• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:

    公开号:NL8815003A
    申请号:NL8815003
    申请日:1988-05-03
    公开日:1998-11-02
    发明作者:
    申请人:Secr Defence Brit；
    IPC主号:
    专利说明:

    Passive rangefinder.
    The invention relates to a passive identification and rangefinder device for identifying or measuring the distance to a distant object that emits infrared radiation, such as a beam, missile or projectile, using infrared spectrophotometer measurements.
    For the identification and distance measurement of projectiles and aircraft in war conditions, passive equipment operating by response to radiation inherent in the flight of the projectile or aircraft has obvious advantages.
    The possibility of determining the distance to an aircraft by measuring its infrared radiation is disclosed by Ovrebo et al in U.S. Patent 3,103,586 and by Jenness et al in U.S. Patent 3,117,228. These patents disclose embodiments in which the total of an aircraft's received infrared radiation is compared to the portion of the received radiation that passes through a filter that cuts off radiation within the absorption bands of atmospheric carbon dioxide and nitric oxide. When the aircraft is at a relatively short distance on the order of one kilometer or less, there will be a significant difference in these measurements because some of the radiation emitted by the aircraft within the absorption band will reach the sensing point despite atmospheric absorption. Assuming that the initially emitted radiation has the spectral distribution of a Planck black body radiation curve at some specific temperature, these patents disclose methods and devices for deriving a distance measurement from the difference between the measurements. At greater distances, however, atmospheric absorption becomes approximately equal to the absorption effected by the filter. The difference between the measurements becomes comparatively small and insensitive to a further increase in distance or range.
    British patent application 8310933 discloses a passive rangefinder that can measure distances above 1 kilometer. An interval or partial spectrum technique is used to measure changes near atmospheric absorption properties in the transferred spectrum. The amount of radiation received from these areas of the spectrum depends on the distance or range and can be measured quite easily. However, such a method does not use the entire spectrum delivered by the target. It depends on a spectral profile of unknown shape due to source temperature and line broadening by pressure, collision and temperature. British patent application 8321752 discloses an optical spectrum analyzer which allows a full spectrum to be measured very quickly, thus obtaining a suitable device to perform real time measurements of the optical spectrum.
    The present invention aims to provide a passive range finder that is effective for long distances and that exploits the wide electromagnetic spectral emission of a target.
    The invention provides a passive rangefinder for determining the distance to an object, such as an aircraft, missile or projectile that emits electromagnetic radiation, which rangefinder is provided with: means for forming a real image of a field of view, spec -trophotometer means having an input aperture positioned to receive at least a portion of the real image, dispersion means for separating radiation of different wavelengths, and detector means for measuring the spectrum of radiation received from distant parts of the input aperture, and data processing means for recording radiation measurement signals from the detector means, the data processing means being arranged to deconvolute the received spectral profile with a stored representation of a distance-dependent atmospheric transmission spectral profile so as to represent a representative ie obtain the spectral emission profile of radiation from the object, to derive therefrom a characteristic emission temperature and then a Planck emission spectrum for the object, and then determine the distance from the calculated emission spectrum and the observed spectrum.
    Once an estimated source temperature has been determined, the exact shape of the emission spectrum is then determined from Planck's law and since the manner in which the spectrum has been changed by atmospheric transmission is known, it must be possible to calculate the received spectrum.
    In contrast to the known devices, the above-described invention makes additional use of spectral information in the non-absorbent regions of the atmospheric transmission or transmission. These measurements are least affected by atmospheric absorption and are therefore most reliable in determining the source temperature and are therefore important in the present invention. The invention is particularly useful in the infrared spectral region but can also be used wherever suitable components are available, for example: visible light, ultraviolet, microwave and radiation.
    Preferably, the data processing means includes an iterative processor whereby the temperature of the object and the distance are optimized. Therefore, the atmospheric transmission and the Planck radiation curve of the object are changed until the measured spectrum is reconstructed.
    Preferably, the data processing means adjusts an assigned value for the emissivity of the object in order to improve the adaptation of the calculated spectrum at the rangefinder to the measured spectrum.
    In a particularly advantageous embodiment, the received spectrum is quickly scanned by means of a fast spectrum analyzer as described in British patent application 8321752. In spectral regions where there is near total atmospheric absorption, data from the processor calculations can be disregarded. On the other hand, when there is little absorption, greater weight can be assigned to the measurements as they will accurately indicate the correct Planck radiation curve. Difficult spectral regions, for example, when there is almost a near total atmospheric absorption, are preferably ignored and conventional statistical methods are used to provide the best adaptation to the measured results. Distance determination can be improved by taking measurements in different target temperature ranges using different Planck profiles. Furthermore, the atmospheric absorption profile can be calibrated against targets of known distance prior to use. For example, an active rangefinder can be used for initial calibration under the prevailing conditions.
    The invention will now be described with reference to an exemplary embodiment with reference to the accompanying drawings, in which: Figure 1 shows a known fast spectrum analyzer;
    Figure 2 shows a block diagram of the spectrum analyzer of Figure 1 incorporated into a passive rangefinder according to the invention;
    Figure 3 shows graphs of the wavelength as a function of the radiation emission for different characteristic source temperatures; Figure 4 shows the curves for a log-log scale shown in Figure 3;
    Figure 5 shows a typical received signal spectrum;
    Figure 6 shows a typical graph for the wavelength depending on atmospheric transmission;
    Figure 7 shows graphs of the operation of the comparator circuit from the block diagram of Figure 2; and
    Figure 8 shows the influence of source emissivity on the radiation emission curves of Figure 4.
    Figure 1 shows a spectrum analyzer as described in British patent application 8321752. Parallel light 10, for example electromagnetic radiation, from a field of view is incident on a first lens 11 which focuses the light in the focus of a second lens 13. Parallel light from the lens 13 passes through an acousto-optic (A-0) cell 15 and is then focused by a third lens 21 in a Fourier plane 22 which has an off-axis slit 25. The light which passes through the gap 25 by the detector 24. A field stop 27 is provided at the focus of the lens.
    The acousto-optic cell 15 has a piezoelectric input converter 16 driven by an oscillator 28 the frequency of which is swept by a sawtooth circuit 29. The acousto-optic cell 15 causes a phase delay in the path of the light depending on the refractive index of the transparent medium contained within the cell. Over the length of the acousto-optic cell, there are variations in the phase delay caused by voltage variations in the acoustic waves, the frequency of which is time dependent, driven by the sweep frequency applied to the converter 16. An adapted acoustic load 17 prevents acoustic wave reflections. The embodiment is such that light Fourier emerging from the acousto-optical cell 15 is transformed by the lens 21 in such a manner that a series of refractive orders appears in the Fourier plane 22. The energy distribution in the plane 22 is therefore the spectrum of the electromagnetic input energy 10.
    When a monochromatic flat wave, such as from a distant laser source, falls on the acousto-optic cell 15 and a sinusoidal signal is applied to the cell 15, the signal exiting the acousto-optic cell is the product of the incident flat wave signal and the applied sinusoidal signal. This product signal is then Fourier transformed to provide the incident signal spectrum in the Fourier plane 22. In the Fourier plane, in addition to the zero order, there will be a positive and a negative refractive order, and the distance from the origin of the positive order (for example) is a function of the wavelength of the laser source. When the spectrum of the source is broadened, the first orders of refraction corresponding to each quasi-monochromatic element of the source spectrum will then overlap. By sweeping the frequency of the applied sinusoidal signal, the spectrum of a polychromatic incident signal can then be shifted and displayed at the output of a detector in the Fourier plane 22.
    The above-described optical spectrum analyzer can quickly scan the optical frequency range, making it possible to measure real or real time changes in broad-band source spectra. This embodiment is suitable for use in the passive rangefinder according to the invention.
    A block diagram of the invention is shown in Figure 2. A spectrum analyzer 201 as shown in Figure 1, respectively, produces X and Y signals corresponding to the external sweep frequency applied to the acousto-optic cell 15 and the measured variation of detected signal amplitude. A scanner is provided at the entrance to the spectrum analyzer 201 to vary the field of view. The X and Y signals are processed in processor 203 to produce the optical spectrum of the analyzed light. This detected spectrum is equivalent to the optical spectrum of a light source in the field of view modulated by the distance and wavelength dependent atmospheric absorption function. The received spectrum output from processor 203 is applied to an input of a deconvolution device. An atmospheric transmission function corresponding to a certain selected distance or range R is supplied from a transmission function memory 205 to a second input 204 of the deconvolution device 204. The deconvolution device 204 generates an output spectrum corresponding to the source emission spectrum prior to the transmission over the atmospheric distance R This output spectrum of the deconvolution device 204 is applied to a second processing circuit 204 which derives a characteristic source temperature from the spectrum. This characteristic temperature is then processed in a circuit 207 to give a Planck emission spectrum corresponding to the temperature. The Planck source spectrum and the deconvoluted received spectrum are then compared by a comparator 208. Comparator 208 generates an output signal corresponding to differences between the compared spectra. The output signal is applied to the atmospheric transfer function memory 205 such that another atmospheric transfer function, corresponding to an improved distance / source temperature / emissivity estimate, is supplied to the deconvolution device 204. By an iterative process, the passive rangefinder produces a measurement of distance and source temperature which is usable for both distance measurement and target identification.
    Once an interesting target has been identified, the optical scan can be bridged. With suitable large targets, after distance measurement on a part of the target with a characteristic temperature Tj, a distance measurement can be carried out on a second part with a different characteristic temperature T2 · These two parts will have different Planck emission spectra but the same distance and therefore a second iterative distance measurement process is performed on the same target. Signals representing the measured distance and characteristic temperature of the target are applied to a display 209.
    The operation of the passive rangefinder will now be described in more detail. Figure 3 shows the Planck radiant emission curves (W. cm-2yu -1) versus wavelength in microns for sources of different temperatures Tj to. Each curve has a peak at different wavelength determined by the Wien displacement rule. On the linear scale as shown in Figure 3, the Wien displacement rule defines curve 301. When the Planck curves are drawn on a log-log scale, as shown in Figure 4, the curves will now all have the same shape and the Wien- displacement rule now a straight line 401. The passive rangefinder processor 207 uses the log-log relationship to shift a shape of curve 402 along the linear Wien rule curve 401 to generate any of the required profiles. The position of each temperature curve can be found by calculating the peak for any absolute temperature using the Wien relationship: max T = 2897.9 / h "k.
    After the transmission or transmission over a depth R (distance) from the atmosphere, the spectral profile of the radiation emitted by a source undergoes a change due to the selective transmission properties of the atmosphere. A typical received signal, as shown in Figure 5, is the result of convolution of the Planck emission spectrum with the atmospheric transmission function as shown in Figure 6, for example. When the true atmospheric transmission function is known, one of the temperature profiles of Figure 4 is produced by deconvolution of the received spectrum with the atmospheric transmission function. If the atmospheric spectral profile (Figure 6) generated by the memory 205 and the source temperature T obtained from the processor are exact, then the deconvoluted received spectrum output signal from the deconvolution device 204 against the Planck source spectrum output signal of the unit 207 will result in a straight line 701 as shown in Figure 7. In this case, comparator 208 will cause distance R and T to be displayed. If the source temperature T were too low resulting in the selection of an erroneous Planck curve from Figure 4, the resulting comparator curve will then be on one side of line 701, for example, one of two lines 702 or 703 depending on the temperature error. When the estimated temperature T is too high, the resulting curve will be above line 701 (eg 704, 705) and there will be a peak deviation from the straight line, eg 706 or 707, which will indicate where the true temperature peak (of Figure 4). Therefore, the deviations from the straight line 701 indicate the magnitude and direction of the temperature error, and by an iterative process, the shape (one of 702-705 e.g.) can be output to "come" to the true line 701.
    The source emissivity, another unknown, is between 0 and 1. While temperature (T) changes cause wavelength displacements of the release curves (Figure 4), changes in emissivity shift only the characteristic release curves up or down. This is indicated in figure 8.
    The radiation emission curves 801-803 are indicated for different source temperatures TJ-T3 assuming an emissivity = 1. For the same source temperature Tj, by making the emissivity {1, the curve 801 equals 804. This will result in a completely different and distinct deviation in comparator 208 from straight line 701. Therefore, the "bump" or bump will appear in a completely different place and will indicate that the emissivity value needs to be adjusted to allow the measured comparator curve to adjust will "relax or decrease" to the straight line 701. Therefore, an incorrect source temperature can be distinguished from a correction to be applied to target emissivity. Therefore, the rangefinder can also be designed to display target emissivity in addition to distance and temperature.
    When the atmospheric transmission profile of the unit 208 has an error in a certain spectral range, such as, for example, by underestimating or overestimating the absorption of one of the atmospheric constituents, the deviation from the line 701 will then again be recognizable as this occurs at a wavelength of known gas absorption and a distinction can be made against this in order to leave adjacent areas of the comparator curve unaffected.
    In practice, a microprocessor will have the necessary stored data to allow the iterative processing of the received optical spectrum to derive the required source parameters.
    The known embodiment disclosed in British Patent Application 8310933 does not use spectral information obtained from the non-absorption regions of atmospheric transmission or from regions having different absorption effects from the currently used constituents (i.e. oxides of carbon and nitrogen). However, points on the comparator curve (702-705), where little or no absorption occurs, indicate where the correction source parameters are and thus aid the iterative process of correcting the under or over estimated points.
    Difficult areas of cycling spectrum can be eliminated by removing data from those areas and conventional statistical methods adopted to yield the "best adjustments".
    By making observations on a target at several different temperature ranges, more accurate results can be obtained since the recorded spectrum is successively deconvoluted by different Planck curves.
    Although the invention has been described in conjunction with the optical spectrum analyzer of British Patent Application 8321752, other spectrum analyzers may be used. However, the described device has the advantage of a fast spectral observation, so that measurements can be made on moving targets.
    If the target is a true Planck radiator, then the emission spectrum is continuous and follows the Planck rule. However, if the target is a chemical target, characteristic spectral lines will occur. However, the peaks of these lines will lie on the Planck curve and so the described technique will still work herein.
    Conclusions
    权利要求:
    Claims (9)
    [1]
    A passive rangefinder for determining the distance to an object, such as an aircraft, missile or projectile, that emits electromagnetic radiation, provided with means for forming a real image of a field of view; spectrophotometer means with an input aperture arranged to receive at least a portion of the real image, dispersion means for separating radiation of different wavelengths, and detector means for measuring the spectrum from distant parts of the input aperture recorded radiation, and data processing means for recording radiation measurement signals from the detector means; wherein the data processing means is arranged to deconvolute the received spectral profile with a stored representation of a distance-dependent atmospheric transmission spectral profile to obtain a representation of the spectral emission profile of radiation from the object, from which a characteristic emission temperature and then a Derive Planck's emission spectrum for the object, and then determine the distance from the calculated emission spectrum and the observed spectrum.
    [2]
    The passive rangefinder according to claim 1, wherein the data processing means includes an iterative processor whereby the object temperature and distance are optimized.
    [3]
    The passive rangefinder according to claim 1 or 2, wherein the data processing means adjusts an assigned emissivity value of the object to improve the adaptation of the calculated spectrum at the rangefinder to the measured spectrum.
    [4]
    Passive rangefinder according to any one of the preceding claims, wherein absorption data of the processor calculations in spectral regions, in which there is an almost total atmospheric absorption, are disregarded.
    [5]
    The passive rangefinder of any preceding claim, wherein in spectral regions where there is little absorption, more weight is given to the measurements as they will closely indicate the correct Planck radiation curve.
    [6]
    A passive rangefinder according to any one of the preceding claims, wherein in difficult spectral regions, for example where near total atmospheric absorption occurs, results are ignored and conventional statistical methods are used to provide the best adaptation to the measured results.
    [7]
    Passive rangefinder according to any one of the preceding claims, wherein means are provided for determining the distance from two areas of a target at different temperatures using different Planck profiles.
    [8]
    Passive rangefinder according to any of the preceding claims, wherein the atmospheric absorption profile is calibrated against targets of known distance prior to use.
    [9]
    The passive rangefinder of claim 8, wherein an active rangefinder is used for the initial calibration under the prevailing conditions.
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    同族专利:
    公开号 | 公开日
    IT8848692D0|1988-12-20|
    GB8810367D0|1998-07-22|
    FR2775084A1|1999-08-20|
    GB8710567D0|1998-07-08|
    GB2322985B|1998-12-16|
    US5894343A|1999-04-13|
    DE3843302C2|1999-10-21|
    NL194928C|2003-07-04|
    GB2322985A|1998-09-09|
    FR2775084B1|2000-06-23|
    DE3843302A1|1999-03-04|
    NL194928B|2003-03-03|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US3026413A|1952-11-01|1962-03-20|Rca Corp|Determining the range of an infra-red source with respect to a point|
    US3117228A|1956-10-12|1964-01-07|Jr James R Jenness|Apparatus for passive infrared range finding|
    US3103586A|1958-12-08|1963-09-10|Gen Mills Inc|Passive infrared ranging device using absorption bands of water vapor or carbon dioxide|
    GB1481545A|1974-10-22|1977-08-03|Pusch G|Methods of determining the range of infrared equipment|
    GB2323730B|1983-04-21|1999-01-13|Secr Defence|Passive identification and rangefinder apparatus|
    GB2144847B|1983-08-12|1987-01-07|Secr Defence|Optical spectrum analyser|
    JPH058392B2|1983-09-16|1993-02-02|Fujitsu Ltd|US6980151B1|2004-06-14|2005-12-27|General Dynamics Advanced Information Systems, Inc.|System and method for onboard detection of ballistic threats to aircraft|
    DE102008011123B4|2008-02-26|2012-09-06|Eads Deutschland Gmbh|Method for determining the distance of an object emitting an IR signature|
    WO2019034836A1|2017-08-14|2019-02-21|Bae Systems Plc|Passive sense and avoid system|
    EP3447527A1|2017-08-21|2019-02-27|BAE SYSTEMS plc|Passive sense and avoid system|
    DE102019204499A1|2019-03-29|2020-10-01|Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.|Method and device for distance measurement|
    法律状态:
    1998-11-02| A1A| A request for search or an international-type search has been filed|
    1999-07-01| BB| A search report has been drawn up|
    1999-09-01| BC| A request for examination has been filed|
    2002-09-02| CNR| Transfer of rights (patent application after its laying open for public inspection)|Free format text: QINETIQ LIMITED |
    2005-02-01| V1| Lapsed because of non-payment of the annual fee|Effective date: 20041201 |
    优先权:
    申请号 | 申请日 | 专利标题
    GBGB8710567.2A|GB8710567D0|1987-05-05|1987-05-05|A passive rangefinder|
    GB8710567|1987-05-05|
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