Measurement of Speed or Vibration Characteristics Using a Lidar Device with Heterodyne Detection
First Claim
Patent Images
1. Process for measuring a speed or vibration characteristic which uses a LIDAR device with heterodyne detection, wherein an optical wave emission signal is emitted from an optical head of said device in the direction of a target volume, and a backscattered signal is collected by said optical head then is detected by heterodyne detection so as to produce a heterodyne detection signal,said process comprising the following steps for a measurement cycle:
- /1/ producing a modulation of a phase characteristic of the optical wave in the emission signal,/2/ demodulating the heterodyne detection signal relative to the modulation of the phase characteristic, with compensating for a propagation delay of the emission signal and backscattered signal between the optical head of the device and the target volume,/3/ combining a spectral analysis of the demodulated heterodyne detection signal with an accumulation over successive analysis time windows, so as to isolate a contribution to the heterodyne detection signal coming from the target volume, and/4/ obtaining a result for the speed or vibration characteristic measurement, from a Doppler analysis of the contribution isolated in step /3/,and wherein;
the modulation is obtained by shifting the phase characteristic of the optical wave during successive modulation time slots, by a fixed increment which is multiplied by factors q respectively assigned to said modulation time slots,the factors q are determined according to one of the two following methods /i/ or /ii/, with only one of said methods used during the entire measurement cycle;
/i/ the scale factors q are equal to b+ap[n], where for said method method /i/;
n is an integer greater than or equal to four, and is constant during the measurement cycle,a and b are two other integers, which are also constant during the measurement cycle,p is an exponent integer which is positive or zero and is strictly less than φ
(n), where φ
is a Euler'"'"'s totient function, and p has varying values which are respectively assigned to the modulation time slots,b+ap[n] indicates the b+ap modulo n reduction, anda is selected such that a[n] is not zero or one,/ii/ the factors q are equal to d+c·
(p+1)·
p/2 [n], where for said method /ii/;
n is an integer greater than or equal to four, and is constant during the measurement cycle,d and c are two integers, which are also constant during the measurement cycle,p is an integer factor of variation which is positive or zero, strictly less than n, and with varying values respectively assigned to the modulation time slots,d+c·
(p+1)·
p/2 [n] designates the d+c·
(p+1)·
p/2 modulo n reduction, andc is selected such that c[n] is not zero.
1 Assignment
0 Petitions
Accused Products
Abstract
A process for measuring speed or vibration characteristics using a LIDAR device allows the separation of a useful contribution and an interfering contribution in a backscattered signal. To this purpose, a phase characteristic of an optical wave emitted in the direction of a target volume is modulated. The interfering contribution, which originates from a source at a distance from the target volume, appears with variable shifts of said phase characteristic in a heterodyne detection signal. An accumulation then isolates the useful contribution, from which a result is obtained for the speed or vibration measurement. The process can be implemented with a frequency modulation or phase modulation of the optical wave.
32 Citations
23 Claims
-
1. Process for measuring a speed or vibration characteristic which uses a LIDAR device with heterodyne detection, wherein an optical wave emission signal is emitted from an optical head of said device in the direction of a target volume, and a backscattered signal is collected by said optical head then is detected by heterodyne detection so as to produce a heterodyne detection signal,
said process comprising the following steps for a measurement cycle: -
/1/ producing a modulation of a phase characteristic of the optical wave in the emission signal, /2/ demodulating the heterodyne detection signal relative to the modulation of the phase characteristic, with compensating for a propagation delay of the emission signal and backscattered signal between the optical head of the device and the target volume, /3/ combining a spectral analysis of the demodulated heterodyne detection signal with an accumulation over successive analysis time windows, so as to isolate a contribution to the heterodyne detection signal coming from the target volume, and /4/ obtaining a result for the speed or vibration characteristic measurement, from a Doppler analysis of the contribution isolated in step /3/, and wherein; the modulation is obtained by shifting the phase characteristic of the optical wave during successive modulation time slots, by a fixed increment which is multiplied by factors q respectively assigned to said modulation time slots, the factors q are determined according to one of the two following methods /i/ or /ii/, with only one of said methods used during the entire measurement cycle; /i/ the scale factors q are equal to b+ap[n], where for said method method /i/; n is an integer greater than or equal to four, and is constant during the measurement cycle, a and b are two other integers, which are also constant during the measurement cycle, p is an exponent integer which is positive or zero and is strictly less than φ
(n), where φ
is a Euler'"'"'s totient function, and p has varying values which are respectively assigned to the modulation time slots,b+ap[n] indicates the b+ap modulo n reduction, and a is selected such that a[n] is not zero or one, /ii/ the factors q are equal to d+c·
(p+1)·
p/2 [n], where for said method /ii/;n is an integer greater than or equal to four, and is constant during the measurement cycle, d and c are two integers, which are also constant during the measurement cycle, p is an integer factor of variation which is positive or zero, strictly less than n, and with varying values respectively assigned to the modulation time slots, d+c·
(p+1)·
p/2 [n] designates the d+c·
(p+1)·
p/2 modulo n reduction, andc is selected such that c[n] is not zero. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
with the device additionally comprising; a phase modulator arranged to modulate at least the emission source signal, a control unit, connected to a control input of the phase modulator and adapted to control an operation of said phase modulator to implement a process according to claim 1, and means for compensating for a propagation delay of the emission signal and backscattered signal between the optical head and the target volume.
-
-
20. Device according to claim 19, wherein the phase modulator comprises a Pockels cell, or four Pockels cells arranged to form a Dual Parallel Mach-Zehnder modulator.
-
21. Device according to claim 19, wherein the phase modulator is arranged to receive as input the emission source signal produced by the optical splitter, and to output said emission source signal modulated to the optical amplifier, with the device additionally comprising demodulation means arranged for demodulating the heterodyne detection signal in accordance with the operation of the phase modulator, the delay compensation means being arranged to compensate for the propagation delay in the emission signal and in the backscattered signal during demodulation.
-
22. Device according to claim 19, wherein the phase modulator is arranged to receive as input the optical wave produced by the laser oscillator, and to output said optical wave modulated to the optical splitter, so that the emission source signal and the reference signal are modulated in an identical manner, the delay compensation means being arranged to delay the reference signal sent to the mixing and detection unit.
-
23. Process according to claim 6, wherein the factors q are determined according to method /i/, and wherein the integer a is a primitive root of a quotient group (Z/nZ)* under multiplication, where Z is the ring of integers and * indicates that the zero value is excluded, the factors q being φ
- (n) distinct values for p varying from 0 to φ
(n)−
1.
- (n) distinct values for p varying from 0 to φ
Specification
-
- Resources
Litigation Campaign Assessment
Thank you for your request. You will receive a custom alert email when the Litigation Campaign Assessment is available.
×
-
Current AssigneeOffice National D'Etudes et de Recherches Aerospatiales
-
Original AssigneeOffice National D'Etudes et de Recherches Aerospatiales
-
InventorsValla, Matthieu, Augere, Beatrice, Besson, Claudine
-
Granted Patent
-
Time in Patent OfficeDays
-
Field of Search
-
US Class Current356/28.5
-
CPC Class CodesG01F 1/661 using lightG01F 1/663 by measuring Doppler freque...G01P 5/26 by measuring the direct inf...G01S 17/58 Velocity or trajectory dete...
