WO2005068977A1 - Sulphur dioxide detection method - Google Patents

Sulphur dioxide detection method Download PDF

Info

Publication number
WO2005068977A1
WO2005068977A1 PCT/AU2005/000035 AU2005000035W WO2005068977A1 WO 2005068977 A1 WO2005068977 A1 WO 2005068977A1 AU 2005000035 W AU2005000035 W AU 2005000035W WO 2005068977 A1 WO2005068977 A1 WO 2005068977A1
Authority
WO
WIPO (PCT)
Prior art keywords
radiation
wavelengths
sulphur dioxide
water vapour
subsidiary
Prior art date
Application number
PCT/AU2005/000035
Other languages
French (fr)
Inventor
Alfredo Jose Prata
Original Assignee
Commonwealth Scientific And Industrial Research Organisation
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
Priority claimed from AU2004900213A external-priority patent/AU2004900213A0/en
Application filed by Commonwealth Scientific And Industrial Research Organisation filed Critical Commonwealth Scientific And Industrial Research Organisation
Priority to EP05700067A priority Critical patent/EP1706726A4/en
Priority to AU2005205610A priority patent/AU2005205610A1/en
Publication of WO2005068977A1 publication Critical patent/WO2005068977A1/en

Links

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
    • G01N21/17—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 invention relates to a sulphur dioxide detection method and apparatus.
  • Volcanic ash and sulphur dioxide clouds constitute a serious hazard to aircraft even after the clouds have moved from the site of a volcanic eruption.
  • the clouds include gases such as S0 2 which after a few days oxidises and hydrolises to form sulphuric acid droplets, either as an ash-acid mixture or as a coating over ash particles.
  • gases such as S0 2 which after a few days oxidises and hydrolises to form sulphuric acid droplets, either as an ash-acid mixture or as a coating over ash particles.
  • Both the ash particles and the sulphuric acid droplets of volcanic ash clouds are capable of causing significant damage to and possible 5 loss of an aircraft which encounters an ash cloud.
  • the present invention relates to a method of detecting sulphur dioxide clouds comprising: measuring infrared radiation at a viewing elevation at or above the horizon and at a key wavelength at which there is a sulphur dioxide feature and in the vicinity of which there is a region where the amount of infrared radiation from water vapour in the atmosphere varies in accordance with a predetermined relationship; measuring radiation at two or more subsidiary wavelengths in said region; determining the amount of radiation from water vapour at the key wavelength from the measured radiation at the subsidiary wavelengths using the predetermined relationship; and determining whether a sulphur dioxide cloud is present from the measured infrared radiation at the key wavelength and the determined amount of radiation from water vapour.
  • said subsidiary wavelengths are located either side of said key wavelength.
  • the inventor has determined that the key wavelength should be one of 7.3 ⁇ m and 8.6 ⁇ m and that 7.3 ⁇ m is the preferred key wavelength.
  • the key wavelength is 7.3 ⁇ m
  • subsidiary wavelengths at ⁇ 0.5 ⁇ m are used.
  • the inventor has established that for the region of these wavelengths the predetermined relationship is that radiation from water vapour varies in a substantially linear manner. Accordingly, the radiation from water vapour at the key wavelength can be interpolated from the radiation at the subsidiary wavelengths on the basis of this predetermined relationship.
  • the inventor has also established that there is substantially less S0 2 absorption at this wavelength.
  • the method may also involve compensating for background S0 2 in the atmosphere.
  • the invention also provides a detection apparatus for detecting a sulphur dioxide cloud comprising: measurement means that measures infrared radiation at a viewing elevation at just below, or above the horizon and at a key wavelength at which there is a sulphur dioxide feature and in the vicinity of which there is a region where the amount of infrared radiation from water vapour in the atmosphere varies in accordance with a predetermined relationship, said measurement means also measuring infrared radiation at two or more subsidiary wavelengths in said region; and processing means for determining the amount of radiation from water vapour at the key wavelength from the measured radiation at the subsidiary wavelengths using the predetermined relationship and determining whether a sulphur dioxide cloud is present from the measured infrared radiation at the key wavelength and the determined amount of radiation from water vapour; and output means for generating an output signal indicative of the presence of a sulphur dioxide cloud when a sulphur dioxide cloud is present.
  • the inventor has also determined that the method and apparatus of the present invention can be used to detect sulphur dioxide clouds from the ground or from an aircraft.
  • Figure 1 illustrates the S0 2 absorption feature in the region 1200cm "1 to 1500cm "1 and the preferred measurement wavelengths of the invention
  • Figure 2 is a schematic diagram of a S0 2 detection apparatus of the preferred embodiment
  • Figure 3 illustrates two modes of operation of the apparatus
  • Figure 4 is a schematic diagram of apparatus to be used from an aircraft
  • Figures 5a - 5c represent normal climatic conditions
  • Figures 6a and 6b represent variations on normal conditions to allow testing of the invention
  • Figure 7 represents variations in S0 2 for testing
  • Figure 8 shows variation in temperature with S0 2 concentration
  • Figure 9 shows temperature plotted as a function of absorber amount.
  • the term "key wavelength” is used to refer to a wavelength at which there is an appropriate S0 2 feature.
  • a “wavelength” in the context of this specification does not imply a single wavelength but rather encompasses a band of radiation. Typically the width of the band will depend on the filter used to observe/measure light at the wavelength of interest.
  • the numerical figures given in this specification are used to denote, in general terms, the centre of such bands, however, it will be appreciated by persons skilled in the art that some variation of the centre wavelength is possible.
  • the term "subsidiary wavelength” is used to refer to a wavelength in a region in the vicinity of the key wavelength where a relationship can be established between radiation from water vapour at two or more subsidiary wavelengths and radiation from water vapour at the key wavelength.
  • the preferred embodiment provides a method and apparatus that allows identification of sulphur dioxide clouds in the free atmosphere.
  • the apparatus of the preferred embodiment uses an infrared detector, interference filters and focussing optics.
  • the filters divide radiation within the band between 6.8 and 8.1 ⁇ m into three narrow bands .
  • the central band corresponds to a strong S0 2 absorption feature caused by the antisymmetric stretch of the S0 2 molecule at 7.3 ⁇ m.
  • the other bands are above and below this feature.
  • the central band B c is sensitive to S0 2 concentrations.
  • the lower band, Bj and higher band B h are used to account for the effects of water vapour on the absorption in band B c .
  • B c is the key wavelength and Bi and B h are the subsidiary wavelengths in the preferred embodiment.
  • Figure 1 illustrates the absorption feature due to S0 2 for the infrared region extending from 1200 cm “1 (8.33 ⁇ ) to 1500 cm “1 (6.67 ⁇ m) .
  • B h (7.633-8.065 ⁇ m)
  • B c (7.143-7.57 ⁇ m)
  • Bi (6.897-7.042 ⁇ m
  • the response functions are normalised to unity and scaled appropriately for plotting.
  • the central wavenumber for the S0 2 absorption is 1363 cm -1 and the band extends from about 1320 cm “1 to about 1390 cm “1 .
  • a filter covering this region responds to all the radiation from this band; whether the S0 2 feature be due to absorption or emission.
  • water vapour and clouds also absorb and emit radiation in the region 7-8 ⁇ m.
  • the inventor has realised that the two bands positioned either side of the central band can be used to eliminate the effects of water vapour.
  • Water vapour absorbs and emits radiation throughout the region 7-8 ⁇ m.
  • the amount of radiation absorbed or emitted depends on the amount of water vapour and on its location in the atmospheric column. Water vapour near the boundary of the earth's surface is generally warm and abundant. Water vapour near the tropopause (i.e. at jet aircraft cruising altitudes) is cold and sparse.
  • the central band B c of the S0 2 detector of the preferred embodiment responds to radiation due to both S0 2 and water vapour.
  • the lower and higher bands B c , B h of the detector are only sensitive to water vapour.
  • the inventor has determined that the radiation from water vapour in the region surrounding B c behaves in a sufficiently linear manner to enable it to eliminate the effects of water vapour on the central band sufficiently for the purpose of detecting a sulphur dioxide cloud.
  • the Planck blackbody radiation from Bi and Bh are linearly interpolated to estimate the radiation detected in B c due to water vapour only. This radiation amount is subtracted from the radiation actually measured by B c . The residual amount is due to S0 2 .
  • the preferred embodiment utilises a predetermined relationship that water vapour behaves in a linear manner. Persons skilled in the art will appreciate that other predetermined relationships could be used, for example, relationships that are approximately linear.
  • the detection apparatus 6 consists of four major components:
  • Fore-optics 1 that focus a beam of incoming infrared radiation onto a detector.
  • a filter wheel 2 consisting of at least three narrow band interference filters that isolate radiation into the bands: B 2 , B c and B h .
  • An infrared detector array 3 sensitive to radiation in the 7-8 ⁇ m region.
  • Processing means 4 for processing the detector signal to determine whether S0 2 and hence a sulphur dioxide cloud is present.
  • Figure 3 is a schematic diagram illustrating two modes of operation of a detection apparatus 6 that senses infrared radiation in order to detect S0 2 clouds.
  • a first mode assumes that the detection apparatus 6 is on board an aircraft 7 and views the S0 2 cloud ahead at a small angle to the horizontal.
  • the second mode assumes that the detection apparatus 6 is based on the ground and views the cloud at a large angle to the horizontal (e.g. zenith viewing) .
  • the detection apparatus of the preferred embodiment may be operated from the ground viewing the sky above or from an aircraft viewing forwards at just below or above the horizon.
  • the principal mode of operation is anticipated to be from an aircraft with the instrument having an unobstructed view of the atmosphere ahead of the aircraft as the inventor has established that the method works best when water vapour path amount is less than lg cm "2 .
  • water vapour path is defined as the integral of the water vapour concentration with distance along the line of sight between instrument and target.
  • the view should be horizontal or a few degrees (3-5°) above the horizon, so that the background radiation is cold.
  • the processor 4 can be configured to account for changes in viewing zenith angle, making the technique insensitive to the viewing direction. For the case of a detection apparatus 6 viewing ahead of an aircraft at a zenith angle of Z degrees, the detection apparatus 6 provides three signals to the processor 4. A synthetic signal corresponding to the amount of radiation from water vapour is determined through linear interpolation of the signals from Bj and B h . This signal labeled B c is compared to the signal from B c .
  • the processor 4 then computes the S0 2 amount at the key wavelength B c using B c and the original signal B c .
  • the processor 4 uses pre-defined look-up tables that account for standard atmospheric conditions (tropical, mid-latitude, and polar) and the viewing geometry to compensate for background S0 2 .
  • the detector array 3 provides an image of the S0 2 amount with a spatial resolution that depends on the exact number of detector elements in the array (320x240 is recommended) and the distance to the S0 2 cloud. Distance information is supplied by the detection apparatus 6, however, the S0 2 anomaly will be detected at distances of up to several 100 kms depending on the cruising altitude and clarity of the atmosphere ahead.
  • the detection apparatus 6 produces an output 5, for example in the form of an amount of S0 2 or an alarm signal indicating the presence of sufficient S0 2 to pose a problem.
  • the alarm signal may cause an audible or visual alarm in an aircraft.
  • Figure 4 illustrates how the apparatus works in the case of being mounted in an aircraft.
  • the processor 4 In addition to signals from the detector 3 the processor 4 also receives aircraft altitude information 8 from the aircraft and standard atmosphere information 9 from a memory associated with the processor.
  • a sophisticated radiative transfer model-MODTRAN (Berk, et al., 1989) is used to model the response expected from a single-element detector viewing arealistic atmosphere.
  • the viewing geometry is varied in the simulations to account for viewing from below the S0 2 cloud, viewing from above, and viewing at a small angle along a nearly horizontal path.
  • the amount of S0 2 is varied, as is the main other gaseous absorber in the region-water vapour. We refer to the amount of S0 2 as the cloud thickness.
  • the temperature profile is shown in Figure 6a. Varying the profile has little effect on the retrieval and detection algorithm because the algorithm uses differences in temperatures. No further simulations were performed on this parameter because of its insensitivity.
  • model simulations have been performed for the case of horizontal viewing from a platform (e.g. an aircraft) directly ahead and towards an S0 2 cloud.
  • the cloud thickness (as measured in the viewing direction) is varied from 10 km to 500 km and the concentration within the cloud is varied from background levels to «0.1 ppmV. This range of concentration covers the smallest eruptions (that are likely to reach these heights, e.g. Hekla-style eruptions) to the largest observed this century (e.g. Pinatubo-style eruptions) .
  • the results of these model simulations are summarised in two figures.
  • Figure 8 shows the variation of the temperature anomaly (the temperature difference between the synthetic signal and the measured signal as a function of cloud thickness) .
  • the family of curves 20-27 generated from the modelling are lines of constant concentration for S0 2 concentration varying from 0.0136 ppmV 20 to 0.1083 pp V 27.
  • the points that lie on vertical lines correspond to lines of constant cloud thickness.
  • the temperature anomaly increases towards a limiting value (AT « -2 K) .
  • the opaque limit is reached either by increasing concentration or increasing cloud thickness, since both quantities increase optical depth and hence absorption. Beyond a thickness of 500 km, the cloud is essentially opaque and the radiative process changes from absorption to emission.
  • Figure 9 provides an alternate way of understanding the physical processes involved in S0 2 detection.
  • the temperature anomaly is plotted as a function of absorber amount.
  • the plot indicates that for a given anomaly, several values of absorber amount are possible, depending on the cloud thickness and concentration. Thus, it is not possible to uniquely quantify the absorber amount from the temperature anomaly without knowing either the concentration or the cloud thickness . In practice it is not necessary to know these quantities, as the purpose of the invention is to detect the presence of S0 2 gas in the free atmosphere, rather than quantify the amount.
  • the modelling does give an indication of the limits within which detection of S0 2 is possible. At the lower end, for cloud thicknesses of 10 km or less, the S0 2 concentration must be larger than «0.06 ppmV.

Abstract

There is disclosed a method of detecting sulphur dioxide clouds. The method comprises measuring infrared radiation at a viewing elevation at or above the horizon and at a key wavelength at which there is a sulphur dioxide feature and in the vicinity of which there is a region where the amount of infrared radiation from water vapour in the atmosphere varies in accordance with a predetermined relationship, measuring radiation at two or more subsidiary wavelengths in said region, determining the amount of radiation from water vapour at the key wavelength from the measured radiation at the subsidiary wavelengths using the predetermined relationship, and determining whether a sulphur dioxide cloud is present from the measured infrared radiation at the key wavelength and the determined amount of radiation from water vapour.

Description

SULPHUR DIOXIDE DETECTION METHOD
Field of the Invention The invention relates to a sulphur dioxide detection method and apparatus.
Background to the Invention Volcanic ash and sulphur dioxide clouds constitute a serious hazard to aircraft even after the clouds have moved from the site of a volcanic eruption. Apart from containing ash particles, the clouds include gases such as S02 which after a few days oxidises and hydrolises to form sulphuric acid droplets, either as an ash-acid mixture or as a coating over ash particles. Both the ash particles and the sulphuric acid droplets of volcanic ash clouds are capable of causing significant damage to and possible5 loss of an aircraft which encounters an ash cloud.
A number of aircraft encounters with volcanic ash clouds or sulphur dioxide clouds have been recorded in the past where significant damage has occurred. It will be appreciated that the sulphur dioxide may be found in areas separate from the volcanic ash. In the year 2000, a National Aeronautics and Space Administration (NASA) DC-8 Airborne Sciences research airplane flew through what was described as a diffuse volcanic ash cloud from the mount HEKLA Volcano when flying from Edwards, California to
Kiruna, Sweden. The ash cloud was not visible to flight crew, however, the research airplane carried sensitive research equipment which was capable of detecting the sulphur dioxide. In-flight checks and post-flight visual inspections revealed no damage to the airplane. However, detailed examination of the engines revealed damage to some of the turbine cooling passages. Furthermore, high levels of sulphur were found in the oil.
It seems likely that this ash cloud actually was predominantly a sulphur dioxide cloud. Even if it was not, it raises the possibility that an aircraft can fly through sulphur dioxide without passing through ash. The post encounter treatment of the engine in the case of sulphur dioxide encounter would be different to and considerably cheaper than the equivalent treatment required of an engine during an ash encounter.
Accordingly, it would be desirable to provide a sulphur dioxide cloud detection technique.
Summary of the Invention
The present invention relates to a method of detecting sulphur dioxide clouds comprising: measuring infrared radiation at a viewing elevation at or above the horizon and at a key wavelength at which there is a sulphur dioxide feature and in the vicinity of which there is a region where the amount of infrared radiation from water vapour in the atmosphere varies in accordance with a predetermined relationship; measuring radiation at two or more subsidiary wavelengths in said region; determining the amount of radiation from water vapour at the key wavelength from the measured radiation at the subsidiary wavelengths using the predetermined relationship; and determining whether a sulphur dioxide cloud is present from the measured infrared radiation at the key wavelength and the determined amount of radiation from water vapour.
Preferably, said subsidiary wavelengths are located either side of said key wavelength. The inventor has determined that the key wavelength should be one of 7.3μm and 8.6μm and that 7.3μm is the preferred key wavelength.
Where the key wavelength is 7.3μm, it is preferred that subsidiary wavelengths at ±0.5μm are used. The inventor has established that for the region of these wavelengths the predetermined relationship is that radiation from water vapour varies in a substantially linear manner. Accordingly, the radiation from water vapour at the key wavelength can be interpolated from the radiation at the subsidiary wavelengths on the basis of this predetermined relationship. The inventor has also established that there is substantially less S02 absorption at this wavelength.
The method may also involve compensating for background S02 in the atmosphere.
The invention also provides a detection apparatus for detecting a sulphur dioxide cloud comprising: measurement means that measures infrared radiation at a viewing elevation at just below, or above the horizon and at a key wavelength at which there is a sulphur dioxide feature and in the vicinity of which there is a region where the amount of infrared radiation from water vapour in the atmosphere varies in accordance with a predetermined relationship, said measurement means also measuring infrared radiation at two or more subsidiary wavelengths in said region; and processing means for determining the amount of radiation from water vapour at the key wavelength from the measured radiation at the subsidiary wavelengths using the predetermined relationship and determining whether a sulphur dioxide cloud is present from the measured infrared radiation at the key wavelength and the determined amount of radiation from water vapour; and output means for generating an output signal indicative of the presence of a sulphur dioxide cloud when a sulphur dioxide cloud is present.
The inventor has also determined that the method and apparatus of the present invention can be used to detect sulphur dioxide clouds from the ground or from an aircraft.
Brief Description of the Drawings
Figure 1 illustrates the S02 absorption feature in the region 1200cm"1 to 1500cm"1 and the preferred measurement wavelengths of the invention; Figure 2 is a schematic diagram of a S02 detection apparatus of the preferred embodiment; Figure 3 illustrates two modes of operation of the apparatus; Figure 4 is a schematic diagram of apparatus to be used from an aircraft; Figures 5a - 5c represent normal climatic conditions; Figures 6a and 6b represent variations on normal conditions to allow testing of the invention; Figure 7 represents variations in S02 for testing; Figure 8 shows variation in temperature with S02 concentration; and Figure 9 shows temperature plotted as a function of absorber amount.
Description of the Preferred Embodiment Herein, the term "key wavelength" is used to refer to a wavelength at which there is an appropriate S02 feature. Persons skilled in the art will appreciate that a "wavelength" in the context of this specification does not imply a single wavelength but rather encompasses a band of radiation. Typically the width of the band will depend on the filter used to observe/measure light at the wavelength of interest. The numerical figures given in this specification are used to denote, in general terms, the centre of such bands, however, it will be appreciated by persons skilled in the art that some variation of the centre wavelength is possible.
The term "subsidiary wavelength" is used to refer to a wavelength in a region in the vicinity of the key wavelength where a relationship can be established between radiation from water vapour at two or more subsidiary wavelengths and radiation from water vapour at the key wavelength. The preferred embodiment provides a method and apparatus that allows identification of sulphur dioxide clouds in the free atmosphere. The apparatus of the preferred embodiment uses an infrared detector, interference filters and focussing optics. The filters divide radiation within the band between 6.8 and 8.1 μm into three narrow bands . The central band corresponds to a strong S02 absorption feature caused by the antisymmetric stretch of the S02 molecule at 7.3 μm. The other bands are above and below this feature. The central band Bc, is sensitive to S02 concentrations. The lower band, Bj and higher band Bh, are used to account for the effects of water vapour on the absorption in band Bc.
Accordingly, Bc is the key wavelength and Bi and Bh are the subsidiary wavelengths in the preferred embodiment. Figure 1 illustrates the absorption feature due to S02 for the infrared region extending from 1200 cm"1 (8.33 μ ) to 1500 cm"1 (6.67 μm) . The ordinate in this plot is line strength and the abscissa is wavenumber (cm"1; wavelength in μm = 10, OOO/wavenumber in cm"1). Also, shown are three idealised filter response functions which isolate radiation within the three narrow regions corresponding to: Bh (7.633-8.065 μm) Bc (7.143-7.57 μm) and Bi (6.897-7.042 μm) .
The response functions are normalised to unity and scaled appropriately for plotting. The central wavenumber for the S02 absorption is 1363 cm-1 and the band extends from about 1320 cm"1 to about 1390 cm"1. A filter covering this region responds to all the radiation from this band; whether the S02 feature be due to absorption or emission. In the case of a detection apparatus viewing a cold background, i.e. viewing from the ground to space or from an aircraft towards the horizon, there would be more radiation in this band in the presence of the S02 cloud than if it were absent.
In practice, water vapour and clouds also absorb and emit radiation in the region 7-8 μm. The inventor has realised that the two bands positioned either side of the central band can be used to eliminate the effects of water vapour.
Water vapour absorbs and emits radiation throughout the region 7-8 μm. The amount of radiation absorbed or emitted depends on the amount of water vapour and on its location in the atmospheric column. Water vapour near the boundary of the earth's surface is generally warm and abundant. Water vapour near the tropopause (i.e. at jet aircraft cruising altitudes) is cold and sparse. The central band Bc of the S02 detector of the preferred embodiment responds to radiation due to both S02 and water vapour. The lower and higher bands Bc, Bh of the detector however, are only sensitive to water vapour. The inventor has determined that the radiation from water vapour in the region surrounding Bc behaves in a sufficiently linear manner to enable it to eliminate the effects of water vapour on the central band sufficiently for the purpose of detecting a sulphur dioxide cloud. The Planck blackbody radiation from Bi and Bh are linearly interpolated to estimate the radiation detected in Bc due to water vapour only. This radiation amount is subtracted from the radiation actually measured by Bc. The residual amount is due to S02. Accordingly the preferred embodiment utilises a predetermined relationship that water vapour behaves in a linear manner. Persons skilled in the art will appreciate that other predetermined relationships could be used, for example, relationships that are approximately linear.
A schematic of the detection apparatus is shown for illustrative purposes in Figure 2. The detection apparatus 6 consists of four major components:
• Fore-optics 1 that focus a beam of incoming infrared radiation onto a detector.
• A filter wheel 2 consisting of at least three narrow band interference filters that isolate radiation into the bands: B2, Bc and Bh.
• An infrared detector array 3 sensitive to radiation in the 7-8 μm region.
• Processing means 4 for processing the detector signal to determine whether S02 and hence a sulphur dioxide cloud is present.
Figure 3 is a schematic diagram illustrating two modes of operation of a detection apparatus 6 that senses infrared radiation in order to detect S02 clouds. A first mode assumes that the detection apparatus 6 is on board an aircraft 7 and views the S02 cloud ahead at a small angle to the horizontal. The second mode assumes that the detection apparatus 6 is based on the ground and views the cloud at a large angle to the horizontal (e.g. zenith viewing) .
The detection apparatus of the preferred embodiment may be operated from the ground viewing the sky above or from an aircraft viewing forwards at just below or above the horizon. The principal mode of operation is anticipated to be from an aircraft with the instrument having an unobstructed view of the atmosphere ahead of the aircraft as the inventor has established that the method works best when water vapour path amount is less than lg cm"2. For example, at heights over 3000 m or in dry atmosphere water vapour path is defined as the integral of the water vapour concentration with distance along the line of sight between instrument and target. Ideally the view should be horizontal or a few degrees (3-5°) above the horizon, so that the background radiation is cold. Typically, aircraft fly with their nose at an angle of about 3 degrees to horizontal. However, the processor 4 can be configured to account for changes in viewing zenith angle, making the technique insensitive to the viewing direction. For the case of a detection apparatus 6 viewing ahead of an aircraft at a zenith angle of Z degrees, the detection apparatus 6 provides three signals to the processor 4. A synthetic signal corresponding to the amount of radiation from water vapour is determined through linear interpolation of the signals from Bj and Bh . This signal labeled Bc is compared to the signal from Bc.
The processor 4 then computes the S02 amount at the key wavelength Bc using Bc and the original signal Bc.
The processor 4 uses pre-defined look-up tables that account for standard atmospheric conditions (tropical, mid-latitude, and polar) and the viewing geometry to compensate for background S02. The detector array 3 provides an image of the S02 amount with a spatial resolution that depends on the exact number of detector elements in the array (320x240 is recommended) and the distance to the S02 cloud. Distance information is supplied by the detection apparatus 6, however, the S02 anomaly will be detected at distances of up to several 100 kms depending on the cruising altitude and clarity of the atmosphere ahead. The detection apparatus 6 produces an output 5, for example in the form of an amount of S02 or an alarm signal indicating the presence of sufficient S02 to pose a problem. The alarm signal may cause an audible or visual alarm in an aircraft.
Figure 4 illustrates how the apparatus works in the case of being mounted in an aircraft.
In addition to signals from the detector 3 the processor 4 also receives aircraft altitude information 8 from the aircraft and standard atmosphere information 9 from a memory associated with the processor.
Examples
A sophisticated radiative transfer model-MODTRAN (Berk, et al., 1989) is used to model the response expected from a single-element detector viewing arealistic atmosphere. The viewing geometry is varied in the simulations to account for viewing from below the S02 cloud, viewing from above, and viewing at a small angle along a nearly horizontal path. The amount of S02 is varied, as is the main other gaseous absorber in the region-water vapour. We refer to the amount of S02 as the cloud thickness.
1. Model Atmosphere
Vertical profiles of the model atmosphere used in the simulations are shown in Figure 5 and variations used to test the present invention are shown in Figure 6 and Figure 7.
(a) Temperafcure
The temperature profile is shown in Figure 6a. Varying the profile has little effect on the retrieval and detection algorithm because the algorithm uses differences in temperatures. No further simulations were performed on this parameter because of its insensitivity.
(b) Water vapour Water vapour was varied by increasing the amounts in the lowest layers from less than 0.1 cm of precipitable water to more than 3 cm. No effect was found on the detection or retrieval because the water vapour lies below the S02 cloud. Water vapour was also increased in the layer that contained the S02 and this has a major effect. The perturbed water vapour profile is shown in Figure 6b.
(c) Sulphur dioxide The vertical profile of the background S02 is taken from the US standard atmosphere. The profile corresponds to a well-mixed gas with a constant vertical concentration of 10"5 ppmV (parts per million by volume) . Perturbed profiles, with increasing S02 concentration, are shown in Figure 7. Eight profiles are shown. The integrated amount of S0 in a vertical column for the profiles varies from 10 illi atm-cm to 100 milli atm-cm. Depending on the pathlength travelled the total absorber amount can be much larger. Results for SO2 absorber amounts of more than 1000 milli atm-cm are given.
2. Viewing the SO2 cloud along horizontal paths For the purpose of example, model simulations have been performed for the case of horizontal viewing from a platform (e.g. an aircraft) directly ahead and towards an S02 cloud. The viewing direction is assumed to be horizontal at the altitude of the platform (8 km, or =26,000 feet is assumed). The cloud thickness (as measured in the viewing direction) is varied from 10 km to 500 km and the concentration within the cloud is varied from background levels to «0.1 ppmV. This range of concentration covers the smallest eruptions (that are likely to reach these heights, e.g. Hekla-style eruptions) to the largest observed this century (e.g. Pinatubo-style eruptions) . The results of these model simulations are summarised in two figures. Figure 8 shows the variation of the temperature anomaly (the temperature difference between the synthetic signal and the measured signal as a function of cloud thickness) . The family of curves 20-27 generated from the modelling are lines of constant concentration for S02 concentration varying from 0.0136 ppmV 20 to 0.1083 pp V 27. The points that lie on vertical lines correspond to lines of constant cloud thickness. As the cloud thickens the curves follow the same trend with increasing anomalous signal until the cloud starts to become opaque. At this point, which varies with SO2 concentration, the temperature anomaly increases towards a limiting value (AT « -2 K) . Note that the opaque limit is reached either by increasing concentration or increasing cloud thickness, since both quantities increase optical depth and hence absorption. Beyond a thickness of 500 km, the cloud is essentially opaque and the radiative process changes from absorption to emission.
Figure 9 provides an alternate way of understanding the physical processes involved in S02 detection. Here the temperature anomaly is plotted as a function of absorber amount. The plot indicates that for a given anomaly, several values of absorber amount are possible, depending on the cloud thickness and concentration. Thus, it is not possible to uniquely quantify the absorber amount from the temperature anomaly without knowing either the concentration or the cloud thickness . In practice it is not necessary to know these quantities, as the purpose of the invention is to detect the presence of S02 gas in the free atmosphere, rather than quantify the amount. The modelling does give an indication of the limits within which detection of S02 is possible. At the lower end, for cloud thicknesses of 10 km or less, the S02 concentration must be larger than «0.06 ppmV. This corresponds to an absorber amount of »25 milli atm-cm. S02 clouds that intercept air-routes (i.e. heights >20,000 feet) will have horizontal dimensions of 10 's of kilometres and absorber amounts well in excess of 25 milli atm-cm would be expected.
Persons skilled in the art will appreciate that various modifications may be made to the preferred embodiment without departing from the scope of the appended claims,

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A method of detecting sulphur dioxide clouds comprising: measuring infrared radiation at a viewing elevation at or above the horizon and at a key wavelength at which there is a sulphur dioxide feature and in the vicinity of which there is a region where the amount of infrared radiation from water vapour in the atmosphere varies in accordance with a predetermined relationship; measuring radiation at two or more subsidiary wavelengths in said region; determining the amount of radiation from water vapour at the key wavelength from the measured radiation at the subsidiary wavelengths using the predetermined relationship; and determining whether a sulphur dioxide cloud is present from the measured infrared radiation at the key wavelength and the determined amount of radiation from water vapour.
2. A method as claimed in claim 1, wherein said method is performed from a position or position where the water vapour path amount is less than lg cm"2.
3. A method as claimed in claim 1, wherein said subsidiary wavelengths are located either side of said key wavelength.
4. A method as claimed in claim 1, wherein said key wavelength is one of 7.3μm and 8.6μm.
5. A method as claimed in claim 1, wherein the key wavelength is 7.3μm.
6. A method as claimed in claim 4, wherein subsidiary wavelengths at ±0.5μm are used.
7. A method as claimed in claim 5, wherein subsidiary wavelengths at ±0.5μm are used.
8. A method as claimed in claim 5, wherein determining the amount of the radiation from water vapour at the key wavelength is performed by a linear interpolation based on the radiation measured at the subsidiary wavelengths.
9. A method as claimed in claim 1, further comprising compensating for background sulphur dioxide in the atmosphere.
10. A method as claimed in claim 1, wherein said method is performed from an aircraft.
11. A method as claimed in claim 2, wherein said method is performed from the ground.
12. A detection apparatus for detecting a sulphur dioxide cloud comprising: measurement means that measures infrared radiation at a viewing elevation at just below, or above the horizon and at a key wavelength at which there is a sulphur dioxide feature and in the vicinity of which there is a region where the amount of infrared radiation from water vapour in the atmosphere varies in accordance with a predetermined relationship, said measurement means also measuring infrared radiation at two or more subsidiary wavelengths in said region; and processing means for determining the amount of radiation from water vapour at the key wavelength from the measured radiation at the subsidiary wavelengths using the predetermined relationship and determining whether a sulphur dioxide cloud is present from the measured infrared radiation at the key wavelength and the determined amount of radiation from water vapour; and output means for generating an output signal indicative of the presence of a sulphur dioxide cloud when a sulphur dioxide cloud is present.
13. Apparatus as claimed in claim 12, wherein said subsidiary wavelengths are located either side of said key wavelengths .
14. Apparatus as claimed in claim 12 , wherein said key wavelength is one of 7.3μm and 8.6μm.
15. Apparatus as claimed in claim 12 , wherein the key wavelength is 7.3μm.
16. Apparatus as claimed in claim 14, wherein said subsidiary wavelengths are at ±0.5μm.
17. Apparatus as claimed in claim 15, wherein said subsidiary wavelengths are at ±0.5um.
18. Apparatus as claimed in claim 15, wherein determining the amount of the radiation from water vapour at the key wavelength is performed by a linear interpolation of the radiation measured at the subsidiary wavelengths.
19. Apparatus as claimed in claim 12, wherein said processing means compensates for background sulphur dioxide in the atmosphere.
20. An aircraft having a detection apparatus as claimed in claim 12.
PCT/AU2005/000035 2004-01-16 2005-01-14 Sulphur dioxide detection method WO2005068977A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP05700067A EP1706726A4 (en) 2004-01-16 2005-01-14 Sulphur dioxide detection method
AU2005205610A AU2005205610A1 (en) 2004-01-16 2005-01-14 Sulphur dioxide detection method

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU2004900213A AU2004900213A0 (en) 2004-01-16 Sulphur dioxide detection method
AU2004900213 2004-01-16

Publications (1)

Publication Number Publication Date
WO2005068977A1 true WO2005068977A1 (en) 2005-07-28

Family

ID=34754156

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU2005/000035 WO2005068977A1 (en) 2004-01-16 2005-01-14 Sulphur dioxide detection method

Country Status (2)

Country Link
EP (1) EP1706726A4 (en)
WO (1) WO2005068977A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7371335B2 (en) 2004-10-21 2008-05-13 E.I. Dupont De Nemours And Company Curable thick film compositions for use in moisture control
WO2011135060A1 (en) 2010-04-29 2011-11-03 Norsk Institutt For Luftforskning System and method for detecting adverse atmospheric conditions ahead of an aircraft

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3805074A (en) * 1973-01-02 1974-04-16 Texas Instruments Inc Spectral scan air monitor
EP0087077A2 (en) * 1982-02-23 1983-08-31 Siemens Aktiengesellschaft Measuring device for optical gas analysis
US5654700A (en) * 1990-04-09 1997-08-05 Commonwealth Scientific And Industrial Research Organization Detection system for use in an aircraft
US6822236B1 (en) * 2002-05-25 2004-11-23 Ophir Corporation Method of optimizing a response of a gas correlation radiometer to a trace amount of a target gas

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6011122A (en) * 1983-07-01 1985-01-21 Shimadzu Corp Method for compensating interference in non-dispersive type infrared analysis
WO2002066966A1 (en) * 2001-01-08 2002-08-29 California Analytical Instruments, Inc. Method and apparatus for the determination of total sulfur in a gas

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3805074A (en) * 1973-01-02 1974-04-16 Texas Instruments Inc Spectral scan air monitor
EP0087077A2 (en) * 1982-02-23 1983-08-31 Siemens Aktiengesellschaft Measuring device for optical gas analysis
US5654700A (en) * 1990-04-09 1997-08-05 Commonwealth Scientific And Industrial Research Organization Detection system for use in an aircraft
US6822236B1 (en) * 2002-05-25 2004-11-23 Ophir Corporation Method of optimizing a response of a gas correlation radiometer to a trace amount of a target gas

Non-Patent Citations (6)

* Cited by examiner, † Cited by third party
Title
ALAN ROBOCK. ET AL.: "Volcanism and the earth's atmosphere.", 2003, GEOPHYSICAL MONOGRAPH., article PRATA J. ET AL: "Global, long term sulphur dioxide measurements from TOVS data: A new tool for study explosive volcanism and climate." *
DATABASE WPI Week 198336, Derwent World Patents Index; Class S03, AN 1983754335 *
PATENT ABSTRACTS OF JAPAN *
PUGNAGHIS S. ET AL: "Estimation of SO2 abundance in the eruption plume of Mt. Etna using two MIVIS thermal infrared channels: a cade study from the Sicily-1997 Campaing.", BULL VOLCANO., vol. 64, 2002, pages 328 - 337 *
See also references of EP1706726A4 *
WATSON I.M. ET AL: "Thermal infrared remote sensing of volcanic emissions using the moderate resolution imaging spectroradiometer.", JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH., vol. 135, 2004, pages 75 - 89 *

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7371335B2 (en) 2004-10-21 2008-05-13 E.I. Dupont De Nemours And Company Curable thick film compositions for use in moisture control
WO2011135060A1 (en) 2010-04-29 2011-11-03 Norsk Institutt For Luftforskning System and method for detecting adverse atmospheric conditions ahead of an aircraft
DE212011100091U1 (en) 2010-04-29 2013-02-22 Norsk Institutt For Luftforskning A system for detecting adverse atmospheric conditions in front of an aircraft
US10063794B2 (en) 2010-04-29 2018-08-28 Nicarnica Aviation As System and method for detecting adverse atmospheric conditions ahead of an aircraft
US10440291B2 (en) 2010-04-29 2019-10-08 Nicarnica Aviation As System and method for detecting adverse atmospheric conditions ahead of an aircraft

Also Published As

Publication number Publication date
EP1706726A4 (en) 2008-03-12
EP1706726A1 (en) 2006-10-04

Similar Documents

Publication Publication Date Title
US7352464B2 (en) Oxygen sensor for aircraft fuel inerting systems
Yoshida et al. Retrieval algorithm for CO 2 and CH 4 column abundances from short-wavelength infrared spectral observations by the Greenhouse gases observing satellite
Knobelspiesse et al. Combined retrievals of boreal forest fire aerosol properties with a polarimeter and lidar
Schmid et al. Column closure studies of lower tropospheric aerosol and water vapor during ACE‐Asia using airborne Sun photometer and airborne in situ and ship‐based lidar measurements
JPH02210216A (en) Front watch window shower detector and its method
US10336465B2 (en) Ice crystals and volcanic ash detection system
JP2007003308A (en) Method of estimating ground temperature and program for it
CA2129329A1 (en) Method of determining the humidity and temperature of atmospheric air
Gatebe et al. Sensitivity of off-nadir zenith angles to correlation between visible and near-infrared reflectance for use in remote sensing of aerosol over land
Frish et al. Low-cost lightweight airborne laser-based sensors for pipeline leak detection and reporting
Bony et al. EUREC 4 A observations from the SAFIRE ATR42 aircraft
Vogel et al. Early in-flight detection of SO 2 via Differential Optical Absorption Spectroscopy: a feasible aviation safety measure to prevent potential encounters with volcanic plumes
Shin et al. The retrieval of the Asian dust depolarization ratio in Korea with the correction of the polarization-dependent transmission
WO2005068977A1 (en) Sulphur dioxide detection method
Stefanutti et al. The APE-THESEO tropical campaign: An overview
Yan et al. Theoretical analysis of the effect of meteorologic factors on passive ranging technology based on oxygen absorption spectrum
AU2005205610A1 (en) Sulphur dioxide detection method
US9952146B1 (en) Determining gas concentration near planetary surfaces
Teggi et al. Evaluation of SO2 emission from Mount Etna using diurnal and nocturnal multispectral IR and visible imaging spectrometer thermal IR remote sensing images and radiative transfer models
Kullmann et al. Cryogenic infrared spectrometers and telescopes for the atmosphere: new frontiers
Wilson et al. The applicability of LOWTRAN 5 computer code to aerial thermographic data correction
Ershov et al. Airborne laser IR thermographic system for detecting gas leaks from underground pipelines
Gerilowski et al. MAMAP–A new spectrometer system for columnaveraged methane and carbon dioxide observations from aircraft: Instrument description and initial performance assessment
Vogel et al. Early in-flight detection of SO
Granados et al. Early in-flight detection of SO 2 via Differential Optical Absorption Spectroscopy: A feasible aviation safety measure to prevent...

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BW BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE EG ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NA NI NO NZ OM PG PH PL PT RO RU SC SD SE SG SK SL SY TJ TM TN TR TT TZ UA UG US UZ VC VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): GM KE LS MW MZ NA SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LT LU MC NL PL PT RO SE SI SK TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
NENP Non-entry into the national phase

Ref country code: DE

WWW Wipo information: withdrawn in national office

Country of ref document: DE

WWE Wipo information: entry into national phase

Ref document number: 2005700067

Country of ref document: EP

WWE Wipo information: entry into national phase

Ref document number: 2005205610

Country of ref document: AU

WWP Wipo information: published in national office

Ref document number: 2005700067

Country of ref document: EP

ENP Entry into the national phase

Ref document number: 2005205610

Country of ref document: AU

Date of ref document: 20050114

Kind code of ref document: A

WWP Wipo information: published in national office

Ref document number: 2005205610

Country of ref document: AU