Self-adaptive airborne radar low-altitude wind shear detection method

Abstract

The invention discloses a self-adaptive airborne radar low-altitude wind shear detection method, and belongs to the technical field of radar signal processing, an airborne Doppler radar is used for transmitting radar waveforms to a wind shear dangerous area in front of an air route, radar echo IQ data are analyzed to obtain wind speed estimation in the transmitting direction, and a radar echo processing strategy is followed. After an IQ signal is received, frequency domain correction is carried out, data is preprocessed according to information such as spectrum width, and an outlier region is eliminated. In the landing stage of the aircraft, the scanning angle along the glide path of the aircraft is preferentially selected, the beam pitching angle is optimized and adjusted in combination with the intensity characteristics of clutters, and the clutter suppression effect in the landing stage is guaranteed. In the take-off stage of the aircraft, the scanning angle lower than the climbing path of the aircraft is preferentially selected, and the estimation effect on the near-ground horizontal radiation is optimized. And when the clutter intensity is greater than the threshold value, adjusting the pitch angle of the radar and selecting a nonlinear vertical wind speed model which is more accurate for estimating the wind speed at the higher altitude.

Description

Technical Field

[0001] This invention relates to the field of radar signal processing technology, and in particular to an adaptive airborne radar method for detecting low-altitude wind shear. Background Technology

[0002] Low-level wind shear refers to sudden changes in wind direction and speed occurring near the ground at the same or different altitudes over a short distance. Among these, micro-downburst type low-level wind shear is characterized by its short duration (2-20 minutes), small area (diameter less than 4 km), and high intensity (horizontal wind speed divergence gradient can exceed ±10 m / s / km), making it the most serious meteorological hazard during takeoff and landing. When an aircraft is exposed to downburst type wind shear of sufficient intensity and duration, it may crash due to loss of airspeed or altitude. An aircraft is considered to be in danger when wind shear reduces its state of energy at a rate faster than the aircraft engine thrust can replenish it. The aviation industry typically uses a dimensionless wind shear F-factor to measure the degree of wind shear hazard.

[0003]

[0004] in, For horizontal wind speed, This is the acceleration due to gravity. Vertical wind speed, This refers to the aircraft's airspeed.

[0005] The main factors limiting the accuracy of the above wind speed measurements are: 1. interference from ground clutter; 2. the accuracy of the vertical wind speed estimation model. To reduce interference from ground clutter, the scanning beam is usually raised. However, because the beam is higher off the ground, the horizontal wind speed divergence is not significant, which will cause errors in the estimation of the horizontal wind speed gradient, and thus affect the estimation of the vertical wind speed. Summary of the Invention

[0006] The purpose of this invention is to propose an optimized scanning and wind speed calculation method based on the application scenario of airborne Doppler radar for low-altitude wind shear detection. This addresses the shortcomings of traditional airborne radar detection of low-altitude wind shear, which suffers from inaccurate wind speed estimation due to strong clutter interference, resulting in an underestimation of the F-factor. During the aircraft's landing phase, a scanning angle along the aircraft's glide path is prioritized, and the beam pitch angle is optimized and adjusted based on the clutter intensity characteristics. During the aircraft's takeoff phase, a scanning angle below the aircraft's climb path is prioritized, and the subsequent pitch angle and model calculation method are adjusted based on the clutter intensity of the echo.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: an adaptive airborne radar low-altitude wind shear detection method, characterized in that:

[0008] Using an airborne Doppler radar, radar waveforms are transmitted toward the wind shear hazard area 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.

[0009] The radar uses azimuth scanning and follows the radar echo processing strategy. After receiving the IQ signal, it performs frequency domain correction based on the aircraft's attitude and speed information, preprocesses the data based on the spectrum width information, removes outlier regions, and analyzes the takeoff and landing phases after preprocessing.

[0010] The takeoff phase analysis steps are as follows:

[0011] Step 0: Set the pitch angle for radar scanning based on the aircraft's takeoff climb angle. The default value is half of the climb angle.

[0012] Step 1: Use a frequency domain clutter suppression algorithm to suppress potential ground clutter regions near zero frequency;

[0013] Step 2: Compare the spectra before and after clutter suppression to estimate the signal-to-clutter ratio (S / C);

[0014] Step 3: Using frequency domain analysis algorithms, the distribution of the radial velocity of meteorological echoes with distance in each horizontal azimuth scan of the radar is obtained;

[0015] Step 4: Based on the radial wind speed gradient Calculate the wind shear level F-factor;

[0016] Step 5: If the noise-to-signal ratio S / C is higher than the threshold in the region where the horizontal F factor is greater than the threshold, then the pitch angle is raised to the aircraft takeoff climb angle in the next scan.

[0017] Step 6: If the pitch angle needs to be increased, repeat steps 1 to 4 and calculate the F-factor using the empirical model; otherwise, calculate the F-factor using the linear model.

[0018] The landing phase analysis steps are as follows:

[0019] Step 0: Set the initial pitch angle for radar scanning based on the aircraft's glide slope angle. The default value is the glide slope angle.

[0020] Step 1: The aircraft continues to descend, and the pitch angle is adjusted according to the preset pitch angle Vs altitude relationship based on the aircraft altitude;

[0021] Step 2: Use a frequency domain clutter suppression algorithm to suppress potential ground clutter regions near zero frequency;

[0022] Step 3: Compare the spectra before and after clutter suppression to estimate the signal-to-clutter ratio (S / C);

[0023] Step 4: Using frequency domain analysis algorithms, the distribution of the radial velocity of the meteorological echoes from each horizontal azimuth scan of the radar as a function of distance is obtained;

[0024] Step 5: Based on the radial wind speed gradient Calculate the wind shear level F-factor;

[0025] Step 6: If the noise-to-signal ratio (S / C) is higher than the threshold in the region where the horizontal F factor is greater than the threshold, then raise the pitch angle in the next scan and recalculate the noise-to-signal ratio (S / C).

[0026] Step 7: Calculate the vertical wind speed using a linear model, and then calculate the F-factor.

[0027] As a preferred embodiment of the present invention, step 1 of the takeoff phase specifically comprises:

[0028] Based on the radar scanning system parameters, the zero-frequency clutter window width of the wind shear is set, and the signal of the removed frequency unit is supplemented by a linear fitting method.

[0029] As a preferred embodiment of the present invention, step 2 of the takeoff phase specifically comprises:

[0030] Calculate whether the ratio of the total frequency domain integrated signal strength before clutter suppression to the integrated signal strength after removing the zero-frequency signal and background noise exceeds the clutter-to-signal ratio (S / C) threshold.

[0031] In a preferred embodiment of the present invention, step 4 of the takeoff phase specifically involves: calculating the wind shear level F-factor.

[0032] ;

[0033] Where V is the airspeed of the aircraft and g is the acceleration due to gravity.

[0034] In a preferred embodiment of the present invention, step 5 of the takeoff phase specifically comprises:

[0035] The number of range gates whose F-factor in a single sector scan is greater than the threshold F=0.05 is counted. F=0.05 is an empirical value for distinguishing clutter and noise fluctuations from wind shear horizontal divergence signals. If the S / C of more than 30% of the range gates is higher than the threshold, the pitch angle is determined to need adjustment.

[0036] In a preferred embodiment of the present invention, step 6 of the takeoff phase specifically comprises:

[0037] If step 5 determines that the pitch angle needs to be increased, then the vertical wind speed is calculated using an empirical model. This empirical model is the Vicroy model, expressed as follows:

[0038]

[0039]

[0040] .

[0041] in, For the fitting parameters, The height corresponding to the maximum horizontal outflow velocity estimated by the model.

[0042] In a preferred embodiment of the present invention, step 1 of the landing phase specifically comprises:

[0043] Based on radar system parameters and the type of clutter echo from the ground target, the clutter-to-signal ratio between wind shear targets and ground clutter echoes is calculated. Since the echoes from meteorological targets are inversely proportional to the square of the distance, while the echoes from clutter targets are inversely proportional to the cube of the distance, as the aircraft descends and gradually approaches the wind shear detection area, the increase in clutter echoes is faster than the increase in meteorological echoes. At this point, the pitch angle needs to be adjusted upwards. The basis for adjusting the pitch angle is to keep the clutter-to-signal ratio of strong clutter types greater than a preset threshold, which is 20 dB.

[0044] In a preferred embodiment of the present invention, in step 6 of the landing phase, the magnitude of the elevation angle is given by an empirical formula:

[0045] ∆θ = (S / C + 20)⁄10

[0046] The signal-to-noise ratio (S / C) is in dB, and Δθ is in degrees.

[0047] Compared with the prior art, the present invention has the following advantages:

[0048] 1. During the aircraft's descent phase, this invention prioritizes the scanning angle along the aircraft's glide path and optimizes the beam pitch angle based on clutter intensity characteristics to ensure effective clutter suppression during descent. During takeoff, it prioritizes scanning angles below the aircraft's climb path to optimize the estimation of near-ground horizontal divergence. If the clutter intensity exceeds a threshold, the radar pitch angle is adjusted, and a nonlinear vertical wind speed model that provides more accurate estimation of wind speeds at higher altitudes is selected.

[0049] 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

[0050] Figure 1 This is a schematic diagram of the low-altitude wind shear detection method for aircraft takeoff phase of the present invention.

[0051] Figure 2 This is a schematic diagram of the low-altitude wind shear detection method during the aircraft landing phase of the present invention.

[0052] Figure 3 This is a diagram of the standard dataset for wind shear.

[0053] Figure 4 This is a schematic diagram of the simulation calculation results of wind shear hazard factors during the takeoff phase of an aircraft in this invention.

[0054] Figure 5 This is a schematic diagram illustrating the change in signal-to-clutter ratio with aircraft altitude during the urban clutter environment in the aircraft landing phase of this invention. Detailed Implementation

[0055] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments.

[0056] like Figure 1-3 As shown in the figure, this embodiment discloses an adaptive airborne radar low-altitude wind shear detection method. It uses an airborne Doppler radar to transmit radar waveforms to possible wind shear hazard areas ahead of the flight path, and analyzes the radar echo IQ data to obtain a wind speed estimate in the transmission direction.

[0057] The radar employs azimuth scanning. Following common radar echo processing strategies, after receiving the IQ signal, frequency domain correction is performed based on information such as aircraft attitude and speed. Data preprocessing is then performed based on information such as spectral width to remove outlier regions. After preprocessing, the takeoff and landing phases are described separately. The main analysis steps for the takeoff phase are as follows:

[0058] Step 0: Set the pitch angle for radar scanning based on the aircraft's takeoff climb angle. The default value is half of the climb angle of 5.73°.

[0059] Step 1: Use a frequency domain clutter suppression algorithm to suppress potential ground clutter regions near zero frequency;

[0060] Step 2: Compare the spectra before and after clutter suppression to estimate the signal-to-clutter ratio (S / C);

[0061] Step 3: Using frequency domain analysis algorithms, the distribution of the radial velocity of meteorological echoes with distance in each horizontal azimuth scan of the radar is obtained;

[0062] Step 4: Based on the radial wind speed gradient Calculate the wind shear level F-factor;

[0063] Step 5: If the noise-to-signal ratio S / C is higher than the threshold in the region where the horizontal F factor is greater than the threshold, then the pitch angle is raised to the aircraft takeoff climb angle in the next scan.

[0064] Step 6: If the pitch angle needs to be increased, repeat steps 1 to 4 on the next scan and calculate the F-factor using the empirical model; otherwise, calculate the F-factor using the linear model.

[0065] Step 1 above is implemented using the following preferred solution:

[0066] Based on the radar scanning system parameters, the zero-frequency (Doppler editing) clutter window width for wind shear is set to ±3 m / s. A frequency domain sampling gate corresponding to this window width is selected. A linear fitting method is used to complete the signal of the removed frequency units.

[0067] Step 2 above is implemented using the following preferred solution:

[0068] Calculate whether the ratio of the total integrated signal strength in the frequency domain before clutter suppression to the integrated signal strength after removing the zero-frequency signal and background noise exceeds the clutter-to-signal ratio (S / C) threshold (20dB).

[0069] Step 2 above is implemented using the following preferred scheme: Calculate the wind shear level F-factor:

[0070] ;

[0071] Where V is the airspeed of the aircraft and g is the acceleration due to gravity.

[0072] Step 5 above is implemented using the following preferred solution:

[0073] The number of range gates with an F-factor greater than the threshold F=0.05 in a single sector scan is counted. F=0.05 is an empirical value for distinguishing clutter and noise fluctuations from wind shear horizontal divergence signals. If the S / C ratio is higher than the threshold in more than 30% of the range gates, the pitch angle is determined to need adjustment. To reduce the probability of false alarms, the algorithm sets the area where the F-factor is greater than the threshold to be greater than 0.5 km^2.

[0074] Step 6 above is implemented using the following preferred solution:

[0075] If step 5 determines that the pitch angle needs to be increased, then an empirical (non-linear) model is used to calculate the vertical wind speed. The advantage of the empirical model, compared to the linear model, is that it can more accurately estimate the vertical wind speed using measurements of the horizontal wind speed gradient at heights of 300-600 meters, making it suitable for wind speed estimation at higher pitch angles. This empirical model (Vicroy model) can be expressed as:

[0076]

[0077]

[0078]

[0079] in, These are the fitting parameters. A preferred set of parameters is as follows: .

[0080] The main analytical steps during the descent phase are as follows:

[0081] Step 0: Set the initial pitch angle for radar scanning based on the aircraft's glide slope angle. The default value is the glide slope angle.

[0082] Step 1: The aircraft continues to descend, and the pitch angle is adjusted according to the preset pitch angle Vs altitude relationship based on the aircraft altitude;

[0083] Step 2: Use a frequency domain clutter suppression algorithm to suppress potential ground clutter regions near zero frequency;

[0084] Step 3: Compare the spectra before and after clutter suppression to estimate the signal-to-clutter ratio (S / C);

[0085] Step 4: Using frequency domain analysis algorithms, the distribution of the radial velocity of the meteorological echoes from each horizontal azimuth scan of the radar as a function of distance is obtained;

[0086] Step 5: Based on the radial wind speed gradient Calculate the wind shear level F-factor;

[0087] Step 6: If the noise-to-signal ratio (S / C) is higher than the threshold in the region where the horizontal F factor is greater than the threshold, then raise the pitch angle in the next scan and recalculate the noise-to-signal ratio (S / C).

[0088] Step 7: Calculate the vertical wind speed using a linear model, and then calculate the F-factor.

[0089] Step 1 above is implemented using the following preferred solution:

[0090] Based on radar system parameters and common surface target clutter echo types, the clutter-to-signal ratio (SNR) between meteorological (wind shear) targets and ground clutter echoes is calculated. Since meteorological target echoes exhibit an inverse square relationship with range, while clutter echo targets exhibit an inverse cube relationship, as the aircraft descends and gradually approaches the wind shear detection area, the increase in clutter echoes is faster than that of meteorological echoes. At this point, the pitch angle needs to be adjusted upwards. The adjustment of the pitch angle is based on maintaining a SNR greater than a threshold for specific strong clutter types (such as urban environments), typically 20 dB.

[0091] In step 6 of the descent phase described above, the elevation pitch angle is given by an empirical formula:

[0092] ∆θ = (S / C + 20)⁄10

[0093] The signal-to-noise ratio (S / C) is in dB, and Δθ is in degrees.

[0094] Figure 4The simulation results for the wind shear hazard factor during takeoff are shown. The blue line represents the true value of the wind shear factor along the aircraft's flight path, the green line represents the measured wind speed along the radar scanning direction, and the red line represents the calculated wind shear factor along the flight path (estimated based on the vertical wind speed model). The upper left figure shows the result without clutter suppression, where the wind speed measurement is significantly underestimated. The upper right figure shows the result when the pitch angle is the same as the aircraft's flight path climb angle (5.73°), and the lower left figure is a comparison when the pitch angle is half the aircraft's flight path climb angle (3°). It can be seen that when using the scanning strategy of this invention, because the lower left figure uses a lower pitch angle and the scanning position is closer to the ground divergence center of the radial wind speed, the estimation of the F-factor is more accurate than the estimation along the aircraft's flight path.

[0095] Figure 5 This chart shows the signal-to-clutter ratio (SCR) of the urban clutter environment during the descent phase as a function of aircraft altitude. The meteorological target intensity is taken as a typical strong echo meteorological target intensity, 40 dBZ. The four smaller plots at the top show the SCR when the radar pitch angle coincides with the aircraft's glide slope angle (-3°) at 1200, 800, 400, and 50 feet (1200 feet and below is the minimum altitude at which the aircraft needs to provide wind shear warnings). The four smaller plots at the bottom show the correction for the aircraft's pitch angle at different altitudes using a SCR threshold of -20 dB, as detailed in the table below. After correction, the SCR of the radar detecting ground clutter during the descent phase remains consistently above -20 dB. At this point, the zero-frequency Doppler cancellation method effectively suppresses main lobe clutter, while the impact of side lobe clutter on the meteorological signal is negligible, enabling accurate measurement of the wind shear radial wind speed signal.

[0096] Table 1 shows the default pitch settings at different altitudes in an urban clutter environment:

[0097] Flight altitude 50 feet 400 feet 800 feet 1200 feet Radar elevation -0° -1° -2° -3°

[0098] Table 1

[0099] When the measured signal-to-clutter ratio (SCR) of the airborne radar is below the threshold, the elevation angle can be appropriately increased. Through simulations of different scenarios, a relatively accurate empirical formula can be summarized as follows: every 1° elevation corresponds to a 10dB improvement in SCR.

[0100] 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 adaptive airborne radar method for detecting low-altitude wind shear, characterized in that: Using an airborne Doppler radar, radar waveforms are transmitted toward the wind shear hazard area 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 uses azimuth scanning and follows the radar echo processing strategy. After receiving the IQ signal, it performs frequency domain correction based on the aircraft's attitude and speed information, preprocesses the data based on the spectrum width information, removes outlier regions, and analyzes the takeoff and landing phases after preprocessing. The takeoff phase analysis steps are as follows: Step 0: Set the pitch angle for radar scanning based on the aircraft's takeoff climb angle. The default value is half of the climb angle. Step 1: Use a frequency domain clutter suppression algorithm to suppress potential ground clutter regions near zero frequency; Step 2: Compare the spectra before and after clutter suppression to estimate the signal-to-clutter ratio (S / C); Step 3: Using frequency domain analysis algorithms, the distribution of the radial velocity of meteorological echoes with distance in each horizontal azimuth scan of the radar is obtained; Step 4: Based on the radial wind speed gradient Calculate the wind shear level F-factor; Step 5: If the noise-to-signal ratio S / C is higher than the threshold in the region where the horizontal F factor is greater than the threshold, then the pitch angle is raised to the aircraft takeoff climb angle in the next scan. Step 6: If the pitch angle needs to be increased, repeat steps 1 to 4 and calculate the F-factor using the empirical model; otherwise, calculate the F-factor using the linear model. The landing phase analysis steps are as follows: Step 0: Set the initial pitch angle for radar scanning based on the aircraft's glide slope angle. The default value is the glide slope angle. Step 1: The aircraft continues to descend, and the pitch angle is adjusted according to the preset pitch angle Vs altitude relationship based on the aircraft altitude; Step 2: Use a frequency domain clutter suppression algorithm to suppress potential ground clutter regions near zero frequency; Step 3: Compare the spectra before and after clutter suppression to estimate the signal-to-clutter ratio (S / C); Step 4: Using frequency domain analysis algorithms, the distribution of the radial velocity of the meteorological echoes from each horizontal azimuth scan of the radar as a function of distance is obtained; Step 5: Based on the radial wind speed gradient Calculate the wind shear level F-factor; Step 6: If the noise-to-signal ratio (S / C) is higher than the threshold in the region where the horizontal F factor is greater than the threshold, then raise the pitch angle in the next scan and recalculate the noise-to-signal ratio (S / C). Step 7: Calculate the vertical wind speed using a linear model, and then calculate the F-factor.

2. The adaptive airborne radar low-altitude wind shear detection method according to claim 1, characterized in that, Step 1 of the takeoff phase specifically includes: Based on the radar scanning system parameters, the zero-frequency clutter window width of the wind shear is set, and the signal of the removed frequency unit is supplemented by a linear fitting method.

3. The adaptive airborne radar low-altitude wind shear detection method according to claim 1, characterized in that, Step 2 of the takeoff phase specifically includes: Calculate whether the ratio of the total frequency domain integrated signal strength before clutter suppression to the integrated signal strength after removing the zero-frequency signal and background noise exceeds the clutter-to-signal ratio (S / C) threshold.

4. The adaptive airborne radar low-altitude wind shear detection method according to claim 1, characterized in that, Step 4 of the takeoff phase specifically involves: calculating the wind shear level F-factor. ； Where V is the airspeed of the aircraft and g is the acceleration due to gravity.

5. The adaptive airborne radar low-altitude wind shear detection method according to claim 1, characterized in that, Step 5 of the takeoff phase specifically includes: The number of range gates whose F-factor in a single sector scan is greater than the threshold F=0.05 is counted. F=0.05 is an empirical value for distinguishing clutter and noise fluctuations from wind shear horizontal divergence signals. If the S / C of more than 30% of the range gates is higher than the threshold, the pitch angle is determined to need adjustment.

6. The adaptive airborne radar low-altitude wind shear detection method according to claim 5, characterized in that, Step 6 of the takeoff phase specifically includes: If step 5 determines that the pitch angle needs to be increased, then the vertical wind speed is calculated using an empirical model. This empirical model is the Vicroy model, expressed as follows: in, For the fitting parameters, The height corresponding to the maximum horizontal outflow velocity estimated by the model.

7. The adaptive airborne radar low-altitude wind shear detection method according to claim 1, characterized in that, Step 1 of the descent phase specifically includes: Based on radar system parameters and the type of clutter echo from the ground target, the clutter-to-signal ratio between wind shear targets and ground clutter echoes is calculated. Since the echoes from meteorological targets are inversely proportional to the square of the distance, while the echoes from clutter targets are inversely proportional to the cube of the distance, as the aircraft descends and gradually approaches the wind shear detection area, the increase in clutter echoes is faster than the increase in meteorological echoes. At this point, the pitch angle needs to be adjusted upwards. The basis for adjusting the pitch angle is to keep the clutter-to-signal ratio of strong clutter types greater than a preset threshold, which is 20 dB.

8. The adaptive airborne radar low-altitude wind shear detection method according to claim 1, characterized in that, In step 6 of the descent phase, the magnitude of the elevation pitch angle is given by an empirical formula: ∆θ = (S / C + 20)⁄10 The signal-to-noise ratio (S / C) is in dB, and Δθ is in degrees.

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