Radar real-time double-frequency radio wave refraction error correction method

Abstract

The invention discloses a radar real-time double-frequency radio wave refraction error correction method. According to the method, the principle that instantaneous propagation paths of electromagnetic waves are approximately the same when two working frequency points of the radar are switched for detection is utilized, the error correction amount of the required frequency points is directly obtained, and the working time sequence of the radar can be adaptively adjusted according to the importance of a target and the radar resource utilization rate. The radio wave refraction error correction method can directly complete radio wave refraction error correction without participation of a GNSS receiver, and has high real-time performance and correction precision.

Description

Technical Field

[0001] The present invention relates to the technical field of radar system design, and in particular to a radar real-time dual-frequency radio wave refraction error correction method. Background Art

[0002] Due to the strong radiation from the sun, some gas molecules in the atmosphere at an altitude of 80 to 2000 kilometers above the ground are ionized to form a large number of free electrons and positive ions, forming the ionosphere. When the radar electromagnetic wave passes through the ionosphere, due to the uneven parameters and time-varying characteristics of the ionosphere, the electromagnetic wave will be absorbed, scattered, reflected, refracted and flickered, causing the propagation time delay and path bending of the radio wave signal, causing the apparent distance and elevation angle of the target to deviate from the target, resulting in a certain distance, elevation angle and refraction deviation (such as Figure 1 When the radar detects at different operating frequencies, the correction data for the radio wave refraction error is also different. The lower the frequency, the larger the refraction error. As the elevation angle decreases, the propagation path of the radio wave signal in the ionosphere is longer, and the refraction error will increase rapidly. Therefore, the ionosphere has a greater impact on low-frequency radars.

[0003] The cycle of ionospheric activity is generally 11.5 years. We are currently in the 25th solar activity cycle, which began in December 2019. Solar activity will become increasingly stronger and is expected to reach a maximum in July 2024. By then, the horizontal inhomogeneity of the ionosphere in the low-latitude equatorial region will be extremely obvious and change dramatically, resulting in radar distance errors of up to several hundred meters. This is the main source of error in radar ranging accuracy and will seriously affect radar detection and precise tracking of targets.

[0004] The existing radio wave refraction correction method is to use the GNSS receiver to obtain the total electron content of the ionosphere above the radar and invert the ionosphere electron density based on the model, and then use the spherical layering method to calculate the refraction error correction. The correction accuracy of this method depends on the perception accuracy of the ionosphere through which the radar signal passes. However, the radar detection distance is long and the area is wide. In the radar coverage area, the radio wave environment characteristics vary greatly, and the refraction error also has obvious differences. On the one hand, the ionospheric electron content inversion model is an indirect means, which is difficult to effectively reflect the true state of the ionosphere. In the year of high solar activity, the correction residual error is still large; on the other hand, the radar's operating frequency band range is wide and there are many detection frequency points. When calculating the refraction error correction value, the existing method cannot calculate the refraction error for each frequency point. Otherwise, the calculation amount is too large and the running time is too long, and it is impossible to achieve the requirement of near real-time correction. Therefore, direct and near real-time processing measures are needed to improve the accuracy of refraction error correction. Summary of the invention

[0005] In view of this, the present invention provides a radar real-time dual-frequency radio wave refraction error correction method, which can realize the correction of radio wave refraction error by allowing the low-frequency radar to adaptively adopt the corresponding working frequency point, and the correction accuracy is high and the real-time performance is strong. It is suitable for low elevation angle detection scenarios during high solar activity years.

[0006] The radar real-time dual-frequency radio wave refraction error correction method of the present invention is characterized by comprising:

[0007] S1, the radar uses two different frequencies f1 and f2 to detect the target at the same location, and obtains the distance measurement value R at the two frequencies f1 , R f2 ; Among them, the frequencies f1 and f2 satisfy: the distance measurement value R f1 , R f2 The distance difference between them is greater than 10 times the radar measurement error;

[0008] S2, calculate the radar wave refraction error ΔR at frequency f2 f2 :

[0009]

[0010] Where v is the radial velocity of the target relative to the radar; T 切换 It is the dual frequency switching time;

[0011] S3, using ΔR f2 Correct the detection distance of the radar at frequency f2.

[0012] The preferred method also includes: analyzing the electromagnetic environment in which the radar is located, calculating the noise floor amplitude within the working frequency band, and selecting the working frequency point that is less affected by the electromagnetic environment; the frequencies f1 and f2 satisfy: the distance measurement value R f1 , R f2 The distance difference is greater than 10 times the radar measurement error.

[0013] Preferably, a radio wave refraction error correction device is used to count the radio wave refraction error values ​​of the radar at each frequency in years with high and low solar activity, and the minimum interval of frequencies f1 and f2 is determined based on the radar's measurement error, that is, the distance measurement difference of radio wave refraction at frequencies f1 and f2 in years with high and low solar activity is greater than 10 times the radar measurement error.

[0014] Preferably, when electromagnetic waves with frequencies f1 and f2 are emitted by any of the following methods:

[0015] (1) During two consecutive tracking operations, the radar uses frequencies f1 and f2 to detect targets respectively;

[0016] (2) Each time the radar tracks a target, it continuously emits two frames of electromagnetic waves with frequencies f1 and f2 respectively;

[0017] (3) The radar continuously transmits two pulses with frequencies f1 and f2 in a repetition cycle of each target tracking;

[0018] Radar radio wave refraction error ΔR at frequency f2 f2 for:

[0019]

[0020] Beneficial effects:

[0021] 1. Radar can use the electromagnetic waves emitted by itself to independently and directly correct the radio wave refraction error. Radar does not need to obtain the electron content through the GNSS receiver and then invert the electron density to indirectly obtain the radio wave refraction error correction. Instead, it uses the electromagnetic waves emitted by itself to directly correct the radio wave refraction error while detecting the target.

[0022] 2. Radar can correct radio wave refraction errors in real time

[0023] The method of electron density inversion usually updates the radio wave refraction error correction every 5 to 10 minutes, which is difficult to meet the real-time error correction needs of the radar, and post-correction is often used. This method can complete the error correction while detecting the target, which can greatly improve the timeliness of error correction.

[0024] 3. Improve the accuracy of radio wave refraction error correction in years with high solar activity

[0025] The electron content obtained by the GNSS receiver is difficult to accurately reflect the electron content on the radio wave propagation path of the radar's actual detection target, which will cause the electron density inversion to be inaccurate, especially in years with high solar activity and drastic changes in the ionosphere. This method uses the reflected echo of the radar's own detection target to perform error correction, which can accurately obtain the radio wave refraction correction error on the detection path, thereby improving the error correction accuracy.

[0026] 4. Radar resource adaptive scheduling

[0027] When the radar switches frequencies to obtain radio wave refraction errors, it can adaptively adjust resource scheduling strategies based on target importance and target capacity requirements, which is beneficial to improving error correction accuracy, ensuring multi-target tracking capabilities, and improving resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the radio wave refraction effect.

[0029] Figure 2The present invention is a flow chart of a real-time correction method for radio wave refraction error based on dual-frequency operation of radar.

[0030] Figure 3 It is the relationship between the distance change Δr and the dual frequency point interval Δf.

[0031] Figure 4 It is a method of twice scheduling frequency conversion.

[0032] Figure 5 It is a method of intra-pulse frequency conversion.

[0033] Figure 6 It is a method of intra-pulse frequency conversion. DETAILED DESCRIPTION

[0034] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0035] The present invention provides a radar real-time dual-frequency radio wave refraction error correction method, which uses the principle that the instantaneous propagation path of electromagnetic waves is approximately the same when the two working frequencies of the radar are switched for detection, directly obtains the error correction amount of the required frequency point, and can adaptively adjust the radar working sequence according to the importance of the target and the radar resource utilization rate. The present invention can realize the direct completion of radio wave refraction error correction without the participation of a GNSS receiver. The method of the present invention establishes a discrimination process of first determining the radar dual-frequency working switching mode and then obtaining the dual-frequency point measurement data to directly correct the radio wave refraction error. It is based on conventional radar data processing methods and has high real-time performance. It enables the radar to adopt corresponding working methods and processing methods according to the importance of the target and the target capacity constraints, effectively improves the accuracy of radar detection error correction in the solar high year, and realizes direct, real-time and accurate correction of radar radio wave refraction errors.

[0036] The process of this method is as follows Figure 2 As shown in the figure. First, the magnitude of the distance error caused by the ionosphere and the measurement error of the radar itself (without considering the propagation error) are calculated. Then, the electromagnetic environment of the radar is analyzed, the interference of all the radar working frequencies is comprehensively evaluated, and the interval between the dual-frequency points of the radar is determined to ensure that the distance change caused by the ionosphere between the dual-frequency points can be effectively obtained. Finally, according to the importance of the target and the target capacity constraint, the radar adaptively selects the switching frequency point between two schedulings, between frames or within the pulse to observe the target, obtains the target distance measurement value, and obtains the refraction error correction value of a certain frequency point by calculation.

[0037] 1) Radar dual-frequency working interval selection

[0038] The observed distance value when the radar operating frequency is f1 is The observed distance value when the radar operating frequency is f2 is in are the true distance, ΔRf1 , ΔR f2 are radio wave refraction errors.

[0039] The relationship between the radio wave refraction error, the electron density profile of the propagation path, and the radar operating frequency can be expressed as

[0040]

[0041] Among them, ΔR f is the radio wave refraction error when the radar frequency is f; N e When the radar uses two frequencies to detect targets at the same location, the radar electromagnetic waves of the two frequencies travel along the same path from the radar to the target, even if the electron density term N on the propagation path is e is unknown. Since electromagnetic waves propagate on the same path (the shorter the time, the smaller the change in the path through the ionosphere), the electron density terms on the same path are the same. Therefore, the distance change between the distance observation values ​​of the dual frequency points f1 and f2 is

[0042]

[0043] Where Δf is the interval between the dual frequency points f1 and f2, v is the radial velocity of the target relative to the radar, T 切换 is the dual-frequency switching time. From formula (2), it can be seen that the distance change between the dual-frequency points is related to the radio wave refraction error, the frequency interval and the dual-frequency switching time. Therefore, the relationship curve between the distance change and the dual-frequency interval is given, as shown in Figure 3 shown.

[0044] If the distance change between the two frequency points is greater than 10 times the radar's own measurement error (not considering the propagation error), this distance change can be obtained during radar data processing; if the distance change between the two frequency points is less than or equal to 10 times the radar's own measurement error, it is difficult to obtain this value during data processing. Therefore, two different frequencies f1 and f2 can be transmitted, where the frequencies f1 and f2 satisfy their distance measurement values ​​R f1 , R f2 If the distance difference between them is greater than 10 times of the radar measurement error, the radar wave refraction error ΔR at frequency f2 can be calculated by formula (3): f2 :

[0045]

[0046] Using ΔR f2 The detection distance of the radar at frequency f2 can be corrected:

[0047] R′ f2 =R f2 -ΔRf2 (4)

[0048] Among them, R f2 is the distance observation value when the radar operating frequency is f2, R′ f2 is the detection distance of the corrected frequency point f2.

[0049] from Figure 3 It can be seen that in years with strong solar activity, due to the large error in radio wave refraction, the interval between the two frequencies does not need to be very large to obtain the distance change. However, in years with weak solar activity, the error in radio wave refraction becomes smaller and the interval between the two frequencies needs to be very large to obtain the distance change. Therefore, this method will be more effective in years with strong solar activity.

[0050] The radio wave refraction error correction equipment can be used to count the radio wave refraction error values ​​of the radar in years with high and low solar activity, and then combined with the radar's own measurement error, the minimum interval between the radar's operating frequencies f1 and f2 can be determined, that is, in years with high and low solar activity, the distance measurement difference of radio wave refraction at frequencies f1 and f2 is greater than 10 times the radar measurement error.

[0051] In addition, in actual application, it is also necessary to analyze the electromagnetic environment in which the radar is located, calculate the noise floor amplitude within the working frequency band, and select dual-frequency points that are less affected by the electromagnetic environment.

[0052] 2) Adaptive scheduling dual-frequency working mode

[0053] It can be seen from formula (2) that the shorter the dual-frequency switching time, the smaller the impact of the target radial distance movement on the distance change. Therefore, a variety of switching modes can be selected in the radar working mode, from scheduling level (seconds) to inter-frame (milliseconds) and even intra-pulse (microseconds). The switching frequency between scheduling will not waste additional tracking time resources, and the accuracy of the switching frequency correction for two consecutive frames will be improved. However, if the same target is detected twice in a row, the tracking time will double and the tracking target capacity will decrease; the switching frequency correction accuracy within the same repetition period will be improved, but at the same time the multi-beam capability will decrease, affecting the multi-target tracking performance and also wasting additional tracking resources. In summary, the adaptive scheduling dual-frequency working mode is considered: first, according to the radar deployment position and the annual solar activity, within the specified elevation angle range, the dual-frequency correction method is used for all targets twice to improve the low-elevation angle distance accuracy, and then the dual-frequency correction method for two consecutive frames or repetition periods can be selected for specific or key targets to improve the distance accuracy of key targets;

[0054] a) Method 1 (double-frequency correction with two dispatches)

[0055] The radar tracks ordinary targets, uses different frequencies in two consecutive tracking dispatches (the tracking data rate can be set to 1s and 2s), records the track data, and obtains the distance observation values ​​R of the two frequency points respectively. f1 , R f2 .

[0056] b) Mode 2 (two consecutive frames of dual-frequency correction)

[0057] The radar tracks the key target and transmits two frames continuously each time the target is tracked. Different frequencies are used between frames to record the track data and obtain the distance observation values ​​R of the two frequencies respectively. f1 , R f2 .

[0058] c) Mode 3 (dual frequency correction within pulse)

[0059] The radar tracks a specific target, and emits two pulses continuously in a repetition cycle of each tracking target. It uses different frequencies to record track data and obtain the distance observation values ​​R of the two frequencies respectively. f1 , R f2 .

[0060] When any of the above methods is adopted, v×T in formula (2) 切换 can be ignored, that is, the f2 frequency point distance error correction ΔR caused by the ionosphere f2 As shown in formula (5):

[0061]

[0062] Since the radio wave refraction distance error is inversely proportional to the square of the frequency, the radio wave refraction errors caused by different frequencies are different. The present invention directly obtains the error correction amount based on this relationship. To this end, the present invention first calculates the distance error magnitude caused by the ionosphere and the measurement error of the radar itself (without considering the propagation error), then analyzes the electromagnetic environment in which the radar is located, comprehensively evaluates the interference of all working frequencies of the radar, and determines the interval between the dual-frequency points of the radar to ensure that the distance change caused by the ionosphere between the dual-frequency points can be effectively obtained; finally, according to the importance of the target and the target capacity constraint, the radar adaptively selects the switching frequency point between two dispatches, between frames or within the pulse to observe the target, obtains the target distance measurement value, and obtains the refraction error correction amount of a certain frequency point by calculation. It has been verified by actual measurement that the present invention effectively realizes the correction of radio wave refraction error, especially can significantly improve the distance accuracy at low elevation angles, wherein the maximum error of the dual-frequency correction method between two dispatches can be controlled below 100 meters, and the correction accuracy of the dual-frequency correction method between frames is improved by more than 10% compared with the dual-frequency correction method between dispatches.

[0063] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A radar real-time dual-frequency radio wave refraction error correction method, characterized in that: include: S1, the radar uses two different frequencies f1 and f2 to detect the target at the same location, and obtains the distance measurement value R at the two frequencies f1 , R f2 ; Among them, the frequencies f1 and f2 satisfy: the distance measurement value R f1 , R f2 The distance difference between them is greater than 10 times the radar measurement error; S2, calculate the radar wave refraction error ΔR at frequency f2 f2 : Where v is the radial velocity of the target relative to the radar; T 切换 It is the dual frequency switching time; S3, using ΔR f2 Correct the detection distance of the radar at frequency f2.

2. The method according to claim 1, characterized in that Also includes: Analyze the electromagnetic environment of the radar, calculate the noise floor amplitude within the working frequency band, and select the working frequency point that is less affected by the electromagnetic environment; Frequencies f1 and f2 satisfy: distance measurement value R f1 , R f2 The distance difference is greater than 10 times the radar measurement error.

3. The method according to claim 1 or 2, characterized in that The radio wave refraction error correction equipment is used to count the radio wave refraction error values ​​of the radar at each frequency in years with high and low solar activity. Combined with the radar's measurement error, the minimum interval between frequencies f1 and f2 is determined, that is, in years with high and low solar activity, the distance measurement difference of radio wave refraction at frequencies f1 and f2 is greater than 10 times the radar measurement error.

4. The method according to claim 1, 2 or 3, characterized in that: When electromagnetic waves with frequencies f1 and f2 are emitted by any of the following methods: (1) During two consecutive tracking operations, the radar uses frequencies f1 and f2 to detect targets respectively; (2) Each time the radar tracks a target, it continuously emits two frames of electromagnetic waves with frequencies f1 and f2 respectively; (3) The radar continuously transmits two pulses with frequencies f1 and f2 in a repetition cycle of each target tracking; Radar radio wave refraction error ΔR at frequency f2 f2 for:

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