Laser ranging method for photoelectric pod

Abstract

The invention discloses a laser ranging method for a photoelectric pod, and belongs to the technical field of laser ranging. When the aircraft is fixed, multiple sections of single-frequency laser signals with different frequencies are transmitted, and corresponding reflection signals are obtained. Calculating a first initial distance by extracting an effective frequency and a corresponding phase from the reflected signal; filtering the reflected signal, calculating the relevance between each part of the filtered signal and the transmitted signal, and calculating a second initial distance according to the starting time of the signal relevance part and the laser round-trip time; and forming a set by all the first and second initial distances, and finding a distance gathering area so as to calculate a target distance. According to the invention, the precision of photoelectric pod laser ranging is improved.

Description

Technical Field

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

[0002] With the continuous development of aircraft technology, an optoelectronic pod is a payload device for an aircraft. The traditional laser ranging method for an optoelectronic pod gradually exposes some limitations in practical applications. In a complex environment, the laser signal is easily interfered by the outside world, such as atmospheric scattering, background light noise, etc., resulting in the distortion of the reflected signal, and it is difficult to accurately extract effective information to calculate the target distance. In the atmospheric environment, the laser signal will be affected by the scattering of atmospheric molecules and suspended particles, resulting in the weakening of the reflected light intensity and the distortion of the signal. At the same time, the background light noise will also seriously interfere with the reflected signal, making the characteristics of the extracted effective signal blurred, difficult to accurately identify and process, and thus leading to a significant decrease in ranging accuracy. Summary of the Invention

[0003] Aiming at the above deficiencies in the prior art, a laser ranging method for an optoelectronic pod provided by the present invention solves the problem of low ranging accuracy existing in the prior art.

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

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

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

[0007] Calculate the first initial distance for each effective phase;

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

[0009] Calculate the second initial distance according to the starting time of the signal correlation part in the filtered signal and the laser round-trip time;

[0010] Construct an initial distance set from all the first initial distances and all the second initial distances, find the aggregation area of the initial distances in the initial distance set, and calculate the target distance.

[0011] Further, 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 magnitudes;

[0014] Extract the frequencies corresponding to the first several amplitudes to construct the first frequency set;

[0015] Extract the emission frequency corresponding to the laser reflection signal, calculate the distances between the emission frequency and the frequencies in each amplitude-frequency pair, arrange the distances in ascending order, and extract the frequencies in the amplitude-frequency pairs corresponding to the first several distances to construct the second frequency set;

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

[0017] Obtain the effective phases according to each effective frequency.

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

[0019] , where d f,i is the i-th distance, f e is the emission frequency, f i is the frequency in the i-th amplitude-frequency pair, and 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 emitted laser signal, ω is the angular frequency of the emitted laser signal, φ re is the effective phase of the laser reflection signal, and φ e is the phase of the emitted laser signal.

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

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

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

[0025] Based on the discrete correlation function, calculate the correlation between the discretized corrected emitted laser signal and the discretized corrected filtered signal;

[0026] Select the discrete value of the time delay corresponding to the maximum correlation, and calculate the start time of the signal correlation part.

[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, and s e (k) is the k-th amplitude in the discretized and corrected transmitted laser signal, and s re (k + n) is the (k + n)-th amplitude in the discretized and corrected filtered signal, k is the amplitude number, 0 ≤ n ≤ (N re -N e ), N re is the length of the discretized and corrected filtered signal, and N e is the length of the discretized and corrected transmitted laser signal.

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

[0030] , where t s is the starting time of the signal correlation part, T is the sampling interval time, and 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, and t re is the laser round-trip time, and t s is the starting time of the signal correlation part.

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

[0034] Sort all the 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] Obtain the radius length according to the difference: , where r is the radius length, C is the difference, and L is the number of divisions;

[0037] Search for the number of initial distances existing in the neighborhood range with each sorted initial distance as the center, where d is the m-th center, and m is a positive integer; m Extract the neighborhood range with the largest number of initial distances as the aggregation area;

[0038] Weight each initial distance in the aggregation area to obtain the target distance.

[0039]

[0040] ​Further, the weighting formula is as follows:

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

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

[0043] 1. By emitting laser signals of multiple different frequencies and separately obtaining their reflected signals, the present invention collects data from multiple dimensions. The effective frequency and corresponding phase are extracted from the reflected signals to calculate the first initial distance. At the same time, the second initial distance is calculated by combining filtering processing and signal correlation analysis. This multi-path calculation and comprehensive consideration method effectively reduces the errors that may be brought by a single measurement method. Compared with the prior art, the ranging accuracy is greatly improved.

[0044] 2. The present invention performs filtering processing on the laser reflected signals, which can remove the influence of interference factors such as environmental noise and stray light on the signals. By calculating the correlation between the filtered signals and the emitted laser signals to determine the starting time of the signal correlation part, a more reliable second initial distance is obtained, enabling the ranging method to still maintain a high accuracy in a complex environment and overcoming the problem of low ranging accuracy caused by interference in the prior art.

[0045] 3. The present invention forms an initial distance set by combining the first initial distance and the second initial distance calculated by different methods, and uses the distribution characteristics of the data in the set to find the aggregation area of the initial distances. This aggregation area reflects the central tendency of multiple measurement results. Based on this, the target distance is calculated, further improving the reliability and stability of the ranging result and being able to more accurately determine the actual distance between the target and the optoelectronic pod. Description of the Drawings

[0046] Figure 1 is a flowchart of a laser ranging method for an optoelectronic pod. Detailed Embodiments

[0047] The following describes the detailed embodiments of the present invention to facilitate those skilled in the art to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

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

[0049] When the aircraft is stationary, multi-segment single-frequency laser signals are emitted, and the corresponding laser reflection signals are obtained. Among them, the frequencies of each segment of laser signals are different;

[0050] For each laser reflection signal, the effective frequency is extracted, the phase corresponding to the effective frequency is obtained, and the effective phase is obtained;

[0051] For each effective phase, the first initial distance is calculated;

[0052] Each laser reflection signal is filtered, and the correlation between each part of each filtered signal and the emitted laser signal is calculated to obtain the starting time of the signal correlation part in each filtered signal;

[0053] According to the starting time of the signal correlation part in the filtered signal and the laser round-trip time, the second initial distance is calculated;

[0054] All the first initial distances and all the second initial distances form an initial distance set, the aggregation area of the initial distances in the initial distance set is found, and the target distance is calculated.

[0055] When the multi-segment single-frequency laser signals are emitted in the present invention, the position of the aircraft remains unchanged. Specifically, the multi-segment single-frequency laser signals emitted in the present invention are: laser signals of various frequencies are emitted in time periods to avoid mutual interference of reflection signals, and each laser signal has one frequency.

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

[0057] In this embodiment, a first-order low-pass filtering algorithm is used for filtering, making the waveform of the laser reflection signal smoother and facilitating morphological comparison.

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

[0059] Each laser reflection signal is subjected to discrete Fourier transform to obtain amplitude-frequency pairs;

[0060] According to the amplitude magnitude, the amplitudes are sorted in descending order;

[0061] The frequencies corresponding to the first several amplitudes are extracted to construct a first frequency set;

[0062] The emission frequency corresponding to the laser reflection signal is extracted, the distances between the emission frequency and the frequencies in each amplitude-frequency pair are calculated, the distances are sorted in ascending order, and the frequencies in the amplitude-frequency pairs corresponding to the first several distances are extracted to construct a second frequency set;

[0063] Take the intersection of the second frequency set and the first frequency set to obtain the effective frequencies.

[0064] Obtain the effective phases according to each effective frequency.

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

[0066] In this embodiment, the first frequency set can be constructed by selecting the frequencies corresponding to the first 2 or 3 amplitudes, and the second frequency set can be constructed by selecting the frequencies corresponding to the first 2 or 3 distances. Since the laser signal emitted in the present invention is 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, measurement equipment accuracy 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, by selecting the first 2 or 3 frequencies with larger amplitudes, it can be ensured to the greatest extent that the main frequency component is included. It is not limited to the number of amplitudes and distances set in this embodiment and can be adjusted according to requirements.

[0067] The present invention preferentially extracts the frequencies with larger amplitudes through discrete Fourier transform and amplitude sorting, which can highlight the main signal components and filter out the low-amplitude spurious signals generated by environmental noise, interference from other light sources, etc. The present invention calculates the distances between the emission frequency and each frequency and filters them, which can exclude the abnormal frequencies caused by factors such as multipath effects and object surface characteristics during the reflection process, and retain the frequencies with high correlation with the emission frequency and strong signals. The effective phases determined thereby can more accurately reflect the time difference of the laser round trip, thereby improving the accuracy of laser ranging. The present invention extracts the frequencies with high amplitudes and close to the emission frequency by taking the intersection of the second frequency set and the first frequency set.

[0068] In this embodiment, the formula for calculating the distance is: , where d f,i is the i-th distance, f e is the emission frequency, f i is the frequency in the i-th amplitude-frequency pair, and 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 emitted laser signal, ω is the angular frequency of the emitted laser signal, φ re is the effective phase of the laser reflection signal, and φ e is the phase of the emitted laser signal.

[0071] In this embodiment, the specific process of obtaining the start time of the signal correlation 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 correlation part.

[0072] Preferably, subtract the average amplitude of the emitted laser signal from the emitted laser signal to obtain the corrected emitted laser signal;

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

[0074] Based on the discrete correlation function, calculate the correlation between the discretized corrected emitted laser signal and the discretized corrected filtered signal;

[0075] Select the discrete value of the time delay corresponding to the maximum correlation, and calculate the start time of the signal correlation part.

[0076] Since there is energy attenuation in the reflected laser signal, therefore, in the present invention, the average amplitude of both the emitted laser signal and the filtered signal is subtracted, and the signal becomes a relative change amount, highlighting the waveform characteristics, reducing the interference of energy attenuation on the 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 k-th amplitude in the discretized corrected emitted laser signal, s re (k + n) is the (k + n)-th amplitude in the discretized corrected filtered signal, k is the amplitude number, 0 ≤ n ≤ (N re -N e ), N re is the length of the discretized corrected filtered signal, N e is the length of the discretized corrected emitted laser signal, and n is an integer.

[0079] The present invention sums the products of the corresponding amplitudes of the discretized corrected emitted laser signal and the corrected filtered signal, can quantify the morphological similarity of the two signals at different time delays, and obtain the correlation at delay n. In laser ranging, accurately find the corresponding relationship between the emitted signal and the reflected filtered signal, so as to determine the accurate round-trip time of the laser.

[0080] The reflected laser signal includes 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 reflecting surfaces during propagation, the time and intensity of its arrival at the receiving end are different from those of the direct reflected signal. When the laser beam encounters multiple reflecting surfaces during propagation, multipath reflection occurs, resulting in interference in the received signal. In a laser ranging system, due to signal interference during propagation, the reflected laser signal will be distorted and broadened, so that the arrival time of the first signal value in the reflected laser signal is not the signal value of the true reflection of the target. To achieve a more accurate estimation of the laser round-trip time, the present invention compares and analyzes the discretized corrected transmitted laser signal and the corrected filtered signal to determine the starting time of the region with the highest correlation, calibrate the laser round-trip time, and improve the ranging accuracy.

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

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

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

[0084] When discretely processing the transmitted laser signal and the filtered signal, the same sampling interval time 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, and t s is the starting time of the signal correlation part.

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

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

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

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

[0091] Search for the neighborhood range with each sorted initial distance as the center The number of initial distances, where d m is the m-th center, and m is a positive integer;

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

[0093] Weight each initial distance in the aggregation area to obtain the target distance.

[0094] The present invention sorts the initial distances and analyzes the differences, enabling an intuitive understanding of the data distribution range. By searching for the number of initial distances within the neighborhood range and taking the neighborhood range with the largest number as the aggregation area, relatively concentrated and stable data can be screened out, isolated outliers can be excluded, and the reliability of the distance data can be improved.

[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. Then, when taking one initial distance as the center each time, it is equivalent to taking the neighborhood within one-third of the difference range on both 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 relatively narrower than when L is 3. When a larger amount of data is required, L can be set to 3. When a more precise screening of the data aggregation area is needed, 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 fewer reference data. The specific value of L selected in this embodiment is not limited, and it can be adjusted according to experiments or experience.

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

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

[0098] The present invention sets the neighborhood range search with each initial distance as the center, considering the local aggregation characteristics of the data. By weighting the initial distances in the aggregation area and determining the target distance by integrating multiple reliable data, compared with individual data, it can effectively reduce the measurement error and enhance the ranging accuracy.

[0099] Short distance (within a few hundred meters): A relatively high frequency can be selected, between 100 THz and 400 THz (terahertz). Medium distance (from a few hundred meters to several kilometers): The frequency can be appropriately reduced, in the range of 30 THz to 100 THz. Long distance (more than several kilometers): A lower frequency can be selected, in the range of 10 THz to 30 THz. When a laser with a lower frequency propagates in the atmosphere, the losses such as scattering and absorption are relatively small, and it can propagate a longer distance. If the target is more than several kilometers away, a frequency in the range of 10 THz to 30 THz is adopted. In this embodiment, laser signals with frequencies such as 10 THz, 15 THz, and 20 THz are selected. The more frequencies are selected, the more laser signals are sent, and thus the more initial distances can be obtained. 10 to 20 frequencies can be selected, and the number of initial distances obtained is more than 20. It is not limited to the frequencies and the number of frequencies selected in this application and can be set according to actual needs.

[0100] The present invention emits laser signals of multiple different frequencies and respectively obtains their reflected signals, collecting data from multiple dimensions. The effective frequency and the corresponding phase are extracted from the reflected signals to calculate the first initial distance. At the same time, the second initial distance is calculated by combining filtering processing and signal correlation analysis. This multi-way calculation and comprehensive consideration method effectively reduces the errors that may be brought by a single measurement method. Compared with the prior art, the ranging accuracy is greatly improved.

[0101] The present invention performs filtering processing on the laser reflection signal, which can remove the influence of interference factors such as environmental noise and stray light on the signal. By calculating the correlation between the filtered signal and the emitted laser signal to determine the starting time of the signal correlation part, a more reliable second initial distance is obtained, enabling the ranging method to still maintain a high accuracy in a complex environment and overcoming the problem of low ranging accuracy caused by interference in the prior art.

[0102] The present invention combines the first initial distance and the second initial distance calculated by different methods to form an initial distance set, and uses the distribution characteristics of the data in the set to find the aggregation area of the initial distance. This aggregation area reflects the central tendency of multiple measurement results. Based on this, the target distance is calculated, further improving the reliability and stability of the ranging result and being able to more accurately determine the actual distance between the target and the optoelectronic pod.

[0103] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope 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 of 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; Calculating a first initial distance for each valid phase; 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; Calculate the second initial distance according to the starting time of the signal correlation part in the filtered signal and the laser round trip time; 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.

2. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: The specific process of obtaining the effective phase includes: Perform discrete Fourier transform on each laser reflection signal to obtain an amplitude-frequency pair; According to the magnitude, the amplitudes are sorted in descending order; Extracting frequencies corresponding to the first plurality of amplitudes to construct a first frequency set; Extract the emission frequency corresponding to the laser reflection signal, calculate the distance between the emission frequency and the frequencies in each amplitude-frequency pair, arrange the distances in ascending order, extract 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; Based on each effective frequency, obtain the effective phase.

3. The laser ranging method of the optoelectronic pod according to claim 2, 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.

4. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: The formula for calculating the first initial distance is: , where d initial,1 is the first initial distance, λ is the wavelength of the emitted laser signal, ω is the angular frequency of the emitted laser signal, φ re is the effective phase of the laser reflection signal, φ e is the phase of the emitted laser signal.

5. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: 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; 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.

6. The laser ranging method of the optoelectronic pod according to claim 5, 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, and s e (k) is the kth amplitude of the laser signal emitted after discretization 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.

7. The laser ranging method of the optoelectronic pod according to claim 5, characterized in that: The formula for calculating the start time of the correlation part of the signal is: , 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.

8. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: The formula for calculating the second initial distance is: , 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.

9. The laser ranging method of the optoelectronic pod according to claim 1, characterized in that: The specific process of calculating the target distance includes: According to the numerical values ​​of the initial distances in the initial distance set, all initial distances are sorted; 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 initial distances in the cluster are weighted to obtain the target distance.

10. The laser ranging method of the optoelectronic pod according to claim 9, 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.

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