WO2000055602A1 - Passive remote sensor of chemicals - Google Patents
Passive remote sensor of chemicals Download PDFInfo
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- WO2000055602A1 WO2000055602A1 PCT/US2000/004027 US0004027W WO0055602A1 WO 2000055602 A1 WO2000055602 A1 WO 2000055602A1 US 0004027 W US0004027 W US 0004027W WO 0055602 A1 WO0055602 A1 WO 0055602A1
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- WIPO (PCT)
- Prior art keywords
- sample
- remote sensor
- filter
- radiation
- detector
- Prior art date
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/59—Transmissivity
- G01N21/61—Non-dispersive gas analysers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet light
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
Definitions
- the present invention relates to a passive, remote device and method
- the present invention relates to a passive,
- NFCR filter correlation radiometer
- Remote detectors are also needed to monitor and study trends in environmental conditions in order that their causes may be understood and addressed, as well as to identify and provide warnings regarding day-to-day conditions that may affect the health of local and global populations.
- Passive remote detectors of chemicals in gaseous forms primarily in the atmosphere ideally operate in the 8-13.3 ⁇ m spectral range, where (a) many objects and gases at a standard temperature of about 25° C have strong infrared (IR) emissions; (b) the atmosphere is relatively transparent over long distances; and (c) many target species have strong absorption (or emission) depending on their
- a remote detector generally may effectively operate in the 3-5 ⁇ m spectral range only where alternative radiation
- CAM Chemical Agent Monitor
- ECAM Enhanced CAM
- SAW surface acoustic wave
- this device is an in-situ sensor. In addition, this system can detect
- FTIR spectroscopy
- multi or hyper spectral techniques such as gas filter
- GFCR correlation radiometry
- LARS CO 2 DIAL system must be cooled in a liquid nitrogen environment.
- Typical LIF systems like DIAL systems, include a tunable-wavelength laser and a large aperture telescope and detector system. Unlike DIAL systems,
- the signal is weaker than that of the DIAL
- FTIR systems including the RSCAAL system
- RSCAAL system depend on a complete spectral scan followed by detailed analysis of the spectrum. To accomplish that scan, the system requires a complex, highly refined mechanical tunning arrangement which is difficult
- the radiation available at each spectral location is only fraction of the radiation collected during the time of the
- Hyperspectral images may be obtained by an imaging spectrometer, in which case a narrow strip in the FOV is imaged onto the front slit of the spectrometer.
- the dispersive element in the spectrometer creates a full spectrum for each point of
- a full hyperspectral data cube may be obtained by imaging additional strips in the FOV while recording the point-by-point spectral distribution.
- the data cube may be divided into spectral "slices," e., the two- dimensional FOV may be viewed through a tunable bandpass filter that transmits one color at a time.
- Monochromatic images of the two-dimensional object are recorded sequentially to obtain a stack of images of the same object - each at a different wavelength.
- Hyperspectral techniques may require up to 200 such images covering a wide spectral range.
- Multispectral techniques typically cover 20 spectral slices per object.
- systems employing hyperspectral techniques may provide greater spectroscopic detail and therefore have higher specificity (i.e.. the
- AOTF tunable acousto-optic filter
- a typical GFCR includes a sample cell containing a target species, and a reference vacuum cell. The sample cell and reference cell are moved mechanically into and out of the detector FOV. See Herget, et al., "Infrared Gas-Filter Correlation Instrument for In-Situ Measurement of Gaseous Pollutant Concentrations," App. Opt. 15 (1976) at 1222-28. Such systems have been used to monitor smoke stack pollutants such as CO, NO,
- the primary drawback of GFCRs is the need for the sensor to include a
- FOV significantly reduces system reliability and speed, and may prevent the imaging of proliferated chemicals, such as gas clouds or liquid spills, due to a loss of registration between consecutive images.
- the grating-based GFCR requires that a narrow slit be positioned between the grating and the detector in order to separate radiation directed by the grating that has the desired spectral characteristics from radiation that does not have
- the slit is also used to reduce interferences by stray light, to which the grating-based system is particularly susceptible. Without such a slit, the system loses some of its spectral resolving capabilities. Although the detector itself may be used as a relatively wide slit, the spectral resolution of the system would be
- the slit required by the design of the '571 patent also prevents the possibility of imaging the spatial distribution of chemical clouds.
- the slit required by the design of the '571 patent also prevents the possibility of imaging the spatial distribution of chemical clouds.
- the grating-based GFCR must include a train of optical elements
- the system is sensitive to optical alignment between the grating and the slit
- the grating-based GFCR system clearly is not capable of miniaturization.
- grating and spatial filter assemblies renders the system complex and cumbersome.
- multispectral technique which uses an imaging system followed by a cylindrical lens that creates a line focus of an image, which is then projected on a planar diffraction grating.
- the radiation diffracted from the grating is made of numerous strips, each at
- Althouse, et al. recommend the use of cryogenically cooled filters, and the positioning of such filters sufficiently far
- each filter is selected to have a
- the design requires that the filters be cryogenically cooled.
- the design does not provide for methods to correct for the effects of background radiation or emission, or absorption by atmospheric or other background species.
- the Wimmers, et al. method also does not contemplate correcting for background interferences.
- the filter is designed as a linear array of various bandpass filters.
- the transmission line-center of each filter can be selected to match the absorption or emission of a selected species.
- a sensor that is capable of remotely detecting, and preferably imaging, gaseous, liquid, solid or adsorbed chemicals even when the background, its constituents and its illumination change rapidly.
- a sensor preferably would be sufficiently simple in design to be compact, rugged,
- a sensor that is sufficiently compact and rugged to be configured and used as a handheld chemical detector, while having a satisfactory sensitivity, specificity, ability to correct for effects of background radiation or
- Such a sensor would also be desirable for such a sensor to be designed alternatively to have a large FOV for large area coverage, and to be sufficiently energy efficient to be useful for long-duration, stand-alone operation.
- Such a sensor preferably would be capable of detecting, and preferably imaging, gaseous chemicals such as dust, atmospheric effluents, pollution, pesticide vapors, naturally occurring atmospheric gases (e.g., H 2 O, CO 2 , O 3 N 2 O, NO x , and CO gases),
- gaseous chemicals such as dust, atmospheric effluents, pollution, pesticide vapors, naturally occurring atmospheric gases (e.g., H 2 O, CO 2 , O 3 N 2 O, NO x , and CO gases)
- Such a sensor also preferably would have an exceptionally large
- the senor of the present invention has a first optical path and a second optical path, light collecting optics configured to collect light or other radiation to be transmitted or emitted along the first and second optical paths, and a sample filter assembly positioned in the first optical path after the light collecting optics.
- the sensor may also include a reference filter assembly positioned in the
- One or more detector assemblies may be used to detect the light or other radiation transmitted through the sample and reference filter assemblies, and one or more associated detector output comparison
- the output comparison devices are used to compare, and preferably normalize, the sample and reference output signals.
- the output comparison device preferably subtracts one output signal from the other.
- the output comparison device preferably divides the difference of the sample and reference outputs by the sample output or the reference output.
- both sample and reference filter assemblies are identical to each sample and reference filter assemblies.
- the sample bandpass filter may be configured to be capable of transmitting at a radiation frequency that coincides with an absorption or emission line of a target species (preferably a strong absorption or
- the sample bandpass filter may be matched by a reference bandpass filter configured to transmit at a frequency that does not coincide with a
- the bandpass frequency of the sample bandpass filter assembly coincides also with an absorption or emission line of a non-target species such as atmospheric H 2 O, CO 2 , O 3 N 2 O, NO x , or CO gas, or another gas or aerosol that may be found in the
- the reference bandpass filter assembly is configured to transmit at a
- sample filter assembly or another spectral line of the non-target species where absorption or emission by that non-target species is the same as or comparable in
- comparison device will be indicative of the net target species absorption or emission
- sample filter assembly is positioned in the first optical path, the sample filter assembly
- a notch filter a filter which blocks one frequency or a range of frequencies
- the sample notch filter may be configured to
- the second optical path may include no filter at all and therefore provide no
- the blank being made of the substrate of the sample notch filter.
- notch filter may be placed either in front of both the first and second optical paths
- sample and reference filter assemblies may be made up of several components
- sample and reference filters may be paired sets of sample and reference filters.
- the sample and reference filters may
- a corresponding plurality of detectors or detector arrays may be used.
- the detector output comparison device may be configured to minimize
- detector output comparison device may include a computer, lock-in amplifier or other suitable devices, or a combination thereof, for subtracting and/or normalizing the
- sample and reference signals preferably includes noise
- BTD balanced ratiometric detector
- the senor may include a first beam splitter configured to transmit a first portion of the
- the light or other radiation along a second optical path.
- sample filter assembly is positioned in the first optical path after the first beam
- the reference filter assembly is positioned in the second optical path after
- a single detector assembly is positioned after the sample and reference filter assemblies, and means for directing the first and second portions of the
- the directing means may
- the directing means may include a switching
- the detector output comparison device may include a memory device
- the switching device may be any suitable
- the sensor of the present invention preferably will include light
- the senor may be used as a remote sensor.
- the sensor may be made in any form for such use,
- the senor is
- a low power DC power supply such as a 12 V battery.
- the present invention also includes a method of determining the present invention
- detector assembly and detecting its power using the detector assembly; directing the light or other radiation along the first path from the reference filter assembly to the
- detector assembly and detecting its power using the detector assembly; and using a
- detector output comparison device such as one or more BRDs, to compare the sample
- the method may include, if it is desired to use a single beam of light or
- sample signal to the reference signal and produce a signal which is indicative of the absorption or emission of the light or other radiation by the target species.
- method of the present invention may be performed using the remote sensor of the
- sensing method of the present invention may be used to remotely detect and determine
- FIG. 1 is a schematic illustration of one embodiment of the sensor of the present invention.
- FIG. 2 is a schematic illustration of another embodiment of the sensor of the present invention.
- FIG. 3 is a schematic illustration of a technique for using a bandpass filter as a notch filter in the sensor of the present invention.
- FIG. 4 is a graph illustrating the absorption coefficient/frequency curves for DIMP and DMMP, and exemplary sample and reference filter selections for two DMMP -DAR sensors.
- FIG. 5 is a graph illustrating, with DMMP as the target species, the variation of the normalized net DAR signal with reference bandpass filter assembly
- FIG. 6 is a graph illustrating, with DMMP as the target species, the variation of the normalized net DAR signal with path length through "water only" and
- FIG. 7 is a schematic illustration of a quadrant detector which may be
- FIG. 8A is a schematic illustration of a striped filter configuration for
- FIG. 8B is a schematic illustration of an image of a cloud of a target species as imaged using the striped filter configuration of FIG. 8 A.
- the senor of the present invention generally comprises a first filter assembly 10 positioned in a first optical path 12, and a second filter assembly 14 positioned in a second optical path 16.
- first and second optical paths 12 and 16 may correspond to wholly separate first and second beams of incident light 18 and 20, as shown in FIG. 1 , or may correspond to beams derived from a single incident light beam 22, as illustrated in connection with
- light is intended to include any wavelength of optical radiation, regardless of source, from the ultraviolet (UV) through the infrared (IR) regions of the spectrum.
- the incident light beam to be detected typically is the product of the absorption or emission spectra by a target chemical species.
- radiation from artificial sources such as lamps, lasers, glow bars, light emitting diodes, or black body sources, or natural sources such as the sun, or far infrared sources such as the
- incident light or radiation beam(s) are formed by radiation emitted by a target species
- first filter assembly 10 may be any suitable filter assembly.
- sample filter assembly 10 may be referred to as “sample” filter assembly 10
- second filter assembly 14 may be referred to as “reference” filter assembly 14.
- First incident light or radiation beam 18 and second incident light or radiation beam 20 are collected by suitable light collecting optics 24, which may comprise one or more optical elements known to the
- sample and reference filter As discussed in detail below, sample and reference filter
- assemblies 10 and 14 may be bandpass or notch filters. Where they are notch filters (or when sample filter assembly 10 is a notch filter and reference filter assembly 14 is not included, as will be described), an additional bandpass filter assembly 25, which
- bandpass filter assembly 25 may be positioned anywhere in first and second optical paths 12 and 16, and preferably has a line center at or near
- the power of the light or radiation is detected by sample and reference
- Sample and reference detector assemblies 26 and 28 produce sample and reference signals, respectively, which are
- detectors used in connection with the present invention including sample detector
- any detector known to the art such as, for example, an infrared detector or infrared focal plane array (FPA), photo-diode, avalanche-photo-diode, photomultiplier tube, semiconductor detector (e.g., including silicon, germanium, gallium arsenide, indium arsenide, indium gallium arsenide, indium antimonide, lead sulfide, lead selenide, mercury cadmium telluride), thermal detector (e.g., pyroelectric, thermopile or bolometer), charge- coupled device, linear-diode array, or linear-detector array.
- FPA infrared detector or infrared focal plane array
- photo-diode e.g., avalanche-photo-diode
- photomultiplier tube e.g., including silicon, germanium, gallium arsenide, indium arsenide, indium gallium arsenide, indium antimonide, lead
- Detector output comparison device 30 may include a computer, lock-in amplifier or another similar device to subtract the sample detector signal from the reference detector signal, or vice-versa. Detector output comparison device 30 may also, or alternatively, include noise cancellation
- circuitry such as a balanced ratiometric detector (BRD) or another system which is
- a sample and reference detector capable of providing high quality signal, to divide the difference between the sample and reference detector outputs by either the sample or reference detector signal.
- BRD assembly is capable of performing the subtraction function, then dividing the
- detector assembly 26 or 28 to provide a normalized difference (e.g., (A-B)/B, (B-
- sample detector signal a digital computer or lock-in amplifier, as well as other conventional devices, could be used to perform
- the single beam configuration illustrated in FIG. 2 makes possible the use of a single detector, which is beneficial because it allows comparing two images, one obtained through the sample filter assembly and one through the reference filter assembly without loss of registration. It also reduces cost when an
- single incident light or radiation beam 22 is
- first beam splitter 34 is collected by light collecting optics 32 and divided by a first beam splitter 34 into a first portion 36 of incident beam 22 transmitted along a first optical path 38 and a
- second light or radiation beam portions 36 and 40 then are passed through a first filter
- sample filter assembly 44 (which may be referred to as a "sample” filter assembly 44) and second filter 46 (which may be referred to as a “reference” filter 46), respectively.
- sample and reference filter assembly 44 (which may be referred to as a "sample” filter assembly 44) and second filter 46 (which may be referred to as a “reference” filter 46), respectively.
- sample and reference filter assembly 44 (which may be referred to as a "sample” filter assembly 44) and second filter 46 (which may be referred to as a “reference” filter 46), respectively.
- reference filter 46 which may be referred to as a "reference” filter 46
- first and second beam portions 36 and 40 then are redirected by a first mirror 48 and a
- First and second switching devices 54 and 56 are used to modulate or selectively direct first and second portions 36 and 40 of beam 22 to a detector 60, and may be positioned anywhere between light collecting optics 32 and detector 60. First and second switching devices 54 and 56
- chopping wheel may be separate devices, or may be a single device such as a chopping wheel or tunning fork chopper.
- a single detector assembly 60 alternately receives the signals from first optical path 38 and second optical path
- detector assembly 60 may first detect the power of first portion 36 of beam 22.
- the detector assembly 60 produces a sample signal based on this detection, and the sample signal is stored in a memory device, which may be part of a detector output comparison device 62, such as a conventional computer memory.
- switching devices 54 and 56 operate to direct second portion 40 of light or
- Detector output comparison device 62 may further include a computer, lock-in amplifier or another such signal
- Detector output comparison device 62 also preferably includes a device which normalizes the resulting difference in a manner described in connection with detector output comparison device 30 in the embodiment of FIG. 1.
- a digital computer which may store the sample and reference signals, subtract them, and normalize them
- a lock-in amplifier or another device capable of performing the normalization function.
- the net target species absorption or emission may then be recorded.
- a bandpass filter assembly 25 (FIG. 1) or 64 (FIG. 2) optionally may be positioned before detector assemblies 26 and 28 (FIG. 1) or detector assembly 60 (FIG. 2) to further reduce unwanted radiation outside the detection bandwidth.
- light collecting optics 24 and 32 are used to collect and collimate the light or radiation in optical paths 12, 16 or 38, 40.
- a lens assembly 29 (FIG. 1) and 65 (FIG. 2) is used
- This assembly also effects the normalization of the detected signal by dividing the difference by either the sample detector signal or the reference detector signal. It will be appreciated that there are several noise components that can limit optical
- uncooled optical filters may be induced by the thermal emission of uncooled optical filters themselves.
- uncooled optical elements or detectors which is preferable for some applications such as handheld or unattended sensors, subtraction of the signal induced by their thermal emission must take place before the signal is amplified to avoid
- the BRD is superior in that it is very accurate, compact, fast, inexpensive, and integrates the normalization of the sample and reference signals.
- the BRD has had demonstrated success in other fields of use.
- the BRD may be of the type described in U.S. Patent No. 5,134,276, issued July 28, 1992 to Hobbs, which is incorporated by reference herein in its entirety. It is a commercially available, simple electronic circuit designed to
- a BRD may be purchased from New Focus (Santa Clara,
- the BRD reduces excess noise by monitoring the signals of the sample
- one detector views the signal through sample filter assembly 10, which includes some background radiation, and provides the sample photocurrent I s .
- the reference detector assembly 28 views the target
- the circuit attempts to continuously maintain a preset ratio between I s and I R using a negative feedback that
- the sample current is set to be I s > I R .
- the feedback line attempts to rebalance the currents to their preset ratio.
- the voltage in the feedback line is:
- measurement of the feedback voltage can be used to directly measure the difference between the sample and reference currents normalized by the
- species-specific detection may be accomplished by selecting as sample filter assembly 10 or 44 a bandpass filter that transmits within a narrow band (e.g., in the far infrared 15 cm "1 ) centered at a frequency that coincides with an absorption or emission line of one or more target species, and selecting as reference filter assembly 14 or 46 a bandpass filter having the same or approximately the same bandwidth but a center frequency that does not coincide with any prominent absorption or emission line of the target
- center frequency of reference filter assembly 14 or 46 may be any one species. Instead, the center frequency of reference filter assembly 14 or 46 may be any one species. Instead, the center frequency of reference filter assembly 14 or 46 may be any one species. Instead, the center frequency of reference filter assembly 14 or 46 may be any one species. Instead, the center frequency of reference filter assembly 14 or 46 may be any one species. Instead, the center frequency of reference filter assembly 14 or 46 may be any one species. Instead, the center frequency of reference filter assembly 14 or 46 may be any other species.
- a second sample filter assembly may be used that coincides with another absorption (or emission) line of the same target species, and a reference filter assembly that corrects for the absorption (or emission) by non-target species that coincide with the
- assembly pairs can be added for detection of other target species and correction of background signals associated with them.
- DAR Differential Absorption Radiometer
- interference by the selected non-target species on the sample detector assembly 26 or 60 may be eliminated or minimized, effecting an increase in the sensitivity and
- (1) may be used for target species detection regardless of atmospheric conditions (e.g.,
- sample filter assembly 10 or 44 comprises a notch filter with an attenuation band that coincides with a prominent spectral feature of the target species
- reference filter assembly 14 or 46 comprises a blank made of the substrate of the notch filter of sample filter assembly
- Detection also may be accomplished at a reduced sensitivity even without
- Radiation collected by light collecting optics 24 or 32 and passed through bandpass filter 25 or 64 is passed once through the notch filter and
- NFCR Notch Filter Correlation Radiometer
- the background itself which may include spectral lines of other species that do not match the attenuation spectrum of notch filter assembly 10 or 44, is only slightly attenuated. Therefore, subtracting the signal obtained through the reference blank 14 or 46 from that obtained through the notch filter assembly 10 or 44 cancels most of the interfering features that were outside the notch filter band and part of the features that coincide with that band. This difference is strongly related to the correlation (or
- target species can be used to positively identify the target species signature and
- detection bandwidth may be limited by a bandpass filter assembly 25, or 64, that may
- Bandpass filter assembly 25 or 64 is chosen to pass at a range of frequencies where
- the signature of the target species is most pronounced (e.g., to an approximately about 15 cm “1 range around 1086 cm “1 for the detection of DMMP).
- the NFCR may be used for remote sensing or remote imaging. For example, for imaging, where a chemical cloud in the atmosphere is to be detected
- the image obtained through reference blank 46 may be stored digitally and then subtracted pixel-by-pixel from the image obtained separately through notch filter assembly 44. The difference between these two images may not vanish even in the absence of the target species.
- the magnitude of this difference depends upon, among other things, the overall magnitude of the incident radiation, which in turn depends on parameters, such as albedo or surface temperature in the case of sensing infrared radiation, that vary from point to point or from pixel to pixel on the
- the difference image may be normalized by a BRD assembly or other such system, when using an NFCR such as that illustrated in FIG. 1 for point measurements, or simply by dividing the difference pixel-by-pixel
- the NFCR system is particularly useful for imaging and detection from fast
- the NFCR system is well-suited for broad area search, acquisition and targeting of fixed or mobile agents, having the same advantages as previously discussed in connection with the combination of the DAR and the BRD assembly.
- Both the NFCR and the DAR may be considered multispectral or simplified hyperspectral imaging techniques.
- hyperspectral techniques that are presently proposed, an entire spectrum is scanned rapidly by a dispersive or interferometric imaging spectrometer and numerous images of the target are recorded, each at a specified wavelength and bandwidth. See, e ⁇ , Gittins, et al., "Passive Standoff Infrared Detection of Bio- Aerosols," 4 th Joint Workshop on Standoff
- FPAs provide imaging rates of less than 50 Hz. Thus, recording a full hyperspectral scan takes nearly one second. From a moving platform, the image at the
- the spatial shift between the two images at that rate will be less than 30 ft and may be corrected by digitally shifting the images before processing.
- the NFCR and DAR embodiments of the present invention also provide other important advantages.
- the DAR can provide superior detection sensitivity from short distances.
- it is more susceptible than the NFCR to interference by absorption by non-target species or to spectral
- bandpass filters in the ultraviolet (UN), visible and infrared (180nm - 20 ⁇ m) ranges are available from several manufacturers. Typically, they may be custom designed for specified line-centers, specific bandwidth (e.g., 11 cm “1 or 15 cm “1 in the far infrared and less than 1 cm “1 in the visible and UN)
- the filters can replace the detectors' windows, thereby providing an integrated design to reduce size while providing mechanical support to the thin filters.
- notch For use in the ⁇ FCR, notch
- functionality of a notch filter can be achieved by using the reflection off the
- first and second mirror 72 and 74 are added to the embodiment of the device shown in FIG. 2 to reflect first portion 36 of beam 22 off the surface of a dielectric-coated bandpass filter 44 and return it to its original path, first optical path 38.
- a similar notch filter may be configured for use in the embodiment of the present invention illustrated in FIG. 1. Irrespective of whether a NFCR or DAR type sensor is used, the spectrum of the target species to be identified and the non-target species to be corrected must be analyzed in order to determine the characteristics of bandpass or
- notch filters to be used in the sensor. This is a result of the fact that remote sensing techniques of toxic agents, atmospheric pollutants and other potential target species necessarily utilize either the emission or absorption properties of such species, such that the radiation between a light source (natural or artificial) and the target species, and then between the target species and the detector, must propagate through the atmosphere and other interfering substances.
- the NFCR and DAR may be used for atmospheric remote sensing. In that application, atmospheric transmission is an important parameter. Atmospheric
- Molecules such as H 2 O, CO 2 , O 3 , CH 4 and N 2 O mainly cause molecular absorption. Aerosols contribute significantly when their density is high, e ⁇ g., clouds and fog (this
- Turbulence is in addition to the molecular absorption of their constituents). Turbulence may also
- the present invention will correct most effects of aerosols and turbulence and, depending on the selection of the reference filter where bandpass filters are used, also most of the atmospheric molecular absorption. Therefore, as long as the signal
- each DAR or NFCR sensor must operate within a limited atmospheric window. Although the exact extent of these windows depends on the detection range and acceptable
- the most significant windows are believed to be in the wavelength ranges of from about 0.3 ⁇ m to about 1.5 ⁇ m, from about 3 ⁇ m to about 5.5 ⁇ m, and from about 8 ⁇ m to about 13.3 ⁇ m.
- the optical absorptions and emissions of such target species must occur by transitions between naturally populated states (unlike LIF where emission is by transitions between artificially
- Figure 4 illustrates, as an example, the spectral variation of two agents that are used as pesticides, dimethyl methylphosphonate (DMMP) and diisopropyl methylphosphonate (DIMP). Since both have spectral features that are similar to those of other highly toxic chemicals, including band-peak frequency, bandwidth and
- FIG. 4 are comparable to those illustrated in Hoffland, et al., Spectral Signatures of Chemical Agents and Simulants. Opt. Eng., vol. 24, 982-84 (1985). It is evident that (a) both chemicals have spectral lines that overlap each other at least partially. For example, the primary line of DMMP which is peaked at 1086 cm "1 overlaps one of the
- NFCR configurations may be desirable when distinction between species, i e., specificity, is required. This is illustrated by the following analysis.
- a numerical model describing the transmission through horizontal atmospheric paths and by certain target species or agents at various optical densities C x L) was developed in connection with the present invention.
- the model was used to optimize parameters of the DAR and NFCR when used to detect such species and to estimate the difference between its signal with and without an agent in the FOV.
- the variation of the normalized net DAR signal as the center frequency of the reference filter is varied was calculated, assuming an atmosphere
- absorbers such as CO 2 or O 3 also contributed to this structure, their effect at standard
- the center line frequency of the sample filter was at 1086 cm “ 1 , where DMMP has a strong absorption.
- the bandwidth and transmission of both filters were 12.6 cm “1 and 0.64 respectively.
- the normalization was modeled by dividing the photocurrent of each detector with the current of the reference detector, as previously
- ground is only 5 K hotter than the species that difference reduces to approximately 1.5%. Similar variations (but with reversed sign) can be expected when the detection of a target species is by emission, e., when the target species is warmer then its background.
- the atmosphere contains only 0.0075 atm water vapor and when the detected radiation
- DMMP can be detected by the absolute reading of the DAR. At longer distances, DMMP can be detected by
- the use of one pair of detectors together with one sample filter and one optimally selected reference filter can provide sensitive detection of one target species while correcting for absorption or emission effects of one background gas such as water vapor.
- one background gas such as water vapor.
- a DAR sensor configured to:
- detect DMMP by using a sample filter centered at 1086 cm "1 may detect abso ⁇ tion by
- DIMP is present instead.
- a mixture of DMMP and DIMP in the FOV may
- DMMP a DAR sensor optimized to detect DMMP alone may provide no net signal when a mixture of these species in these optical densities is in the FOV.
- the sample detector is still providing DMMP-dependent output, but this output alone is not background-corrected and is influenced by atmospheric humidity.
- a commercially available quadrant detector such as that illustrated in FIG. 7, consisting of four separate detectors, can be configured by
- a third detector with a bandpass filter centered 948 cm "1 to coincide with one of the secondary lines of
- DMMP and a fourth detector with a bandpass filter centered at 1007.75 cm "1 to correct for abso ⁇ tion or emission effects by water vapor together with a second BRD can form a secondary DMMP DAR sensor.
- the filters are assumed to have a bandwidth of 12.6 cm '1 and a peak transmission of 64%.
- the net normalized DAR signal measured by the secondary DMMP DAR when 0.01 gr*cm/liter of DMMP is present in the FOV at a distance of 1 km is approximately 4.1 % above the background signal.
- the net normalized signal by the primary DMMP DAR top two quadrant detectors FIG. 7 is 15.5 % above the background signal. The ratio between these two signals is comparable to the ratio of the peak abso ⁇ tion coefficients of the
- this ratio may vary as the optical densities of DMMP increase or when the abso ⁇ tion path
- a third DIMP-DAR sensor consisting of a detector with a filter at 985 cm “1 at the strongest line of DIMP and one at 934 cm “1 for background correction. Additional quadrant detectors with dedicated filters and BRDs can be added to the system for further specificity or to detect of additional target species.
- linear detector arrays with a linear filter array can be added to the system for further specificity or to detect of additional target species.
- the NFCR sensor collects the background radiation at
- filters e.g., filters 25 or 64 in FIGS. 1 and 2. This was demonstrated by computing
- DMMP-NFCR the net NFCR signal of a DMMP-NFCR induced by 0.01 gr*cm/liter of DMMP.
- the design of this DMMP-NFCR included a notch filter at 1086 cm “ ' bandwidth of 12.6 cm “1 and transmission of 0.3 and a bandwidth-limiting filter with bandwidth of 15 cm “ 1 and transmission of 0.64.
- data processing of two unitary (single element) detectors is best performed by a BRD connected to the sample and reference
- the net normalized DMMP NFCR signal increases by approximately 2.5% above the background.
- DIMP may offset the signal induced by DMMP in a DMMP-NFCR sensor when included as a mixture with DMMP.
- a second NFCR sensor such as a DIMP -NFCR is needed to overcome such ambiguity.
- the signal associated with the same DIMP optical density of 0.1 gr*cm/liter DIMP is 8.7% below background.
- the DIMP NFCR sensor included a notch filter
- NFCR sensor for the detection of the secondary line of DMMP, or one of the secondary lines of DIMP, or both.
- the use of additional quadrant detectors or linear arrays may permit extension of the measurement to additional species.
- the NFCR can provide a specificity comparable to that of the
- notch filters currently are not available at all spectral regions. Although notch-like performance can be achieved by using bandpass filters as mirrors (e.g., as illustrated in FIG. 3), such an approach
- detector noise as determined by the noise equivalent power (NEP) or the detectivity
- Equation 2 is an approximation of the etandue as derived using geometrical optics and includes the lens f/# and the diameter d d of the detector's active
- infrared detector can be specified by:
- a D is the detector area
- D* 2.5 10 8 cm Hz 1/2 /W " ' is the detectivity of a potential thermopile (D* for pyroelectrics
- ⁇ SR 1.98xl0 "8 W/(cm 2 -sr-cm " ').
- a sensor having these properties can provide a signal-to-noise ratio (SNR) of:
- bandpass filters can be estimated by calculating separately the irradiance transmitted
- the detection solid angle ⁇ (which is defined by the FOV) and the
- the broadband detection of 15 cm “1 by the DAR/BRD provides a large signal relative to that of narrowband detection.
- thermopiles and pyroelectrics as well
- thermopile j ⁇
- the current j ⁇ associated with I p is determined similarly by substituting I F for I T .
- the sensor of the present invention may be configured to detect
- passively gaseous chemicals in the far infrared including, for explanation pu ⁇ oses only and without limitation, pollution (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x , CO), CH 4 and other pollutants (e.g., pesticides, N 2 O, NO x ,
- the sensor may also be used to detect the OH
- OH in flames emits brightly both in the ultra-violet and the infrared regions, detection of its emission can provide warnings of the onset of fires that otherwise are invisible.
- Particular examples include fires that may occur during the launch of space
- the most sensitive and quietest detector in the far infrared is the HgCdTe (MCT), which needs to be cooled cryogenically to 77° K. It can operate either in the photocurrent or photovoltaic mode. It can be manufactured
- Maintaining the MCT at 77° K is not convenient for handheld sensors and may not be
- Each of the practical uncooled detectors currently available in the 8- 13.3 ⁇ m range are essentially thermal detectors that sense slight increases in temperature induced by the incident infrared radiation.
- the major shortcomings of these detectors are lower detectivity and longer response time (about 2.5x10 8 cm Hz 1/2 W '1 and 1 ms, respectively) relative to that of a typical MCT (about 2.5xl0 10 cm HZ 1/2
- Such detectors also should have a large aperture that in turn provide the large FOV that is necessary for large signals (of course, large FOV reduces imaging resolution and therefore imaging may come at reduced sensitivity). It is expected that an aperture of about 3 mm will be required to
- Thermopiles and pyroelectric detectors are the most favored detectors
- RSV remotely piloted vehicle
- detectors can operate uncooled, have an exceptionally broadband response (0.6 - 35 ⁇ ), with a long rise time (1 - 200 ms) and a large aperture (possibly greater than 5 mm).
- their low cost about $40 for a thermopile and about $500 for a quadrant pyroelectric makes it possible even now to combine several pairs of these detectors with their own BRDs for multiple-species sensing or for same-species multiple-line detection for added specificity or for multiple background species correction.
- thermopile generally consists of arrays of thermocouple junctions (e.g., 72) connected in series to measure directly the temperature of a detecting surface relative to a heat sink that acts as a cold junction. The response is temperature
- thermopiles of the two thermopiles that are used as a pair for the sensor are kept both at the same temperature (such as, for example, by physically connecting them with a good heat conductor), then drifts in that common temperature will be
- thermopile e.g., 3MTM model from Dexter Research Center, Inc.
- target species detection at a 15 ppm-m level may be possible
- BRD assembly having a plurality circuits, with one or more sample detectors in the
- sample detector assembly being configured to sense a different target or group of targets, and one or more reference detectors in the reference detector assembly being configured to sense background radiation associated with different spectral lines of the same background species or with lines of other background species.
- the output of each sample sensor will be fed into the sample leg of one BRD, whereas the output of
- the reference detector(s) will be fed to the matched reference leg of that BRD.
- the bandpass or notch filters may be integrated with their respective thermopiles as windows thereby making the detectors compact and robust.
- Pyroelectric detectors can be an alternative to thermopiles as uncooled detectors for infrared sensing. Although their detectivity is similar to that of
- thermopiles pyroelectric detectors have a voltage responsivity of up to 900 V/W and internal resistance of up to 10 11 ⁇ , which are significantly higher than those of thermopiles. Pyroelectrics accordingly offer lower Johnson noise and higher pre- amplified output, thus a better signal to noise ratio (SNR). Pyroelectrics consist of ferroelectric crystals (e.g., LiTaO 3 ) that contain bound ions that are positioned non- symmetrically. When the temperature changes, these ions shift slightly, thereby
- Pyroelectrics are commercially packaged either as unitary 5 mm detectors or as 20 mm quadrant detectors (see, for example, FIG. 7). There, one or two of the quadrants may be used for background sensing and correction, and the remaining quadrants may be used to sense one or more different types of target species.
- the DAR and NFCR sensors of the present invention may be used for imaging (e.g.. with a FPA) as well as for single point detection. They may be used in many forms including, for example, in simple handheld devices that can be pointed by the user towards a target area like a flashlight, in order to scan a broad area for one or
- the present invention are embodied in handheld devices, it may be desirable that they
- Imaging is possible, for example, when the detection is by a FPA
- bandpass filters through the bandpass filters.
- the specificity of both the NFCR and DAR systems may be enhanced by replacing the single-band sample filter with a striped filter consisting of repeating sequence of a plurality of strips of bandpass (or notch) filters
- striped filter is for ease of description only. Although it may be that a “striped filter” may be more economically manufactured in a stripe or strip format, it may also be made using a checker, concentric circle,
- honeycomb honeycomb, or other suitable format.
- striped filter is intended to include any such format.
- Figure 8A illustrates one possible configuration for a striped sample filter 66 having a sequence of three bandpass transmissions (or notches) centered at frequencies v,, v 2 and v 3 .
- the sequence is repeated through the entire filter.
- the detector 68 behind this filter is an FPA consisting of a number of pixels sufficient so that radiation passing through each of the filter strips illuminates several pixel rows.
- the reference filter 70 of the DAR (or the bandwidth-limiting filter for the NFCR) consists of a repeating sequence of bandpass strips that match the strips of sample filter 66 for optimal background subtraction.
- the strips of reference filter 70 at v, ⁇ v 2 ' and v 3 ' are the frequencies of
- Figure 8B illustrates the possible image of a target agent cloud, such as
- FIGS. 8 A and 8B is a multiplexed triple-channel sensor that trades part of the spatial resolution
- a companion system such as a DIAL or FTIR can further probe the image.
- a companion system such as a DIAL or FTIR can further probe the image.
- Detection will be achieved when an agent is detected through at least one strip.
- Positive identification will be achieved by detection through two or more strips dedicated for that agent and not through strips dedicated to other agents.
- the approach of the present invention can double either the spatial resolution or the number of detectable species by dividing the detection into two paths.
- switching devices 54 and 56 may be required to selectively permit first and second portions 36 and 40 of beam 22 to reach detector 60. Until recently, switching between two filters was accomplished
- the device also is undesirably complex and
- the switching device may instead comprise a simple, inexpensive
- Such a device may include two asynchronous, electronically controlled mechanical-shutters 54, 56, one in each of first and second optical paths 38 and 40, or tuning fork shutters, to selectively switch viewing between
- the switching devices may comprise slotted chopper wheels, which also are simple devices, have faster switching rates than shutters, and can be easily inco ⁇ orated into a portable sensor.
- the use of asynchronous mechanical shutters 54, 56 does not affect the optical path alignment that is necessary
- the light collecting optics 22 or 32 used in connection with the sensor of the present invention may comprise one or more optical
- elements including, for example, lenses, holographic lenses, mirrors, optical fibers,
- the slits Preferably, the sensor of the present invention is constructed to be a highly portable device capable of operation in adverse
- the non-imaging sensor may be constructed as a compact device having a rugged construction.
- the components of the sensor may be integrated.
- the collecting optics may include a non- fragile lens. Although the collecting optics preferably will provide excellent light gathering capabilities for non-imaging
- the lens it is not essential that the lens provide high imaging resolution. It preferably will provide a large etandue (Equation 2) which is achieved partly by a large ⁇ .
- a large FOV, or ⁇ , may be achieved by large d d or low ⁇ #.
- the material is amo ⁇ hous and non-fragile, available in 12"x 18" sheets thereby allowing design of any reasonable aperture size.
- the hologram can be designed either to provide multiple focal spots - one for each detector - thus permitting imaging of the same target area on separate detectors. Alternatively, a single-focus lens will provide images on each of the detectors of
- the sensor of the present invention is designed to
- thermopiles or ⁇ pyroelectrics Combined power demand for the thermopiles or ⁇ pyroelectrics
- a handheld sensor therefore may operate on a standard 12 V battery.
- the 12 V Eveready EnergizerTM alkaline battery can provide approximately 0.2 W-hour before its voltage declines below 11 V.
- continuous operation of 2 hrs is possible with a single 12 V battery.
- thermoelectric cooler having a coefficient of performance of 0.05 thereby requiring 4 W can remove this heat. Short operation may be possible, for example, with larger battery packs or with rechargeable Li batteries.
- the sensor of the present invention may be packaged in any of a
- it may be packaged as a handheld device, as
- the senor may be integrated with a Fourier Transform Infrared Spectrometer (FTIR) system, a differential abso ⁇ tion lidar (DIAL), or in-situ sensors such as an ion-mobility spectrometer (IMS) or sorbing sensor.
- FTIR Fourier Transform Infrared Spectrometer
- DIAL differential abso ⁇ tion lidar
- IMS ion-mobility spectrometer
- sorbing sensor sorbing sensor.
- IMS or sorbing sensors are able to provide detection only at the point of measurement, thereby necessitating the collection and analysis of samples at numerous locations
- the search procedure may be significantly simplified and accelerated to provide coverage without gaps.
- the senor of the present invention will be particularly useful for pollution and toxic agent detection.
- it When packaged as a handheld sensor, it may, for example, be available to domestic rescue personnel in
- the handheld sensor in non-imaging applications may be configured generally in the shape of a gun, with an easily grippable handle and sight, as a binocular with one "eye" dedicated to sensing, or in any other useful
- the senor may be made to provide rapid detection and identification capabilities of several agents simultaneously by use of a plurality of detector pairs and BRDs or other data processing circuits.
- the operator may scan the
- the senor of the present invention may be designed to operate continuously for 30 days on a single battery charge while providing communication link with a central control center.
- Ground sensors may be designed for airdrop deployment or manual deployment to monitor compliance, covert activities or for advanced warning.
- the sensor of the present invention may be designed to operate continuously for 30 days on a single battery charge while providing communication link with a central control center.
- Ground sensors may be designed for airdrop deployment or manual deployment to monitor compliance, covert activities or for advanced warning.
- the sensor of the present invention may be designed to operate continuously for 30 days on a single battery charge while providing communication link with a central control center.
- Ground sensors may be designed for airdrop deployment or manual deployment to monitor compliance, covert activities or for advanced warning.
- the sensor of the present invention may be designed to operate continuously for 30 days on a single battery charge while providing communication link with a central control center.
- Ground sensors may be designed for airdrop deployment or manual deployment to monitor compliance, covert activities or for advanced warning.
- the invention may, for example, provide forward-looking warning capabilities for helicopter personnel. Similarly, when deployed on a RPV, the sensor may provide
- the present invention provides a sensor and method for determining the presence or optical density C x L) of a target species
- the remote sensor of the present invention is simple, compact, energy efficient and easy to use. It also has
- the senor also is well-suited for handheld, mobile or stand-alone operation for detecting and imaging
- gaseous chemicals such as pesticides, their precursors and reduced products, atmospheric effluents, hydrogen and hydrocarbon fires.
- the sensor is also well suited for applications in the UV and visible
- it can be configured as a DAR or NFCR for the detection of the
- the sample filter 10 or 44 may include safety devices for space launches, race cars, or pipe lines and refineries.
- the sample filter 10 or 44 may have a transmission at about 308 nm and bandwidth of approximately 15 nm, where OH in flames has its strongest natural emission. This emission is well defined and it is formed as a spectral band that extends to approximately 320 nm.
- the intensity of daylight or skylight radiation at 308 nm is
- DAR application may be centered at 350 nm. There, the emission by OH is at least ten times lower than at 308 nm. Therefore, most of the radiation at that wavelength is from the background. Although the intensity of daylight or skylight is more than
- the senor of the present invention is configured as a NFCR, a
- notch filter centered at 308 nm and a bandwidth of 15 nm may be used as the sample filter 10 or 44.
- a bandwidth-limiting filter 25 or 64 may be used, as previously
- Unitary detectors 26 and 28 that are used for non-imaging applications
- PMTs photomultiplier tubes
- UN sensitive photo-cathodes include preferably photomultiplier tubes (PMTs) with UN sensitive photo-cathodes.
- PMTs photomultiplier tubes
- UN sensitivity are now also becoming available and may also be used.
- the flame sensing DAR or ⁇ FCR can be configured as shown in FIG. 2 using the switching device described in the '797
- detector 60 may included an UN sensitive CCD array or UN sensitive intensified CCD array or other similar UV sensitive imaging device including photographic material.
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- Chemical & Material Sciences (AREA)
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- General Health & Medical Sciences (AREA)
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Abstract
Description
Claims
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/936,833 US6853452B1 (en) | 1999-03-17 | 2000-02-18 | Passive remote sensor of chemicals |
JP2000605185A JP2002539446A (en) | 1999-03-17 | 2000-02-18 | Passive remote sensor for chemicals |
IL14541300A IL145413A (en) | 1999-03-17 | 2000-02-18 | Passive remote sensor of chemicals |
EP00937498A EP1169631A4 (en) | 1999-03-17 | 2000-02-18 | Passive remote sensor of chemicals |
CA002365866A CA2365866C (en) | 1999-03-17 | 2000-02-18 | Passive remote sensor of chemicals |
AU52658/00A AU5265800A (en) | 1999-03-17 | 2000-02-18 | Passive remote sensor of chemicals |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US12475599P | 1999-03-17 | 1999-03-17 | |
US60/124,755 | 1999-03-17 | ||
US12568699P | 1999-03-23 | 1999-03-23 | |
US60/125,686 | 1999-03-23 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2000055602A1 true WO2000055602A1 (en) | 2000-09-21 |
Family
ID=26822924
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2000/004027 WO2000055602A1 (en) | 1999-03-17 | 2000-02-18 | Passive remote sensor of chemicals |
Country Status (6)
Country | Link |
---|---|
EP (1) | EP1169631A4 (en) |
JP (1) | JP2002539446A (en) |
AU (1) | AU5265800A (en) |
CA (1) | CA2365866C (en) |
IL (1) | IL145413A (en) |
WO (1) | WO2000055602A1 (en) |
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- 2000-02-18 EP EP00937498A patent/EP1169631A4/en not_active Withdrawn
- 2000-02-18 JP JP2000605185A patent/JP2002539446A/en active Pending
- 2000-02-18 CA CA002365866A patent/CA2365866C/en not_active Expired - Fee Related
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Also Published As
Publication number | Publication date |
---|---|
IL145413A0 (en) | 2002-06-30 |
IL145413A (en) | 2005-11-20 |
JP2002539446A (en) | 2002-11-19 |
CA2365866C (en) | 2007-07-24 |
AU5265800A (en) | 2000-10-04 |
EP1169631A4 (en) | 2007-02-28 |
EP1169631A1 (en) | 2002-01-09 |
CA2365866A1 (en) | 2000-09-21 |
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