WO2006032854A1 - Dispositif de detection de particules - Google Patents

Dispositif de detection de particules Download PDF

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Publication number
WO2006032854A1
WO2006032854A1 PCT/GB2005/003591 GB2005003591W WO2006032854A1 WO 2006032854 A1 WO2006032854 A1 WO 2006032854A1 GB 2005003591 W GB2005003591 W GB 2005003591W WO 2006032854 A1 WO2006032854 A1 WO 2006032854A1
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WO
WIPO (PCT)
Prior art keywords
signal
peak
cross
mls
modulation signal
Prior art date
Application number
PCT/GB2005/003591
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English (en)
Inventor
Christopher John Morcom
Richard Kenneth Avery
Original Assignee
Instro Precision 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 Instro Precision Limited filed Critical Instro Precision Limited
Priority to EP05784736A priority Critical patent/EP1800148A1/fr
Publication of WO2006032854A1 publication Critical patent/WO2006032854A1/fr
Priority to IL181347A priority patent/IL181347A0/en

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Classifications

    • 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
    • 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
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • 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
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/95—Lidar systems specially adapted for specific applications for meteorological use
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Definitions

  • This invention relates to a particle detection device for detecting fog or other particulate airborne or liquid-borne matter which may obscure a field of view.
  • range finding devices are available for measuring the distance to a remote object, and are generally referred to as range finding devices. Such devices may be used, for example, in vehicle collision avoidance systems. This invention relates to the use of a range finding device architecture in order to detect fog or other particulate matter obscuring a field of view.
  • LRF's laser range finders
  • LiDAR light detection and ranging
  • a known LRF is shown in Figure 1 and comprises a laser 1, an optical transmission system 2, an optical reception system 3, a light sensitive detector 4, pulse detection circuitry 5, and timing calculation and display electronics 6.
  • the user initiates a measurement of range using input 7, which causes a laser fire pulse to be sent to the laser 1 and the laser to emit a pulse of light at time TO as represented by the plot 10.
  • This pulse is focussed by the transmission optics 2 and travels to the remote object 8 where it is reflected.
  • the receiving optics 3 collects a portion of the reflected light pulse illustrated as plot 12 and focuses the energy onto the light sensitive detector 4.
  • the detector 4 converts the received light pulse into an electrical signal and the pulse detector 5 discriminates against any electrical noise generated by the light sensitive detector to provide a clean, logic level pulse from the incoming light detector signal at time Tl.
  • Timing calculation and display electronics 6 which calculates and displays the range to the remote object based upon the time of flight of the laser pulse (TI ⁇ TO) and the speed of light (c) in the intervening medium.
  • PCT GB00/04968 discloses an optical distance measurement apparatus using a signal known as the Maximal Length Sequence (MLS).
  • MLS Maximal Length Sequence
  • PRBS pseudo random noise binary signal
  • the maximal length sequence is the pseudo random noise sequence with the longest period which can be generated with a shift register of r sections. It has a length N-2 r -l shift register clock cycles and has good auto ⁇ correlation properties as the auto-correlation function has only two values; either -1/N or a peak of 1.0 at the point of correlation.
  • Figure 2 illustrates one example of a maximal length sequence generated by a four stage shift register 20.
  • Alternative length sequences can be generated by using longer shift registers with the appropriate feedback taps.
  • the system of PCT GB00/04968 provides various advantages and refinements to the basic use of an MLS sequence and provides a low cost apparatus for distance measurement and which can function over long range.
  • the processing power required to operate the system is kept to a minimum.
  • a difficulty remains, however, in detecting the presence of fog or other particulate matter, which can render the optical distance measurement inaccurate or prevent a signal from being obtained.
  • the ability to detect fog using an optical detection apparatus can enable more reliable interpretation of the distance measurement values, or can be used in isolation simply as means of detecting fog for other purposes.
  • a detection device for detecting particulate matter, comprising: a signal source for supplying a modulation signal; a transmission system connected to the signal source for transmitting a transmission signal modulated by the modulation signal; a reception system for receiving a received optical signal which is a reflected and delayed version of the transmitted signal; a cross-correlator for determining a cross correlation function between a time delayed version of the modulation signal and the received signal, for different values of the time delay; and means for analysing the cross correlation function to detect peaks, and wherein a peak is determined to represent particulate matter based on a shape of the cross correlation function peak.
  • the invention thus enables the hardware of a range finding device to be used to detect particulate material such as fog.
  • the signal source is preferably an optical signal source, and the device is for detecting fog or other particulate material obscuring a field of view.
  • the modulation signal preferably comprises an MLS sequence, and which has a bit period which is an integer multiple a master clock bit period.
  • the reception system preferably comprises an analogue to digital converter clocked at the master clock bit rate.
  • a peak is preferably determined to represent fog or other airborne particulate material based on the width of the peak and the MLS bit period, hi particular, a peak is determined to represent fog or other airborne particulate material when the width of the peak at half the peak maximum is substantially greater than the MLS bit period.
  • the cross correlation peak for reflection from a target will comprises a triangular pulse having a half-height width of one MLS bit period, and the peak for fog, or other distributed particulate target, will be of lower intensity but greater width.
  • the cross-correlator may comprise: a coarse cross-correlator for coarsely determining the time delay of the modulation signal needed to maximise the correlation between the time delayed modulation signal and the received signal, and a fine cross-correlator for calculating the correlation between the modulation signal and the received signal as a function of the time delay of the modulation signal with respect to the received signal in a time delay range around the time shift determined by the coarse cross-correlator.
  • This approach enables a reduction of processing power in order to determine the exact location of cross correlation peaks.
  • the invention also provides a method of detecting particulate matter, comprising: supplying a modulation signal, transmitting a transmission signal modulated by the modulation signal, receiving a signal which is a reflected and delayed version of the transmission signal, determining a cross correlation function between a time delayed version of the modulation signal and the received signal, for different values of the time delay; analysing the cross correlation function to detect peaks; and determining that a peak represents particulate material based on a shape of the cross correlation function peak.
  • Figure 1 shows a known laser range finding apparatus
  • Figure 2 shows circuitry for generating a maximal length sequence
  • Figure 3 shows a schematic diagram optical distance measuring equipment using a time delay measurement technique which can be used by the system of the invention
  • Figure 4 shows a signal generated by the distance measuring equipment in Figure 3;
  • Figure 5 shows a schematic diagram of a second embodiment of optical distance measuring equipment which can be used by the system of the invention
  • Figure 6 shows how the distance measurement apparatus can distinguish between a target and fog
  • Figure 7 shows more clearly how the discrimination between target and fog can be made.
  • the invention uses an optical distance measurement arrangement using the cross- correlation between a time delayed version of a modulation signal and a received reflected version of the modulation signal.
  • This cross correlation function is analysed to detect fog instead of, or as well as, detecting a peak which represents the distance to a target.
  • the invention enables fog or other airborne particulate material to be detected.
  • the user initiates a measurement of range at input 32 which causes an MLS generator 34 to generate an MLS signal.
  • the MLS generator clock signal is derived from the system master clock Fmck 36 by divider 38 so that the MLS clock frequency FmIs is a known sub-multiple M of the master clock signal. In effect, the MLS is stretched in time by factor M.
  • the "stretched" MLS signal causes the laser 1 to emit an optical stretched MLS signal starting at time TO, as represented at 40.
  • This optical signal is focussed by the transmission optics 2 and travels to the remote object 8 where it is reflected.
  • the receiving optics 3 collects a portion of the reflected optical signal and focuses this energy onto a light sensitive detector 4. This detector converts the collected light signal into an electrical signal which is digitised by the analogue to digital converter 42 and passed to coarse 44 and fine 46 cross-correlation calculation units.
  • the digital to analogue converter sample clock is set equal to the system master clock frequency, hi this way, an oversampling D/A conversion is implemented, and the oversampling ratio M is used to interpret the results as will become apparent from the description below.
  • the coarse cross-correlation unit 44 is clocked at the MLS clock frequency FmIs and hence correlates a sub-sampled version of the digitised reflected MLS signal and original stretched MLS transmitted signal.
  • the output from this cross correlation unit is a peak which is detected by pulse detector 48 and which indicates the coarse time delay TcI of " the reflected signal.
  • the fine cross-correlation unit 46 is clocked at the master clock frequency Fmck.
  • the control electronics 50 then causes the fine cross-correlator 46 to calculate the cross- correlation of the transmitted and reflected signals only in the region of time delay XcI.
  • the fine cross-correlation function would be calculated for 2M samples before and after TcI.
  • the cross-correlation operation may be viewed as being similar to convolving the MLS with a delayed version of itself and then sampling the result at a frequency equal to the cross correlator clock frequency.
  • the cross correlation function output by the fine cross correlator 46 takes the form shown in Figure 4.
  • the x-axis in Figure 4 is the master clock sample number, and this can be converted into time.
  • the width of the peak at half height is equal to the cross correlator clock sampling period, or M times the master- clock period. In the example of Figure 5, this is 4 master clock cycles.
  • This signal is passed to the timing calculation and control electronics which calculates using known standard techniques the coefficients m 1 and k 1 for equation of the best fit line through the M samples prior to the peak of the signal :
  • T _ (*2 - *l ) ⁇ o
  • T 0 is an estimate of the time of the peak of the signal which equates to the time delay between the transmitted and reflected signals.
  • the distance to the object is then calculated from the determined time T 0 ; it is half the speed of light multiplied by the time taken.
  • the system described above has particular advantages which may be seen by comparison with an MLS system just using one correlator. Assume such a system is constructed using an MLS of order 10, a master clock period of 3OnS and a delay step size equal to one fifth of the MLS clock sample frequency. As described above, the total number of calculations required to compute the full cross-correlation for one MLS signal is 1023 2 or 1046529 operations. Thus to determine the position of the cross correlation peak to within one master clock period (or 5m) is 1046529 operations.
  • the coarse correlator 44 is clocked at the MLS frequency and hence the total number of calculations required to compute the coarse correlation is 127 2 or 16129 operations.
  • the system uses a prior knowledge of the triangular form of the MLS cross correlation function in combination with the stretched form of the MLS to allow the time T 0 of the peak of the cross correlation function to be estimated using the approach described above with a precision better than the duration of one master clock cycle.
  • the position of cross correlation peak can be estimated to better than one quarter of the master clock cycle giving a distance precision very similar to the known system, but without the need for transmitting additional MLS cycles.
  • Figure 5 shows a second embodiment of the range finding apparatus wherein a memory 52 is provided on the output of the analogue to digital converter.
  • a memory 52 is provided on the output of the analogue to digital converter.
  • the coarse cross-correlation unit sub-samples the received and stretched MLS signals at a different frequency to the MLS clock signal, hi this case the coarse cross-correlator is clocked at a frequency FCcc which is a different sub-multiple N of the master clock signal, obtained by divider 54.
  • FCcc which is a different sub-multiple N of the master clock signal, obtained by divider 54.
  • the coarse cross-correlation unit may be preceded by a low pass filter to further improve the detection of the coarse position of the cross correlation function when the signal to noise ratio is poor.
  • the low pass filter may be implemented very simply by adding together N successive samples of the received signal.
  • the coarse correlator periodically calculates the signal stored in the memory 52 until it detects that the signal to noise ratio is sufficient for a fine measurement to be made. Then, a fine measurement is made by the fine cross-correlation unit
  • the use of the system to calculate the distance to a remote object has so far been described.
  • the invention uses the system to detect fog.
  • a full cross correlation function is obtained, for all time delay values.
  • the coarse cross correlator 44 is associated with a memory for storing all of the coarse cross correlator values.
  • the fine cross correlator 46 will be used for all peaks in the coarse cross correlation function, and again the fine cross correlator is associated with a memory for storing all values.
  • the unit 50 has a processor for analysing all of the received data in the manner explained below.
  • the full cross correlation function may instead be determined at the fine resolution, particularly as the determination of the presence of fog will typically be required less frequently than the range finding measurement.
  • Figure 6 shows the cross-correlation signal (CCF- cross correlation function) against time, when sighting on a chimney 60 at a distance of about 230m in the presence of fog.
  • the system detects the target as a con-elation peak 62 whose duration at half maximum is approximately equal to the oversampled clock period (M times the master clock period). This half maximum peak duration will generally be termed ⁇ T in the following, and the oversampled clock period will be termed ⁇ T 0 .
  • another peak 64 is detected whose duration is substantially greater than that of the target peak 62.
  • the two peaks are seen clearly in the the graph, and the inset photo 66 shows the target 60 in representative foggy conditions.
  • the duration of the fog peak depends on a number of factors, including fog density and uniformity, fog droplet size distribution and laser wavelength. However, it is often substantially greater than that of the target peak because it arises from reflections from fog droplets along the length of the modulated laser beam, whereas the target peak arises from reflection at the target only. The height of the fog peak increases and the height of the target peak decreases with increasing fog density.
  • the range of the target from the LRF is:
  • D fog (T fo g - T rd ) .
  • c/2 (1220 - 632) x IO ⁇ 9 .
  • 3xlO 8 / 2 88m.
  • the duration of the ideal correlation peak at half maximum for a 50MHz clock frequency and oversampling of 8 is:
  • ⁇ T 0 8 x 20ns - 160ns. Note that ⁇ T t arge t ⁇ ⁇ T 0 as expected. ⁇ T tar g et is slightly greater than ⁇ T 0 because the laser pulse train is not perfectly square and this has the effect of rounding the peak of the cross correlation function and thus increasing the measured duration at half maximum.
  • the duration of the fog peak at half maximum is equivalent to:
  • the fog is therefore characterised by an object of effective depth « 72m at a distance of « 88m from the laser source. Based on the difference in correlation peak duration, the system can easily discriminate between peaks due to reflection from targets and peaks due to reflections from fog.
  • Line 70 shows the ideal cross correlation signal for a solid target. Its value is approximately zero at times ⁇ T 0 from the peak.
  • Line 72 shows a typical real cross correlation signal between times ⁇ T 0 . It has non-zero intercepts at + ⁇ T 0 from the peak, due to the laser pulse train not being perfectly square.
  • the dashed line 74 shows the shape of the cross correlation signal between times ⁇ T for an extended target such as fog. In this case, the intercepts at ⁇ T from the peak are half the peak signal value, and this can be used as a criterion for rejecting this broader peak as being due to fog.
  • the invention uses analysis of the cross correlation function to detect peaks, and a criteria is applied to a peak to determine if it represents fog or other airborne particulate material based on a shape, in particular a width, of the cross correlation function peak.
  • the analysis can be carried out simply in software based on the cross correlation values for different time shifts.
  • the invention has been described applied to one specific cross correlation system which uses an MLS sequence. However, the invention can be applied to other correlation based systems. Furthermore, the invention has been described as implemented with a system using coarse and fine cross correlators. This system has the advantage that peaks can be accurately located with low processing power, and this enables real time distance measurement, The invention can be applied to systems which are only for measuring fog, and in this case there may be no need for fast processing of distance information. Thus, the invention can be applied to more simple cross correlation based distance measurement systems.
  • the apparatus combines distance measurement and fog detection.
  • distance detection can be enhanced by a fog warning.
  • the invention can be applied to systems only for fog detection, such as remote sensors on airport runways or other areas where a fog indication can provide useful safety information.
  • Implementations of the invention have been described using optical range finding equipment.
  • the invention can be applied more generally to discriminate against any scattering media in the line of sight when measuring distance using time of flight techniques.
  • the invention may be used under water, with light or ultrasound, to discriminate against particulates or turbidity.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

L'invention concerne un dispositif de détection de particules fondé sur l'intercorrélation entre un signal émis et une réflexion reçue. La fonction d'intercorrélation est analysée pour détecter des pics et un pic est déterminé pour représenter un voile ou toute autre matière particulaire en suspension dans l'air ou dans un liquide, en fonction d'une forme du pic de fonction d'intercorrélation.
PCT/GB2005/003591 2004-09-21 2005-09-19 Dispositif de detection de particules WO2006032854A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
EP05784736A EP1800148A1 (fr) 2004-09-21 2005-09-19 Dispositif de detection de particules
IL181347A IL181347A0 (en) 2004-09-21 2007-02-15 Particle detection device

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0420981.3 2004-09-21
GB0420981A GB0420981D0 (en) 2004-09-21 2004-09-21 Particle detection device

Publications (1)

Publication Number Publication Date
WO2006032854A1 true WO2006032854A1 (fr) 2006-03-30

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EP (1) EP1800148A1 (fr)
GB (1) GB0420981D0 (fr)
IL (1) IL181347A0 (fr)
WO (1) WO2006032854A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014082690A1 (fr) * 2012-11-30 2014-06-05 Rosenberger Hochfrequenztechnik Gmbh & Co. Kg Procédé de localisation de points défectueux dans une voie de transmission de signaux hf
CN109642949A (zh) * 2016-07-13 2019-04-16 德克萨斯仪器股份有限公司 用于窄带测距系统的方法和装置

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0269902A2 (fr) * 1986-11-27 1988-06-08 Deutsche Aerospace AG Procédé et dispositif pour mesurer la distance entre deux objets, en particulier entre deux véhicules à moteur
US5621514A (en) 1995-01-05 1997-04-15 Hughes Electronics Random pulse burst range-resolved doppler laser radar
US20030048430A1 (en) * 2000-01-26 2003-03-13 John Morcom Optical distance measurement

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0269902A2 (fr) * 1986-11-27 1988-06-08 Deutsche Aerospace AG Procédé et dispositif pour mesurer la distance entre deux objets, en particulier entre deux véhicules à moteur
US5621514A (en) 1995-01-05 1997-04-15 Hughes Electronics Random pulse burst range-resolved doppler laser radar
US20030048430A1 (en) * 2000-01-26 2003-03-13 John Morcom Optical distance measurement

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014082690A1 (fr) * 2012-11-30 2014-06-05 Rosenberger Hochfrequenztechnik Gmbh & Co. Kg Procédé de localisation de points défectueux dans une voie de transmission de signaux hf
US9331726B2 (en) 2012-11-30 2016-05-03 Rosenberger Hochfrequenztechnik Gmbh & Co. Kg Method for locating defective points in a high frequency (HF) signal transmission path
CN109642949A (zh) * 2016-07-13 2019-04-16 德克萨斯仪器股份有限公司 用于窄带测距系统的方法和装置
EP3504562A4 (fr) * 2016-07-13 2019-11-27 Texas Instruments Incorporated Procédé et appareil pour systèmes de télémétrie à bande étroite
US11231493B2 (en) 2016-07-13 2022-01-25 Texas Instruments Incorporated Methods and apparatus for narrowband ranging systems using coarse and fine delay estimation
CN109642949B (zh) * 2016-07-13 2024-04-19 德克萨斯仪器股份有限公司 用于窄带测距系统的方法和装置

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EP1800148A1 (fr) 2007-06-27
GB0420981D0 (en) 2004-10-20
IL181347A0 (en) 2007-07-04

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