A dual-polarization weather radar velocity resolution method based on lag-1 cross-correlation

Abstract

The application discloses a dual-polarization weather radar speed ambiguity resolution method based on lag-1 cross-correlation, which utilizes lag-1 cross-correlation of adjacent radial directions instead of radial velocity of the adjacent radial directions in a traditional algorithm to calculate an ambiguity resolution reference speed. This makes the ambiguity resolution speed range of the ATAR mode expand to twice that of the traditional algorithm, so that the speed measurement range is consistent with that of the single-polarization mode. Application of the algorithm improves the reliability of speed data of the ATAT mode weather radar in severe weather detection.

Description

Technical Field

[0001] This invention relates to the field of weather radar technology, and in particular to a velocity deambiguation method for dual-polarized weather radar based on hysteresis-1 cross-correlation. Background Technology

[0002] Severe weather (such as typhoons, tornadoes, and thunderstorms) is usually accompanied by strong winds and violent air currents. Therefore, weather radar should have a large speed measurement range to provide accurate speed information, thereby enabling early warning and forecasting of severe weather. Weather radar often uses uniform sampling dual-pulse repetition frequency (DPRF) technology to extend the speed measurement range and obtain unambiguous speeds of meteorological targets.

[0003] Polarimetric weather radar acquires more polarization parameter information, such as differential reflectivity, differential phase, correlation coefficient, and differential phase shift rate, by transmitting and receiving horizontal (H) and vertical (V) polarized waves. This is of great significance for improving the accuracy of early warnings and the precision of rainfall estimation. Alternating transmit and receive (ATAR) mode can be used in weather radar to achieve dual polarization functionality. Single-channel ATAR mode weather radar has the advantages of being lightweight, low-power, and low-cost, and can be applied to high-altitude platforms (HAPS) with limited payload and power consumption (such as near-space airships, Zephyr-S UAVs, and stratospheric balloons).

[0004] In ATAR mode, the radar alternately transmits and receives H and V polarized waves. Therefore, the time interval between echoes of the same polarization is twice the pulse repetition time (PRT), i.e., the equivalent time interval is 2PRT, which is twice the time interval of echoes of the same polarization in single-polarization mode. After unambiguation using the traditional algorithm based on the difference between adjacent radial velocities, the maximum unambiguous velocity (Nyquist velocity) is inversely proportional to the equivalent time interval. Therefore, after unambiguation using the traditional algorithm, the Nyquist velocity in ATAR mode is half that of single-polarization radar, which hinders the application of ATAR mode in extreme weather detection. To expand the application of ATAR in HAPS, it is necessary to expand the velocity measurement range of ATAR mode polarimetric weather radar. Summary of the Invention

[0005] The present invention provides a velocity deambiguation algorithm for ATAR mode polarimetric weather radar, which mainly solves the technical problem of expanding the velocity measurement range of ATAR mode dual-polarimetric weather radar.

[0006] To address the aforementioned technical problems, this invention provides a velocity deambiguation method for dual-polarized weather radar based on hysteresis-1 cross-correlation, comprising:

[0007] Step 1: Estimate the hysteresis-1 cross-correlation based on the radar H and V polarization echo sequences;

[0008] Step 2: Estimate the radial velocity and unambiguous velocity interval based on hysteresis-1 cross-correlation;

[0009] Step 3, fuzzy number estimation: Based on the phase difference estimation of adjacent radial hysteresis-1 cross-correlation, the unfuzzy reference velocity is obtained, and then the fuzzy number is estimated by using the difference between it and the radial velocity in step 2.

[0010] Step 4, Defuzzification speed estimation: The defuzzification speed after the range is extended is obtained by adding the radial speed to the unfuzzy speed interval which is several times the fuzzy speed.

[0011] Step 5: Change the radial direction and repeat steps 1 to 4 to obtain the unfuzzing speed for all radial directions.

[0012] Optionally, step 1 includes:

[0013] For radars using DPRF technology, M pulses with a fixed PRF are first transmitted, followed by M pulses with another fixed PRF (M is the radial in-pulse accumulation number). The ratio of the two PRFs is usually set to (K+1):K, where K is often 2, 3, 4, etc.

[0014] The radar alternately transmits and receives H and V polarized waves in each radial direction, denoted as H. m,i V m,i These are the HH (transmit H, receive H) polarized echo and VV (transmit V, receive V) polarized echo in the i-th radial direction, respectively. Assuming the total number of data radial directions is L, then i ranges from 2 to L. Assuming the radar first transmits the H-polarized wave, the echo sequence of the radar in the i-th radial direction is H... 0,i V 1,i H 2,i V 3,i ,...,H m-1,i V m,i ...,V M-1,i Where M represents the pulse accumulation number, so m ranges from 0 to M-1. Then the hysteresis-1 cross-correlation functions of VH and HV are respectively:

[0015]

[0016]

[0017] Optionally, step 2 includes:

[0018] In ATAR mode, R a The phase is the sum of the Doppler frequency shift and the differential phase, R b The phase is the difference between the Doppler frequency shift and the differential phase; therefore, the radial velocity of the i-th radial target is:

[0019]

[0020] In the formula, λ is the wavelength, and PRF i Arg(R) represents the pulse repetition frequency in the i-th radial direction. a,i ·R b,i ) / 2 represents the Doppler frequency shift, where Arg represents the argument operation. Since the argument range is -π to π, the maximum value of formula (3), i.e., the maximum unambiguous velocity (Nyquist velocity) of the i-th radial direction, is:

[0021]

[0022] The maximum unambiguous velocity with an unambiguous velocity interval of twice can be expressed as:

[0023]

[0024] Optionally, step 3 includes:

[0025] Step 31, resolve fuzzy reference velocity estimation:

[0026] For weather radars employing DPRF technology, the deambiguation velocity of the i-th radial direction can be calculated based on the Doppler frequency shift difference between the i-th and (i-1)-th radial directions. Since this deambiguation result contains Doppler frequency shift information from both radial directions, it includes twice the phase error. Therefore, it is generally used only as a reference and is denoted as the deambiguation reference velocity:

[0027]

[0028] In the formula, PRF i-1 Let represent the pulse repetition frequency of the (i-1)th radial direction, and Δθ represent the Doppler frequency shift difference between the ith and (i-1)th radial directions. In this invention, the hysteresis-1 cross-correlation function (Ri-1) of adjacent radial directions is used. a,i-1 and R a,i Calculate the adjacent radial Doppler frequency shift difference Δθ:

[0029]

[0030] In the formula, θ i θ i-1 These represent the Doppler frequency shifts in the i-th radial direction and the (i-1)-th radial direction, respectively. R represents a,i . conjugate.

[0031] Step 32, fuzzy number estimation:

[0032] Using formulas (3), (5) and (6), estimate the fuzzy number:

[0033]

[0034] In the formula, N represents the fuzzy number and is an integer, and <> represents rounding operation.

[0035] Optionally, step 4 includes:

[0036] To reduce the impact of phase error, the unambiguous velocity can be estimated by adding the unambiguous velocity interval (Equation (5)) to the radial velocity (Equation (3)) plus the ambiguity factor (Equation (8)):

[0037]

[0038] The beneficial effects of this invention are:

[0039] ATAR mode, as a key polarization mode, allows dual-polarization weather radars to acquire polarization information using only a single channel, thereby reducing radar weight, power consumption, and cost. ATAR-mode dual-polarization weather radars have broad application prospects on high-altitude platforms with limited payload and power. In weather radars employing DPRF technology, the unambiguous velocity range of dual-polarization is only half that of single-polarization modes because the co-polarization signal time interval in ATAR mode is twice the PRT, hindering the application of ATAR mode in severe weather detection. This paper proposes a velocity unambiguity algorithm that utilizes the hysteresis-1 cross-correlation of adjacent radial directions, instead of the radial velocities of adjacent directions in traditional algorithms, to calculate the unambiguous reference velocity. This expands the unambiguous velocity range in ATAR mode to twice that of traditional algorithms, making its velocity measurement range consistent with that of single-polarization modes. Applying the algorithm proposed in this paper improves the reliability of velocity data for ATAR mode weather radar detection in severe weather. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of a velocity deambiguation method for dual-polarized weather radar based on hysteresis-1 cross-correlation according to Embodiment 1 of the present invention.

[0041] Figure 2 This is a radial velocity diagram of Embodiment 1 of the present invention;

[0042] Figure 3 This is a defuzzification speed diagram of Embodiment 1 of the present invention;

[0043] Figure 4 This is a diagram showing the defuzzification speed deviation distribution of Embodiment 1 of the present invention; Detailed Implementation

[0044] To make the objectives and technical solutions of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] Example 1:

[0046] In this embodiment, IQ data is obtained by echo simulation using SA radar base data to verify the content of the invention. The SA radar is in simultaneous transmission and reception mode, and the simulation PRF is set to 800 and 600 Hz. H-polarized echo data in each radial direction are selected to construct single-polarized data. After deambiguation using a traditional algorithm, the velocity measurement range in single-polarized mode is -64.2 m / s to 64.2 m / s. In addition, the nth H-polarized echo and the (n+1)th V-polarized echo in each radial direction are selected, where n = 0, 2, 4, ... M-2, to form the ATAR mode echo sequence.

[0047] This embodiment provides a velocity deambiguation method for ATAR-mode dual-polarization weather radar. Please refer to [link to relevant documentation]. Figure 1 Specifically, it includes the following steps:

[0048] Table 1

[0049]

[0050] Step 1 specifically includes:

[0051] For the ATAR mode SA weather radar data constructed using DPRF technology, M=128 pulses with a fixed PRF are first transmitted, followed by M=128 pulses with another fixed PRF. The ratio of the two PRFs is (K+1):K=4:3, therefore K=3. Other radar parameters are shown in Table 1.

[0052] The radar alternately transmits and receives H and V polarized waves in each radial direction, denoted as H. m,i V m,i These are the HH (transmit H, receive H) polarized echo and VV (transmit V, receive V) polarized echo in the i-th radial direction, respectively. The total number of data radial directions is L = 32, so i ranges from 2 to 32. Assuming the radar first transmits an H-polarized wave, the echo sequence of the radar in the i-th radial direction is H... 0,i V 1,i H 2,i V 3,i ,...,V M-1,i Where M = 128, therefore m ranges from 0 to 127. The hysteresis-1 cross-correlation functions of VH and HV are then:

[0053]

[0054]

[0055] Step 2 specifically includes:

[0056] The radial velocity of the target is as follows Figure 2 As shown. The radial velocity of the i-th radial target is:

[0057]

[0058] In the formula, Arg represents the argument operation. Since the argument range is -π to π, the maximum value of formula (12), that is, the maximum unambiguous velocity (Nyquist velocity) of the radial direction, is:

[0059]

[0060] The maximum unambiguous velocity with an unambiguous velocity interval of twice can be expressed as:

[0061]

[0062] Step 3 specifically includes:

[0063] Step 31, resolve fuzzy reference velocity estimation:

[0064] For weather radars employing DPRF technology, the deambiguation velocity of the i-th radial direction can be calculated based on the Doppler frequency shift difference between the i-th and (i-1)-th radial directions. Since this deambiguation result contains Doppler frequency shift information from both radial directions, it includes twice the phase error. Therefore, it is generally used only as a reference and is denoted as the deambiguation reference velocity:

[0065]

[0066] In the formula, Δθ represents the Doppler frequency shift difference between the i-th radial direction and the (i-1)-th radial direction. In this invention, the hysteresis-1 cross-correlation function (Ri) of adjacent radial directions is used. a,i-1 and R a,i-1 Calculate the adjacent radial Doppler frequency shift difference Δθ:

[0067]

[0068] In the formula, Δθ represents the Doppler frequency shift difference between the i-th radial direction and the (i-1)-th radial direction, θ i θ i-1 These represent the Doppler frequency shifts in the i-th radial direction and the (i-1)-th radial direction, respectively. R represents a,i . conjugate.

[0069] Step 32, fuzzy number estimation:

[0070] Using formulas (12), (14) and (15), the fuzzy number is estimated as follows:

[0071]

[0072] In the formula, N represents the fuzzy number and is an integer, and <> represents rounding operation.

[0073] Step 4 specifically includes:

[0074] To reduce the impact of phase error, the unambiguous velocity can be estimated by adding the radial velocity to the unambiguous velocity interval (Equation (14)) in Equation (12) (Equation (17)).

[0075]

[0076] The results of the defuzzification speed are as follows Figure 3 As shown.

[0077] Figure 4 The distribution of the defuzzification velocity deviation is shown in the figure below. The defuzzification velocity results from single-polarization data are used as the true values, and the results from the algorithm presented in this paper are used as the measured values. The difference between the measured values ​​and the true values ​​is denoted as the defuzzification velocity deviation, and its distribution is shown in the figure below. Figure 4 As shown in the figure, the horizontal axis represents the velocity deviation, the vertical axis represents the number of distance libraries, and the vertical axis is a logarithmic axis. The simulation data covers 2552 distance libraries. As can be seen from the figure, the proportion of data with defuzzification velocity deviation concentrated within ±1m / s is 99.73%. In addition, after defuzzification using the algorithm of this invention, the maximum value of formula (15) shows that the maximum unfuzzy velocity after defuzzification is 64.2m / s, so the velocity measurement range is -64.2m / s to 64.2m / s. Its velocity measurement range is consistent with that of the single-polarization mode. Therefore, it can be considered that after defuzzification using the algorithm of this invention, the defuzzification velocity in ATAR mode is consistent with that in the single-polarization mode.

[0078] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A dual-polarization weather radar velocity resolution ambiguity method based on lag-1 cross-correlation, characterized in that, include: Step 1: Estimate the hysteresis-1 cross-correlation function based on the alternating transmit and receive (ATAR) mode polarized weather radar echo sequence; Step 2: Estimate the radial velocity and the unambiguous velocity interval based on hysteresis-1 cross-correlation; Step 3, fuzzy number estimation: Based on the phase difference estimation of adjacent radial hysteresis-1 cross-correlation, the unfuzzy reference velocity is obtained, and then the fuzzy number is estimated by using the difference between it and the radial velocity in step 2; Step 4, Defuzzification speed estimation: The defuzzification speed after expanding the range is obtained by adding the fuzzy speed interval to the radial speed by a factor of several times the unfuzzy speed interval; Step 5: Change the radial direction and repeat steps 1 to 4 to obtain the unambiguity rate for all radial directions; Step 1 includes: For radars employing DPRF technology, determine the pulse accumulation number. M and repetition rate ratio ( K +1): K middle K The value of ; determine the radial number L of the radar data; construct the radar echo sequence for each radial direction, assuming the radar first transmits H-polarized waves, then the i The echo sequence of the radial radar is ,in, M This represents the number of pulse accumulations, therefore m The range is 0~ M -1, i The range is 2~L; then VH and HV The hysteresis-1 cross-correlation functions are as follows: (1)； (2)； Step 2 includes: the first i Radial velocity estimation of the target: (3)； In the formula, For wavelength, PRF i Indicates the first i Radial pulse repetition frequency, This represents the Doppler frequency shift, where Arg represents the argument operation, since the argument range is... ~ Therefore, the maximum value of formula (3), i.e. the first... i The radial Nyquist velocity is: (4)； The maximum unambiguous velocity with an unambiguous velocity interval of twice can be expressed as: (5); Step 3 includes: Step 31, resolve fuzzy reference velocity estimation: For weather radars using DPRF technology, it is possible to determine the first... i radial and first i -1 radial Doppler frequency shift difference is calculated to obtain the first i The radial deblurring velocity, because the deblurring result contains two radial Doppler frequency shifts, thus including twice the phase error; therefore, it is generally only used as a reference and is denoted as the deblurring reference velocity: (6)； In the formula, PRF i-1 Indicates the first i -1 radial pulse repetition frequency; Indicates the first i radial and first i -1 radial Doppler frequency shift difference, using the hysteresis-1 cross-correlation function of adjacent radial directions. and Calculate the difference in radial Doppler frequency shift between adjacent frequencies. : (7)； In the formula, , They represent the first i radial and first i -1 radial Doppler frequency shift; express The conjugate; Step 32, fuzzy number estimation: Using formulas (3), (5) and (6), estimate the fuzzy number: (8)； In the formula, N Represents fuzzy numbers, and N It is an integer. This indicates rounding operations.

2. The velocity deambiguation method for dual-polarized weather radar based on hysteresis-1 cross-correlation as described in claim 1, characterized in that, Step 4 includes: To reduce the impact of phase error, the radial velocity can be obtained from equation (3), and by adding the fuzzy multiple obtained from equation (8) to the unfuzzy velocity interval obtained from equation (5), the unfuzzy velocity can be estimated. (9)。

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