A synchronous frequency correction method for polarization modulation ranging of unmanned aerial vehicles

Abstract

The present application belongs to the technical field of polarization modulation ranging method, and in particular, relates to a synchronization frequency correction method for polarization modulation ranging of unmanned aerial vehicles. The method includes the following steps: completing the determination of basic parameters, based on the basic principle of polarization modulation ranging, determining the frequency range and step length and other basic parameters of ranging according to the effective measurement optical path of the equipment and the ranging range of the unmanned aerial vehicle during inspection; adjusting the various parameters of the equipment to ensure smooth ranging; completing the preliminary estimation of the synchronization frequency and interval, loading the initial modulation signal, obtaining the synchronization frequency value and frequency interval, and correcting the modulation signal based on the preliminary measurement; the present application has low requirements on the software and hardware level of the system, and can easily solidify it or form nestable control instructions to integrate it into the existing system based on polarization modulation ranging, without the need to significantly change the structure and working mode of the original system, which is convenient for implementation and promotion.

Description

Technical Field

[0001] The present application belongs to the technical field of polarization modulation ranging methods, and in particular, relates to a synchronization frequency correction method for polarization modulation ranging of unmanned aerial vehicles. Background Art

[0002] With the rapid development and application of UAV technology, technologies such as remote mapping and positioning based on UAVs have gradually matured, and have broad application prospects in daily inspection and maintenance of power grids, planning and design of distribution areas, and survey and monitoring. Among them, the use of polarization modulation ranging technology combined with UAV platforms can quickly and efficiently complete real-time ranging tasks, which effectively improves the efficiency of information acquisition in various power grid projects and work sites. However, on the other hand, compared with ground equipment, the overall stability of UAV platforms is relatively low, and it is not convenient to correct the calibration parameters of internal equipment after takeoff, which has a certain impact on the accuracy and efficiency of UAV real-time ranging. Summary of the invention

[0003] The purpose of this application is to provide a method based on polarization modulation ranging technology, which can be used to realize predictive measurement and automatic correction of synchronization frequency parameters in the automated implementation of the ranging process to improve the accuracy and efficiency of the second measurement.

[0004] To achieve the above objectives, this application adopts the following technical solutions.

[0005] A synchronous frequency correction method for polarization modulation ranging of unmanned aerial vehicles comprises the following steps:

[0006] Step 1: Complete the determination of basic parameters. Based on the basic principle of polarization modulation ranging, determine the basic parameters such as the frequency range and step length of ranging according to the effective measurement optical path of the equipment and the ranging range of the drone during inspection; adjust the parameters of the equipment in all directions to ensure smooth ranging;

[0007] Step 2: Complete the preliminary estimation of the synchronization frequency and interval, load the initial modulation signal, and obtain the synchronization frequency value and frequency interval, including:

[0008] 2.1 Estimation of synchronization frequency value. Use the modulator to load the initial sinusoidal modulation signal. Suppose the initial modulation depth is D∈(0,1], and the angular frequency is ω. Suppose the measurement signal intensity obtained by the detector is Q, and the amplitude is H0. Based on the basic principle of polarization modulation ranging, the detection signal intensity Q T Relationship with modulation phase difference φ:

[0009]

[0010] The detection signal intensity includes the outgoing signal and the reflected signal. Through orthogonal decomposition and expansion, the DC component associated with the modulation phase difference and the high-frequency component associated with the modulation signal are obtained, that is:

[0011]

[0012] where k i is the Jones matrix; based on the fact that the integral response speed of the detection signal can be ignored relative to the modulation rate in actual implementation, after removing the high-frequency component, the correlation expression between the detection signal intensity and the modulation phase difference is obtained:

[0013] Using the Bessel equation, we can simplify it to get:

[0014] Ignoring higher-order terms, we get For a sinusoidal modulated signal, Where c is the speed of light, S is the optical path, based on the above formula, by controlling the modulation frequency, the optical path S can be solved and then the distance of the target to be measured can be solved;

[0015] From the previous formula, we can get:

[0016] Based on the above basic principles, the modulation signal frequency is adjusted to obtain the detection signal light intensity Q T Take the minimum value of several synchronization frequencies. Under this synchronization frequency, the detection signal takes the minimum value, which means that the phase difference between the outgoing signal and the reflected signal is zero, that is, the optical path S to be measured is the modulation wavelength that satisfies f n is the synchronization frequency corresponding to the nth minimum point;

[0017] 2.2 Estimation of frequency interval: Starting from the starting frequency of the polarization modulation ranging device, forward scanning is performed to obtain two adjacent synchronization frequencies f p and f p+1 ; Then reverse scan from the end frequency of the polarization modulation ranging device to obtain a synchronization frequency f p+q , according to the calculation formula of frequency interval:

[0018] Frequency interval number Frequency interval

[0019] Step 3: Modulation signal correction based on preliminary measurement, specifically including:

[0020] 3.1 Based on the above step 2, due to the existence of frequency error and random error, the frequency interval number U has an error, and its error value is

[0021]

[0022] Where Δf p+1 is the synchronization frequency f p+1 Relative to the synchronization frequency f p Drift error; Δf p+q is the synchronization frequency f p+q Relative to the synchronization frequency f p Drift error; u p is the synchronization frequency f p The measurement error of u p+q is the synchronization frequency f p+q The measurement error of

[0023] In actual implementation, the frequency interval J is on the order of 10 6 Above Hz, it far exceeds the values ​​of drift error and measurement error. Combined with the above formula, the actual error values ​​of drift error and measurement error will be compressed by U times;

[0024] 3.2 Based on the above step 3.1, the frequency interval error can be determined through the estimated values ​​of the synchronization frequency and frequency interval. According to the current distance between the target to be measured and the UAV and the corresponding error value, the optimal modulation frequency value range is calculated, and a better modulation depth is given;

[0025] Step 4: Acquisition of a demodulated signal based on the corrected signal, specifically including:

[0026] 4.1 Based on the aforementioned optimal modulation frequency range and modulation depth, the forward and reverse frequency scanning range and starting step size of the modulator are corrected, and a second scan is performed based on the correction results.

[0027] To further improve and supplement the aforementioned synchronous frequency correction method for UAV polarization modulation ranging, during the inspection operation, the frequency interval is set to 10 to 15.

[0028] The above-mentioned synchronization frequency correction method for polarization modulation ranging of unmanned aerial vehicles is further improved and supplemented. In order to reduce the degree of orthogonal signal interference caused by phase delay, the contrast of the measurement signal is improved by adjusting the polarization controller.

[0029] Its beneficial effects are:

[0030] Through the idea of ​​pre-estimation and secondary correction, the present application provides a method for improving the measurement accuracy of ranging by performing initial parameter correction through preliminary estimated values ​​combined with actual parameters without the need for repeated equipment adjustment or correction data. The method has low requirements on the software and hardware level of the system, and can be easily solidified or formed into nested control instructions to be integrated into the existing system based on polarization modulation ranging. There is no need to make major changes to the structure and working mode of the original system, so it is easy to implement and promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of a polarization modulation ranging system; DETAILED DESCRIPTION

[0032] The present application is described in detail below in conjunction with specific embodiments.

[0033] The synchronous frequency correction method for polarization modulation ranging of unmanned aerial vehicles in the present application is applicable to polarization modulation ranging systems, and is used to improve the existing ranging algorithm process and measurement process, and improve the accuracy of secondary measurements by pre-testing and correcting initial scanning parameters.

[0034] The basic structure of the polarization modulation ranging system is as follows: Figure 1 shown.

[0035] The basic steps of the synchronous frequency correction method for polarization modulation ranging of unmanned aerial vehicles in this application include:

[0036] Step 1: Complete the determination of basic parameters. Based on the basic principle of polarization modulation ranging, determine the basic parameters such as the frequency range and step length of ranging according to the effective measurement optical path of the equipment and the ranging range of the drone during inspection; adjust the parameters of the equipment in all directions to ensure smooth ranging;

[0037] In the actual system, the measurement signal emitted by the transmitter passes through the display and the polarizer and then enters the polarization controller to generate the orthogonal component and the initial phase deviation. In order to reduce the degree of orthogonal signal interference caused by phase delay, in the actual measurement process, the polarization controller should be adjusted to improve the contrast of the measurement signal to improve the measurability as much as possible.

[0038] Step 2: Complete the preliminary estimation of the synchronization frequency and interval, load the initial modulation signal, and obtain the synchronization frequency value and frequency interval, including:

[0039] 2.1 Estimation of synchronization frequency value. Use the modulator to load the initial sinusoidal modulation signal. Suppose the initial modulation depth is D∈(0,1], and the angular frequency is ω. Suppose the measurement signal intensity obtained by the detector is Q, and the amplitude is H0. Based on the basic principle of polarization modulation ranging, the detection signal intensity Q T Relationship with modulation phase difference φ:

[0040]

[0041] The detection signal intensity includes the outgoing signal and the reflected signal. Through orthogonal decomposition and expansion, the DC component associated with the modulation phase difference and the high-frequency component associated with the modulation signal are obtained, that is:

[0042]

[0043] where k i is the Jones matrix; based on the fact that the integral response speed of the detection signal can be ignored relative to the modulation rate in actual implementation, after removing the high-frequency component, the correlation expression between the detection signal intensity and the modulation phase difference is obtained:

[0044] Using the Bessel equation, we can simplify it to get:

[0045] Ignoring higher-order terms, we get For a sinusoidal modulated signal, Where c is the speed of light, S is the optical path, based on the above formula, by controlling the modulation frequency, the optical path S can be solved and then the distance of the target to be measured can be solved;

[0046] From the previous formula, we can get:

[0047] Based on the above basic principles, the modulation signal frequency is adjusted to obtain the detection signal light intensity Q T Take the minimum value of several synchronization frequencies. Under this synchronization frequency, the detection signal takes the minimum value, which means that the phase difference between the outgoing signal and the reflected signal is zero, that is, the optical path S to be measured is the modulation wavelength that satisfies f n is the synchronization frequency corresponding to the nth minimum point;

[0048] 2.2 Estimation of frequency interval: Starting from the starting frequency of the polarization modulation ranging device, forward scanning is performed to obtain two adjacent synchronization frequencies f p and f p+1 ; Then reverse scan from the end frequency of the polarization modulation ranging device to obtain a synchronization frequency f p+q , according to the calculation formula of frequency interval:

[0049] Frequency interval number Frequency interval

[0050] Step 3: Modulation signal correction based on preliminary measurement, specifically including:

[0051] 3.1 Based on the above step 2, due to the existence of frequency error and random error, the frequency interval number U has an error, and its error value is

[0052]

[0053] Where Δf p+1 is the synchronization frequency f p+1 Relative to the synchronization frequency f p Drift error; Δf p+q is the synchronization frequency fp+q Relative to the synchronization frequency f p Drift error; u p is the synchronization frequency f p The measurement error of u p+q is the synchronization frequency f p+q The measurement error of

[0054] In actual implementation, the frequency interval J is on the order of 10 6 Above Hz, it far exceeds the values ​​of drift error and measurement error. Combined with the above formula, the actual error values ​​of drift error and measurement error will be compressed by U times;

[0055] 3.2 Based on the above step 3.1, the frequency interval error can be determined through the estimated values ​​of the synchronization frequency and frequency interval. According to the current distance between the target to be measured and the UAV and the corresponding error value, the optimal modulation frequency value range is calculated, and a better modulation depth is given;

[0056] Step 4: Acquisition of a demodulated signal based on the corrected signal, specifically including:

[0057] 4.1 Based on the above-mentioned optimal modulation frequency range and modulation depth, correct the modulator forward and reverse frequency scanning range and starting step size, and perform a second scan based on the correction results;

[0058] In the actual inspection process, considering that the direct distance between the power grid drone and the target to be measured is generally within 5 to 50 meters, the frequency interval can be directly set to 10 to 15, thereby simplifying the calculation process.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application, rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A synchronization frequency correction method for polarization modulation ranging of unmanned aerial vehicles, characterized in that: The steps include: Step 1: Complete the determination of basic parameters. Based on the basic principle of polarization modulation ranging, the frequency range and step size of ranging are determined according to the effective measurement optical path of the equipment and the ranging range of the UAV inspection. Adjust the various parameters of the equipment to ensure smooth ranging. Step 2: Complete the preliminary estimation of the synchronization frequency and interval, load the initial modulation signal, and obtain the synchronization frequency value and frequency interval, including: 2.1 Estimation of synchronization frequency value, use the modulator to load the initial sinusoidal modulation signal, set the initial modulation depth to D∈(0,1], angular frequency to ω; set the measurement signal intensity obtained by the detector to Q, amplitude to H0, based on the basic principle of polarization modulation ranging, the detection signal intensity Q T Relationship with modulation phase difference φ: The detection signal intensity includes the outgoing signal and the reflected signal. Through orthogonal decomposition and expansion, the DC component associated with the modulation phase difference and the high-frequency component associated with the modulation signal are obtained, namely: where k i is the Jones matrix. Based on the fact that the integral response speed of the detection signal can be ignored relative to the modulation rate in actual implementation, after removing the high-frequency component, the correlation expression between the detection signal intensity and the modulation phase difference is obtained: Using the Bessel equation to simplify, we get: Ignoring higher-order terms, we get For a sinusoidal modulated signal, Where c is the speed of light, S is the optical distance. Based on the above formula, by controlling the modulation frequency, the optical distance S can be solved and the distance of the target to be measured can be solved; From the previous formula, we can get: Based on the above basic principles, the modulation signal frequency is adjusted to obtain the detection signal intensity Q T Take the minimum value of several synchronization frequencies. At this synchronization frequency, the detection signal takes the minimum value, which means that the phase difference between the outgoing signal and the reflected signal is zero, that is, the optical path S to be measured is the modulation wavelength that satisfies f n is the synchronization frequency corresponding to the nth minimum point; 2.2 Estimation of frequency interval: Starting from the starting frequency of the polarization modulation ranging device, forward scanning is performed to obtain two adjacent synchronization frequencies f p and f p+1 ; Then reverse scan from the end frequency of the polarization modulation ranging device to obtain a synchronization frequency f p+q , according to the calculation formula of frequency interval: Frequency intervals Frequency interval Step 3: Modulation signal correction based on preliminary measurements, specifically including: 3.1 Based on the above step 2, due to the existence of frequency error and random error, the frequency interval number U has an error, and its error value is Where Δf p+1 is the synchronization frequency f p+1 Relative to the synchronization frequency f p Drift error; Δf p+q is the synchronization frequency f p+q Relative to the synchronization frequency f p Drift error; u p is the synchronization frequency f p The measurement error of u p+q is the synchronization frequency f p+q measurement error; 3.2 Based on the above step 3.1, the frequency separation error is determined using the estimated values ​​of the synchronization frequency and frequency separation. Based on the current distance between the target and the UAV and the corresponding error value, the optimal modulation frequency range is calculated and the optimal modulation depth is determined. Step 4: Acquiring a demodulated signal based on the corrected signal, specifically including: 4.1 Based on the aforementioned optimal modulation frequency value range and modulation depth, modify the modulator's forward and reverse frequency scanning range and starting step size, and perform a second scan based on the modified results.

2. The synchronous frequency correction method for polarization modulation ranging of unmanned aerial vehicle according to claim 1, characterized in that: In order to reduce the degree of orthogonal signal interference caused by phase delay, the polarization controller is adjusted to improve the contrast of the measurement signal.

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