US20130135470A1 - System and method for detecting adverse atmospheric conditions ahead of an aircraft - Google Patents

System and method for detecting adverse atmospheric conditions ahead of an aircraft Download PDF

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US20130135470A1
US20130135470A1 US13/695,171 US201113695171A US2013135470A1 US 20130135470 A1 US20130135470 A1 US 20130135470A1 US 201113695171 A US201113695171 A US 201113695171A US 2013135470 A1 US2013135470 A1 US 2013135470A1
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infrared
aircraft
adverse atmospheric
atmospheric conditions
ash
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Alfredo Jose Prata
Cirilo Bernardo
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Nicarnica Aviation As
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NORSK INSTITUTT FOR LUFTFORSKNING
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Assigned to NICARNICA AVIATION AS reassignment NICARNICA AVIATION AS ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: NORSK INSTITUTT FOR LUFTFORSKNING
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B64—AIRCRAFT; AVIATION; COSMONAUTICS
    • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
    • B64D45/00—Aircraft indicators or protectors not otherwise provided for
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/30—Transforming light or analogous information into electric information
    • H04N5/33—Transforming infrared radiation
    • 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
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
    • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/53—Determining attitude
    • 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
    • G01S3/00—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received
    • G01S3/78—Direction-finders for determining the direction from which infrasonic, sonic, ultrasonic, or electromagnetic waves, or particle emission, not having a directional significance, are being received using electromagnetic waves other than radio waves
    • G01S3/781—Details
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01W—METEOROLOGY
    • G01W1/00—Meteorology
    • G01W1/08—Adaptations of balloons, missiles, or aircraft for meteorological purposes; Radiosondes
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B21/00—Alarms responsive to a single specified undesired or abnormal condition and not otherwise provided for
    • G08B21/18—Status alarms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/20—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only
    • H04N23/23—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only from thermal infrared radiation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/90—Arrangement of cameras or camera modules, e.g. multiple cameras in TV studios or sports stadiums

Definitions

  • the present invention relates to a system and method for detecting adverse atmospheric conditions ahead of an aircraft.
  • the system has a plurality of infrared cameras that may detect, for example, sulphur dioxide and particles such as volcanic ash, wind-blown dust and ice particles. It also comprises a computer that processes the images and a display to show the crew of the aircraft the adverse conditions.
  • Volcanic clouds contain silicate ash and gases that are hazardous to aviation.
  • Several encounters between jet aircraft and volcanic ash have resulted in significant damage due to ingestion of ash into the hot parts of the engine, subsequent melting and fusing onto the turbine blades. Ash can also block the pitot static tubes and affect sensitive aircraft instruments, as well as abrade the leading edges of parts of the airframe structure.
  • Volcanic gases principally SO 2 are less dangerous to aircraft, but detection of SO 2 can be used as an indicator of volcanic ash as these substances are often collocated and are transported together by atmospheric winds.
  • Another important gas in volcanic clouds is water vapour (H 2 O gas). Water vapour occurs in copious amounts in volcanic clouds either through entrainment of ambient air or from water from the volcanic source (e.g.
  • sea water is a common source for volcanoes on islands or in coastal regions). Once in the atmosphere, the water vapour can condense on ash nuclei rapidly forming ice with a much smaller radius than ice in normal meteorological clouds. These abundant, small-sized ice particles are hazardous to aircraft because the rapid melting of the ice when in contact with the hot engines, releases the ash nuclei which then fuses onto the turbine blades, affecting the engine performance and potentially causing the engine to stall.
  • SO 2 clouds from volcanoes will react with water vapour in the atmosphere to produce sulphuric acid which can damage aircraft.
  • the sulphur dioxide may be found in areas separate from the volcanic ash.
  • An aircraft can fly through sulphur dioxide without passing through ash.
  • 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 be able to warn aircraft of SO 2 clouds.
  • Ash and other particles can under the right conditions initiate ice particle formation when water freezes around these cores. Accordingly, wind-blown dust and ice particles can be a significant hazard to aircraft, vehicles and the like.
  • WO2005031321A1 WO2005068977A1 and WO2005031323A1 teach methods and apparatus for monitoring of sulphur dioxide, volcanic ash and wind-blown dust, using at least two wavelengths of infrared radiation corresponding to an adverse atmospheric condition.
  • U.S. Pat. No. 3,931,462 teaches the use of an UV video system for measuring SO 2 in plume from a smokestack.
  • U.S. Pat. No. 4,965,572 teaches methods and apparatus for detecting low level wind shear type turbulence remotely, such as by an infrared temperature detector.
  • U.S. Pat. No. 5,140,416 discloses a system and method for fusing or merging video imagery from multiple sources such that the resultant image has improved information content.
  • the sensors are responsive to different types of spectral content in the scene being scanned, such as short and long wavelength infrared.
  • U.S. Pat. No. 5,654,700 and U.S. Pat. No. 5,602,543 teach an adverse atmospheric condition detection system for aircraft that monitors conditions ahead of aircraft using infrared detectors, displays the position, warns and reroutes aircraft.
  • the present invention provides a system for detecting adverse atmospheric conditions ahead of an aircraft, including a plurality of infrared cameras mounted on the aircraft, wherein: the infrared cameras are adjusted to spatially detect infrared radiance in different bands of infrared light, each camera is connected to an image processing computer that processes and combines the images, and generates video display signals for producing a video display which indicates the position of the adverse atmospheric conditions relative to the aircraft; each of the cameras is provided with a respective filter adjusted to filter infrared light with a bandwidth corresponding to infrared bandwidth characteristics of an adverse atmospheric condition from a set of adverse atmospheric conditions; the image processing computer is adapted to identify adverse atmospheric conditions, said identifying being based on threshold conditions and using the detected infrared radiance, data from a look-up table and measured parameters including information on the position and/or attitude of the aircraft; and the image processing computer is further adapted to display the identified adverse atmospheric conditions as a spatial image on a display.
  • the present invention is advantageous in that it provides an apparatus suited for aircraft that detects adverse atmospheric conditions, in particular caused by volcanoes, and visualizes them for the crew of the aircraft.
  • the invention is particularly useful for detecting volcanic clouds.
  • the present invention can enable the rapid detection of volcanic substances ahead of a jet aircraft at cruise altitudes and the simultaneous detection and discrimination of volcanic ash, SO 2 gas and ice-coated ash particles.
  • the invention provides algorithms and processes for converting raw camera data to identify ash, SO 2 gas and ice coated ash.
  • the system preferably monitors the field of view of the aircraft.
  • the cameras of the invention may be uncooled microbolometer collocated cameras.
  • the pitch angle and ambient temperature are accounted for in the look-up table.
  • the adverse atmospheric conditions preferably include volcanic ash, ice coated ash, water vapour and sulphur dioxide.
  • the measured parameters can include pitch angle and ambient temperature.
  • the threshold conditions are pre-computed using a radiative transfer model of the atmosphere.
  • the image processing computer is arranged to determine brightness temperatures from the detected infrared radiance, and said identifying includes determining whether values related to the brightness temperatures meet the threshold conditions.
  • the system may also include one or more external blackened shutters against which the imaging cameras are pre-calibrated for providing in-flight calibration values.
  • the system provides a statistical alert based on analysis of images determined to show an adverse condition of ash, sulphur dioxide or ice-coated ash.
  • the statistical alert uses spatial and temporal information and can be tuned according to in-flight tests to reduce false-alarms and ensure robustness.
  • a computer program product stored on a computer readable medium, comprising a readable program for causing a processing unit in a computer based system, to control an execution according to the said steps.
  • the system is arranged to detect at least the three volcanic substances (ash, SO 2 and ash coated ice particles) in the air ahead of the aircraft by a remote method, and in addition be capable of discriminating these from other meteorological clouds of water droplets and ice.
  • volcanic substances ash, SO 2 and ash coated ice particles
  • the invention also more generally provides a system for detecting adverse atmospheric conditions ahead of an aircraft, including a plurality of infrared cameras mounted on the aircraft, wherein: the infrared cameras are adjusted to spatially detect infrared radiance in different bands of infrared light; each camera is connected to an image processing computer that processes and combines the images, wherein each of the cameras is provided with a respective filter adjusted to filter infrared light with a bandwidth corresponding to infrared bandwidth characteristics of an adverse atmospheric condition from a set of adverse atmospheric conditions; and the image processing computer is adapted to identify and display adverse atmospheric conditions, said identifying being based on threshold conditions and using the detected infrared radiance and measured parameters including information on the position and/or attitude of the aircraft.
  • the present invention provides a method for detecting adverse atmospheric conditions ahead of an aircraft and displaying said adverse atmospheric conditions, comprising spatially detecting infrared radiance in different bands of infrared light using a plurality of infrared cameras; and, for each camera: i) Filtering the infrared radiation with a filter adjusted to filter infrared light with a bandwidth corresponding to infrared bandwidth characteristics of an adverse atmospheric condition in a set of adverse atmospheric conditions; ii) identifying likely occurrences of adverse atmospheric conditions based on threshold conditions and using the detected infrared radiance, data from a look-up table and measured parameters including information on the position and/or attitude of the aircraft; and iii) processing the identified likely occurrences of adverse atmospheric conditions to create a spatial image.
  • the method further comprises the step of iv) combining the image with images from other cameras and information on the aircraft flight path.
  • the adverse atmospheric conditions preferably include volcanic ash, ice coated ash, water vapour and sulphur dioxide.
  • the measured parameters can include pitch angle and ambient temperature.
  • the invention provides a system for detecting volcanic clouds ahead of an aircraft, including one or more infrared cameras mounted on the aircraft, the infrared cameras are adjusted to spatially detect infrared radiance in different bands of infrared light, each camera is connected to an image processing computer that process and combines the images, combining them with flight path information from the aircraft and generates video display signals for producing a video display which indicates the position of the adverse conditions relative to the aircraft; characterized in that each of the cameras is provided with a respective filter adjusted to filter infrared light with a bandwidth corresponding to infrared bandwidth characteristics of one of the volcanic species in a set of volcanic species, and that the image processing computer is adapted to identify and display species as a spatial image on a display by means of threshold look-up tables for the respective species mapping thresholds for the infrared radiance, above which species are likely to occur, with measured parameters.
  • the invention provides a method for detecting a volcanic cloud ahead of an aircraft and displaying said cloud, processing information from one or more infrared cameras spatially detecting infrared radiance in different bands of infrared light, combining the information with flight path information from the aircraft characterized in the steps of for each camera:
  • FIG. 1 is a schematic of a single camera with filter, lens, shutter and protective window
  • FIG. 2 is an example configuration for the multiple camera system
  • FIG. 3 shows an ash cloud on the display
  • FIG. 4 shows a diagram of radiative transfer calculation for a horizontal path in a clear atmosphere for three different flight altitudes
  • FIG. 5 shows a diagram of line strengths for the two bands of SO 2 at 8.6 ⁇ m and 7.3 ⁇ m. The response functions for the filters of the system are also shown.
  • the basic principle of detection of volcanic substances ahead of the aircraft relies on the use of filtered infrared radiation in the region of 6-13 p.m. Within this region, narrow (0.5-1.0 ⁇ m) bands are selected for detection of ash, water vapour, SO 2 gas and ice coated ash.
  • the preferred detection method is to use wide-field-of-view, rapid sampling, imaging, uncooled microbolometer cameras.
  • a microbolometer is used as a detector in thermal cameras. Infrared radiation strikes the detector material, heating it, and thus changing its electrical resistance. This resistance change is measured and processed into temperatures which can be used to create an image. Unlike other types of infrared detecting equipment, microbolometers do not require cooling.
  • this camera may contain 640 ⁇ 512 pixels ⁇ lines, have a noise equivalent temperature difference of 50 mK (or better) at 300 K in the 10-12 ⁇ m region, and provide sampling rates up to 60 Hz.
  • Five collocated cameras are envisaged for the simultaneous detection of ash, SO 2 gas, H 2 O gas, and ice-coated ash.
  • Each camera has a detector that is sensitive to infrared radiation within the region 6-13 ⁇ m.
  • Narrowband filters are placed over each camera to restrict the spectral content of the radiation for the purpose of species identification.
  • the cameras share the same field of view ahead of the aircraft and therefore, in principle, multiple, simultaneous narrowband infrared images can be acquired in real-time at sampling rates of up to 60 Hz.
  • These collocated images can be rapidly processed using special algorithms to identify each of the four target species specified earlier.
  • FIG. 1 A generic example of the camera in the system is shown in FIG. 1 .
  • Infrared radiation from ahead of the aircraft enters the filter 1 of each camera and is focused through the camera lens 2 and falls on the detector array 3 .
  • the shutter 4 is used for calibration (see below).
  • the signals are transferred via a standard high-speed communication protocol 5 to a computer for further processing.
  • an IR transparent window 7 e.g. Germanium glass
  • the shutter is temperature controlled 6 and blackened on the side facing the optics.
  • FIG. 2 An example configuration for the multiple camera system is shown in FIG. 2 with five cameras 8 .
  • the protective shutter 4 may be mechanically driven in front of the assembly 9 and withdrawn when the system is in use.
  • the germanium glass window 7 provides protection from debris, while in viewing mode.
  • the signal 5 and power 10 lines are at the back of the assembly housing 9 , which houses electronics, frame grabber and computer hardware.
  • Five cameras are shown, but the configuration could consist of more or less cameras depending on the number of hazards to be identified. For example a system with two cameras would permit identification of volcanic ash and ice-coated ash.
  • the cameras are pre-calibrated prior to installation on the aircraft so that each camera registers the same digital signal when exposed to the same amount of infrared radiation. This can be achieved by pointing each camera, without its filter, at a known source of infrared radiation (known constant temperature) and recording the digital signal from each pixel of each camera.
  • a look-up table can be determined by varying the source temperature through the range 210 to 300 K, in steps of 10 K (for example) for each camera, giving a table of 640 ⁇ 512 ⁇ 10 ⁇ 2 values, assuming a linear calibration. This process can be repeated for each narrowband filter used.
  • intermittent re-calibrations can be performed by inserting a heated and blackened shutter in front of the filter and recording the digital counts corresponding to the known (controlled) temperature of the shutter.
  • the shutter also serves the dual purpose of providing protection against debris and dirt directed toward the camera during take-off and landing, when the system of the present invention is deactivated.
  • a second shutter could be used to provide a second calibration point in a linear calibration equation. The use of a second shutter is simply a matter of practical convenience and does not alter the main operating principle of the invention.
  • the system is activated once the aircraft has reached cruise altitude and whenever an airborne hazard is detected and the aircraft conducts evasive manoeuvres by altering direction-flight altitude and heading.
  • deactivated mode the shutter is closed. Before activation a pre-calibration cycle for the system (all 5 cameras) is conducted. The shutter is opened and the system begins to collect images.
  • Commercial cameras can sample as fast as 60 Hz and this is the preferred sampling rate (or higher). However, some export restrictions apply to some cameras and this means lower sampling rates may apply. In the discussion that follows we assume a sampling rate of 8 Hz, as at this frequency there are no export restrictions. The basic principle is unchanged when using a higher sampling frequency.
  • Each camera provides 8 images of size N pixels by M lines every second.
  • the brightness temperature is determined from:
  • R i , j , k c 1 ⁇ v k 3 ⁇ c 2 ⁇ v k / BT i , j , k - 1
  • R i,j,k is the radiance at pixel i, line j and filter k
  • v k is the central wavenumber for camera filter k
  • BT i,j,k is the brightness temperature
  • c 1 and c 2 are the Einstein radiation constants
  • the radiance R i,j,k is determined from the pre- and post-calibration procedures and is assumed to be a linear function of the digital signal counts. Camera images may be averaged in order to reduce noise and improve the signal-to-noise ratio of the system.
  • the data for one pixel consists of the measurements: BT1, BT2, BT3, BT4 and BT5, where these represent brightness temperatures from each of the five cameras (e.g BT1 is the brightness temperature for that pixel in camera 1 which has filter 1 ).
  • the system of the present invention is linked into the aircraft instrument data stream so that GPS coordinates, altitude (z), longitude (l), latitude (q), heading (h), direction (d), roll (r), yaw (y), pitch (x), time (t), speed over the ground (v), wind speed (w) and ambient temperature (Ta) are available at a sampling rate of at least 1 and preferably faster.
  • the system uses filters at the following central wavenumbers (in cm ⁇ 1 ):
  • a pixel is declared to be ash if the following conditions are met at each instance:
  • T1 Ash and T2 Ash are temperature differences determined from pre-computed radiative transfer calculations for a set of parameters, including ambient temperature (Ta) and realistic aircraft roll, pitch and yaw values. Note that DT1 Ash and DT2 Ash are non-dimensional quantities and are strictly indices.
  • An alert is sounded if a sequence of 8 consecutive occurrences of condition (1) and (2) happen for a pre-defined fraction of the total image.
  • a value of 5% of the total number of pixels in the difference image is used, but this can be tuned as necessary a lower value set if the aircraft is operating in airspace declared, or likely to be influenced by volcanic ash; a higher value in unaffected areas.
  • a pixel is declared to be water vapour affected if the following conditions are met at each instance:
  • T wv is a temperature difference determined from pre-computed radiative transfer calculations for a set of parameters, including ambient temperature (Ta), and realistic aircraft roll, pitch and yaw values.
  • T wv is used with the ice algorithm if that alert is sounded.
  • a pixel is declared to be ICA if the following conditions are met at each instance,
  • T ICA is a temperature difference determined from pre-computed radiative transfer calculations for a set of parameters, including ambient temperature (Ta), and realistic aircraft roll, pitch and yaw values.
  • An alert is sounded if a sequence of 8 consecutive occurrences of condition (4) happen for a pre-defined fraction of the total image.
  • a value of 5% of the total number of pixels in the difference image is used, but this can be tuned as necessary a lower value set if the aircraft is operating in airspace declared or likely to be influenced by volcanic ash; a higher value in unaffected areas.
  • the alert is sounded condition (3) is checked and if this condition is met, the pixel is confirmed to be ICA.
  • the use of the water vapour condition is entirely novel and reduces the false alarm rate for detecting hazardous small-sized ice-coated ash particles.
  • a pixel is declared to be SO 2 if the following conditions are met at each instance,
  • DT 1 SO2 ( BT 1 ⁇ BT 2)/ Ta ⁇ T 1 SO2 ( Ta,r,y,x )/ Ta (5)
  • DT 2 SO2 ( BT 3 ⁇ BT 5)/ Ta ⁇ T 2 SO2 ( Ta,r,y,x )/ Ta (6)
  • T1 SO2 and T2 SO2 are temperatures determined from pre-computed radiative transfer calculations for a set of parameters including ambient temperature (Ta), and realistic aircraft roll, pitch and yaw values.
  • An alert is sounded if a sequence of 8 consecutive occurrences of conditions (5) and (6) happen for a pre-defined fraction of the total image.
  • a value of 5% of the total number of pixels in the difference image is used, but this can be tuned as necessary—a lower value set if the aircraft is operating in airspace declared to be or likely to be influenced by volcanic ash; a higher value is used in unaffected areas.
  • FIG. 3 An example of the display shown to the crew for the detection of an ash cloud is shown in FIG. 3 .
  • This is based on an ash cloud composed of silicate material and shows the DT1 Ash signal for 6 frames separated by a constant short time difference from two cameras imaging ahead of the aircraft. Highest concentrations of ash are indicated in red (or dark in FIG. 3 that is in black and white); the background sky is shown in light purple (or light grey in FIG. 3 ). As the aircraft approaches the hazard, the pilot can alter the heading of the aircraft to avoid it.
  • FIG. 4 shows a horizontal path simulation of the radiance of the clear atmosphere from 700-1600 cm ⁇ 1 at three different flight altitudes. At 9.5 km the atmosphere appears very cold—the equivalent blackbody temperature of the horizontal path is about 227 K. Any volcanic cloud placed between the aircraft and the cold background will alter the radiance received by the system in a known way.
  • the spectral content of the radiation contains signatures of ash, SO 2 , H 2 O and ice-coated ash particles.
  • the ash signal in these spectra is characterised by a higher brightness temperature in filter 4 (BT4) than in F5 (BT5), when viewing a cold background.
  • the threshold values are determined by using refractive index data for silicates and scattering calculations are based on measured particle size distribution for particle with radii in the range 1-20 ⁇ m according to the art.
  • the instrument would look in the horizontal or slightly upwards (aircraft usually have a 3° pitch angle upwards). However, the aircraft may pitch downwards, in which case the background temperature might change from a cold background to a warm background.
  • the ash signature is identified by BT4 ⁇ BT5.
  • the look-up table is constructed in such a way that the pitch angle and ambient temperature are accounted for. Additionally, the roll and yaw angles are compensated for, although these have only a minor influence on the detection algorithm. Extra fail-safe thresholds are also incorporated into the detection algorithm by utilizing a filter near 8.6 ⁇ m that has sensitivity to volcanic ash.
  • the operation of the ice-coated ash algorithm is similar to the ash algorithm, except the threshold look-up table is now determined using data for ice (refractive indices and scattering data for small particles, radii ⁇ 30 ⁇ m).
  • BT4 ⁇ BT5 for viewing into a cold background (the opposite to ash without an ice coating). Background conditions are accounted for in a similar way to that used for the ash detection.
  • SO 2 and H 2 O look-up tables are also used.
  • SO 2 has very strong absorptions near to 8.6 ⁇ m and 7.3 ⁇ m as FIG. 5 illustrates.
  • the principle of detecting SO2 has been described earlier and is based on radiative transfer calculations assuming the line strengths and transmissions applicable to the case of an atmosphere loaded with SO2. Under normal conditions SO 2 has an extremely low abundance ( ⁇ 10 ⁇ 3 ppm), and so detection of SO 2 using these absorptions features is very effective in the case of volcanic clouds ahead of an aircraft.

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Cited By (10)

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US20150138355A1 (en) * 2013-11-15 2015-05-21 The Boeing Company Visual Detection of Volcanic Plumes
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