US-12625272-B2 - Detection and telemetry by electromagnetic radiation pulses

US12625272B2US 12625272 B2US12625272 B2US 12625272B2US-12625272-B2

Abstract

A process and system for detection and telemetry using electromagnetic radiation pulses allows characterization of a radial velocity distribution as a function of a separation distance within an exploration zone. An impulse response from the system is used for decomposing a measurement signal which is collected for each acquisition sequence performed for a useful measurement. The result of the decomposition includes an estimate of the radial velocity distribution as a function of the separation distance.

Inventors

David Tomline MICHEL
Laurent Mugnier
Matthieu Valla

Assignees

OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AÉROSPATIALES

Dates

Publication Date: 20260512
Application Date: 20210423
Priority Date: 20200506

Claims (18)

1 . A detection and telemetry process using electromagnetic radiation pulses, in order to characterize a radial velocity distribution as a function of a separation distance within an exploration zone, comprising the following steps: 1) getting a system for detection and telemetry by using electromagnetic radiation pulses, that is adapted for, during an acquisition sequence, emitting at least one electromagnetic radiation pulse, detecting a portion of said at least one radiation pulse which was backscattered by at least one target present in the exploration zone, and producing a measurement signal which corresponds to the backscattered and detected radiation pulse portion, where said measurement signal contains information on a separation distance and a radial velocity of each target, the information on the radial velocity of each target corresponds to a frequency shift due to a Doppler effect which occurs when the radiation is backscattered by this target; and 2) performing an acquisition sequence by controlling the system for emitting the at least one pulse into the exploration, wherein the process further comprises the following additional steps: 3) getting a characterization of an impulse response of the system, where the impulse response corresponds to the measurement signal which is produced by said system during an acquisition sequence and when a single backscattering element is in the exploration zone, said single backscattering element corresponding to a single separation distance value and having a known radial velocity value relative to the system, and when the exploration zone has no backscattering element other than the so-called single backscattering element; and 4) by treating the measurement signal which was produced in step 2) as a sum of contributions which each correspond to the impulse response applied to a value for the separation distance and to a value for the radial velocity, and multiplied by a backscattering amplitude value, getting by decomposition of the measurement signal into several contributions, a measurement result in a form of pairs which are each comprised of a backscattering amplitude value and a radial velocity value, and which are assigned respectively to several separation distance values within the exploration zone.
2 . The process according to claim 1 , wherein the impulse response is a function of both the separation distance, or round-trip time of the radiation from an optical outlet of the system, and also of one among: a spectral component frequency of the radiation pulse portion which was backscattered and then detected by the system; a frequency shift between a spectral component of the radiation pulse portion which was backscattered and then detected by the system, and the radiation of each pulse as emitted by said system, or a radial velocity value associated with said frequency shift by the Doppler effect; and a frequency of a spectrum of the measurement signal which is used in step 3).
3 . The process according to claim 1 , wherein the characterization of the impulse response is obtained in step 3) by performing at least one acquisition sequence with the detection and telemetry system by using electromagnetic radiation pulses, and with a single backscattering element which is positioned at a determined separation distance in the exploration zone, or by performing a numerical simulation of operation of the system when a single backscattering element is present at a determined separation distance in the exploration zone.
4 . The process according to claim 1 , wherein the detection and telemetry system by using electromagnetic radiation pulses is adapted for implementing a heterodyne detection mode, and the measurement signal which is produced at each acquisition sequence and which is used in step 4), is a heterodyne measurement signal.
5 . The process according to claim 1 , wherein the detection and telemetry system by using electromagnetic radiation pulses is of LIDAR type and the radiation of each pulse emitted by said system is a laser radiation, or the detection and telemetry system by using electromagnetic radiation pulses is of RADAR type and the radiation of each pulse emitted by said system has a vacuum wavelength comprised between 1 mm and 7.5 mm.
6 . The process according to claim 5 , wherein the detection and telemetry system by using electromagnetic radiation pulses is of LIDAR type, and wherein each radiation pulse has at least one of the following features: a radiation wavelength inside the pulse is comprised between 250 nm and 10 μm; a duration of the pulse is comprised between 50 ns and 1 μs; and the pulse has a frequency width at half-maximum which is less than 1 GHz.
7 . The process according to claim 1 , wherein the measurement result is deduced from the measurement signal in step 4) by applying a two-dimensional decomposition algorithm which uses a method selected in the list comprising a a-posteriori maximum method, a maximum likelihood method, and a stochastic method.
8 . The process according to claim 7 , further comprising an additional step which is executed from the measurement result provided by the two-dimensional decomposition algorithm, in order to reduce widths of radial velocity distributions which are separately assigned to several values of the separation distance in the exploration zone.
9 . The process according to claim 1 , wherein step 4) includes assigning a single radial velocity value and a single backscattered amplitude value to each value of the separation distance, for a sampling of values of the separation distance inside the exploration zone, and then calculating a reconstruction of the measurement signal as a sum of contributions each equal to the impulse response applied to a separation distance value and to the radial velocity value which was assigned to said separation distance value, and multiplied by the backscattered amplitude value which was also assigned to the same separation distance value, for all the separation distance values in the sampling, and then performing a series of iterative adjustments of the assigned radial velocity and backscattered amplitude values, so as to reduce a deviation between the measurement signal which was produced in step 2) and the reconstruction of the measurement signal resulting from the values assigned to the radial velocity and backscattered amplitude, wherein the measurement result is then formed by the radial velocity and backscattered amplitude values assigned to the separation distance values, which provide a minimum deviation between the measurement signal and the reconstruction of the measurement signal.
10 . The process according to claim 1 , used for at least one of the following applications: meteorological measurements; measurements of diffusion of atmospheric pollutants; measurements of local concentration of backscattering particles suspended in an environment, or of chemical compounds which absorb and re-emit the radiation of the pulses; measurements of shearing of an atmospheric flow; measurements of position and/or lifetime of at least one vortex which is present in a fluid flow; anemometric measurements which are performed from an aircraft in flight; anemometric measurements which are performed to optimize operation of a wind turbine; and anemometrical measurements which are performed for adjusting aircraft flight in formation, or for adjusting a drone flight.
11 . The process according to claim 2 , wherein the characterization of the impulse response is obtained in step 3) by performing at least one acquisition sequence with the detection and telemetry system by using electromagnetic radiation pulses, and with a single backscattering element which is positioned at a determined separation distance in the exploration zone, or by performing a numerical simulation of operation of the system when a single backscattering element is present at a determined separation distance in the exploration zone.
12 . The process according to claim 2 , wherein the detection and telemetry system by using electromagnetic radiation pulses is adapted for implementing a heterodyne detection mode, and the measurement signal which is produced at each acquisition sequence and which is used in step 4), is a heterodyne measurement signal.
13 . The process according to claim 3 , wherein the detection and telemetry system by using electromagnetic radiation pulses is adapted for implementing a heterodyne detection mode, and the measurement signal which is produced at each acquisition sequence and which is used in step 4), is a heterodyne measurement signal.
14 . The process according to claim 2 , wherein the detection and telemetry system by using electromagnetic radiation pulses is of LID AR type and the radiation of each pulse emitted by said system is a laser radiation, or the detection and telemetry system by using electromagnetic radiation pulses is of RADAR type and the radiation of each pulse emitted by said system has a vacuum wavelength comprised between 1 mm and 7.5 mm.
15 . The process according to claim 3 , wherein the detection and telemetry system by using electromagnetic radiation pulses is of LID AR type and the radiation of each pulse emitted by said system is a laser radiation, or the detection and telemetry system by using electromagnetic radiation pulses is of RADAR type and the radiation of each pulse emitted by said system has a vacuum wavelength comprised between 1 mm and 7.5 mm.
16 . The process according to claim 4 , wherein the detection and telemetry system by using electromagnetic radiation pulses is of LID AR type and the radiation of each pulse emitted by said system is a laser radiation, or the detection and telemetry system by using electromagnetic radiation pulses is of RADAR type and the radiation of each pulse emitted by said system has a vacuum wavelength comprised between 1 mm and 7.5 mm.
17 . The process according to claim 2 , wherein the measurement result is deduced from the measurement signal in step 4) by applying a two-dimensional decomposition algorithm which uses a method selected in the list comprising a a-posteriori maximum method, a maximum likelihood method, and a stochastic method.
18 . The process according to claim 3 , wherein the measurement result is deduced from the measurement signal in step 4) by applying a two-dimensional decomposition algorithm which uses a method selected in the list comprising a a-posteriori maximum method, a maximum likelihood method, and a stochastic method.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is the U.S. national phase of International Application No. PCT/FR2021/050711 filed Apr. 23, 2021 which designated the U.S. and claims priority to FR Patent Application No. 20 04482 filed May 6, 2020, the entire contents of each of which are hereby incorporated by reference. FIELD OF THE INVENTION The present description relates to a process and a system for detection and telemetry by electromagnetic radiation pulses, in particular for conducting anemometric measurements. DESCRIPTION OF RELATED ART Systems for detection and telemetry by using electromagnetic radiation pulses are used for many applications, in particular for characterizing fluid flows. The radiation pulses are emitted towards an exploration zone which could contain one or more targets to be characterized, and a portion of each pulse which is backscattered or retroreflected by each target is detected by the system on return. In the case of a fluid flow to be characterized, the targets are comprised of backscattering particles which are present in suspension in the fluid, and which are driven into movement in accordance with the velocity of the fluid at each location in the exploration zone. For atmospheric flows, the targets are comprised of aerosol droplets, dust, ice grains, etc. which are suspended in the air. Such systems for detection and telemetry by using electromagnetic radiation pulses can be of LIDAR (“Light Detection and Ranging”) type or RADAR type (“Radio Detection and Ranging”). For LIDAR systems, the emitted radiation is of laser type, where the frequency of this radiation is commonly comprised between about 30 THz (terahertz) and 1200 THz, corresponding to wavelengths comprised between about 250 nm (nanometer) and 10 μm (micron). For RADAR systems, the radiowave frequency used is commonly of between 3 MHz (megahertz) and 300 GHz (gigahertz). High-frequency RADAR systems correspond to radiation wavelengths which are of between 1 mm (millimeter) and 7.5 mm, typically. The use of such systems for characterizing a single target, or few targets, each with a separation distance value and a radial velocity value is well known when the number of targets simultaneously contributing to the measurement signal is small, and/or the respective separation distance and radial velocity values of the targets are well separated from each other. But in the case of characterizing fluid flows, the backscattering targets are continuously distributed in the exploration zone involved with each measurement and have continuously varying radial velocity values. The determination of the radial velocity distribution as a function of the separation distance is then much more difficult. A known method for determining the radial velocity distribution as a function of the separation distance, by using an electromagnetic radiation pulse detection and telemetry system, consists in calculating the intensity of the detected radiation for each detection instant and for each emitted radiation pulse. To this purpose, the contributions from parts of the content of the exploration zone which correspond to a same value of detection time of the backscattered radiation, after a round trip of the radiation between the system and each part of the content, are added. This calculation method uses a “laminated model,” wherein the exploration zone is cut into successive spatial slices depending on the separation distance, and a single radial velocity value is associated with each spatial slice. Backscattered radiation intensities are thus calculated for several possible radial velocity distributions as a function of the separation distance, and then the one of these distributions which best corresponds to the backscattered radiation which was actually detected is accepted as the measurement result. However, such a measurement method has the following disadvantages: contributions to the backscattered radiation which correspond to a same emitted pulse, but to portions of this pulse which were emitted at different times and backscattered from different separation distances in the exploration zone, are detected at the same time. For this reason, the spatial resolution obtained by such method is of the order of C·τ/2, where C is the propagation speed of the radiation outside of the detection and telemetry system, and τ is the duration of each pulse. In other words, spatial resolution finer than C·τ/2 is not possible with a laminated model method; andbecause the radial velocity value of the targets is deduced from the frequency of the backscattered radiation which is detected, it can only be estimated based on an analysis of this backscattered radiation which is limited to within a time window. Since this time window is generally selected in order to have a duration which is equal to that of the emitted laser radiation pulse, it then follows that the spatial resolution is of order C·τ; andin order to get a spatial resolution wh