Lidar system for differential absorption measurement and background distance measurement

Abstract

To provide a new LIDAR system attainable by an optical fiber that can execute IPDA (Integrated Path Differential Absorption) and can determine separation distance from an obstacle existing in the background of a measurement region.SOLUTION: A LIDAR system is configured so as to execute differential absorption measurement of a chemical compound between two separate optical frequencies (ν1, ν2) and measure separation distance from an obstacle existing in the background of a measurement region in which absorption occurs. Since the LIDAR system can implement an optical fiber technique while having sufficient light emitting power, a light emitting light power value is changed at a different time interval between radiation light emitting sequences. The LIDAR system can evaluate the amount of chemical compounds included in the measurement region, and separation distance from an obstacle positioned in the background of the measurement region.SELECTED DRAWING: Figure 1a

Description

Detailed Description of the Invention

[0001] [Technical Field] The description provided herein relates to a LIDAR (Light Detection and Ranging) system suitable for performing differential absorption measurements and background distance measurements. The present invention also relates to a method for measuring the amount of a chemical compound using such a system.

[0002] [Prior Art] It is known to use differential absorption measurements to evaluate the amount of a chemical compound contained in a measurement region. For this purpose, the absorption of the emitted radiation light directed towards the measurement region is measured for a first frequency of the radiation light that does not correspond to the absorption band of the chemical compound and for a second frequency of the radiation light that corresponds to the absorption band of the chemical compound. Therefore, it is necessary to radiate the radiation light of both frequencies towards the measurement region and compare the absorption levels measured for each frequency. Such a measurement method is generally called IPDA (Integrated Path Differential Absorption). Also, for example, it is necessary to know the depth of the measurement region, such as the distance to the position of an obstacle present in the background of the measurement region.

[0003] Performing such IPDA measurements using a LIDAR system is useful, especially for reasons of detection sensitivity and the ability to analyze the detection signals provided by such a system. Therefore, enabling the use of a LIDAR system made from optical fibers is an important issue. This is because such systems have reduced size and weight, better energy efficiency, and high resistance to losses in the cooperation between the optical components of which they are composed.

[0004] However, IPDA measurements need to meet the following requirements: Compared to variations that may affect the chemical compounds contained in the measurement area, at least two radiation lights must be emitted at different optical frequency values quickly enough, continuously, and in succession. More precisely, the pulses of both radiation lights must be emitted at a repetition frequency that is high enough compared to the variations of the chemical compounds in the measurement area, for example, enabling the analysis of detection signals at a repetition frequency higher than 1 kHz (kilohertz); Both radiation lights, that is, the radiation light outside the absorption band of the chemical compound to be measured and the radiation light corresponding to one of the absorption bands of the chemical compound, must be emitted using sufficient energy for each; The radiation light corresponding to one of the absorption bands of the chemical compound must have a sufficiently narrow spectral linewidth to provide sufficient accuracy when determining absorption by the chemical compound. In particular, when the central wavelength of the radiation light is approximately 1.6 μm (micrometers), this spectral width of the radiation corresponding to one of the absorption bands of the chemical compound may need to be less than 100 MHz (megahertz); The measurement of the separation distance of background obstacles by characterizing the elapsed time is very short and typically requires the use of radiation light pulses for individual periods of less than about 100 ns (nanoseconds).

[0005] However, the well-known phenomenon of stimulated Brillouin scattering occurring in optical fibers limits the peak power of the radiation light pulses that can be emitted by LIDAR systems made of optical fibers. As a result, it will limit the maximum distance of these fiber optic LIDAR systems.

[0006] [Technical Problem] Taking these constraints into account, an object of the present invention is to provide a novel LIDAR system achievable using optical fibers that realizes both performing IPDA measurements and determining the separation distance from obstacles present in the background of the measurement area.

[0007] More specifically, the present invention is implemented using at least one optical fiber and transmits the emitted radiation light, and aims to provide a LIDAR system in which the peak power limitation caused by stimulated Brillouin scattering is extended or eliminated.

[0008] [Summary of the Invention] To achieve this object or other objects, a first aspect of the present invention provides a LIDAR system configured to perform differential absorption measurement between two separate optical frequencies and measurement of the separation distance from an obstacle existing in the background of the measurement region where absorption occurs. The LIDAR system of the present invention includes a laser source assembly suitable for generating radiation light at either of the two optical frequencies, intensity modulation means configured to apply a pulse envelope shape including a pulse period and a pulse optical power value to each radiation light, and a light emission control device configured to control the intensity modulation means.

[0009] In the context of the present invention, the pulse optical power is understood to mean a value characterizing the intensity of each pulse, and this value probably corresponds to the peak power of the pulse or the average power evaluated over the entire period of the pulse. It is understood that the peak power value and the average power value increase one as a function of the other in a certain period and pulse shape.

[0010] According to the present invention, the LIDAR system is configured to emit a radiation emission sequence in the target direction in which differential absorption measurement and measurement of the separation distance from the background obstacle are performed during the operation of the LIDAR system, and the radiation emission sequence includes the emission light spectrally lies at a first optical frequency among the two optical frequencies, and a first time interval having a first spectral width, a first pulse period, and a first pulse optical power value has and the emission light spectrally lies at a second optical frequency among the two optical frequencies, and a second time interval having a second spectral width, a second pulse period, and a second pulse optical power value has and has has a radiation emission sequence.

[0011] The first time interval and the second time interval may be consecutive in any manner in the emission light sequence, and the emission light sequence may have any number of first time intervals between two second time intervals, and vice versa. Additionally or alternatively, the emission light sequence may have any number of pulses arranged around the first optical frequency between two pulses located around the second optical frequency, and vice versa.

[0012] Furthermore, the emission light sequence i) The first spectral width and the second spectral width are such that the emission light during the first time interval and the second time interval non-overlapping with each other spectrum region has a width corresponding thereto, the first spectral width being larger than the second spectral width, ii) the first pulse optical power value is larger than the second pulse optical power value, and iii) the first pulse duration is shorter than the second pulse duration.

[0013] Such a LIDAR system may be made of an optical fiber. In particular, its laser source assembly may be of the MOPFA type (Master Oscillator Power Fiber Amplifier: master oscillator power amplifier). In such a MOPFA-type LIDAR system, the emitted optical pulses are first generated with a desired spectral width, modulated according to a desired envelope shape, separated between consecutive pulses, and then these pulses are amplified and emitted externally.

[0014] Thanks to the first spectral width being larger than the second spectral width, the first pulse optical power value can be selected to be high or very high without causing an induced Brillouin scattering effect that would interfere with the operation or use of this system in the optical fiber used to create such a LIDAR system.

[0015] For use in IPDA measurement, the emission during the first time interval is selected to be outside the absorption band of the chemical compound relevant to the measurement. The emission during the first time interval is further used to estimate the separation distance from obstacles present in the background of the measurement area. This remote measurement is performed by determining the elapsed time of the emitted light pulse radiated during the first time interval for the round trip between the LIDAR system and the background obstacle. During these first time intervals, the high pulse optical power realized by expanding the spectral width and the shortening of the pulse duration improve the accuracy in estimating the separation distance from the background obstacle. The emission during the second time interval is selected to be within a range of one of the absorption bands of the chemical compound. During the second time interval, the low spectral width of the pulse results in higher accuracy in estimating the amount of the chemical compound. The amount of the chemical compound is estimated based on the absorption ratio determined by the LIDAR system between the emitted light during the second time interval around the second optical frequency and the emitted light during the first time interval around the first optical frequency, taking into account the estimated value of the separation distance from the background obstacle.

[0016] Preferably, i) the repetition frequency of the emission sequence may be between 1 kHz and 50 kHz, ii) the first time interval may have individual periods of 10 ns to 200 ns, preferably 50 ns to 100 ns, iii) the second time interval may have individual periods of 0.1 μs (microsecond) to 10 μs, preferably 0.5 μs to 5 μs, iv) the first spectral width of the emitted light radiated by the LIDAR system in the measurement area during the first time interval may be between 100 MHz and 2000 MHz, preferably between 500 MHz and 1000 MHz, v) the first spectral width of the emitted light radiated by the LIDAR system in the measurement area during the second time interval may be between 10 MHz and 200 MHz, preferably between 50 MHz and 100 MHz, and one or more of the characteristics i) to v) above may be selected by the emission control device.

[0017] Finally, the laser source assembly may be configured such that the emitted radiation light by the LIDAR system within the measurement region during each of the first time interval and the second time interval has a first optical frequency value and a second optical frequency value corresponding to wavelengths located between 1.3 μm and 1.8 μm, particularly between 1.5 μm and 1.6 μm, or at approximately 2 μm. Such a wavelength region is particularly suitable for measuring the amount of carbon dioxide contained in the measurement region.

[0018] Furthermore, the LIDAR system of the present invention includes a detection path configured to independently detect, process, and analyze the backscattered radiation light corresponding to the first optical frequency and the second optical frequency and corresponding to the light emission during the first time interval and the second time interval, respectively.

[0019] In some cases, the LIDAR system may further include a computing unit connected from an input part to at least one output part of the detection path. The computing unit is configured to provide an estimated value of the separation distance from the background obstacle and the amount of chemical compounds contained in the measurement region based on the analysis signal generated by the detection path.

[0020] Depending on different possible embodiments of the present invention, particularly depending on different types of laser oscillators used in the laser source assembly to generate radiation light at each of the two optical frequencies, the first spectral width and / or the second spectral width may be inherent or may be generated by dedicated spectral broadening means. The inherent spectral width is understood to mean the spectral width of the emitted radiation light generated by the corresponding laser oscillator. In other words, in the former case, the spectral width of the pulse emitted during the first time interval and / or the second time interval coincides with the spectral width of the corresponding laser oscillator. Otherwise, the LIDAR system further includes spectral broadening means arranged to modify the spectral width of at least one of the radiation lights generated by the laser source assembly.

[0021] In a first embodiment of the present invention, the emission control device may be configured to control a laser source assembly, an intensity modulation means, and, if appropriate, a spectral broadening means. In the emission light sequence, the first optical frequency of the two optical frequencies is exclusively associated with the first spectral width, the first pulse duration, and the first pulse optical power value within the first emission light pulse, excluding the second spectral width, the second pulse duration, and the second pulse optical power value. Also, the second optical frequency of the two optical frequencies is exclusively associated with the second spectral width, the second pulse duration, and the second pulse optical power value within the second emission light pulse separated from the first pulse, excluding the first spectral width, the first pulse duration, and the first pulse optical power value.

[0022] Regarding such a first embodiment, the LIDAR system may be configured to include a first laser oscillator configured such that the laser source assembly generates emission light of the first optical frequency, and a second laser oscillator configured to generate emission light of the second optical frequency having a second spectral width. Next, the spectral broadening means includes a phase modulator disposed in the path of the emission light generated by the first laser oscillator and controlled by the emission control device to provide the first spectral width to the emission light generated by the first laser oscillator. Further, the LIDAR system further includes an optical switch controlled by the emission control device to transmit either the emission light resulting from the phase modulator or the emission light generated by the second laser oscillator to the downstream portion of the emission optical path shared by the emission light resulting from the phase modulator and the emission light generated by the second laser oscillator and including the intensity modulation means.

[0023] According to another configuration that is also feasible for the first embodiment of the present invention, the laser source assembly includes a first laser oscillator configured to generate radiation light of a first optical frequency, and a second laser oscillator configured to generate radiation light of a second optical frequency having a second spectral width. The spectrum broadening means is disposed in the path of the radiation light generated by the first laser oscillator, and includes a phase modulator controlled by a light emission control device to provide a first spectral width to the radiation light generated by the first laser oscillator. However, in this other configuration, the intensity modulation means includes a first intensity modulator disposed in the path of the radiation light generated from the phase modulator and controlled by a light emission control device to exert an effect on the radiation light generated from the phase modulator, and a second intensity modulator disposed in the path of the radiation light generated by the second laser oscillator and controlled by a light emission control device to exert an effect on the radiation light generated by the second laser oscillator. Next, the LIDAR system further includes an optical coupler configured to transmit the radiation light generated from the first intensity modulator and the second intensity modulator to a downstream portion of the radiation optical path shared by the radiation light generated from the first intensity modulator and the second intensity modulator.

[0024] In the case of these two configurations, the downstream portion of the light emission optical path is controlled by a light emission control device, and may include an optical radiation amplifier, or an optical radiation amplification chain, that generates a first optical power value and a second optical power value according to the features of the present invention regarding the radiation emission sequence.

[0025] In a second embodiment of the present invention, which is an alternative to the first embodiment described above, the emission control device has a radiation emission sequence comprising a series of radiation light pulses spectrally located at either a first optical frequency or a second optical frequency of two optical frequencies, and all the radiation light pulses have the same envelope shape with a first period in which the radiation emission has a first spectral width and a first optical power value and a second period in which the radiation emission has a second spectral width and a second optical power value for both the first optical frequency and the second optical frequency. The first period is shorter than the second period, and in each radiation light pulse, the laser source assembly, the spectral broadening means, and the intensity modulation means are configured to be controlled so as to be before or after this second period.

[0026] Generally with respect to the present invention, a LIDAR system may implement optical fiber technology.

[0027] Also, generally with respect to the present invention, a LIDAR system may include polarization means configured such that radiation light emitted towards a measurement region by the LIDAR system has orthogonal polarization, particularly counter-rotating circular polarization, when emitted during a first time interval or a second time interval. In this case, the detection path may include a first detector that is sensitive in a first spectrum including a first optical frequency combined with a first spectral width, or a second detector that is sensitive in a second spectrum including a second optical frequency combined with a second spectral width, and a polarization beam splitter configured to transmit the backscattered radiation according to the polarization of the backscattered radiation. Possibly, if the common sensitivity spectrum of the two detectors includes both a first optical frequency combined with a first spectral width and a second optical frequency combined with a second spectral width, the two detectors may be the same. region in a first detector that is sensitive in a first spectrum including a first optical frequency combined with a first spectral width, or a second detector that is sensitive in a second spectrum including a second optical frequency combined with a second spectral width region and a polarization beam splitter configured to transmit the backscattered radiation according to the polarization of the backscattered radiation. Possibly, if the common sensitivity spectrum of the two detectors region includes both a first optical frequency combined with a first spectral width and a second optical frequency combined with a second spectral width, the two detectors may be the same.

[0028] A second aspect of the present invention provides a method for measuring the amount of a chemical compound present in a target direction as follows. A LIDAR system according to the first aspect of the present invention is selected such that the chemical compound has a lower absorption ability value at a first optical frequency than at a second optical frequency. The selected LIDAR system is directed towards the target direction so as to emit light according to an emission light sequence towards a measurement region that may contain the chemical compound, and the operation of the LIDAR system is induced. The separation distance from an obstacle present in the background of the measurement region is estimated based on the backscattered radiation associated with the first optical frequency and corresponding to the emission during a first time interval. The amount of the chemical compound contained in the measurement region, integrated over the path of the pulse between the LIDAR system and the background obstacle, is estimated based on the luminance values separately associated with the backscattered radiation at the first optical frequency and the second optical frequency, corresponding respectively to the first time interval and the second time interval in the emission light sequence, and these backscattered radiation lights are detected by the detection path of the LIDAR system.

[0029] Preferably, the separation distance from an obstacle present in the background of the measurement region may be estimated based on the elapsed time measured with respect to the backscattered radiation associated with the first optical frequency. In this case, the separation distance estimated based on the backscattered radiation associated with the first optical frequency can be used to estimate the amount of the chemical compound integrated over the path of the pulse contained in the measurement region. The path of the pulse is separately associated with the backscattered radiation detected at the first optical frequency and the second optical frequency, and is combined with the intensity values corresponding respectively to the emission during the first time interval and the second time interval.

[0030] The chemical compound related to the measurement method of the present invention may be any one of carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water (H2O).

[0031] Finally, different conditions for implementing the present invention are enumerated as follows. Regarding the first implementation condition, the LIDAR system may be installed on the ground surface and be directed to measure the amount of chemical compounds present between the LIDAR system and an obstacle. Regarding the second implementation condition, the LIDAR system may be mounted on an aircraft in flight, measure the separation distance from the ground surface of a geographical area to the LIDAR system, and be directed to the geographical area to measure the amount of chemical compounds present between the LIDAR system and the ground surface within the geographical area. And regarding the third implementation condition, the LIDAR system may be mounted on a satellite in orbit around the Earth and directed to the geographical area of the ground surface to measure the separation distance from the ground surface of the geographical area to the LIDAR system and measure the amount of chemical compounds present between the LIDAR system and the ground surface of the geographical area.

[0032] Regarding the second and third implementation conditions, the ground surface within the geographical area towards which the LIDAR system is directed serves as an obstacle in the background of the measurement area.

[0033] [Brief Description of the Drawings] The features and advantages of the present invention will become more clearly apparent by referring to the accompanying drawings in the following detailed description of some non-limiting embodiments.

[0034] [Fig. 1a] shows the spectral variation of the first emission light sequence implemented in the first practicable embodiment of the present invention.

[0035] [Fig. 1b] shows the radiation light power variation with respect to the first emission light sequence of [Fig. 1a].

[0036] [Fig. 2a] shows the spectral variation of the second emission light sequence implemented in the second practicable embodiment of the present invention.

[0037] [Fig. 2b] shows the radiation light power variation with respect to the second emission light sequence of [Fig. 2a].

[0038] [Fig. 3a] is a block diagram of the light emission path of a LIDAR system according to the present invention, configured to generate the first emission light emission sequence of [Fig. 1a] and [Fig. 1b].

[0039] [Fig. 3b] is a block diagram of a first modification of the light emission path, compared with the system of [Fig. 3a] regarding another LIDAR system according to the present invention, configured to generate the first emission light emission sequence of [Fig. 1a] and [Fig. 1b] as well.

[0040] [Fig. 3c] is a block diagram of a second modification of the light emission path, compared with the system of [Fig. 3a] regarding still another LIDAR system according to the present invention, configured to generate the first emission light emission sequence of [Fig. 1a] and [Fig. 1b] as well.

[0041] [Fig. 3d] is a block diagram of a third modification of the light emission path, compared with the system of [Fig. 3a] regarding still another LIDAR system according to the present invention, configured to generate the first emission light emission sequence of [Fig. 1a] and [Fig. 1b] as well.

[0042] [Fig. 3e] is a block diagram of a fourth modification of the light emission path, compared with the system of [Fig. 3a] regarding still another LIDAR system according to the present invention, configured to generate the first emission light emission sequence of [Fig. 1a] and [Fig. 1b] as well.

[0043] [Fig. 4a] is a block diagram of the light emission path of still another LIDAR system according to the present invention, configured to generate the first emission light emission sequence of [Fig. 1a] and [Fig. 1b] as well.

[0044] [Fig. 4b] is a block diagram of a modification of the light emission path, compared with the system of [Fig. 4a] regarding still another LIDAR system according to the present invention, configured to generate the first emission light emission sequence of [Fig. 1a] and [Fig. 1b] as well.

[0045] [FIG. 5a] is a block diagram of the light emission path of yet another LIDAR system according to the present invention, which is also configured to generate the second emission light emission sequence of [FIG. 2a] and [FIG. 2b].

[0046] [FIG. 5b] is a block diagram of a modification of the light emission path for yet another LIDAR system according to the present invention, which is also configured to generate the second emission light emission sequence of [FIG. 2a] and [FIG. 2b], compared with the system of [FIG. 5a].

[0047] [FIG. 6a] is a block diagram of the detection path of the LIDAR system according to the present invention.

[0048] [FIG. 6b] is a block diagram of a modification of the detection path compared with the system of [FIG. 6a].

[0049] [FIG. 6c] is a block diagram of another modification of the detection path compared with the system of [FIG. 6a].

[0050] [FIG. 6d] is a block diagram of yet another modification of the detection path compared with the system of [FIG. 6a].

[0051] [Mode for Carrying Out the Invention] For clarity, the dimensions of the members represented in [FIG. 1a], [FIG. 1b], [FIG. 2a], and [FIG. 2b] do not correspond to the actual dimensions or the actual dimensional ratios. In addition, all members are merely symbolically represented in the drawings, and the same reference numerals shown in different drawings indicate the same members or members having the same function.

[0052] In the diagrams of [Fig. 1a], [Fig. 1b], [Fig. 2a], and [Fig. 2b], the x-axis identifies the time, indicated by t, between emission light sequences composed of emission light pulses spectrally located around either the first optical frequency indicated by ν1 or the second optical frequency indicated by ν2. The periods of the first time interval and the second time interval between these emission light sequences are represented by Δt1 and Δt2, respectively. In [Fig. 1a] and [Fig. 2a], the y-axis indicates the value of the optical frequency indicated by ν for each time of the emission sequence, and in [Fig. 2a] and [Fig. 2b], the y-axis indicates the instantaneous emission intensity of the emission light indicated by P. Generally, the emission light pulses indicated by reference numeral 1 are spectrally located around the optical frequency ν1 and are assumed to be all identical to each other. Similarly, the emission light pulses indicated by reference numeral 2 are spectrally arranged around the optical frequency ν2 and are assumed to be all identical to each other. To apply the present invention to the measurement of differential absorption of chemical compounds between two different optical frequencies, all the emission light pulses 1 and 2 are emitted in the direction of a measurement region likely to contain the amount of chemical compound to be measured. The optical frequency ν1 is intended to be selected outside the absorption band of the chemical compound, and the optical frequency ν2 is intended to be selected within one range of the absorption band of this chemical compound. In the case where the chemical compound is carbon dioxide, the optical frequency ν1 may be selected to be equal to 190.81 THz corresponding to the wavelength value λ1 equal to 1572.2 nm, and the optical frequency ν2 may be selected to be equal to 190.84 THz corresponding to the wavelength value λ2 equal to 1572.02 nm.

[0053] [Figs. 1a] and [Figs. 1b] relate to the same first emission sequence that can be implemented with respect to the present invention. In such a first emission sequence, all emission light pulses 1 have a first common value of spectral width Δν1 and emission peak power P1, and a pulse duration equal to Δt1. Similarly, all of the emission light pulses 2 of the same emission sequence have a second common value of spectral width Δν2 and emission peak power P2, and a pulse duration equal to Δt2. The emission peak power values P1 and P2 correspond to the emission light emitted by the LIDAR system according to the present invention, and the emission light exits from the LIDAR system in the direction of the measurement region, particularly after final optical amplification in the LIDAR system. In the case of the first emission sequence, the pulses 1 of the individual periods Δt1 correspond to the first time interval introduced in the summary section of this specification, and the pulses 2 of the individual periods Δt2 correspond to the second time interval. Because the spectral broadening for pulse 1 is larger compared to pulse 2, that is, thanks to Δν1>Δν2, the emission peak power value P1 may be greater than the power limit due to stimulated Brillouin scattering represented by P SBS and in contrast, the emission peak power value P2 may be less than the same power limit P SBS .

[0054] [Figs. 2a] and [Figs. 2b] similarly relate to the same second emission sequence that can be implemented with respect to the present invention. In such a second emission sequence, all emission light pulses 1 and emission light pulses 2 emitted toward a measurement region that is likely to contain a measurable chemical compound have the same envelope shape that is transposed at the optical frequency of each pulse, and ν1 representing pulse 1 and ν2 representing pulse 2 appear alternately. The envelope shape has, within each of pulse 1 and pulse 2, a first time of period Δt1 during which the emission light of pulse 1 or pulse 2 has a spectral width value Δν1 and an emission peak power value P1 intervalIt includes a first time interval of the interval and the period Δt2 during which the emission light of pulse 1 or pulse 2 has a spectral width value Δν2 and an emission peak power value P2. The time series order between the first time interval and the second time interval, which have unique correlation values for the spectral width and the emission peak power, may be reversed within each pulse, and the first time interval and the second time interval may also be separated by the intermediate envelope pattern shape within each pulse. As described above, the power limit P related to the induced Brillouin scattering effect SBS may be smaller than the emission peak power value P1 and larger than the emission peak power value P2.

[0055] Regarding the first emission sequence ([Figure 1a] and [Figure 1b]) and the second emission sequence ([Figure 2a] and [Figure 2b]), the separation distance from the background obstacle is determined using the emission light at the optical frequency ν1 during the period Δt1. In the second emission sequence, the portion of pulse 1 corresponding to the period Δt2 having the spectral width value Δν2 and the emission peak power value P2 may not be used to estimate the separation distance from the background obstacle. However, the portion of pulse 2 corresponding to the period Δt1 having the spectral width value Δν1 and the emission peak power value P1 may optionally be used in addition to the portion of pulse 1 corresponding to the period Δt1 to determine the separation distance from the background obstacle.

[0056] Regarding pulses 1 or 2 around the optical frequency ν1 or the optical frequency ν2 respectively, they are spectrally broad and exhibit a sharp increase in optical power that enables ranging measurements, followed by a slow and spectrally narrow reduction in optical power suitable for differential absorption measurements. In this regard, the second pulse sequence can be generalized. [[ID=ll]]

[0057] Regarding these two emission sequences, the first sequence follows [Figure 1a] and [Figure 1b], and the second sequence follows [Figure 2a] and [Figure 2b]. The following numerical values are shown as non-limiting examples: The pulse repetition frequency may be between 1 kHz (kilohertz) and 50 kHz, Δt1 may be between 50 ns and 100 ns, Δt2 may be between 0.5 μs and 5 μs, Δν1 may be between 500 MHz and 1000 MHz, Δν2 may be between 50 MHz and 100 MHz, P1 may be greater than 200 W, P2 may be greater than 50 W.

[0058] Therefore, the period Δt1 of the first time interval may be shorter than the period Δt2 of the second time interval. Furthermore, the first spectral width value Δν1 may be greater than the second spectral width value Δν2, and the first emission peak power value P1 may be greater than the second emission peak power value P2. Next, thanks to the amplified first spectral width value Δν1, the value P1 is distributed over a wider emission spectrum than where the value P2 is distributed. region For this reason, the value P1 may be greater than the stimulated Brillouin scattering threshold P corresponding to the optical fiber used to create the LIDAR system. Preferably, the value P2 may be selected to be below the stimulated Brillouin scattering threshold in order to limit the reduction in energy efficiency in the production of the emitted light released during the second time interval of the individual period Δt2. SBS

[0059] Several LIDAR system structures according to the present invention are described herein, which are designed to emit a sequence of emitted light as described above. The description of these structures is limited to the composition of their main components, and those skilled in the art are familiar with such commercially available components and will understand how to combine them with the described structures without difficulty or without any need for inventiveness. Furthermore, it should be understood that additional components that are used in these structures but are not directly related to the principles of the present invention and are commonly used are not described for the sake of clarity. For the manufacture of the optical components, electro-optical components, and interconnecting components used, it is advantageous to implement all of these LIDAR system structures described below using fiber optic technology or integrated optical circuit technology. In the figure showing the light emission path structure, reference numeral 50, denoted by CTRL, indicates a light emission control device connected to the components of the light emission path to generate a sequence of emitted light having desired characteristics. The control mode implemented by the light emission control device 50 falls within the scope of the ability of those skilled in the art once the sequence of emitted light to be generated is provided to them.

[0060] [Fig. 3a] shows a first feasible emission path structure for a LIDAR system according to the present invention, designed to generate an emission light sequence according to [Fig. 1a] and [Fig. 1b]. Reference numeral 10 indicates a laser source, generally called a laser oscillator, which can generate a continuous laser beam with an optical frequency ν1. It may be, for example, a laser diode or a fiber laser. The laser beam generated by the laser source 10 is emitted to pass through a phase modulator 11 denoted as MOD.PHASE, and a spectral width Δν1 is given to the laser beam. In this case, this is phase modulation outside the laser source. The phase modulator 11 may be, for example, an electro-optic modulator. A random generator of binary signals, usually known by the acronym PRBS of Pseudo-Random Binary Sequence, or a radio frequency noise generator of arbitrary waveforms, known by the acronym AWG of Arbitrary Waveform Generator, may be connected to the electrical control input of the phase modulator 11. The mode used between these alternative control modes of the phase modulator 11 is specified by reference 11c and denoted as GENERATOR. When using a PRBS generator, it generates phase jumps equal to -π or π in a random or pseudo-random sequence. Next, the output of the phase modulator 11 is preferably attached to an optical apodization filter (not shown) to remove a second lobe that can be generated in the spectrum of the radiation directly generated from the phase modulator 11 by such a spectral broadening method. When using an AWG generator, the generator may be programmed to generate various waveforms, such as a sequence of ramps where the slope varies randomly between successive ramps. Alternatively, it may be programmed to generate an electrical control signal that is a sine wave or a linear combination of several sine wave components. Alternatively, other forms of electrical control signals for the phase modulator 11 may be used, and those skilled in the art should understand how to select the characteristics of such electrical control signals to provide a desired spectral envelope waveform with a spectral width Δν1 for the emitted light emerging from the phase modulator 11.The generator 11c may be selectively activated by the light emission control device 50 to generate the pulse 1, or may be continuously activated. The reference numeral 20 indicates another laser source, that is, another laser oscillator, and this laser oscillator can generate another continuous laser beam having an optical frequency ν2 directly having a spectral width Δν2. For example, the laser source 20 may be of a fiber laser type. In fact, the spectral width Δν2 of the present invention is low and can be supplied directly or essentially by the laser source 20, that is, without using any particular additional dedicated components to generate the spectral width value. The two laser sources 10 and 20 constitute a laser source assembly as generally shown herein. Then, two emitted lights respectively generated from the phase modulator 11 and the laser source 20 are injected into two input portions of an optical switch 30 denoted as COMMUTATOR. This may be a 2×1 optical switch controlled by the light emission control device 50 so as to output the emitted light received at one or the other of the two input portions according to the desired order of going back and forth between the emitted light pulse of the optical frequency ν1 and the emitted light pulse of the optical frequency ν2 during the first time interval and / or the second time interval. Alternatively, the optical switch 30 may be replaced by, for example, an optical fiber Y coupler having a 50 / 50 intensity ratio and selectively having a fixed polarization, or may be replaced by, for example, a polarization coupler of a polarization beam splitter cube type. Then, the emitted light output from the optical switch 30 is introduced into an intensity modulator 31 denoted as MOD.INT. and is controlled by the light emission control device 50. This introduction and control are performed so that the emitted light finally emitted toward the measurement region has an instantaneous power value P1 during the period Δt1 of the first time interval when the optical frequency is closer to the value ν1 and an instantaneous power value P2 during the period Δt2 of the second time interval when the frequency is closer to the value ν2. The intensity modulator 31 may be of an electro-optic type, an electro-acoustic type, or a semiconductor optical amplifier type. As is known, such an intensity modulator may incorporate an internal control device or may be associated with an external control device inserted between the intensity modulator and the light emission control device 50.Next, the radiation light generated from the intensity modulator 31 is transmitted to an optical amplification assembly 32, denoted as AMPL., or an optical amplification chain 32, in order to actually generate the emission light power values P1 and P2. Finally, the radiation light generated from the optical amplification assembly 32 is transmitted to the measurement area by the output optical component 33 of the emission path of the LIDAR system, denoted as OPT.

[0061] Using at least one of the following equivalent principles, each applied to the emission path architecture of [Fig. 3a], several alternative architectures of the LIDAR system can be derived from the alternative architecture of [Fig. 3a]: If the laser source 10 is of a type capable of directly generating a laser beam at an optical frequency ν1 having a spectral width value Δν1, similar to the laser source 20 of [Fig. 3a] corresponding to the spectral width value Δν2, the phase modulator 11 may be omitted so that the laser beam generated from the laser source 10 can be directly transmitted to the optical switch 30. In this way, the configuration of [Fig. 3b] is obtained; If the laser source 10 is wavelength-variable, the electrical control signal used to impart the spectral width Δν1 to the radiation light emitted around the optical frequency ν1 may be directly applied to the control input of the wavelength-variable laser source 10. Such a mode of obtaining the desired spectral width is sometimes referred to as internal phase modulation, as opposed to the use of a phase modulator external to the laser source shown in [Fig. 3a]. An internally modulated laser source can be, for example, a laser diode capable of modulating the current injected into the gain region with a low modulation amplitude, or a distributed Bragg reflector diode, commonly known as a DBR diode, capable of modulating the injection with respect to the phase, grating, or semiconductor optical amplification region. Additionally, or alternatively, this method of obtaining the desired spectral width is intrinsic to the laser source and may be applied to the laser source 20, obtaining the spectral width Δν2 if the latter is adjustable. In this way, the configuration of [Fig. 3c] is obtained, where the references 11c and 21c indicate modulation signal generators connected to the respective control inputs of the wavelength-variable laser source 10 and the wavelength-variable laser source 20; Two separate external phase modulators may be used simultaneously, one used between the laser source 10 and the optical switch 30 to give the emitted radiation at the optical frequency ν1 a spectral width Δν1, as in the case of [Fig. 3a], and the other used between the laser source 20 and the optical switch 30 to give the emitted radiation at the optical frequency ν2 a spectral width Δν2. In this way, the configuration of [Fig. 3d] is obtained, where references 11 and 21 denote two external phase modulators associated with the laser sources 10 and 20 respectively, and references 11c and 21c denote phase modulation signal generators connected to the respective control inputs of these phase modulators 11 and 21; A single phase modulator can be effectively used for two emitted radiations separately generated at the optical frequencies ν1 and ν2 by the laser source 10 and the laser source 20. In this case, the laser beams from the two laser sources 10 and 20 are transmitted directly to the input of the optical switch 30, and the single phase modulator is located between the output of the optical switch 30 and the input of the intensity modulator 31. Then, this single phase modulator is controlled in one of the aforementioned ways to generate a spectral width Δν1 during a first time interval when the optical switch 30 transmits the emitted radiation having the optical frequency ν1, and to generate a spectral width Δν2 during a second time interval when the optical switch 30 transmits the emission having the optical frequency ν2. In this way, the configuration of [Fig. 3e] is obtained, where reference 34 denotes an external phase modulator common to the two emitted radiations at the optical frequencies ν1 and ν2, and the reference numeral 34c denotes a phase modulation signal generator connected to the control input of this phase modulator 34.

[0062] The embodiment of [FIG. 4a] can be obtained from the embodiment of [FIG. 3a] by modulating the intensity of the emitted light located around the optical frequencies ν1 and ν2 upstream of the combination of separate paths for generating the emitted light. The emitted light generation path located around the optical frequency ν1 is the same as that of [FIG. 3a], but an intensity modulator 12 is added. Similarly, the radiation generation path located around the optical frequency ν2 is the same as that of [FIG. 3a], but an intensity modulator 22 is added. The two intensity modulators 12 and 22 can be controlled by the light emission control device 50 in a manner temporally correlated with the modulation signal generated by the generator 11c. In particular, they generate a transmission time window that limits the first time interval of the individual period Δt1 and the second time interval of the individual period Δt2 to the desired repetition frequency. In such an embodiment, the separate emitted light generation paths located around the two optical frequencies ν1 and ν2 can be combined using a coupler 35 in the direction of the downstream portion of the emitted light path that is shared by the two optical frequencies and constitutes the optical amplification assembly 32. The coupler 35 may be a conventional Y coupler. Alternatively, it may be a polarization coupler that can impart a specific polarization to the emitted light transmitted during the first time interval of the individual period Δt1 and an orthogonal polarization to the emitted light transmitted during the second time interval of the individual period Δt2. For example, a linearly polarized light parallel to the fixed direction can be imparted to the emitted light transmitted during the first time interval of the individual period Δt1 by the polarization coupler 35, and a linearly polarized light perpendicular to the fixed direction can be imparted to the emitted light transmitted during the second time interval of the individual period Δt2 by the polarization coupler 35.

[0063] The embodiment of [FIG. 4b] can be obtained in the same manner as the embodiment of [FIG. 4a], but is based on the embodiment of [FIG. 3d] instead of the embodiment of [FIG. 3a]. By applying the same technique, one skilled in the art will be able to derive further possible embodiments, for example, by replacing the single intensity modulator in [FIG. 3b], [FIG. 3c], [FIG. 3e] with two intensity modulators specialized separately for the emitted light located around the two optical frequencies ν1 and ν2.

[0064] All embodiments of [FIG. 3a] to [FIG. 3e] and [FIG. 4a] to [FIG. 4b] are suitable for generating emission light sequences according to [FIG. 1a] and [FIG. 1b].

[0065] Unlike the embodiments of [FIG. 3a]-[FIG. 3e] and [FIG. 4a]-[FIG. 4b], in the embodiments of [FIG. 5a] and [FIG. 5b], the phase modulation used to separately obtain the desired spectral widths Δν1 and Δν2 during the intervals of period Δt1 and period Δt2 is shared at two optical frequencies ν1 and ν2. In this case, a single phase modulator can be used, and the single phase modulator is arranged downstream of an optical switch or an optical coupler, and the optical coupler groups together the beams separately arriving from two laser sources 10 and 20 in a shared downstream portion of the emission light path. Therefore, cost reduction of the LIDAR system can be achieved.

[0066] These embodiments of [FIG. 5a] and [FIG. 5b] are suitable for generating emission light sequences according to [FIG. 2a] and [FIG. 2b].

[0067] In the embodiment of [FIG. 5a], both the phase modulation and the intensity modulation are performed downstream of the coupling point of the optical paths of the emission light separately generated from the laser source 10 and. The coupling of the optical paths is executed by the switch 30, the phase modulation is generated by the phase modulator 34, and the intensity modulation is generated by the intensity modulator 31. The phase modulation signal generator 34c may also be of any type of PRBS generator, RF noise generator, or AWG generator. The switch 30, the phase modulation signal generator 34c, and the intensity modulator 31 can all be synchronously controlled by the emission control device 50.

[0068] In the embodiment of [[Fig. 5b]], the radiation light generated separately from laser sources 10 and 20 is intensity - modulated using two separate modulators indicated by references 12 and 22. The intensity - modulated radiation light emitted therefrom may be introduced by a coupler 35 in a shared downstream portion of the emission path. The coupler 35 may also be a Y - coupler or a polarization coupler as shown above. Next, the downstream portion of the emission path includes a phase modulator 34, an optical amplification assembly 32, and output optics 33.

[0069] [Fig. 6a] shows a first detection path architecture that can be used in a LIDAR system according to the present invention. Reference 40 indicates an input optic denoted as OPT. in the detection path. Their function is to collect a portion of the back - scattered radiation light corresponding to the emission light sequence generated by the LIDAR system. The portion of the radiation light thus collected is directed onto an optical sensor 43 denoted as DETECT.OPT. The optical sensor 43 generates an electrical detection signal, and the intensity of the electrical detection signal is a function of the power of the portion of the detected radiation light. The optical sensor 43 may operate in a direct - detection mode or a coherent - detection mode. An optical sensor for direct detection may be composed of, for example, a photodiode associated with a trans - impedance amplifier. An optical sensor for coherent detection, also called heterodyne detection, requires mixing the back - scattered radiation light collected by the input optic 40 with a portion of the radiation light generated by the laser source assembly. The electrical output of the optical sensor 43 is connected to the input of an analysis chain 512 denoted as ANALYS. The analysis chain 512 processes the electrical signals supplied by the sensor 43 regardless of whether each electrical signal corresponds to pulse 1 or 2.

[0070] [Fig. 6b] shows a second detection path architecture that uses two separate analysis chains specialized separately for radiation pulse 1 and radiation pulse 2. An electrical switch 44 labeled COMM.ELEC then sends the detection electrical signal to two separate analysis chains 51 and 52 labeled ANALYS.1 and ANALYS.2 based on detection electrical signals corresponding separately to the first time interval or the second time interval during the emission light sequence. For this purpose, the synchronization of the operation of the electrical switch 44 can be controlled by the emission control device 50. Thus, the analysis chain 51 may be specialized for the first time interval of the individual period Δt1, determine the residual absorption in the measurement region outside the spectral absorption band of the chemical compound whose amount is to be determined, and determine the separation distance from obstacles located in the background of the measurement region. Independently thereof, the analysis chain 52 may be specialized for the second time interval of the individual period Δt2 and designed to determine the absorption in the measurement region in the spectral absorption band of the chemical compound. A calculation module (not shown) generates an evaluation of the amount of the chemical compound as a function of the absorption levels determined by the two analysis chains 51 and 52 and the separation distance from the background obstacles.

[0071] [Fig. 6c] shows a third possible detection path architecture. In the third architecture, two optical sensors 41 and 42 denoted as DETECT.OPT.1 and DETECT.OPT.2 separately generate electrical detection signals that are separately transmitted to analysis chains 51 and 52. The advantage of the third architecture is that it is possible to use optical sensors 41 and optical sensor 42 with different sensitivity levels that separately match the respective instantaneous power values of the relevant portions of the backscattered radiation, i.e., P1 of the first time interval of the individual period Δt1 for sensor 51 and P2 of the second time interval of the individual period Δt2 for sensor 52. In this case, the backscattered radiation collected by the input optical component 40 is directed by the optical switch 45 to sensor 41 or sensor 42. The operation of the optical switch 45 is controlled by the light emission control device 50. Regarding the third detection path architecture, the coupler 35 of the light emission path may be of the Y-coupler type with a 50 / 50 ratio.

[0072] The three architectures of [Fig. 6a] - [Fig. 6c] representing the detection path are each compatible with the variant architectures of [Fig. 3a] - [Fig. 3e], [Fig. 4a] - [Fig. 4b], and [Fig. 5a] - [Fig. 5b] representing the light emission path.

[0073] Finally, [Fig. 6d] shows a fourth possible detection path architecture. In the fourth architecture, the optical switch 45 of [Fig. 6c] is replaced by a polarization beam splitter 46 based on the linear polarization of the emitted light denoted as SEP.POLAR. The fourth architecture representing the detection path is compatible with the embodiment for the light emission path where the coupler 35 is of the polarization coupler type as described above.

[0074] Typically, at least one optical sensor used in the optical sensor or detection path has a short response time to enable sufficiently estimating the separation distance from background obstacles based on the radiation emitted during the period Δt1.

[0075] In addition, the output of each analysis chain of the detection path may be connected to a calculation unit (not shown) integrated over the path of the pulse. The calculation unit is configured to supply an estimated value of the separation distance from the background obstacle and an estimated value of the amount of chemical compound present in the measurement area based on the signals generated by one or two analysis chains. Such a calculation unit may optionally be integrated into the LIDAR system.

[0076] It should be understood that the present invention can be reproduced while modifying the second aspect of the embodiment described in detail above, but still retaining at least some of the cited advantages. In particular, optical components having equivalent functions may be used instead of those described above. Furthermore, the following modifications are mentioned as examples of alternatives that do not have any inventive step available to those skilled in the art: One and the same optical frequency switching laser source may be used to generate pulses of optical frequencies ν1 and ν2; Separate optical amplifiers may be used for the pulses of optical frequency ν1 and the pulses of optical frequency ν2; The interleaving of the pulses of optical frequency ν1 and the pulses of optical frequency ν2 to generate the emission light sequence may be performed before or after applying phase modulation and / or intensity modulation to each pulse; The interleaving of the pulses of optical frequency ν1 and the pulses of optical frequency ν2 to generate the emission light sequence may be performed before or after the optical amplification of the pulses.

[0077] Finally, all the numerical values cited are for illustrative purposes only and may be changed according to the chemical compound for which the amount is determined.

Brief Description of the Drawings

[0078]

Figure 1a

Figure 1b

Figure 2a

Figure 2b

Figure 3a

Figure 3b

Figure 3c

Figure 3d

Figure 3e

Figure 4a

Figure 4b

Figure 5a

Figure 5b

Figure 6a

Figure 6b

Figure 6c

Figure 6d

Claims

1. Two separate optical frequencies (ν １ , ν ２ ), and a distance measurement from an obstacle present in the background of the measurement region where absorption occurs, the LIDAR system being configured to perform differential absorption measurement between The laser source assembly suitable for generating the emitted light at either of the two optical frequencies (ν １ , ν ２ ), and Pulse duration and pulse optical power values (P １ , P ２ ), and intensity modulation means configured to apply a pulse envelope shape including the above to each emitted light A light emission control device (50) configured to control the intensity modulation means, The LIDAR system is configured to emit a radiation emission sequence in a target direction in which differential absorption measurement and separation distance measurement from background obstacles are performed during operation of the LIDAR system, The radiation emission sequence is, The radiated light is spectrally located at a first optical frequency (ν1) of the two optical frequencies, and has a first spectral width (Δν １ ), a first pulse period (Δt １ ), and a first pulsed optical power value (P １ ), and a first time interval; The radiated light is spectrally located at a second optical frequency (ν2) among the two optical frequencies, and has a second spectral width (Δν ２ ), a second pulse period (Δt ２ ), and a second time interval having a second pulsed optical power value (P ２ ). The first spectral width (Δν １ ), and the second spectral width (Δν ２ ) are widths such that the emission light during the first time interval and the second time interval correspond to spectral regions that do not overlap with each other, and the first spectral width is larger than the second spectral width. The first pulse optical power value (P １ ) is larger than the second pulse optical power value (P ２ ). The first pulse period (Δt １ ) is shorter than the second pulse period (Δt ２ ), The first optical frequency (ν １ ), and the second optical frequency (ν ２ ), and further includes a detection path configured to independently detect, process, and analyze the backscattered radiation light corresponding to the light emissions during the first time interval and the second time interval, a LIDAR system.

2. The LIDAR system according to claim 1, further comprising spectral broadening means arranged to modify at least one spectral width of the radiation light generated by the laser source assembly (10, 20).

3. The light emission control device (50) is configured such that, in the emission light sequence, the first optical frequency (ν １ ) is exclusively associated with the first spectral width (Δν ２ ), the first pulse duration (Δt ２ ), and the first pulse optical power value (P ２ ) within the first emission light pulse (1), excluding the second spectral width (Δν １ ), the second pulse duration (Δt １ ), and the second pulse optical power value (P １ ); and the second optical frequency (ν ２ ) among the two optical frequencies is exclusively associated with the second spectral width, the second pulse duration, and the second pulse optical power value, excluding the first spectral width, the first pulse duration, and the first pulse optical power value, within a second emission light pulse (2) separated from the first pulse. The laser source assembly and the intensity modulation means are controlled, and the spectral broadening means is selectively controlled, as described in claim 1 or 2, of the LIDAR system.

4. The laser source assembly includes a first laser oscillator (10) configured to generate radiation light of the first optical frequency (ν １ ), and a second laser oscillator (20) configured to generate radiation light of the second optical frequency (ν ２ ) having the second spectral width (Δν ２ ). The spectrum broadening means is disposed in the path of the emitted light generated by the first laser oscillator (10), and the phase modulator (11) controlled by the light emission control device (50) is provided to provide the first spectral width (Δν １ ) to the laser emission light generated by the first laser oscillator. The LIDAR system according to claims 2 and 3, further comprising an optical switch (30) controlled by the light emission control device (50) so that either the radiation light generated from the phase modulator (11) or the radiation light generated by the second laser oscillator (20) is shared by the radiation light generated from the phase modulator and the radiation light generated by the second laser oscillator, and transmitted to a downstream portion of the light emission optical path including the intensity modulation means (31).

5. The laser source assembly includes a first laser oscillator (10) configured to generate the emitted light of the first optical frequency (ν １ ), and a second laser oscillator (20) configured to generate the emitted light of the second optical frequency (ν ２ ) having the second spectral width (Δν ２ ). The spectrum broadening means is disposed in the path of the emitted light generated by the first laser oscillator (10), and the first spectrum width (Δν １ ) is provided by the light emission control device (50) and includes a phase modulator (11) controlled thereby. The intensity modulation means includes a first intensity modulator (12) arranged in the path of the radiation light generated from the phase modulator (11) and controlled by the light emission control device (50) to exert an effect on the radiation light generated from the phase modulator, and a second intensity modulator (22) arranged in the path of the radiation light generated by the second laser oscillator (20) and controlled by the light emission control device to exert an effect on the radiation light generated by the second laser oscillator, The LIDAR system according to claims 2 and 3, further comprising an optical coupler (35) configured to transmit the radiation light generated from the first intensity modulator (12) and the second intensity modulator (22) to a downstream portion of the radiation optical path shared by the radiation light generated from the first intensity modulator and the radiation light generated from the second intensity modulator.

6. The light emission control device (50) is such that the emission light sequence includes a series of emission light pulses spectrally located at either the first optical frequency (ν １ ), or the second optical frequency (ν ２ ), and all the emission light pulses have the same envelope shape including a first period (Δt １ ) in which the emission light has the first spectral width (Δν １ ) and a first optical power value (P １ ), and a second period (Δt ２ ) in which the emission light has the second spectral width (Δν ２ ) and a second optical power value (P ２ ), the first period being shorter than the second period and being before or after the second period in each emission light pulse, and is configured to control the laser source assembly, the spectral broadening means, and the intensity modulation means, the LIDAR system according to claim 2.

7. The LIDAR system according to any one of claims 1 to 6, implementing optical fiber technology.

8. The LIDAR system includes polarization means (35) configured to have orthogonal polarization when the radiation light emitted toward the measurement region by the LIDAR system is emitted during the first time interval or the second time interval. The detection path is a first detector (41) with high sensitivity in a first spectral region including the first optical frequency (ν １ ), which is combined with the first spectral width (Δν １ ), or a second detector (42) with high sensitivity in a second spectral region including the second optical frequency (ν ２ ), which is combined with the second spectral width (Δν ２ ). The LIDAR system according to any one of claims 1 to 7 includes a polarization beam splitter (46) configured to transmit the backscattered radiation in accordance with the polarization of the backscattered radiation.

9. A method for measuring the amount of a chemical compound present in a target direction, The chemical compound has a lower absorption ability value at the first optical frequency (ν ２ ) than at the second optical frequency (ν １ ), and the LIDAR system according to any one of claims 1 to 8 is selected, the LIDAR system is directed in the target direction to emit light in accordance with the emission light sequence towards a measurement area that may contain the chemical compound, and the operation of the LIDAR system is induced, The separation distance from the obstacle present in the background of the measurement area is related to the first optical frequency (ν １ ) and is estimated based on the backscattered radiation corresponding to the light emission during the first time interval. The amount of chemical compound included in the measurement region, integrated over the path of the pulse between the LIDAR system and the background obstacle, is the first optical frequency (ν １ ), corresponding respectively to the first time interval and the second time interval in the emission sequence, and the intensity value separately associated with the backscattered radiation at the second optical frequency (ν ２ ), and the backscattered radiation is detected by the detection path of the LIDAR system.

10. The separation distance from the obstacle present in the background of the measurement area is estimated based on the elapsed time measured with respect to the backscattered radiation associated with the first optical frequency (ν １ )), the method according to claim 9.

11. The separation distance from the obstacle present in the background of the measurement region, estimated based on the backscattered radiation related to the first optical frequency (ν １ ), is separately related to the backscattered radiation detected at the first optical frequency and the second optical frequency (ν ２ ), and is combined with the intensity values corresponding to the light emission during the first time interval and the light emission during the second time interval, respectively, and is used to estimate the amount of the chemical compound contained in the measurement region. The method according to claim 10.

12. The method according to any one of claims 9 to 11, wherein the chemical compound is any one of carbon dioxide, methane, nitrous oxide, and water.

13. the LIDAR system is installed on the ground surface and is directed to measure the amount of the chemical compound present between the LIDAR system and the obstacle, or alternatively, the LIDAR system is mounted on an aircraft in flight, measures the separation distance from the ground surface of a geographical area to the LIDAR system, and is directed towards the geographical area of the ground surface to measure the amount of the chemical compound present between the LIDAR system and the ground surface within the geographical area, or alternatively, the LIDAR system measures the separation distance from the ground surface of a geographical area to the LIDAR system and is mounted on a satellite in orbit around the Earth and directed towards the geographical area of the ground surface to measure the amount of the chemical compound present between the LIDAR system and the ground surface of the geographical area, The method according to any one of claims 9 to 12.

Images