Laser ranging method for photoelectric pod

Abstract

The present invention discloses a laser ranging method for an optoelectronic pod, belonging to the technical field of laser ranging. When the aircraft is fixed, the present invention transmits multiple segments of single-frequency laser signals of different frequencies and obtains corresponding reflected signals. The first initial distance is calculated by extracting the effective frequency and corresponding phase of the reflected signal; the reflected signal is filtered, and the correlation between each part of the filtered signal and the transmitted signal is calculated. The second initial distance is calculated based on the start time of the signal correlation part and the laser round-trip time. All the first and second initial distances are formed into a set, and the distance cluster area is found to calculate the target distance. The present invention improves the accuracy of optoelectronic pod laser ranging.

Description

Technical Field

[0001] The present invention relates to the technical field of laser ranging, and in particular to a laser ranging method for an optoelectronic pod. Background Art

[0002] With the continuous advancement of aircraft technology, optoelectronic pods are becoming payloads for aircraft. Traditional optoelectronic pod laser ranging methods have gradually exposed limitations in practical applications. In complex environments, laser signals are susceptible to external interference, such as atmospheric scattering and background light noise. This distorts the reflected signal, making it difficult to accurately extract valid information for calculating target distance. In atmospheric environments, laser signals are scattered by atmospheric molecules and suspended particles, weakening the reflected light intensity and distorting the signal. Furthermore, background light noise can severely interfere with the reflected signal, blurring the extracted signal features and making it difficult to accurately identify and process them, significantly reducing ranging accuracy. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a laser ranging method for an optoelectronic pod, which solves the problem of low ranging accuracy in the prior art.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is: a laser ranging method for an optoelectronic pod, comprising the following steps:

[0005] When the aircraft is fixed, multiple segments of single-frequency laser signals are emitted to obtain corresponding laser reflection signals, wherein the frequencies of the laser signals in each segment are different;

[0006] Extract the effective frequency of each laser reflection signal, obtain the phase corresponding to the effective frequency, and obtain the effective phase;

[0007] Calculating a first initial distance for each valid phase;

[0008] Filter each laser reflection signal, calculate the correlation between each part of each filtered signal and the emitted laser signal, and obtain the starting time of the signal correlation part in each filtered signal;

[0009] Calculating a second initial distance based on the start time of the signal correlation portion in the filtered signal and the laser round trip time;

[0010] All first initial distances and all second initial distances constitute an initial distance set, find the clustering area of the initial distances in the initial distance set, and calculate the target distance.

[0011] Furthermore, the specific process of obtaining the effective phase includes:

[0012] Perform discrete Fourier transform on each laser reflection signal to obtain amplitude-frequency pairs;

[0013] Arrange the amplitudes in descending order according to their magnitude;

[0014] Extracting frequencies corresponding to the first plurality of amplitudes to construct a first frequency set;

[0015] Extracting the emission frequency corresponding to the laser reflection signal, calculating the distance between the emission frequency and the frequencies in the middle of each amplitude-frequency pair, arranging the distances in ascending order, and extracting the frequencies in the amplitude-frequency pairs corresponding to the first multiple distances to construct a second frequency set;

[0016] Taking the intersection of the second frequency set and the first frequency set to obtain the effective frequency;

[0017] Based on each effective frequency, obtain the effective phase.

[0018] Furthermore, the formula for calculating the distance is:

[0019] , where d f,i is the i-th distance, f e is the transmitting frequency, f i is the frequency of the i-th amplitude-frequency pair, where i is a positive integer.

[0020] Furthermore, the formula for calculating the first initial distance is:

[0021] , where d initial,1 is the first initial distance, λ is the wavelength of the transmitted laser signal, ω is the angular frequency of the transmitted laser signal, φ re is the effective phase of the laser reflection signal, φ e is the phase of the transmitted laser signal.

[0022] Furthermore, the specific process of obtaining the start time of the signal-related part in each filtered signal includes:

[0023] subtracting the average amplitude of the emitted laser signal from the emitted laser signal to obtain a corrected emitted laser signal;

[0024] Subtracting the average amplitude of the filtered signal from the filtered signal to obtain a corrected filtered signal;

[0025] Based on the discrete correlation function, the correlation between the laser signal emitted after discretization correction and the discretization correction filter signal is calculated;

[0026] The discrete value of the time delay corresponding to the maximum correlation is selected and the start time of the correlated part of the signal is calculated.

[0027] Furthermore, the expression of the discrete correlation function is:

[0028] , where G(n) is the correlation at delay n, n is the discrete value of the time delay, s e (k) is the kth amplitude of the laser signal after discrete correction, s re (k+n) is the k+nth amplitude in the discretized correction filter signal, k is the amplitude number, 0≤n≤(N re -N e ), N re is the length of the discretized correction filter signal, N e is the length of the laser signal emitted after discretization correction.

[0029] Furthermore, the formula for calculating the start time of the signal correlation part is:

[0030] , where t s is the start time of the signal correlation part, T is the sampling interval, n max is the discrete value of the time delay corresponding to the maximum correlation.

[0031] Furthermore, the formula for calculating the second initial distance is:

[0032] , where d initial,2 is the second initial distance, c is the speed of light in vacuum, t re is the laser round trip time, t s is the start time of the associated part of the signal.

[0033] Furthermore, the specific process of calculating the target distance includes:

[0034] Sort all initial distances according to the numerical values of the initial distances in the initial distance set;

[0035] Calculate the difference between the maximum initial distance and the minimum initial distance;

[0036] According to the difference, the radius length is obtained: , where r is the radius length, C is the difference, and L is the number of divisions;

[0037] Search the neighborhood range with each initial distance after sorting as the center The number of initial distances present, where d m is the mth center, m is a positive integer;

[0038] Extract the neighborhood range with the largest number of initial distances as the clustering area;

[0039] The target distance is obtained by weighting the initial distances in the cluster.

[0040] Furthermore, the weighted formula is:

[0041] , where d tar,j is the target distance, d gather,j is the jth initial distance in the cluster, R is the number of initial distances in the cluster, and j is a positive integer.

[0042] The beneficial effects of the present invention are:

[0043] 1. This invention collects data from multiple dimensions by emitting multiple laser signals of varying frequencies and capturing their respective reflected signals. The effective frequency and corresponding phase of the reflected signals are extracted to calculate the first initial distance. A second initial distance is then calculated using filtering and signal correlation analysis. This multi-pronged approach effectively reduces the potential error associated with a single measurement method, significantly improving distance measurement accuracy compared to existing technologies.

[0044] 2. This invention filters the laser reflection signal to remove the effects of interference factors such as ambient noise and stray light. By calculating the correlation between the filtered signal and the transmitted laser signal, the start time of the associated portion of the signal is determined, thereby obtaining a more reliable second initial distance. This allows the ranging method to maintain high accuracy even in complex environments, overcoming the low ranging accuracy caused by interference in existing technologies.

[0045] 3. The present invention combines the first and second initial distances calculated using different methods into an initial distance set. The distribution characteristics of the data in the set are then used to identify clusters of initial distances. This cluster reflects the central tendency of multiple measurement results. Calculating the target distance based on this cluster further improves the reliability and stability of the ranging results, enabling a more accurate determination of the actual distance between the target and the optoelectronic pod. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The present invention is a flow chart of a laser ranging method for an optoelectronic pod. DETAILED DESCRIPTION

[0047] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0048] like Figure 1 As shown, a laser ranging method for an optoelectronic pod includes the following steps:

[0049] When the aircraft is fixed, multiple segments of single-frequency laser signals are emitted to obtain corresponding laser reflection signals, wherein the frequencies of the laser signals in each segment are different;

[0050] Extract the effective frequency of each laser reflection signal, obtain the phase corresponding to the effective frequency, and obtain the effective phase;

[0051] Calculating a first initial distance for each valid phase;

[0052] Filter each laser reflection signal, calculate the correlation between each part of each filtered signal and the emitted laser signal, and obtain the starting time of the signal correlation part in each filtered signal;

[0053] Calculating a second initial distance based on the start time of the signal correlation portion in the filtered signal and the laser round trip time;

[0054] All first initial distances and all second initial distances constitute an initial distance set, find the clustering area of the initial distances in the initial distance set, and calculate the target distance.

[0055] When the present invention transmits multiple single-frequency laser signals, the position of the aircraft remains unchanged. The present invention transmits multiple single-frequency laser signals by transmitting the laser signals of various frequencies in different time periods to avoid mutual interference of reflected signals, and each laser signal has a single frequency.

[0056] The expression of laser signal is: E(t)=Acos(ωt+φ e ), E(t) is the laser signal, A is the amplitude of the laser signal, ω is the angular frequency of the emitted laser signal, t is the time, φ e is the phase of the transmitted laser signal, and cos is the cosine function.

[0057] In this embodiment, the filtering adopts a first-order low-pass filtering algorithm, which makes the waveform of the laser reflection signal smoother and facilitates morphological comparison.

[0058] In this embodiment, the specific process of obtaining the effective phase includes:

[0059] Perform discrete Fourier transform on each laser reflection signal to obtain amplitude-frequency pairs;

[0060] Arrange the amplitudes in descending order according to their magnitude;

[0061] Extracting frequencies corresponding to the first plurality of amplitudes to construct a first frequency set;

[0062] Extracting the emission frequency corresponding to the laser reflection signal, calculating the distance between the emission frequency and the frequencies in the middle of each amplitude-frequency pair, arranging the distances in ascending order, and extracting the frequencies in the amplitude-frequency pairs corresponding to the first multiple distances to construct a second frequency set;

[0063] Taking the intersection of the second frequency set and the first frequency set to obtain the effective frequency;

[0064] Based on each effective frequency, obtain the effective phase.

[0065] For a laser reflection signal, there are multiple effective phases, and there are also multiple first initial distances corresponding to the laser reflection signal.

[0066] In this embodiment, the frequencies corresponding to the first two or three amplitudes can be selected to construct a first frequency set, and the frequencies corresponding to the first two or three distances can be selected to construct a second frequency set. Since the present invention emits a single-frequency laser signal, under ideal conditions, the laser reflection signal should have only one clear frequency component. However, during actual measurement, due to the influence of environmental factors, the accuracy of the measuring equipment and other factors, some spurious frequency components may appear in the reflection signal. The amplitudes of these spurious frequency components are usually smaller than the amplitude of the main frequency component. Therefore, selecting the first two or three frequencies with larger amplitudes can ensure that the main frequency component is included to the greatest extent. The amplitudes and distances set in this embodiment are not limited and can be adjusted according to needs.

[0067] The present invention uses discrete Fourier transforms and amplitude sorting to prioritize frequencies with larger amplitudes, highlighting the primary signal components while filtering out low-amplitude spurious signals generated by environmental noise, interference from other light sources, and so on. By calculating and filtering the distances between the transmission frequency and each frequency, the present invention eliminates abnormal frequencies caused by factors such as multipath effects during reflection and surface characteristics of objects, while retaining frequencies with a high correlation and strong signals with the transmission frequency. The effective phase thus determined can more accurately reflect the time difference between the round trip of the laser, thereby improving the accuracy of laser ranging. By intersecting the second frequency set with the first frequency set, the present invention extracts frequencies with high amplitudes close to the transmission frequency.

[0068] In this embodiment, the formula for calculating the distance is: , where d f,i is the i-th distance, f e is the transmitting frequency, f i is the frequency of the i-th amplitude-frequency pair, where i is a positive integer.

[0069] In this embodiment, the formula for calculating the first initial distance is:

[0070] , where d initial,1 is the first initial distance, λ is the wavelength of the transmitted laser signal, ω is the angular frequency of the transmitted laser signal, φ re is the effective phase of the laser reflection signal, φ e is the phase of the transmitted laser signal.

[0071] In this embodiment, the specific process of obtaining the start time of the signal-correlated part in each filtered signal includes: based on the discrete correlation function, calculating the correlation between the emitted laser signal and the filtered signal, selecting the discrete value of the time delay corresponding to the maximum correlation, and calculating the start time of the signal-correlated part.

[0072] More preferably, the corrected emitted laser signal is obtained by subtracting the average amplitude of the emitted laser signal from the emitted laser signal;

[0073] Subtracting the average amplitude of the filtered signal from the filtered signal to obtain a corrected filtered signal;

[0074] Based on the discrete correlation function, the correlation between the laser signal emitted after discretization correction and the discretization correction filter signal is calculated;

[0075] The discrete value of the time delay corresponding to the maximum correlation is selected and the start time of the correlated part of the signal is calculated.

[0076] Since the reflected laser signal has energy attenuation, the present invention subtracts the average amplitude of each of the emitted laser signal and the filtered signal, converting the signal into a relative change, highlighting the waveform characteristics, reducing the interference of energy attenuation on correlation comparison, and more accurately reflecting the essential correlation of the signal.

[0077] In this embodiment, the expression of the discrete correlation function is:

[0078] , where G(n) is the correlation at delay n, n is the discrete value of the time delay, s e (k) is the kth amplitude of the laser signal after discrete correction, s re (k+n) is the k+nth amplitude in the discretized correction filter signal, k is the amplitude number, 0≤n≤(N re -N e ), N re is the length of the discretized correction filter signal, N e is the length of the laser signal emitted after discretization correction, and n is an integer.

[0079] By summing the products of the corresponding amplitudes of the discretized, corrected transmitted laser signal and the corrected filtered signal, the present invention quantifies the morphological similarity of the two signals at different time delays, and derives the correlation at delay n. In laser ranging, the correspondence between the transmitted signal and the reflected filtered signal is accurately found, thereby determining the precise round-trip time of the laser.

[0080] The reflected laser signal contains the effective reflected signal of the target and the multipath interference signal. Since the multipath interference signal is generated when the laser beam encounters multiple reflection surfaces during propagation, the time and intensity of its arrival at the receiving end are different from those of the direct reflection signal. When the laser beam encounters multiple reflection surfaces during propagation, multipath reflection will occur, resulting in interference in the received signal. In the laser ranging system, due to signal interference during the propagation process, the reflected laser signal will be distorted and broadened, causing the arrival time of the first signal value in the reflected laser signal to be not the signal value actually reflected by the target. In order to achieve a more accurate estimation of the laser round-trip time, the present invention compares and analyzes the discretized corrected emission laser signal and the corrected filtered signal to determine the starting time of the area with the highest correlation, calibrate the laser round-trip time, and improve the ranging accuracy.

[0081] In this embodiment, the formula for calculating the start time of the signal correlation part is:

[0082] , where t s is the start time of the signal correlation part, T is the sampling interval, n max is the discrete value of the time delay corresponding to the maximum correlation.

[0083] n max is the n value corresponding to the largest G(n) among multiple G(n).

[0084] When the emitted laser signal and the filtered signal are discretely processed, the same sampling interval is uniformly adopted.

[0085] In this embodiment, the formula for calculating the second initial distance is:

[0086] , where d initial,2 is the second initial distance, c is the speed of light in vacuum, t re is the laser round trip time, t s is the start time of the associated part of the signal.

[0087] In this embodiment, the specific process of calculating the target distance includes:

[0088] Sort all initial distances according to the numerical values of the initial distances in the initial distance set;

[0089] Calculate the difference between the maximum initial distance and the minimum initial distance;

[0090] According to the difference, the radius length is obtained: , where r is the radius length, C is the difference, and L is the number of divisions;

[0091] Search the neighborhood range with each initial distance after sorting as the center The number of initial distances present, where d m is the mth center, m is a positive integer;

[0092] Extract the neighborhood range with the largest number of initial distances as the clustering area;

[0093] The target distance is obtained by weighting the initial distances in the cluster.

[0094] This method sorts initial distances and analyzes the differences, providing an intuitive understanding of the data's distribution range. By searching for the number of initial distances within a neighborhood and using the neighborhood with the largest number as the cluster, it can filter out relatively concentrated and stable data, eliminate isolated outliers, and improve the reliability of distance data.

[0095] In this embodiment, L is set to 3 or 4, etc. When L is set to 3, it is equivalent to dividing the difference into 3 parts. Each time an initial distance is taken as the center, it is equivalent to taking a neighborhood of one-third of the difference range on the left and right sides of the center value. When L is set to 4, the difference is divided into 4 parts, and the neighborhood range will be narrower than when L is 3. When a large amount of data is required, L can be set to 3. When a more accurate screening of data clusters is required, L can be set to 4. If L is set too small, abnormal target distances will not be effectively eliminated. If L is set too large, there will be less reference data. The specific value of L selected is not limited to this embodiment and can be adjusted according to experiments or experience.

[0096] In this embodiment, the weighted formula is:

[0097] , where d tar,j is the target distance, d gather,j is the jth initial distance in the cluster, R is the number of initial distances in the cluster, and j is a positive integer.

[0098] This method uses a neighborhood search centered around each initial distance, taking into account the local clustering characteristics of data. It weights the initial distances within the cluster and integrates multiple reliable data points to determine the target distance. This effectively reduces measurement errors and enhances ranging accuracy compared to a single data point.

[0099] Short distance (within a few hundred meters): a higher frequency can be selected, between 100THz-400THz (terahertz). Medium distance (a few hundred meters to a few thousand meters): the frequency can be appropriately lowered, in the range of 30THz-100THz. Long distance (more than a few thousand meters): a lower frequency can be selected, in the range of 10THz-30THz. Lasers with lower frequencies are subject to relatively less losses such as scattering and absorption when propagating in the atmosphere, and can propagate over longer distances. If the target reaches more than a few thousand meters, a frequency within the range of 10THz-30THz is used. In this embodiment, laser signals with frequencies such as 10THz, 15THz, and 20THz are selected. The more frequencies are selected, the more laser signals are sent, and thus the more initial distances are obtained. 10 to 20 frequencies can be selected, and the number of initial distances obtained is more than 20. The frequencies and the number of frequencies are not limited to those selected in this application, and can be set according to actual needs.

[0100] The present invention collects data from multiple dimensions by emitting multiple laser signals of varying frequencies and capturing their respective reflected signals. The effective frequency and corresponding phase of the reflected signals are extracted to calculate the first initial distance. A second initial distance is then calculated using a combination of filtering and signal correlation analysis. This multi-pronged approach effectively reduces the potential error associated with a single measurement method, significantly improving distance measurement accuracy compared to existing technologies.

[0101] The present invention filters the laser reflection signal to remove the effects of interference factors such as ambient noise and stray light. By calculating the correlation between the filtered signal and the transmitted laser signal, the start time of the associated portion of the signal is determined, thereby obtaining a more reliable second initial distance. This allows the ranging method to maintain high accuracy even in complex environments, overcoming the low ranging accuracy caused by interference in existing technologies.

[0102] The present invention combines the first and second initial distances calculated using different methods into an initial distance set. The distribution characteristics of the data in the set are then used to identify a cluster of initial distances. This cluster reflects the central trend of multiple measurement results, which is then used to calculate the target distance. This further improves the reliability and stability of the ranging results, allowing for a more accurate determination of the actual distance between the target and the optoelectronic pod.

[0103] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A laser ranging method for an optoelectronic pod, characterized in that: The following steps are involved: When the aircraft is fixed, multiple segments of single-frequency laser signals are emitted to obtain corresponding laser reflection signals, wherein the frequencies of the laser signals in each segment are different; Extract the effective frequency of each laser reflection signal, obtain the phase corresponding to the effective frequency, and obtain the effective phase; Compute the first initial distance for each valid phase: , where d initial,1 is the first initial distance, λ is the wavelength of the transmitted laser signal, ω is the angular frequency of the transmitted laser signal, φ re is the effective phase of the laser reflection signal, φ e is the phase of the transmitted laser signal; Filter each laser reflection signal, calculate the correlation between each part of each filtered signal and the emitted laser signal, and obtain the starting time of the signal correlation part in each filtered signal; The second initial distance is calculated based on the start time of the signal correlation part in the filtered signal and the laser round-trip time: , where d initial,2 is the second initial distance, c is the speed of light in vacuum, t re is the laser round trip time, t s is the start time of the associated part of the signal; All first initial distances and all second initial distances constitute an initial distance set, find the clustering area of the initial distances in the initial distance set, and calculate the target distance; The specific process of obtaining the effective phase includes: Perform discrete Fourier transform on each laser reflection signal to obtain amplitude-frequency pairs; Arrange the amplitudes in descending order according to their magnitude; Extracting frequencies corresponding to the first plurality of amplitudes to construct a first frequency set; Extracting the emission frequency corresponding to the laser reflection signal, calculating the distance between the emission frequency and the frequencies in the middle of each amplitude-frequency pair, arranging the distances in ascending order, and extracting the frequencies in the amplitude-frequency pairs corresponding to the first multiple distances to construct a second frequency set; Taking the intersection of the second frequency set and the first frequency set to obtain the effective frequency; According to each effective frequency, obtain the effective phase; The specific process of obtaining the start time of the signal correlation part in each filtered signal includes: subtracting the average amplitude of the emitted laser signal from the emitted laser signal to obtain a corrected emitted laser signal; Subtracting the average amplitude of the filtered signal from the filtered signal to obtain a corrected filtered signal; Based on the discrete correlation function, the correlation between the laser signal emitted after discretization correction and the discretization correction filter signal is calculated; Select the discrete value of the time delay corresponding to the maximum correlation and calculate the start time of the correlated part of the signal: , where t s is the start time of the signal correlation part, T is the sampling interval, n max is the discrete value of the time delay corresponding to the maximum correlation; The specific process of calculating the target distance includes: Sort all initial distances according to the numerical values of the initial distances in the initial distance set; Calculate the difference between the maximum initial distance and the minimum initial distance; According to the difference, the radius length is obtained: , where r is the radius length, C is the difference, and L is the number of divisions; Search the neighborhood range with each initial distance after sorting as the center The number of initial distances present, where d m is the mth center, m is a positive integer; Extract the neighborhood range with the largest number of initial distances as the clustering area; The target distance is obtained by weighting the initial distances in the cluster.

2. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: The formula for calculating distance is: , where d f,i is the i-th distance, f e is the transmitting frequency, f i is the frequency of the i-th amplitude-frequency pair, where i is a positive integer.

3. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: The expression of the discrete correlation function is: , where G(n) is the correlation at delay n, n is the discrete value of the time delay, s e (k) is the kth amplitude of the laser signal after discrete correction, s re (k+n) is the k+nth amplitude in the discretized correction filter signal, k is the amplitude number, 0≤n≤(N re -N e ), N re is the length of the discretized correction filter signal, N e is the length of the laser signal emitted after discretization correction.

4. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: The weighted formula is: , where d tar,j is the target distance, d gather,j is the jth initial distance in the cluster, R is the number of initial distances in the cluster, and j is a positive integer.

Images