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WO2012110791A1 - Improvements in or relating to detecting illicit substances in a target area - Google Patents

Improvements in or relating to detecting illicit substances in a target area Download PDF

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Publication number
WO2012110791A1
WO2012110791A1 PCT/GB2012/050309 GB2012050309W WO2012110791A1 WO 2012110791 A1 WO2012110791 A1 WO 2012110791A1 GB 2012050309 W GB2012050309 W GB 2012050309W WO 2012110791 A1 WO2012110791 A1 WO 2012110791A1
Authority
WO
WIPO (PCT)
Prior art keywords
target area
fluorescent radiation
illicit substance
discriminatory
illicit
Prior art date
Application number
PCT/GB2012/050309
Other languages
French (fr)
Inventor
John Tyrer
Leon Lobo
John Jones
Original Assignee
Laser Optical Engineering Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Laser Optical Engineering Limited filed Critical Laser Optical Engineering Limited
Publication of WO2012110791A1 publication Critical patent/WO2012110791A1/en

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Classifications

    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/6408—Fluorescence; Phosphorescence with measurement of decay time, time resolved fluorescence
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/4802—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/04—Systems determining the presence of a target
    • 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
    • G01N2021/1793—Remote sensing
    • 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
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64—Fluorescence; Phosphorescence
    • G01N21/645—Specially adapted constructive features of fluorimeters
    • G01N21/6456—Spatial resolved fluorescence measurements; Imaging

Definitions

  • This invention relates to a method of detecting an illicit substance in a target area and a detector assembly for detecting such a substance in a target area.
  • An illicit substance can be a solid, liquid or vapour residue from compounds including explosives, weapons discharge, and narcotics.
  • the residue may be present on a person's skin or clothing, or on articles such as containers, luggage, and vehicles.
  • a method of detecting an illicit substance in a target area comprising the steps of:
  • establishing a emission signature having at least one optical characteristic and at least one temporal characteristic helps to ensure that each emission signature is unique, and so reduces considerably the incidence of false alarms. As a result operators have high confidence in the detection method.
  • establishing at least one optical characteristic helps to identify the nature of the illicit substance, while establishing at least one temporal characteristic assists in distinguishing the illicit substance from unrelated background materials.
  • establishing a fluorescent radiation emission signature for an illicit substance includes establishing a first optical characteristic and first and second temporal characteristics. Establishing such a trio of characteristics for the emission signature provides the emission signature with a desired resolution to allow discrimination of the illicit substance of interest from other substances, and in particular discrimination of the illicit substance of interest from substances having similar emission decay curves.
  • establishing a first optical characteristic of the emission signature includes establishing a discriminatory wavelength range; and checking the fluorescent radiation emitted from the target area includes checking for emitted fluorescent radiation within the discriminatory wavelength range. Establishing a discriminatory wavelength range and utilising the corresponding check for emitted fluorescent radiation allows for isolation of the illicit substance of interest from a wide range of background materials.
  • checking for emitted fluorescent radiation within the discriminatory wavelength range includes capturing an image of the target area and applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range. Capturing an image of the target area and applying a filter is readily achievable in real time, and so permits the desired discrimination and detection of the illicit substance to occur without causing disruption to a person or article passing through the target area. Applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range may include one or more of:
  • Each of the aforementioned steps allows real-time detection of the illicit substance with the option of adding different filters with filtering characteristics corresponding to the discriminatory wavelength range of other illicit substances of interest.
  • Preferably establishing a first temporal characteristic of the emission signature includes establishing a discriminatory delay period; and checking the fluorescent radiation emitted from the target area includes checking whether fluorescent radiation continues to be emitted from the target area at the discriminatory delay period after illumination of the target area.
  • Establishing a discriminatory delay period allows for the discrimination of the illicit substance from other substances which emit fluorescent radiation for more or less time following illumination by a pulse of electromagnetic radiation.
  • checking whether fluorescent radiation continues to be emitted includes capturing an image of the target area at the discriminatory delay period after illumination of the target area.
  • Capturing an image of the target area is readily achievable in real time, and so causes no disruption to persons or articles passing through the target area.
  • image capture may take place in combination with other checks on the fluorescent radiation emitted from the target area.
  • the discriminatory delay period is between Ips and 20ns. Such a range allows for the discrimination of any of a variety of illicit substances of interest.
  • establishing a second temporal characteristic of the emission signature includes establishing a discriminatory exposure period; and checking the fluorescent radiation emitted from the target area includes checking the amount of fluorescent radiation emitted from the target area during the discriminatory exposure period.
  • Establishing a discriminatory exposure period allows for the discrimination of the illicit substance from other substances which emit fluorescent radiation for a similar period of time following illumination by a pulse of electromagnetic radiation, but which emit a greater or lesser amount of fluorescent radiation than the illicit substance of interest over the same period.
  • Preferably checking the amount of fluorescent radiation emitted from the target area during the discriminatory exposure period includes capturing an image of the target area having an exposure duration equal to the discriminatory exposure period.
  • Capturing an image of the target area is readily achievable in real time, and so results in minimal disruption. Such image capture may also take place in combination with other checks on the fluorescent radiation emitted from the target area.
  • the discriminatory exposure period may be between 10ps and 20ns. Such a range allows for the discrimination of any of a variety of illicit substances of interest.
  • Optionally checking the amount of fluorescent radiation emitted during the discriminatory exposure period is initiated within 10ns of illuminating the target area.
  • Initiating the checking within the aforementioned period helps to ensure that maximum use is made of the relatively low amount of fluorescent radiation emitted by substances when excited by incident electromagnetic radiation.
  • Such steps allow for the detection of any one of a range of illicit substances in a reliable manner with minimal disruption to persons and articles passing through the target area.
  • establishing a fluorescent radiation emission signature for an illicit substance of interest includes:
  • the method preferably further includes the steps of:
  • a detector assembly for detecting an illicit substance of interest in a target area, comprising:
  • an electromagnetic radiation pulse generator to illuminate the target area with a pulse of electromagnetic radiation
  • a fluorescent radiation detector to detect fluorescent radiation emitted from the target area
  • a control module to check whether the detected fluorescent radiation includes the or each optical characteristic and the first and second temporal characteristics of a pre-established fluorescent radiation emission signature for the illicit substance, and to indicate that the illicit substance is present in the target area if the detected fluorescent radiation includes each of the or each optical characteristic and the first and second temporal characteristics.
  • the detector assembly allows for reliable discrimination between the illicit substance of interest and any background material or other illicit substances.
  • Figure 1 shows a schematic view of a detector assembly according to a first embodiment of the invention
  • Figures 2(a) to 2(c) illustrate schematically various images produced by the detector assembly shown in Figure 1 ;
  • Figure 3(a) shows fluorescent radiation emission spectra for a first illicit substance of interest and a first background material
  • Figure 3(b) shows a discriminatory wavelength range overlaid on the emission spectra shown in Figure 3(a);
  • Figure 4 shows fluorescent radiation emission decay curves for the first illicit substance of interest and the first background material together with a discriminatory delay period
  • FIG. 5 shows fluorescent radiation emission decay curves for the first illicit substance of interest and the first background material together with a discriminatory exposure period.
  • a detector assembly according to a first embodiment of the invention is designated generally by the reference numeral 10.
  • the detector assembly 10 includes an electromagnetic radiation pulse generator 12 to illuminate a target area 14 with a pulse of electromagnetic radiation.
  • the pulse generator 12 is a pulsed laser 16 which is able to illuminate the target area 14 with pulses of electromagnetic radiation in the ultraviolet range between approximately 150nm and 400nm.
  • the pulsed laser 16 is able to illuminate the target area 14 with first and second wavelengths of ultraviolet radiation at approximately 266nm and 355nm, respectively.
  • the different wavelengths may illuminate the target area 14 simultaneously or sequentially.
  • the pulsed laser 16 may illuminate the target area 14 with first and second wavelengths of radiation that differ from those mentioned above.
  • the duration of each pulse of ultraviolet radiation preferably lies in the range of 1 ps to 4ns, and most preferably is approximately 250ps.
  • the detector assembly 10 also includes a fluorescent radiation detector 18 to detect fluorescent radiation emitted from the target area 14.
  • the fluorescent radiation detector 18 is an image capture device 20 in the form of a first camera 22.
  • the first camera 22 is able to capture images of fluorescent radiation in the ultraviolet range, i.e. between approximately 150nm and 400nm.
  • the detector assembly 10 shown also includes a second camera 24 capable of capturing a visible image of the target area 14, i.e. an image in the visible range of the electromagnetic spectrum between approximately 400nm and 700nm.
  • the detector assembly 10 includes a second camera 24 which is operable in a waveband outside the response of the human eye so as to allow covert night time operation.
  • the detector assembly 10 additionally includes a lens arrangement which has a beam splitter to direct fluorescent radiation from the lens arrangement to the first camera 22 and visible radiation from the lens arrangement to the second camera 24, such that each camera 22, 24 receives an essentially identical image of the target area 14.
  • the detector assembly 10 further includes a control module 26 which checks whether the detected fluorescent radiation includes particular optical and temporal characteristics of a pre-established fluorescent radiation emission signature for an illicit substance 28 of interest.
  • control module 26 is shown separate from, but in communication with each of the pulsed laser 16 and the first and second cameras 22, 24. In other embodiments of the invention the control module 26 may lie within the same enclosure as the laser 16 and the cameras 22, 24.
  • the control module 26 also indicates that the illicit substance 28 is present in the target area 4 if the detected fluorescent radiation includes each of the particular optical and temporal characteristics.
  • control module 26 may indicate that the illicit substance 28 is present in the target area 14 is to combine a composite image 30 of the target area 14, as shown in Figure 2(a), with a visual image 32 of the target area 14, as shown in Figure 2(b), to form a composite context image 34 which indicates where in the target area 14 the illicit substance 28 is located, as shown in Figure 2(c).
  • Detecting an illicit substance 28 in the target area 14 includes a first step of establishing a fluorescent radiation emission signature for the illicit substance 28 of interest.
  • the emission signature has a first optical characteristic and first and second temporal characteristics.
  • Establishing a first optical characteristic of the emission signature includes establishing a discriminatory wavelength range 36, as illustrated in Figure 3(b).
  • Figure 3(a) shows fluorescent radiation emission spectra for a first illicit substance 28 of interest, e.g. SEMTEX®, and a first background material 38, e.g. white cotton, when each is illuminated, i.e. excited, by a pulse of ultraviolet radiation with a first wavelength of approximately 355nm.
  • the discriminatory wavelength range 36 is chosen to isolate a portion of the emission spectra for each material 28, 38.
  • the portion of the emission spectra is chosen to include a distinctive peak in the intensity of fluorescent radiation emitted by the illicit substance of interest 28 together with a low intensity of fluorescent radiation emitted by the background material 38.
  • the discriminatory wavelength range is approximately 380nm to 390nm.
  • the discriminatory wavelength range may vary but preferably has a width of 10nm to 15nm so as to provide a desired degree of discrimination.
  • establishing a first optical characteristic of the emission signature may include establishing a plurality of discriminatory wavelength ranges, and selecting one of the ranges as desired.
  • Such a plurality of discriminatory wavelength ranges may be established by providing an optical filter having two or more bandpass regions each of which defines a desired discriminatory wavelength range.
  • the optical filter may be moved relative to, e.g. the fluorescent radiation detector 18, so that the bandpass region of interest lies between the detector 18 and the target area 14.
  • each of the plurality of discriminatory wavelength ranges may be defined by a separate electronically addressable filter which could be applied to a captured image of the target area.
  • Establishing a first temporal characteristic of the emission signature includes establishing a discriminatory delay period 40 after illumination of the target area 14 takes place, as illustrated in Figure 4.
  • Figure 4 shows fluorescent radiation emission decay curves for the first illicit substance 28 and the first background material 38 when illuminated by a pulse of ultraviolet radiation with a wavelength of approximately 355nm.
  • the discriminatory delay period 40 is chosen to permit discrimination between one decay curve and the other decay curve.
  • the discriminatory delay period 40 is chosen so that one substance 38 has ceased to emit fluorescent radiation while the other substance 28 continues to do so.
  • the discriminatory delay period is 100ns after the point in time 42 at which the target area 14 is illuminated. After this delay period 40 only the illicit substance 28 continues to emit fluorescent radiation, and as such only fluorescent radiation emitted by the illicit substance 28 is detectable.
  • the discriminatory delay period may vary between 1 ps and 200ns.
  • Establishing a second temporal characteristic of the emission signature includes establishing a discriminatory exposure period 44, as illustrated in Figure 5.
  • Figure 5 shows the aforementioned fluorescent radiation emission decay curves for the first illicit substance 28 and the first background material 38, when illuminated by a pulse of ultraviolet radiation with a wavelength of approximately 355nm.
  • the discriminatory exposure period 44 is chosen to permit an alternative means of discriminating between one decay curve and the other decay curve.
  • the discriminatory exposure period 44 is chosen to coincide with a period in which both substances 28, 38 are emitting fluorescent radiation but there is a marked contrast in the amount of fluorescent radiation emitted by each substance 28, 38.
  • the discriminatory exposure period 44 is 20ns and it starts within 10ns of the point in time 42 at which the target area 14 is illuminated. During this discriminatory exposure period 44 the amount of fluorescent radiation emitted by the illicit substance 28 is much greater than the amount emitted by the background material 38.
  • the discriminatory exposure period may vary between 10ps and 20ns.
  • Detecting an illicit substance 28 in the target area 14 also includes a second step of illuminating the target area 14 with a pulse of electromagnetic radiation.
  • the target area 14 is illuminated by a pulse of ultraviolet radiation with a first wavelength of approximately 355nm, i.e. the same wavelength as the incident radiation utilised to establish the emission signature of the illicit substance 28.
  • Detecting an illicit substance 28 in the target area 14 further includes a third step of checking whether the fluorescent radiation emitted from the target area 14 includes the first optical characteristic and the first and second temporal characteristics of the illicit substance.
  • checking the fluorescent radiation emitted from the target area 14 includes checking for emitted fluorescent radiation within the discriminatory wavelength range 36.
  • Such a check is carried out by capturing a first image of the target area 14 using the first camera 22 and applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range 36.
  • the filter may be applied by moving an optical filter (not shown), which has filtering characteristics corresponding to the discriminatory wavelength range 36, between the target area 14 and the first camera 22.
  • the filter may be applied by applying an electronically addressable filter (which has the desired filter characteristics) to the captured first image.
  • checking the fluorescent radiation emitted from the target area 14 also includes checking whether fluorescent radiation continues to be emitted from the target area 14 on expiration of the discriminatory delay period 40 after illumination of the target area 14 with ultraviolet radiation.
  • This check is carried out by capturing a second image of the target area 14 using the first camera 22 at the appropriate moment after illumination of the target area 14.
  • Checking the fluorescent radiation emitted from the target area 14 further includes checking the amount of fluorescent radiation emitted from the target area 14 during the discriminatory exposure period 44.
  • the amount of radiation emitted is checked by capturing a third image of the target area 14 using the first camera 22, with the third image having an exposure duration equal to the discriminatory exposure period 44.
  • Preferably capture of the third image is initiated within 10ns of illuminating the target area 14 with ultraviolet radiation.
  • Each of the first, second and third images are processed, e.g. by an image processor (not shown).
  • the processor compares the greyscale values of corresponding individual pixels in the respective images and determines the presence of relatively light and relatively dark areas, with the light areas indicating a higher intensity of fluorescent radiation.
  • the processor then generates a composite image 30, as shown in Figure 2(a), with a light area indicating the presence of the illicit substance 28.
  • the composite image 30 is then laid over a visual image 32 of the target area 14 captured by the second camera 24, as shown in Figure 2(b).
  • the overlaid images combine to create a composite context image 34, as shown in Figure 2(c).
  • the composite context image 34 indicates the presence and position within the target area 14 of the illicit substance 28 to an operative.
  • a second embodiment of the method of the invention includes establishing respective fluorescent radiation emission signatures for a plurality of illicit substances of interest.
  • Each emission signature has a first optical characteristic and first and second temporal characteristics which are established in the same manner as set out hereinabove in relation to the first embodiment of the method of the invention.
  • the second method includes similar illuminating and checking steps as the first method of the invention.
  • the second method additionally includes repeatedly illuminating the target area 14 and repeatedly checking whether the fluorescent radiation emitted from the target area 14 includes the optical and temporal characteristics of a further illicit substance of interest.
  • Each checking step aims to detect a particular one of the plurality of illicit substances and involves: - checking for emitted fluorescent radiation within the discriminatory wavelength range 36 corresponding to the particular illicit substance;
  • discriminatory wavelength range 36 discriminatory delay period 44, and discriminatory exposure 44 utilised at each checking stage is virtually unique to a particular illicit substance of interest, and so allows not only for the detection of a single illicit substance of interest but also discrimination between different illicit substances that may all be of interest.
  • Checking for emitted fluorescent radiation within different discriminatory wavelength ranges may be achieved by moving different optical filters, e.g. arranged in a filter wheel, over the first camera 22.
  • Repeating the illumination and checking steps may continue until at least one illicit substance is identified as being present in the target area 14, and/or until a check has been carried out for each illicit substance for which an emission signature has been established.
  • establishing a fluorescent radiation emission signature for an illicit substance of interest includes establishing first and second emission signatures for the illicit substance.
  • the first emission signature is established according to an incident first pulse of electromagnetic radiation at a first wavelength and has a first optical characteristic and first and second temporal characteristics.
  • One example of a first pulse of electromagnetic radiation is a pulse at a wavelength of approximately 355nm.
  • the second emission signature is established with reference to an incident second pulse of electromagnetic radiation at a second wavelength which is different to the first wavelength.
  • a suitable second wavelength is approximately 266nm.
  • the second emission signature has a second optical characteristic and third and fourth temporal characteristics.
  • the emission signature for each illicit substance of interest has six characteristics, and so has a great number of unique permutations than, say, an emission signature having three characteristics.
  • Each of the optical and temporal characteristics is established in the same manner as described above in connection with the first method of the invention.
  • the third method of the invention additionally includes modified illumination and checking steps, as set out below.
  • the target area 14 is illuminated with a pulse of electromagnetic radiation at the first wavelength, e.g. approximately 355nm. Checks are then made to determine whether the fluorescent radiation emitted from the target area 14 includes the first optical characteristic and the first and second temporal characteristics, i.e. characteristics associated with excitation of the illicit substance at the first wavelength.
  • the target area 14 is also illuminated with a pulse of electromagnetic radiation at the second wavelength, e.g. approximately 266nm. Checks are then made to determine whether the fluorescent radiation emitted from the target area 14 includes the second optical characteristic and the third and fourth temporal characteristics, i.e. characteristics associated with excitation of the illicit substance at the second wavelength.
  • the third method of the invention may be modified to include steps corresponding to those outlined in connection with the second method of the invention to allow the detection of more than one illicit substance of interest, i.e. establishing first and second emission signatures for each illicit substance and checking for corresponding first and second optical characteristics and first, second, third and fourth temporal characteristics.

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Abstract

In the field of illicit substance detection using emitted fluorescent radiation spectra there is a need for improvements to reduce the number of false alerts and improve operator confidence in the detection regime. A detector assembly (10), for detecting an illicit substance of interest (28) in a target area (14), comprises an electromagnetic radiation pulse generator (12) to illuminate the target area (14) with a pulse of electromagnetic radiation. The detector assembly (10) also includes a fluorescent radiation detector (18) to detect fluorescent radiation emitted from the target area (14), and a control module (26). The control module (26) checks whether the detected fluorescent radiation includes the or each optical characteristic and the first and second temporal characteristics of a pre-established fluorescent radiation emission signature for the illicit substance (28), and indicates that the illicit substance (28) is present in the target area (14) if the detected fluorescent radiation includes each of the or each optical and the first and second temporal characteristics. A method of detecting an illicit substance (28) in a target area (14) comprises the steps of: (a) establishing a fluorescent radiation emission signature for an illicit substance (28) of interest, the emission signature having at least one optical characteristic and first and second temporal characteristic; (b) illuminating the target area (14) with a pulse of electromagnetic radiation; (c) checking whether the fluorescent radiation emitted from the target area (14) includes the or each optical characteristic and the first and second temporal characteristics of the illicit substance (28); and (d) indicating that the illicit substance (28) is present in the target area (14) if the emitted fluorescent radiation includes each of the or each optical characteristic and the first and second temporal characteristics.

Description

IMPROVEMENTS IN OR RELATING TO
DETECTING ILLICIT SUBSTANCES IN A TARGET AREA
This invention relates to a method of detecting an illicit substance in a target area and a detector assembly for detecting such a substance in a target area.
An illicit substance can be a solid, liquid or vapour residue from compounds including explosives, weapons discharge, and narcotics. The residue may be present on a person's skin or clothing, or on articles such as containers, luggage, and vehicles.
It is desirable to detect the presence of such illicit substances in a variety of situations such as anti-terrorist and law enforcement activities.
It is known that different substances emit different fluorescent radiation spectra when excited by electromagnetic radiation. However, many of the emission spectra have similar profiles. As a result conventional systems relying on emitted fluorescent radiation spectra find it difficult to accurately discriminate between an illicit substance of interest and general background material or other illicit substances. Consequently there are a large number of false alerts which reduces operator confidence in the detection system.
There is, therefore, a need for improvements in detecting illicit substances in a target area so as to reduce the number of false alerts and improve operator confidence in the detection regime. According to a first aspect of the invention there is provided a method of detecting an illicit substance in a target area comprising the steps of:
(a) establishing a fluorescent radiation emission signature for an illicit substance of interest, the emission signature having at least one optical characteristic and first and second temporal characteristics;
(b) illuminating the target area with a pulse of electromagnetic radiation;
(c) checking whether the fluorescent radiation emitted from the target area includes the or each optical characteristic and the first and second temporal characteristics of the illicit substance; and
(d) indicating that the illicit substance is present in the target area if the emitted fluorescent radiation includes each of the or each optical characteristic and the first and second temporal characteristics. Establishing a fluorescent radiation emission signature for an illicit substance of interest provides a way of identifying the illicit substance and so allows for discrimination between the illicit substance of interest and any background material or other illicit substance. The method of the invention thereby provides for accurate and reliable detection of the illicit substance of interest.
Moreover, establishing a emission signature having at least one optical characteristic and at least one temporal characteristic helps to ensure that each emission signature is unique, and so reduces considerably the incidence of false alarms. As a result operators have high confidence in the detection method.
In addition, establishing at least one optical characteristic helps to identify the nature of the illicit substance, while establishing at least one temporal characteristic assists in distinguishing the illicit substance from unrelated background materials.
Preferably establishing a fluorescent radiation emission signature for an illicit substance includes establishing a first optical characteristic and first and second temporal characteristics. Establishing such a trio of characteristics for the emission signature provides the emission signature with a desired resolution to allow discrimination of the illicit substance of interest from other substances, and in particular discrimination of the illicit substance of interest from substances having similar emission decay curves. Optionally, establishing a first optical characteristic of the emission signature includes establishing a discriminatory wavelength range; and checking the fluorescent radiation emitted from the target area includes checking for emitted fluorescent radiation within the discriminatory wavelength range. Establishing a discriminatory wavelength range and utilising the corresponding check for emitted fluorescent radiation allows for isolation of the illicit substance of interest from a wide range of background materials.
In a preferred embodiment of the method of the invention checking for emitted fluorescent radiation within the discriminatory wavelength range includes capturing an image of the target area and applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range. Capturing an image of the target area and applying a filter is readily achievable in real time, and so permits the desired discrimination and detection of the illicit substance to occur without causing disruption to a person or article passing through the target area. Applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range may include one or more of:
(e) moving an optical filter having filtering characteristics corresponding to the discriminatory wavelength range into the fluorescent radiation transmission path between the target area and an image capture device; and
(f) applying an electronically addressable filter having filter characteristics corresponding to the discriminatory wavelength range to the captured image.
Each of the aforementioned steps allows real-time detection of the illicit substance with the option of adding different filters with filtering characteristics corresponding to the discriminatory wavelength range of other illicit substances of interest.
Preferably establishing a first temporal characteristic of the emission signature includes establishing a discriminatory delay period; and checking the fluorescent radiation emitted from the target area includes checking whether fluorescent radiation continues to be emitted from the target area at the discriminatory delay period after illumination of the target area.
Establishing a discriminatory delay period allows for the discrimination of the illicit substance from other substances which emit fluorescent radiation for more or less time following illumination by a pulse of electromagnetic radiation.
In another preferred embodiment of the method of the invention checking whether fluorescent radiation continues to be emitted includes capturing an image of the target area at the discriminatory delay period after illumination of the target area.
Capturing an image of the target area is readily achievable in real time, and so causes no disruption to persons or articles passing through the target area. In addition, such image capture may take place in combination with other checks on the fluorescent radiation emitted from the target area.
Optionally the discriminatory delay period is between Ips and 20ns. Such a range allows for the discrimination of any of a variety of illicit substances of interest. In a still further preferred embodiment of the invention establishing a second temporal characteristic of the emission signature includes establishing a discriminatory exposure period; and checking the fluorescent radiation emitted from the target area includes checking the amount of fluorescent radiation emitted from the target area during the discriminatory exposure period.
Establishing a discriminatory exposure period allows for the discrimination of the illicit substance from other substances which emit fluorescent radiation for a similar period of time following illumination by a pulse of electromagnetic radiation, but which emit a greater or lesser amount of fluorescent radiation than the illicit substance of interest over the same period.
Preferably checking the amount of fluorescent radiation emitted from the target area during the discriminatory exposure period includes capturing an image of the target area having an exposure duration equal to the discriminatory exposure period.
Capturing an image of the target area is readily achievable in real time, and so results in minimal disruption. Such image capture may also take place in combination with other checks on the fluorescent radiation emitted from the target area.
The discriminatory exposure period may be between 10ps and 20ns. Such a range allows for the discrimination of any of a variety of illicit substances of interest. Optionally checking the amount of fluorescent radiation emitted during the discriminatory exposure period is initiated within 10ns of illuminating the target area.
Initiating the checking within the aforementioned period helps to ensure that maximum use is made of the relatively low amount of fluorescent radiation emitted by substances when excited by incident electromagnetic radiation.
A still further preferred embodiment of the method of the invention includes:
establishing respective fluorescent radiation emission signatures for a plurality of illicit substances of interest;
illuminating the target area with a pulse of electromagnetic radiation; checking whether the fluorescent radiation emitted from the target area includes the or each optical characteristic and the first and second temporal characteristics of one illicit substance of interest; and
repeatedly illuminating the target area and repeatedly checking whether the fluorescent radiation emitted from the target area includes the or each optical characteristics and the first and second temporal characteristics of another illicit substance of interest until at least one illicit substance is indicated as being present in the target area and/or a check of the fluorescent radiation emitted from the target area has been carried out for each illicit substance of interest.
Such steps allow for the detection of any one of a range of illicit substances in a reliable manner with minimal disruption to persons and articles passing through the target area.
Preferably establishing a fluorescent radiation emission signature for an illicit substance of interest includes:
establishing a first emission signature corresponding to an incident first pulse of electromagnetic radiation at a first wavelength, the first emission signature having a first optical characteristic and first and second temporal characteristics; and
establishing a second emission signature corresponding to an incident second pulse of electromagnetic radiation at a second wavelength, the second emission signature having a second optical characteristic and third and fourth temporal characteristics,
and the method preferably further includes the steps of:
(b) (i) illuminating the target area with a pulse of electromagnetic radiation at the first wavelength;
(c) (i) checking whether the fluorescent radiation emitted from the target area includes the first optical characteristic and the first and second temporal characteristics;
(b)(ii) illuminating the target area with a pulse of electromagnetic radiation at the second wavelength; and
(c)(ii) checking whether the fluorescent radiation emitted from the target area includes the second optical characteristic and the third and fourth temporal characteristics.
Establishing first and second emission signatures and checking for the corresponding optical and temporal characteristics in the fluorescent radiation emitted from the target area further improves the accuracy and reliability of illicit substance detection, and so further increases operators confidence in the detection method. According to a second aspect of the invention there is provided a detector assembly, for detecting an illicit substance of interest in a target area, comprising:
an electromagnetic radiation pulse generator to illuminate the target area with a pulse of electromagnetic radiation;
a fluorescent radiation detector to detect fluorescent radiation emitted from the target area; and
a control module to check whether the detected fluorescent radiation includes the or each optical characteristic and the first and second temporal characteristics of a pre-established fluorescent radiation emission signature for the illicit substance, and to indicate that the illicit substance is present in the target area if the detected fluorescent radiation includes each of the or each optical characteristic and the first and second temporal characteristics. The detector assembly allows for reliable discrimination between the illicit substance of interest and any background material or other illicit substances.
There now follows a brief description of preferred embodiments of the invention, by way of non-limiting example, with reference to the accompanying figures in which:
Figure 1 shows a schematic view of a detector assembly according to a first embodiment of the invention;
Figures 2(a) to 2(c) illustrate schematically various images produced by the detector assembly shown in Figure 1 ;
Figure 3(a) shows fluorescent radiation emission spectra for a first illicit substance of interest and a first background material;
Figure 3(b) shows a discriminatory wavelength range overlaid on the emission spectra shown in Figure 3(a);
Figure 4 shows fluorescent radiation emission decay curves for the first illicit substance of interest and the first background material together with a discriminatory delay period; and
Figure 5 shows fluorescent radiation emission decay curves for the first illicit substance of interest and the first background material together with a discriminatory exposure period. A detector assembly according to a first embodiment of the invention is designated generally by the reference numeral 10. The detector assembly 10 includes an electromagnetic radiation pulse generator 12 to illuminate a target area 14 with a pulse of electromagnetic radiation.
In the embodiment shown the pulse generator 12 is a pulsed laser 16 which is able to illuminate the target area 14 with pulses of electromagnetic radiation in the ultraviolet range between approximately 150nm and 400nm.
In particular the pulsed laser 16 is able to illuminate the target area 14 with first and second wavelengths of ultraviolet radiation at approximately 266nm and 355nm, respectively. The different wavelengths may illuminate the target area 14 simultaneously or sequentially.
In other embodiments of the invention the pulsed laser 16 may illuminate the target area 14 with first and second wavelengths of radiation that differ from those mentioned above.
The duration of each pulse of ultraviolet radiation preferably lies in the range of 1 ps to 4ns, and most preferably is approximately 250ps.
The detector assembly 10 also includes a fluorescent radiation detector 18 to detect fluorescent radiation emitted from the target area 14. In the embodiment shown the fluorescent radiation detector 18 is an image capture device 20 in the form of a first camera 22. The first camera 22 is able to capture images of fluorescent radiation in the ultraviolet range, i.e. between approximately 150nm and 400nm. In addition, the detector assembly 10 shown also includes a second camera 24 capable of capturing a visible image of the target area 14, i.e. an image in the visible range of the electromagnetic spectrum between approximately 400nm and 700nm.
In other embodiments of the invention (not shown) the detector assembly 10 includes a second camera 24 which is operable in a waveband outside the response of the human eye so as to allow covert night time operation.
In still further embodiments of the invention (not shown) the detector assembly 10 additionally includes a lens arrangement which has a beam splitter to direct fluorescent radiation from the lens arrangement to the first camera 22 and visible radiation from the lens arrangement to the second camera 24, such that each camera 22, 24 receives an essentially identical image of the target area 14. The detector assembly 10 further includes a control module 26 which checks whether the detected fluorescent radiation includes particular optical and temporal characteristics of a pre-established fluorescent radiation emission signature for an illicit substance 28 of interest.
In the embodiment shown the control module 26 is shown separate from, but in communication with each of the pulsed laser 16 and the first and second cameras 22, 24. In other embodiments of the invention the control module 26 may lie within the same enclosure as the laser 16 and the cameras 22, 24.
The control module 26 also indicates that the illicit substance 28 is present in the target area 4 if the detected fluorescent radiation includes each of the particular optical and temporal characteristics.
One way in which the control module 26 may indicate that the illicit substance 28 is present in the target area 14 is to combine a composite image 30 of the target area 14, as shown in Figure 2(a), with a visual image 32 of the target area 14, as shown in Figure 2(b), to form a composite context image 34 which indicates where in the target area 14 the illicit substance 28 is located, as shown in Figure 2(c).
Further details of the manner in which the aforementioned detector assembly 10 operates, and the manner in which one or more illicit substances 28 are detected in the target area 14 are set out below.
Detecting an illicit substance 28 in the target area 14 includes a first step of establishing a fluorescent radiation emission signature for the illicit substance 28 of interest.
In a first embodiment of the method of the invention the emission signature has a first optical characteristic and first and second temporal characteristics.
Establishing a first optical characteristic of the emission signature includes establishing a discriminatory wavelength range 36, as illustrated in Figure 3(b). In this regard, Figure 3(a) shows fluorescent radiation emission spectra for a first illicit substance 28 of interest, e.g. SEMTEX®, and a first background material 38, e.g. white cotton, when each is illuminated, i.e. excited, by a pulse of ultraviolet radiation with a first wavelength of approximately 355nm.
The discriminatory wavelength range 36 is chosen to isolate a portion of the emission spectra for each material 28, 38. Preferably the portion of the emission spectra is chosen to include a distinctive peak in the intensity of fluorescent radiation emitted by the illicit substance of interest 28 together with a low intensity of fluorescent radiation emitted by the background material 38. In the example shown the discriminatory wavelength range is approximately 380nm to 390nm.
In other embodiments of the invention the discriminatory wavelength range may vary but preferably has a width of 10nm to 15nm so as to provide a desired degree of discrimination.
In still further embodiments of the invention, establishing a first optical characteristic of the emission signature may include establishing a plurality of discriminatory wavelength ranges, and selecting one of the ranges as desired.
Such a plurality of discriminatory wavelength ranges may be established by providing an optical filter having two or more bandpass regions each of which defines a desired discriminatory wavelength range. The optical filter may be moved relative to, e.g. the fluorescent radiation detector 18, so that the bandpass region of interest lies between the detector 18 and the target area 14.
Alternatively each of the plurality of discriminatory wavelength ranges may be defined by a separate electronically addressable filter which could be applied to a captured image of the target area.
Establishing a first temporal characteristic of the emission signature includes establishing a discriminatory delay period 40 after illumination of the target area 14 takes place, as illustrated in Figure 4. Figure 4 shows fluorescent radiation emission decay curves for the first illicit substance 28 and the first background material 38 when illuminated by a pulse of ultraviolet radiation with a wavelength of approximately 355nm. As can be seen, the fluorescent radiation emitted by each material 28, 38 decays at a specific rate. The discriminatory delay period 40 is chosen to permit discrimination between one decay curve and the other decay curve. Preferably the discriminatory delay period 40 is chosen so that one substance 38 has ceased to emit fluorescent radiation while the other substance 28 continues to do so. In the example shown the discriminatory delay period is 100ns after the point in time 42 at which the target area 14 is illuminated. After this delay period 40 only the illicit substance 28 continues to emit fluorescent radiation, and as such only fluorescent radiation emitted by the illicit substance 28 is detectable. In other embodiments of the invention the discriminatory delay period may vary between 1 ps and 200ns.
Establishing a second temporal characteristic of the emission signature includes establishing a discriminatory exposure period 44, as illustrated in Figure 5.
Figure 5 shows the aforementioned fluorescent radiation emission decay curves for the first illicit substance 28 and the first background material 38, when illuminated by a pulse of ultraviolet radiation with a wavelength of approximately 355nm. The discriminatory exposure period 44 is chosen to permit an alternative means of discriminating between one decay curve and the other decay curve. Preferably the discriminatory exposure period 44 is chosen to coincide with a period in which both substances 28, 38 are emitting fluorescent radiation but there is a marked contrast in the amount of fluorescent radiation emitted by each substance 28, 38.
In addition, because the amount of fluorescent radiation emitted by both substances 28, 38 is relatively low, it is desirable to initiate the discriminatory exposure period 44 as high on each decay curve as possible, i.e. shortly after illumination of the substances 28, 38 occurs.
In the example shown the discriminatory exposure period 44 is 20ns and it starts within 10ns of the point in time 42 at which the target area 14 is illuminated. During this discriminatory exposure period 44 the amount of fluorescent radiation emitted by the illicit substance 28 is much greater than the amount emitted by the background material 38.
In other embodiments of the invention the discriminatory exposure period may vary between 10ps and 20ns.
Detecting an illicit substance 28 in the target area 14 also includes a second step of illuminating the target area 14 with a pulse of electromagnetic radiation. In the first embodiment of the method of the invention the target area 14 is illuminated by a pulse of ultraviolet radiation with a first wavelength of approximately 355nm, i.e. the same wavelength as the incident radiation utilised to establish the emission signature of the illicit substance 28. Detecting an illicit substance 28 in the target area 14 further includes a third step of checking whether the fluorescent radiation emitted from the target area 14 includes the first optical characteristic and the first and second temporal characteristics of the illicit substance. In the first embodiment of the method of the invention, checking the fluorescent radiation emitted from the target area 14 includes checking for emitted fluorescent radiation within the discriminatory wavelength range 36.
Such a check is carried out by capturing a first image of the target area 14 using the first camera 22 and applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range 36.
The filter may be applied by moving an optical filter (not shown), which has filtering characteristics corresponding to the discriminatory wavelength range 36, between the target area 14 and the first camera 22.
Alternatively the filter may be applied by applying an electronically addressable filter (which has the desired filter characteristics) to the captured first image. In the first embodiment of the method of the invention, checking the fluorescent radiation emitted from the target area 14 also includes checking whether fluorescent radiation continues to be emitted from the target area 14 on expiration of the discriminatory delay period 40 after illumination of the target area 14 with ultraviolet radiation.
This check is carried out by capturing a second image of the target area 14 using the first camera 22 at the appropriate moment after illumination of the target area 14.
Checking the fluorescent radiation emitted from the target area 14 further includes checking the amount of fluorescent radiation emitted from the target area 14 during the discriminatory exposure period 44. The amount of radiation emitted is checked by capturing a third image of the target area 14 using the first camera 22, with the third image having an exposure duration equal to the discriminatory exposure period 44.
Preferably capture of the third image is initiated within 10ns of illuminating the target area 14 with ultraviolet radiation.
Each of the first, second and third images are processed, e.g. by an image processor (not shown). In one embodiment of the method of the invention the processor compares the greyscale values of corresponding individual pixels in the respective images and determines the presence of relatively light and relatively dark areas, with the light areas indicating a higher intensity of fluorescent radiation.
The processor then generates a composite image 30, as shown in Figure 2(a), with a light area indicating the presence of the illicit substance 28. The composite image 30 is then laid over a visual image 32 of the target area 14 captured by the second camera 24, as shown in Figure 2(b).
The overlaid images combine to create a composite context image 34, as shown in Figure 2(c). The composite context image 34 indicates the presence and position within the target area 14 of the illicit substance 28 to an operative.
In other circumstances it may be desirable to detect more than one illicit substance of interest. Accordingly, a second embodiment of the method of the invention includes establishing respective fluorescent radiation emission signatures for a plurality of illicit substances of interest. Each emission signature has a first optical characteristic and first and second temporal characteristics which are established in the same manner as set out hereinabove in relation to the first embodiment of the method of the invention.
The second method includes similar illuminating and checking steps as the first method of the invention.
However, the second method additionally includes repeatedly illuminating the target area 14 and repeatedly checking whether the fluorescent radiation emitted from the target area 14 includes the optical and temporal characteristics of a further illicit substance of interest.
Each checking step aims to detect a particular one of the plurality of illicit substances and involves: - checking for emitted fluorescent radiation within the discriminatory wavelength range 36 corresponding to the particular illicit substance;
- checking whether fluorescent radiation continues to be emitted from the target area 14 on expiration of the discriminatory delay period 40 corresponding to the particular illicit substance; and
- checking the amount of fluorescent radiation emitted from the target area 14 during the discriminatory exposure period 44 corresponding to the particular illicit substance.
The combination of discriminatory wavelength range 36, discriminatory delay period 44, and discriminatory exposure 44 utilised at each checking stage is virtually unique to a particular illicit substance of interest, and so allows not only for the detection of a single illicit substance of interest but also discrimination between different illicit substances that may all be of interest.
Checking for emitted fluorescent radiation within different discriminatory wavelength ranges may be achieved by moving different optical filters, e.g. arranged in a filter wheel, over the first camera 22.
Repeating the illumination and checking steps may continue until at least one illicit substance is identified as being present in the target area 14, and/or until a check has been carried out for each illicit substance for which an emission signature has been established.
In still further situations it may be desirable to increase the resolution of the fluorescent radiation emission signature established for the or each illicit substance of interest so as to allow the detection and/or discrimination of an increased number of illicit substances.
In this regard, in a third embodiment of the method of the invention establishing a fluorescent radiation emission signature for an illicit substance of interest includes establishing first and second emission signatures for the illicit substance.
The first emission signature is established according to an incident first pulse of electromagnetic radiation at a first wavelength and has a first optical characteristic and first and second temporal characteristics.
One example of a first pulse of electromagnetic radiation is a pulse at a wavelength of approximately 355nm.
The second emission signature is established with reference to an incident second pulse of electromagnetic radiation at a second wavelength which is different to the first wavelength. One example of a suitable second wavelength is approximately 266nm.
The second emission signature has a second optical characteristic and third and fourth temporal characteristics.
Accordingly the emission signature for each illicit substance of interest has six characteristics, and so has a great number of unique permutations than, say, an emission signature having three characteristics. Each of the optical and temporal characteristics is established in the same manner as described above in connection with the first method of the invention.
The third method of the invention additionally includes modified illumination and checking steps, as set out below.
The target area 14 is illuminated with a pulse of electromagnetic radiation at the first wavelength, e.g. approximately 355nm. Checks are then made to determine whether the fluorescent radiation emitted from the target area 14 includes the first optical characteristic and the first and second temporal characteristics, i.e. characteristics associated with excitation of the illicit substance at the first wavelength.
The target area 14 is also illuminated with a pulse of electromagnetic radiation at the second wavelength, e.g. approximately 266nm. Checks are then made to determine whether the fluorescent radiation emitted from the target area 14 includes the second optical characteristic and the third and fourth temporal characteristics, i.e. characteristics associated with excitation of the illicit substance at the second wavelength. The third method of the invention may be modified to include steps corresponding to those outlined in connection with the second method of the invention to allow the detection of more than one illicit substance of interest, i.e. establishing first and second emission signatures for each illicit substance and checking for corresponding first and second optical characteristics and first, second, third and fourth temporal characteristics.
Any listing or discussion of an apparently known arrangement or method in this specification should not necessarily be taken as an acknowledgement that the arrangement or method is part of the state of the art or is common general knowledge.

Claims

CLAIMS:
1 . A method of detecting an illicit substance in a target area comprising the steps of:
(a) establishing a fluorescent radiation emission signature for an illicit substance of interest, the emission signature having at least one optical characteristic and first and second temporal characteristics;
(b) illuminating the target area with a pulse of electromagnetic radiation;
(c) checking whether the fluorescent radiation emitted from the target area includes the or each optical characteristic and the first and second temporal characteristics of the illicit substance; and
(d) indicating that the illicit substance is present in the target area if the emitted fluorescent radiation includes each of the or each optical characteristic and the first and second temporal characteristics.
2. A method of detecting an illicit substance in a target area according to Claim 1 wherein establishing a fluorescent radiation emission signature for an illicit substance includes establishing a first optical characteristic and first and second temporal characteristics.
3. A method of detecting an illicit substance in a target area according to Claim 2 wherein establishing a first optical characteristic of the emission signature includes establishing a discriminatory wavelength range; and wherein checking the fluorescent radiation emitted from the target area includes checking for emitted fluorescent radiation within the discriminatory wavelength range.
4. A method of detecting an illicit substance in a target area according to Claim 3 wherein checking for emitted fluorescent radiation within the discriminatory wavelength range includes capturing an image of the target area and applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range.
5. A method of detecting an illicit substance in a target area according to Claim 4 wherein applying a filter to remove fluorescent radiation lying outside the discriminatory wavelength range includes one or more of:
(e) moving an optical filter having filtering characteristics corresponding to the discriminatory wavelength range into the fluorescent radiation transmission path between the target area and an image capture device; and (f) applying an electronically addressable filter having filter characteristics corresponding to the discriminatory wavelength range to the captured image.
6. A method of detecting an illicit substance in a target area according to any of Claims 2 to 5 wherein establishing a first temporal characteristic of the emission signature includes establishing a discriminatory delay period; and wherein checking the fluorescent radiation emitted from the target area includes checking whether fluorescent radiation continues to be emitted from the target area at the discriminatory delay period after illumination of the target area.
7. A method of detecting an illicit substance in a target area according to Claim 6 wherein checking whether fluorescent radiation continues to be emitted includes capturing an image of the target area at the discriminatory delay period after illumination of the target area.
8. A method of detecting an illicit substance in a target area according to Claim 6 or Claim 7 wherein the discriminatory delay period is between Ips and 200ns.
9. A method of detecting an illicit substance in a target area according to any of Claims 2 to 8 wherein establishing a second temporal characteristic of the emission signature includes establishing a discriminatory exposure period; and wherein checking the fluorescent radiation emitted from the target area includes checking the amount of fluorescent radiation emitted from the target area during the discriminatory exposure period.
10. A method of detecting an illicit substance in a target area according to Claim 9 wherein checking the amount of fluorescent radiation emitted from the target area during the discriminatory exposure period includes capturing an image of the target area having an exposure duration equal to the discriminatory exposure period.
1 1 . A method of detecting an illicit substance in a target area according to Claim 9 or Claim 10 wherein the discriminatory exposure period is between 10ps and 20ns.
12. A method of detecting an illicit substance in a target area according to any of Claims 9 to 11 wherein checking the amount of fluorescent radiation emitted during the discriminatory exposure period is initiated within 10ns of illuminating the target area.
13. A method of detecting an illicit substance in a target area according to any preceding claim including:
establishing respective unique fluorescent radiation emission signatures for a plurality of illicit substances of interest;
illuminating the target area with a pulse of electromagnetic radiation;
checking whether the fluorescent radiation emitted from the target area includes the or each optical characteristic and the first and second temporal characteristics of one illicit substance of interest; and
repeatedly illuminating the target area and checking whether the fluorescent radiation emitted from the target area includes the or each optical characteristic and the first and second temporal characteristics of another illicit substance of interest until at least one illicit substance is indicated as being present in the target area and/or a check of the fluorescent radiation emitted from the target area has been carried out for each illicit substance of interest.
14. A method of detecting an illicit substance in a target area according to any preceding claim wherein establishing a fluorescent radiation emission signature for an illicit substance of interest includes:
establishing a first emission signature corresponding to an incident first pulse of electromagnetic radiation at a first wavelength, the first emission signature having a first optical characteristic and first and second temporal characteristics; and
establishing a second emission signature corresponding to an incident second pulse of electromagnetic radiation at a second wavelength, the second emission signature having a second optical characteristic and third and fourth temporal characteristics,
the method further including the steps of:
(b) (i) illuminating the target area with a pulse of electromagnetic radiation at the first wavelength;
(c) (i) checking whether the fluorescent radiation emitted from the target area includes the first optical characteristic and the first and second temporal characteristics;
(b) (ii) illuminating the target area with a pulse of electromagnetic radiation at the second wavelength; and
(c) (ii) checking whether the fluorescent radiation emitted from the target area includes the second optical characteristic and the third and fourth temporal characteristics.
15. A detector assembly, for detecting an illicit substance of interest in a target area, comprising:
an electromagnetic radiation pulse generator to illuminate the target area with a pulse of electromagnetic radiation;
a fluorescent radiation detector to detect fluorescent radiation emitted from the target area; and
a control module to check whether the detected fluorescent radiation includes the or each optical characteristic and the first and second temporal characteristics of a pre-established fluorescent radiation emission signature for the illicit substance, and to indicate that the illicit substance is present in the target area if the detected fluorescent radiation includes each of the or each optical and the first and second temporal characteristics.
16. A method of detecting an illicit substance in a target area generally as herein described with reference to and/or as illustrated in the accompanying drawings.
17. A detector assembly for detecting an illicit substance of interest in a target area generally as herein described with reference to and/or as illustrated in the accompanying drawings.
PCT/GB2012/050309 2011-02-14 2012-02-10 Improvements in or relating to detecting illicit substances in a target area WO2012110791A1 (en)

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