An airborne radar downburst optimized detection method

Abstract

The application discloses an airborne radar downburst optimized detection method and belongs to the technical field of radar signal processing. An airborne Doppler radar is used to emit a radar waveform to a possible wind shear dangerous area in front of a route, and wind speed estimation in a transmission direction is obtained by analyzing radar echo IQ data. The application sets a pitch angle of radar scanning according to a take-off or landing stage of an airplane. After receiving the IQ signal, frequency domain correction is performed, data is preprocessed according to spectrum width information, and a wild value area is eliminated. After the preprocessing is completed, a frequency domain clutter suppression algorithm is used to suppress a ground clutter area near zero frequency, and then wind shear wind speed estimation is performed. The application proposes a novel vertical wind speed estimation model, establishes a connection between a downburst core area range and a vertical wind speed gradient, forms a detection and sensing capability for a three-dimensional area of the downburst, and proposes an airplane scanning strategy for optimizing the model.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radar signal processing, and particularly relates to an airborne radar downburst optimized detection method. BACKGROUND

[0002] Doppler radar is a commonly used means for detecting low-level wind shear. Airborne Doppler radar needs to provide early detection of low-level wind shear during the aircraft takeoff and landing phase. The basic principle is to measure the Doppler frequency shift between the radar transmitted pulse and the received echo to represent the wind speed along the beam transmission direction, so as to calculate the wind speed change along the radial direction. By controlling the radar beam scanning, the wind speed in each scanning direction is drawn. Unlike ground-based radars, airborne radars often have to complete the whole process of discovery-evaluation-judgment within about 5s when detecting wind shear. Further, since the power of airborne radar is smaller than that of ground-based radar, the detection distance is relatively short. In summary, the typical application scenario of airborne radar for low-level wind shear is to use a single horizontal scan to complete the detection of wind shear.

[0003] Since airborne radar needs to have the ability to detect the wind speed change of the core area of low-level wind shear below 600 meters from the ground surface at a distance of 5 nautical miles (9 kilometers), due to the limitation of the viewing angle, the Doppler radar needs to use a beam pointing direction approximately along the horizontal direction. Due to the limitation of the Doppler velocity measurement principle, the vertical velocity cannot be directly measured at this time. A commonly used solution is to use a vertical wind model to estimate the vertical component from the horizontal wind measurement. First, the horizontal wind speed gradient change of the low-level wind shear is determined by analyzing the linear correlation coefficient of the radial wind speed profile, and then the vertical wind speed gradient is determined by using the mass continuity equation , and finally the vertical wind is calculated by using the vertical wind speed related model of the height .

[0004] The main factors limiting the accuracy of the above wind speed measurement are:

[0005] 1. The estimation accuracy of , that is, the judgment of the downburst core area; the vertical wind speed gradient is generally obtained by the continuity equation. To solve the vertical wind speed , first, according to the continuity equation in the cylindrical coordinate system, and assuming that the wind shear flow field has no tangential component, there is . In the core area of the wind shear, it is assumed that the wind speed increases uniformly along the radial direction from the center to the periphery, so there is . And in the edge area, the term can be ignored, that is, . As can be seen, the judgment of the size of the center and the edge area will affect the and further affect the vertical wind speed And the measurement of the F-factor. In practical applications of airborne radar, due to the influence of ground clutter, the radar scanning pitch angle during landing is generally higher than the aircraft's actual glide angle. During takeoff, to more accurately estimate the horizontal wind speed, a scanning pitch angle lower than the aircraft's takeoff angle is generally used. The inconsistency between the scanning line of sight and the aircraft's flight altitude often leads to the algorithm misjudging the core area of ​​the downburst on the aircraft's path, thus affecting the accuracy of velocity measurement.

[0006] 2. Accuracy of the vertical wind speed estimation model. On the other hand, since the actual wind shear vertical wind speed gradient varies with height, therefore... With vertical wind speed The accuracy of linear models between these parameters is poor. Existing empirical models typically rely on three-dimensional parametric models of wind shear fields, whose parameters usually need to be fitted to each detection direction, resulting in a large computational burden. Alternatively, they may use pre-defined parameters, which have poor general applicability to different wind shear scenarios. Summary of the Invention

[0007] The purpose of this invention is to propose a novel method for calculating vertical wind speed based on the application scenarios of airborne Doppler radar for low-altitude wind shear detection and the characteristics of downburst outflow distribution. A method for determining the core area of ​​downbursts at different altitudes is also constructed, improving the estimation accuracy of downburst vertical wind speed. This calculation model has low computational complexity, does not rely on preset parameters, and has smaller errors compared to traditional models. Furthermore, by employing an iterative adjustment method of the radar pitch angle, the near-surface horizontal outflow area of ​​the downburst is detected more accurately, improving the model's adaptability to various scenarios during aircraft takeoff and landing.

[0008] To achieve the above objectives, the technical solution adopted in this invention is as follows: an optimized detection method for downbursts using airborne radar, which uses an airborne Doppler radar to transmit radar waveforms toward a possible wind shear hazard area ahead of the flight path, and analyzes the radar echo IQ data to obtain an estimate of the wind speed in the direction of transmission.

[0009] The radar employs azimuth scanning. The elevation angle of the radar scan is set according to the aircraft's takeoff or landing phase. Upon receiving the IQ signal, frequency domain correction is performed based on information such as aircraft attitude and speed. Data preprocessing is conducted based on information such as spectral width to remove outlier regions. After preprocessing, a frequency domain clutter suppression algorithm is used to suppress potential ground clutter regions near zero frequency, followed by wind shear and wind speed estimation.

[0010] Step 0: Calculate the average wind speed in the atmospheric boundary layer of the area where the aircraft is located and subtract it from the wind speed measurement. , in It is the boundary layer wind speed, which can be obtained through airspeed and ground speed information provided by the carrier aircraft;

[0011] Step 1: Use the frequency domain analysis algorithm to obtain the distribution of the meteorological echo radial velocity with respect to distance for each horizontal azimuth scan of the radar; Step 2: Based on the radial wind speed distribution, determine the maximum and minimum values of the wind shear speed and the corresponding distances in each radial direction;

[0012] Step 3: Calculate the horizontal gradient of the radial wind speed using the least squares method according to the radial wind speed distribution;

[0013] Step 4: Calculate the vertical wind speed using the vertical wind speed model based on the horizontal gradient;

[0014] Step 5: If the height at which the radial wind speed detected in Step 4 is consistent with or basically coincides with the aircraft flight path, directly perform the F factor calculation, otherwise go to Step 6;

[0015] Step 6: Estimate the distribution of the vertical wind speed along the vertical direction according to the vertical wind speed model in Step 4. Accordingly, combined with the wind speed extreme value positions calculated in Step 2, calculate the downburst core area at each height layer;

[0016] Step 7, following Step 6, calculate the F factor of the aircraft's expected flight path. And optimize the pitch angle according to the F factor calculation result as appropriate, and return to Step 0 for the next iterative calculation to achieve a better downburst F factor prediction.

[0017] The above Step 2 is implemented using the following preferred scheme:

[0018] According to the distribution of the radial wind speed, first determine the positions xmin and xmax of the maximum and minimum values. If xmin < xmax, it means that the radial wind speed shows surface divergence, then continue: Select the area [xmin - x1, xmin + x2] for quadratic function fitting to determine the accurate positions Xmin and Umin corresponding to the wind speed extreme values. Similarly, determine the position of Xmax and Umax. Finally, for each azimuth direction i , perform quadratic function fitting in the azimuth direction, and take the extreme value R as the downburst core radius at the detection height.

[0019] The above Step 4 is implemented using the following preferred scheme:

[0020] The optimization of the vertical wind speed model is based on the characteristics of the downburst sinking area and outflow area. Before reaching the ground surface, the downburst accelerates downward through processes such as evaporative cooling and raindrop drag. When approaching the ground (about 1 km), it begins to decelerate under the influence of the blocking pressure generated by the ground surface, and the horizontal outflow speed increases. When approaching the ground, the vertical speed is all converted into horizontal speed and diverges in all directions. Therefore, the vertical speed change rate of the downburst can be described according to the deceleration expansion area ( ) and the horizontal outflow area ( ):

[0021]

[0022] in, Represents the height of the near-surface horizontal outflow region. The radius of the downburst is calculated in step 2 above. From the horizontal wind speed gradient in step 3 above Calculations show that the core and edge regions of the downburst have the following characteristics:

[0023]

[0024] .

[0025] Step 5 above is implemented using the following preferred solution:

[0026] The number of distance gates whose F-factor in a single sector scan exceeds a certain preset threshold is counted. If the S / C ratio of distance gates exceeding a certain preset percentage is higher than a threshold, the pitch angle is determined to need adjustment.

[0027] Step 6 above is implemented using the following preferred solution:

[0028] The core region of a downburst varies at different altitudes, generally exhibiting a decreasing horizontal scale from lower altitudes to the altitudes corresponding to the points of maximum vertical velocity. This is because, as the downburst approaches the ground and decelerates downwards, the overall flow field's downward momentum at each altitude level before reaching the near-surface horizontal outflow region remains constant. It remains essentially unchanged. However, after descending to the near-surface horizontal outflow region, it can be approximated as... constant, It decreases linearly with height. Therefore, assuming the radius of the downburst in the horizontal outflow region is known... It can calculate a certain height above the horizontal outflow region. Blowout radius:

[0029]

[0030] in, The outflow function for a downburst represents the proportion of the downburst flow field at a given height that flows outwards from the core region rather than continuing vertically downwards.

[0031] To simplify the computational scenario, we can take... .

[0032] Step 7 above is implemented using the following preferred solution:

[0033] First, based on the speed measurement results from step 6 above, the F-factor of the aircraft's expected trajectory is calculated. Since the key point of the model proposed in this invention is to measure the horizontal wind speed gradient and radius of the near-surface horizontal outflow core region of the downburst, to achieve this, after calculating the F-factor of the aircraft's expected trajectory, if the maximum value of the F-factor is greater than a certain preset threshold, it indicates the existence of a potential downburst disaster event. At this time, the radar elevation angle is adjusted so that when the beam scans to the position of the aforementioned maximum F-factor, the beam center height is located in the horizontal outflow region of the downburst, ensuring that the measured wind field range belongs to the horizontal outflow core region of the downburst. Steps 1-6 above are then repeated to measure the F-factor again.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. This invention proposes a novel vertical wind speed estimation model that establishes a connection between the core area of ​​a downburst and the vertical wind speed gradient, thereby forming a detection and perception capability for the three-dimensional region of the downburst. Furthermore, it proposes an aircraft scanning strategy optimized for this model.

[0036] 2. This invention has the characteristics of simple implementation, small amount of computation and fast speed, high accuracy of wind speed estimation and accurate judgment of wind shear factor. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the airborne radar downburst optimization detection method of the present invention.

[0038] Figure 2 This is a diagram of the standard dataset for wind shear.

[0039] Figure 3 It is the relationship between wind shear horizontal wind speed, core area and height.

[0040] Figure 4 This invention compares the proposed vertical wind speed estimation model with other existing models. Detailed Implementation

[0041] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments.

[0042] like Figures 1-2 As shown in the figure, this embodiment discloses an optimized detection method for downbursts using airborne radar. It uses an airborne Doppler radar to transmit radar waveforms to areas with potential wind shear hazards ahead of the flight path, and analyzes the radar echo IQ data to obtain an estimate of the wind speed in the direction of transmission.

[0043] The radar employs azimuth scanning. The elevation angle for the radar scan is set according to the aircraft's takeoff or landing phase, with a default value of +2° for takeoff and -3° for descent. Upon receiving the IQ signal, frequency domain correction is performed based on aircraft attitude, speed, and other information. Data preprocessing is then performed based on spectral width and other information to remove outlier regions. After preprocessing, a frequency domain clutter suppression algorithm is used to suppress potential ground clutter near zero frequency, followed by wind shear and wind speed estimation.

[0044] Step 0: Calculate the average wind speed in the atmospheric boundary layer of the area where the aircraft is located and subtract it from the wind speed measurement. , in It is the boundary layer wind speed, which can be obtained through airspeed and ground speed information provided by the carrier aircraft;

[0045] Step 1: Use frequency domain analysis algorithms to obtain the distribution of radial velocity of meteorological echoes with distance in each horizontal azimuth scan of the radar; Step 2: Based on the radial wind speed distribution, determine the maximum and minimum values ​​of the wind shear speed in each radial direction and the corresponding distance.

[0046] Step 3: Calculate the horizontal gradient of the radial wind speed using the least squares method based on the radial wind speed distribution;

[0047] Step 4: Calculate the vertical wind speed using the vertical wind speed model based on the horizontal gradient;

[0048] Step 5: If the radial wind speed detected in Step 4 is at the same or basically coincident with the aircraft's flight path (less than 50 meters), then directly perform the F-factor calculation; otherwise, proceed to Step 6.

[0049] Step 6: Based on the vertical wind speed model in Step 4, estimate the vertical wind speed distribution along the vertical direction. Then, combining this with the wind speed extreme value locations calculated in Step 2, calculate the downburst core region at each altitude level.

[0050] Step 7, following Step 6, calculates the F-factor of the aircraft's expected trajectory. Based on the F-factor calculation results, optimizes the pitch angle as needed, and returns to Step 0 for the next iteration calculation to achieve a better downburst F-factor prediction.

[0051] Step 2 above is implemented using the following preferred solution:

[0052] According to the distribution of the radial wind speed, first determine the positions xmin and xmax of the maximum and minimum values. If xmin < xmax, it represents surface divergence of the radial wind speed, and then continue: Select the region [xmin - x1, xmin + x2] for quadratic function fitting to determine the accurate positions Xmin and Umin corresponding to the wind speed extreme values. Here, x1 and x2 are determined based on the wind speed at xmin - x1 and xmin + x2 being 0.8 * Umin (the wind speed at xmin). Similarly, determine the position Xmax and Umax. Finally, for each azimuth i of the , perform quadratic function fitting in the azimuth direction, and use the extreme value R as the radius of the downburst core at the detection height.

[0053] The above step 4 is implemented by the following preferred scheme:

[0054] The optimization of the vertical wind speed model is based on the characteristics of the downdraft sinking area and outflow area. Before reaching the ground surface, the downdraft accelerates downward through processes such as evaporative cooling and raindrop drag. When approaching the ground (about 1 km), it starts to decelerate under the influence of the blocking pressure generated by the ground surface, the horizontal outflow velocity increases, and when approaching the ground, the vertical velocity is completely converted into horizontal velocity and diverges in all directions. Therefore, the vertical velocity change rate of the downdraft can be described according to the deceleration expansion area ( ) and the horizontal outflow area ( ):

[0055]

[0056] Among them, represents the height of the near-ground horizontal outflow area, and is the downburst radius calculated in step 2 above. Calculated from the horizontal wind speed gradient in step 3 above, in the downburst core area and the edge area, there are respectively:

[0057]

[0058] .

[0059] The above step 5 is implemented by the following preferred scheme:

[0060] Statistically count the number of range gates where the F factor in a single sector scan is greater than the threshold F = 0.05. F = 0.05 is an empirical value for distinguishing clutter and noise fluctuations from the horizontal divergence signal of wind shear. If S / C is higher than the threshold in more than 30% of the range gates, it is determined that the elevation angle needs to be adjusted.

[0061] The above step 6 is implemented by the following preferred scheme:

[0062] The core region of a downburst varies at different altitudes, generally exhibiting a decreasing horizontal scale from lower altitudes to the altitudes corresponding to the points of maximum vertical velocity. This is because, as the downburst approaches the ground and decelerates downwards, the overall flow field's downward momentum at each altitude level before reaching the near-surface horizontal outflow region remains constant. It remains essentially unchanged. However, after descending to the near-surface horizontal outflow region, it can be approximated as... constant, It decreases linearly with height. Therefore, assuming the radius of the downburst in the horizontal outflow region is known... It can calculate a certain height above the horizontal outflow region. Blowout radius:

[0063]

[0064] in, Let be the outflow function for the downburst, representing the proportion of the downburst flow field at a corresponding height that flows outwards from the core region rather than continuing vertically downwards. For simplicity in the calculation scenario, we can take . .

[0065] Step 7 above is implemented using the following preferred solution:

[0066] First, based on the speed measurement results from step 6 above, the F-factor of the aircraft's expected trajectory is calculated. Since the key point of the model proposed in this invention is to measure the horizontal wind speed gradient and radius of the near-surface horizontal outflow core region of the downburst, to achieve this, after calculating the F-factor of the aircraft's expected trajectory, if the maximum F-factor value is greater than 0.08, it indicates the existence of a potential downburst disaster event. At this time, the radar elevation angle is adjusted so that the beam center height is 100m when the beam scans to the aforementioned position of the maximum F-factor value, ensuring that the measured wind field range belongs to the horizontal outflow core region of the downburst. Steps 1-6 above are then repeated to measure the F-factor again.

[0067] Figure 3 To utilize downburst wind field data from the US TASS standard wind shear dataset, and combining it with a self-made airborne radar simulation system, the algorithm in step 2 was used to calculate the corresponding core area location based on the changes in horizontal wind speed at different altitudes (the dots in the figure represent the corresponding core area boundaries). The changes in the downburst core area at different altitudes shown in the figure are basically consistent with the theoretical prediction results in step 6 of this invention.

[0068] Figure 4To compare the estimation errors of different vertical wind speed calculation models at different heights of downbursts using the TASS standard wind shear dataset, it is evident that the vertical wind speed estimation model proposed in this invention (numbered SH2, orange line) has significant advantages over existing linear and nonlinear models (Vicroy model, logarithmic correction model) at different height levels.

[0069] Although the present invention has been disclosed above with reference to preferred embodiments, the embodiments and accompanying drawings are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention, and these changes will also be within the protection scope of the invention. Therefore, the protection scope of the present invention should be defined by the scope of the claims of this application.

Claims

1. An optimized detection method for downbursts using airborne radar, characterized in that: Using an airborne Doppler radar, radar waveforms are transmitted toward potential wind shear hazards ahead of the flight path, and the radar echo IQ data is analyzed to obtain an estimate of the wind speed in the direction of transmission. The radar scanning pitch angle is set according to the aircraft's takeoff or landing phase; after receiving the IQ signal, frequency domain correction is performed, and the data is preprocessed based on the spectral width information to remove outlier regions. After preprocessing, a frequency domain clutter suppression algorithm is used to suppress ground clutter in the vicinity of zero frequency. Then, wind shear and wind speed are estimated, specifically including: Step 0: Calculate the average wind speed in the atmospheric boundary layer of the area where the aircraft is located and subtract it from the wind speed measurement. ,in It is the boundary layer wind speed, obtained through airspeed and ground speed information provided by the carrier aircraft; Step 1: Use frequency domain analysis algorithms to obtain the distribution of the radial velocity of the meteorological echo with distance in each horizontal azimuth scan of the radar; Step 2: Based on the radial wind speed distribution, determine the maximum and minimum values ​​of the wind shear speed in each radial direction and the corresponding distances; Step 3: Calculate the horizontal gradient of the radial wind speed using the least squares method based on the radial wind speed distribution; Step 4: Calculate the vertical wind speed using the vertical wind speed model based on the horizontal gradient; Step 5: If the altitude of the radial wind speed detected in Step 4 is consistent with or substantially coincides with the aircraft's flight path, proceed to Step 7; otherwise, proceed to Step 6. Step 6: Based on the vertical wind speed model in Step 4, estimate the distribution of vertical wind speed along the vertical direction, and combine it with the wind speed extreme value location calculated in Step 2 to calculate the core area of ​​downburst at each height level. Step 7: Calculate the F-factor of the aircraft's expected trajectory, and optimize the pitch angle as needed based on the F-factor calculation results. Return to step 0 for the next iteration calculation to achieve downburst F-factor prediction. Step 4 specifically involves: According to the deceleration expansion zone, Horizontal outflow region Describe the rate of change of vertical velocity of the downburst: ； in, Represents the height of the near-surface horizontal outflow region. The radius of the downburst calculated in step 2; From the horizontal wind speed gradient in step 3 Calculations show that the core and edge regions of the downburst burst have the following characteristics: 。 2. The optimized detection method for airborne radar downbursts according to claim 1, characterized in that: Step 2 specifically involves: According to the distribution of the radial wind speed, first determine the positions xmin and xmax of the maximum and minimum values. If xmin < xmax, it represents ground divergence of the radial wind speed, and then continue: Select the region [xmin - x1, xmin + x2] for quadratic function fitting to determine the corresponding positions Xmin and Umin of the accurate wind speed extreme values; if xmax < xmin, then continue: Select the region [xmax - x1, xmax + x2] for quadratic function fitting to determine the corresponding positions Xmax and Umax of the accurate wind speed extreme values; finally, for each azimuthal direction i of the , perform quadratic function fitting in the azimuthal direction, and take the extreme value R as the radius of the downburst core at the detection height.

3. The optimized detection method for airborne radar downbursts according to claim 1, characterized in that: Step 5 specifically involves: The number of distance gates whose F-factor is greater than a certain preset threshold in a single sector scan is counted. If the S / C of distance gates exceeding a certain preset percentage is higher than the threshold, the pitch angle is determined to need adjustment.

4. The optimized detection method for airborne radar downbursts according to claim 1, characterized in that: Step 6 specifically involves: Assuming the radius of the downburst in the horizontal outflow region is known. Calculate a certain height above the horizontal outflow region. Blowout radius: ； in, Let be the outflow function of the downburst, representing the proportion of the downburst flow field at the corresponding height that flows outward from the core region rather than continuing vertically downward. Let be... .

5. The optimized detection method for airborne radar downbursts according to claim 1, characterized in that: Step 7 specifically involves: After calculating the F-factor of the aircraft's expected flight path, if the maximum value of the F-factor is greater than a certain preset threshold, it indicates that there is a potential downburst disaster event. At this time, the radar pitch angle is adjusted so that when the beam scans to the position of the maximum value of the F-factor, the height of the beam center is located in the horizontal outflow region of the downburst, so as to ensure that the measured wind field range belongs to the horizontal outflow core region of the downburst. Then, the above steps 1-6 are repeated to measure the F-factor again.

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