 5.7-km range of DRDC Valcartier. The passive standoff detection of liquid contaminants on surfaces was tested with encouraging results. These results indicate that liquid contaminant agents deposited on high-reflectivity surfaces can be detected, identified and possibly quantified with passive sensors. For low-reflectivity surfaces, the presence of contaminants can usually be detected; however, their identification based on simple correlations with the absorption spectrum of the pure contaminant is not possible. In a field trial (Dugway Proving Ground, 2002) on the standoff detection of bio-aerosols, CATSI has detected large amounts of BG at ranges of up to 3 km. Recent field measurements for a standoff distance of 60 m suggests that the gas constituent ratios of complex mixtures can be properly retrieved from passive spectral measurements performed at 8 cm-1. These results from field experiments clearly show the relevance of the CATSI approach for the passive standoff detection by differential FTIR radiometry.
Over the past year we have initiated a study into the passive standoff detection of radiological materials by Fourier-transform infrared (FTIR) radiometry. The preliminary work has shown that a number of radiological materials have an infrared signature in the 8-14 micron thermal infrared region. As well, through a series of simulations using the MODTRAN4 atmospheric transmission model, we have shown that these materials may potentially be detected at standoff distances of several kilometres. In this paper we present some results of our current work that focus on recent new measurements of spectral signatures, including the uranium oxides UO2 and UO3. Preliminary results from a measurement campaign held at Defence Research and Development Canada-Valcartier this year are also presented which address the passive detection of radiological materials in the field at standoff distances of 10-60 m. These results are analysed in view of determining the potential for measuring nuclear products with a passive standoff FTIR technique.
For a passive spectral sensor, the temperature difference (DT) that exists between a chemical cloud and the background scene is of prime importance because it is linked to the radiative contrast of the target. The larger DT, the better the radiative contrast and the more accurate is the detection and identification, of the cloud.
This paper establishes statistics on realistic air-soil DT to be used to estimate the detection performance of passive spectral sensors in a variety of scenarios and environments. To this end, an analysis of the air-soil DT is presented for five locations around the world. The results of the analysis indicate that the statistics of the air-soil absolute DT are similar from one location to another. The average statistics over the five locations show a mean absolute air-soil DT of 3.5 °C and a median of 2.8 °C. An absolute air-soil DT of less than one degree Celsius occurs less than 14% of the time on the average. This suggests that, on average, air-soil temperature contrasts should yield good detection probabilities 86% of the time.
Spaceborne Fourier-transform spectrometers must use a reliable metrology source to replace the conventional HeNe laser acting as the spatial sampling reference in ground instruments. Because of their lifetime and ruggedness, semiconductor lasers appear to be ideal candidates. However the fringe signal resulting from a semiconductor laser exhibits a noisier behavior than the one from an HeNe laser. This results in more important sampling errors. We present the effect of the phase and intensity noises of semiconductor lasers upon the quality of the reference fringe signal. The semiconductor laser is modelized using a standard rate equations approach, which gives rise to coupled intensity and phase fluctuations. The laser field is sent in a scanning Michelson interferometer modelized as a variable time delay applied to the field in one arm. The recombined field is sent to a fast photodetector, resulting in a noisy fringe signal. We evaluate the signal-to-noise ratio which is used as a measure of the error made when using the zero crossings of the metrology source as a sampling reference. It relies on the noise characteristics of the laser, the optical path differences of the interferometer and the bandwidth of the photodetector. Both theoretical predictions and simulation results are shown.
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