CN110940992B - Signal detection method and system capable of improving detection distance and precision of laser radar - Google Patents
Signal detection method and system capable of improving detection distance and precision of laser radar Download PDFInfo
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- CN110940992B CN110940992B CN201911062137.9A CN201911062137A CN110940992B CN 110940992 B CN110940992 B CN 110940992B CN 201911062137 A CN201911062137 A CN 201911062137A CN 110940992 B CN110940992 B CN 110940992B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
Abstract
The invention belongs to the technical field of laser ranging, and particularly relates to a signal detection method and a signal detection system capable of improving the detection distance and precision of a laser radar. The method combines a photon counting technology and a weak signal detection technology, and comprises non-periodic multi-pulse averaging and autocorrelation detection; the specific process is as follows: when the reflected light signal reaches the laser radar, the stray light is filtered by a narrow-band filter, and then photon counting amplification is carried out by adopting a photon counting technology; non-periodic multi-pulse averaging is carried out, namely multi-pulse accumulation averaging is carried out according to the pulse period; the time interval of the start-stop pulse is measured using a pulse autocorrelation detection method. The system comprises a pulse laser, a photon counter, a multi-time averaging module, an autocorrelation detector and the like; the multiple-time averaging module is used for non-periodic multiple-pulse averaging calculation, and the autocorrelation detector is used for autocorrelation operation to obtain a termination pulse signal. The invention can realize long-distance and high-precision target detection.
Description
Technical Field
The invention belongs to the technical field of laser ranging, and particularly relates to a signal detection method and a signal detection system capable of improving detection distance and accuracy of a laser radar.
Background
The method has a large application space in scientific research fields such as astronomy, military and the like, particularly in the field of space detection, the distance measurement is usually long (hundreds of kilometers to tens of thousands of kilometers), and most of the targets to be detected are space satellites without cooperative targets. Due to the diffuse reflection characteristic of the satellite, the received ranging pulse is very weak and is difficult to directly detect, so that the ranging of the non-cooperative satellite becomes a hot spot of modern space detection.
For extended targets, the range equation for lidar is given by:
in the formula: pr is the target reflected laser power received by the laser radar; pt is laser emission power; r is the distance from the target to the laser range finder; d is the effective optical receive aperture; τ o is the optical efficiency of the receiving optical path of the laser range finder; τ a is the two-way atmospheric transmittance.
The signal output by the amplifier is:
Vs＝GRvPr
in the formula: g is the amplifier gain; rv is the voltage responsivity of the detector.
Therefore:
from the above formula, it can be seen that the detection distance of the laser range finder is mainly related to the laser emission energy, the effective receiving optical aperture, the gain of the amplifier and the signal voltage. Since the instrument is often limited by volume, mass, and power consumption, the energy and optical aperture of the laser cannot be increased indefinitely. This requires trying to increase the gain of the amplifier and minimize the output signal strength with limited laser power and optical aperture. Generally, when the required detection rate is greater than 95%, the signal-to-noise ratio (the ratio of the signal to the noise root mean square) cannot be lower than 10, so that the weak signal detection technology is used to make the noise unchanged (or smaller) when the gain of the amplifier is increased, so as to increase the dynamic range of the signal, thereby improving the sensitivity of the laser radar.
There are many methods for weak signal detection, such as filtering, modulation amplification, phase-locked amplification, correlation, accumulation, etc. The modulation amplification and phase-locked amplification technology is mainly used for detecting the amplitude and the phase of a sinusoidal signal submerged in noise, and the phase-locked amplifier is useless for a weak laser pulse signal submerged in the noise. Because the fast rising edge and the fast falling edge of the pulse waveform contain abundant high-order harmonic components, the narrow-band filter of the output stage of the phase-locked amplifier filters out these high-frequency components, resulting in the distortion of the pulse waveform. Suitable methods for processing the pulse signal include multi-pulse accumulation, autocorrelation detection, correlated double sampling, and the like.
Disclosure of Invention
The invention aims to provide a signal detection method capable of improving the detection distance and the detection precision of a laser radar so as to realize long-distance and high-precision target detection.
The invention provides a signal detection method capable of improving the detection distance and precision of a laser radar, which combines a photon counting technology and a weak signal detection technology and comprises the following steps: aperiodic multi-pulse averaging and autocorrelation detection; the specific process is as follows:
(1) when the reflected light signal reaches the laser radar, the stray light is filtered by a narrow-band filter, and then photon counting amplification is carried out by adopting a photon counting technology;
(2) non-periodic multi-pulse averaging is carried out, namely multi-pulse accumulation averaging is carried out according to the pulse period;
(3) the time interval of the start-stop pulse is measured using a pulse autocorrelation detection method.
In the present invention, the multi-pulse cumulative averaging (see fig. 2) is performed, and the calculation formula is as follows:
wherein: m is the average number of times; delta TjThe jth pulse interval time.
The invention adopts non-periodic multi-pulse averaging, can effectively reduce noise signals and is beneficial to improving the signal-to-noise ratio.
In the present invention, the multi-pulse autocorrelation detection is performed by performing a correlation operation on an original pulse signal and a multi-pulse average signal (see fig. 2), and a calculation formula is as follows:
wherein: x (n) original pulse signal; y (n) is a multipulse average signal; and N is the pulse width.
The invention adopts a multi-pulse autocorrelation detection method, can effectively filter out interference signals and accurately extract rising edge signals.
In the invention, the photon counting technology is adopted, and the specific contents are as follows: counting photons within the integration time is a discrete random variable, subject to a poisson distribution:
in the formula: kn represents the average photon number.
Since the photon detection for each integration interval is still a random process and independent of each other, the detection process for summing the N integration intervals still follows a poisson distribution, except that the mean and variance become NKn, with a signal probability density and a noise probability density of:
the signal-to-noise ratio is:
for photon counting systems, the signal-to-noise ratio can be improved by using a multi-pulse averaging method
And (4) doubling.
Corresponding to the method, the invention also relates to a signal detection system capable of improving the detection distance and the detection precision of the laser radar, and the structure of the signal detection system is shown in figure 1. The signal detection system includes: the system comprises a pulse laser 1, a first lens 2, a second lens 4, a narrow-band filter 5, a photon counter 6, a non-periodic multi-pulse averaging module (namely a multi-averaging module) 7, an autocorrelation detector 8, a beam splitter 9 and a sampling detector 10; the pulse laser 1 emits non-periodic multi-pulse laser, and the non-periodic multi-pulse laser is collimated by the first lens 2 and then reflected by a far target 3; the second lens 4 receives the reflected signal, the reflected signal is filtered by the narrow band filter 5, and the photon counter 6 receives the reflected signal and performs counting and amplification; then the non-periodic multi-pulse average module 7 is entered to perform non-periodic multi-pulse average calculation (from formula (1)), the calculation result and the initial pulse signal output by the sampling detector 10 are entered into the correlation detector 8 together to perform autocorrelation operation (from formula (1)), and the termination pulse signal is obtained.
The photon counter consists of an avalanche diode array working in a Geiger mode, and has the characteristics of high gain, high sensitivity, low bias voltage, insensitivity to a magnetic field, compact structure and the like.
According to the invention, the correlation detector can effectively filter out interference signals and accurately extract rising edge signals.
The invention has the beneficial effects that:
by utilizing an accumulation method, although the performance-to-noise ratio is improved, the accumulation of multiple pulses widens the width of a starting pulse and a terminating pulse, and reduces the precision of distance measurement, aiming at the situation, a pulse autocorrelation detection method is adopted to filter out interference signals and atmospheric turbulence influence, the time interval of the starting pulse and the terminating pulse is measured, the sensitivity of the distance measurement is in direct proportion to the square root of the average number of times, and the precision of the distance measurement can be improved by 3-4 times.
Drawings
Fig. 1 is a schematic representation of the signal detection system of the present invention (lidar signal processing block diagram).
FIG. 2 is a schematic diagram of an aperiodic multi-pulse averaging technique.
Fig. 3 is a schematic diagram of an autocorrelation detection technique.
Reference numbers in the figures: the system comprises a pulse laser 1, a first lens 2 and a target 3, a second lens 4, a narrow-band filter 5, a photon counter 6, a multi-averaging module 7, a correlation detector 8, a beam splitter 9 and a sampling detector 10.
Detailed Description
The present invention is further illustrated by the following figures and specific examples, which are to be understood as illustrative only and not as limiting the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalent modifications thereof which may occur to those skilled in the art upon reading the present specification.
Example (b):
the invention mainly utilizes the method of combining pulse flight time with photon counting detection to develop the measurement experiment of long-distance target laser ranging. The optical caliber of the experimental system is 100 mm; the photon counter is C14193-1325SA produced by the Nippon Hamamatsu company; detecting the target distance to be 1 km; the bandwidth of the narrow-band filter 5 is 10nm, and the transmittance is 80%.
As shown in fig. 1, a distance measuring laser 1 adopts a semiconductor laser, the output wavelength is 905nm, the pulse power is 75W, the pulse width is 20ns, two laser beams are formed through a beam splitter, one laser beam irradiates a target and serves as a distance measuring light source, the other laser beam enters a sampling detector 10, the laser emitted to the target is reflected by the target and then enters a photon counter 6 through a receiving lens 4 and a narrow band filter 5, and a receiving signal is formed. Data were observed and collected using an oscilloscope (Agilent MSO7104B 1G bandwidth, 4G sampling rate). Referring to fig. 2, the measurement is repeated for a plurality of times, the data collected by the oscilloscope is derived, and the data is processed by the computer.
The multi-pulse signals are subjected to integration accumulation and then average calculation, and the calculation formula is as follows:
the sampled pulse signal and the multi-pulse average signal are correlated (see fig. 3), and the calculation formula is as follows:
wherein: x (n) sampling the pulse signal; y (n) is a multipulse average signal; and N is the pulse width.
Experiments show that the minimum resolvable signal amplitude is 0.5V under the condition of not using the correlation detection, the minimum resolvable signal amplitude can be improved by 10 times after the correlation detection is used, and the minimum resolvable signal amplitude can be improved by 10 times according to a laser ranging formula
The distance measurement precision obtained by calculation can be improved by 3-4 times.
The method combines the non-periodic accumulation averaging method and the correlation detection method, thereby not only improving the sensitivity of distance measurement, but also improving the precision of distance measurement; theories and experiments show that the distance measurement sensitivity is in direct proportion to the square root of the accumulation times, and the distance measurement precision can be improved by 3-4 times.
Claims (2)
1. A signal detection method capable of improving detection distance and precision of a laser radar is characterized in that a photon counting technology and a weak signal detection technology are combined, and the method comprises the following steps: non-periodic multi-pulse averaging and correlation detection; the specific process is as follows:
(1) when the reflected light signal reaches the laser radar, the stray light is filtered by a narrow-band filter, and then photon counting amplification is carried out by adopting a photon counting technology;
(2) non-periodic multi-pulse averaging is carried out, namely multi-pulse accumulation averaging is carried out according to the pulse period; the calculation formula is as follows:
wherein: m is the average number of times; delta TjThe j-th pulse interval time;
(3) measuring the time interval of the start-stop pulse by adopting a multi-pulse correlation detection method; the multi-pulse correlation detection is to perform correlation operation on an original pulse signal and a multi-pulse average signal, and the calculation formula is as follows:
wherein: x (n) is the original pulse signal; y (n) is a multipulse average signal; and N is the pulse width.
2. A signal detection system capable of improving detection distance and accuracy of a laser radar is characterized by comprising: the device comprises a pulse laser, a first lens, a second lens, a narrow-band filter, a photon counter, a non-periodic multi-pulse averaging module, a relevant detector, a beam splitter and a sampling detector; the pulse laser emits non-periodic multi-pulse laser, and the non-periodic multi-pulse laser is collimated by the first lens and then reflected by a far target; the second lens receives the reflected signal, the reflected signal is filtered by the narrow-band filter, and the reflected signal is received by the photon counter for counting and amplifying; then entering a non-periodic multi-pulse averaging module to perform non-periodic multi-pulse averaging calculation, and entering a calculation result and an original pulse signal output by a sampling detector into a correlation detector together to perform correlation operation to obtain a termination pulse signal;
the photon counter consists of an avalanche diode array working in a Geiger mode;
the formula for the aperiodic multi-pulse averaging module to calculate the aperiodic multi-pulse average is as follows:
wherein: m is the average number of times; delta TjThe j-th pulse interval time;
the formula for performing correlation operation in the correlation detector is as follows:
wherein: x (n) is the original pulse signal; y (n) is a multipulse average signal; and N is the pulse width.
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| CN113341427A (en) * | 2021-07-09 | 2021-09-03 | 中国科学技术大学 | Distance measuring method, distance measuring device, electronic equipment and storage medium |
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