Improved airborne weather radar reflectivity factor calculation method

Abstract

The application provides an improved airborne weather radar reflectivity factor calculation method, comprising: receiving power and output signal-to-noise ratio relationship curve fitting; calculating noise power and output signal power and obtaining a signal-to-noise ratio value; calculating received echo power according to the signal-to-noise ratio value; and calculating the reflectivity factor according to the echo power. Compared with a traditional calculation method, the method avoids dynamic calculation of a receiving system gain, reduces analog devices required by a receiver chain, and saves the cost of an airborne weather radar system.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and specifically to an improved method for calculating the reflectivity factor of airborne weather radar. Background Technology

[0002] Airborne weather radar can detect weather targets within a certain range in front of an aircraft and use different colors to indicate the degree of danger of the weather targets, thereby ensuring flight safety.

[0003] The reflectivity factor of a meteorological target reflects the intensity of rainfall. By quantifying the reflectivity factor into red, yellow, and green colors, the hazard level of a meteorological target is identified. Therefore, accurate calculation of the reflectivity factor is crucial for airborne weather radar. Traditional methods for calculating the reflectivity factor involve first estimating the received echo power based on the target echo quantization magnitude and system gain, and then solving the reflectivity factor using the weather radar equations. Since system gain is affected by voltage and temperature, traditional methods require placing analog devices at the receiver to calibrate the system gain, increasing the complexity of the receiver link. Summary of the Invention

[0004] In view of this, the embodiments of this specification provide an improved method for calculating the reflectivity factor of airborne weather radar, so as to reduce the complexity of the airborne weather radar receiving link and reduce costs.

[0005] This specification provides the following technical solution in its embodiments: an improved method for calculating the reflectivity factor of airborne weather radar, comprising: fitting the curve of the relationship between received power and output signal-to-noise ratio; calculating the noise power and output signal power and obtaining the signal-to-noise ratio value; calculating the received echo power based on the signal-to-noise ratio value; and calculating the reflectivity factor based on the echo power.

[0006] Furthermore, the curve fitting of the relationship between received power and output signal-to-noise ratio includes: [P] within the receiver's linear amplification region. min ,P max Divide the power points into N (N≥100) equally spaced power points P i (1,2,...N); using a signal source to generate power equal to P i A signal of (1,2,...,N) is fed into the receiver input, and the output signal-to-noise ratio is measured at the digital receiver. And obtain N output signal-to-noise ratios (SNRs) o (1,2,...,N), where AD s The ADC quantization value of the signal, AD n This is the quantization value of the noise ADC.

[0007] Furthermore, the curve fitting of the relationship between received power and output signal-to-noise ratio also includes: utilizing {SNR} o (k),Pi (k)} Calculate the coefficients a, b, and c of the quadratic polynomial fitting curve; then the relationship between the measured output signal-to-noise ratio and the input power of the digital receiver is: P i (k)=aSNR o 2 (k)+bSNR o (k)+c, where k=1,2,...,N.

[0008] Furthermore, the noise power AD is calculated using either the periodic self-test method of airborne weather radar or the method of averaging far-field echo signals. n .

[0009] Furthermore, for each echo range unit, the echo signal magnitude within that range unit is quantized into an AD converter at the digital receiver. t Then the output signal-to-noise ratio is:

[0010] Furthermore, according to P r =aSNR 2 +bSNR+c calculates the received echo power, where P r To receive echo power.

[0011] Furthermore, according to Calculate the reflectivity factor, where Z M P is the reflectivity factor. t τ is the peak power of the transmitter; G is the radar antenna gain; C is the speed of light; τ is the pulse width; and θ is the azimuth beamwidth. The pitch beamwidth; |K| 2 =0.93; λ is the radar operating wavelength; R is the target distance; L is atmospheric attenuation.

[0012] Compared with the prior art, the beneficial effects that can be achieved by the above-mentioned at least one technical solution adopted in the embodiments of this specification include at least the following: compared with the traditional calculation method, this method avoids dynamic calculation of the receiving system gain, reduces the analog devices required for the receiver link, and also saves costs for the airborne weather radar system. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a flowchart illustrating an embodiment of the present invention;

[0015] Figure 2 This is a schematic diagram of the calculation error of the reflectivity factor in an embodiment of the present invention. Detailed Implementation

[0016] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] Weather radar reflectivity factor Z M The calculation formula is:

[0019]

[0020] Among them, P r P is the echo power. t G is the peak power of the transmitter; C is the radar antenna gain; τ is the speed of light; θ is the pulse width; These represent the azimuth and elevation beamwidths, respectively; |K| 2 =0.93; λ is the radar operating wavelength; R is the target range; L is atmospheric attenuation, excluding P r Apart from those requiring real-time calculation, all other parameters are inherent to the system.

[0021] Assuming the maximum value of ADC quantization is AD max The corresponding peak voltage is 1V (system inherent parameter), then the traditional calculation of P... r The method is as follows:

[0022]

[0023] Among them AD t Ω represents the ADC quantization value of the target echo; Ω is the receiver output resistance, taken as 50 ohms; G s This is the receiver link gain. Because G s The reflectivity factor can vary within a certain range due to factors such as the nonlinearity of the automatic gain control of the receiver link, the amplifier's operating voltage, and temperature. Therefore, traditional methods for calculating the reflectivity factor require the addition of real-time calibration using analog devices. s The value of .

[0024] Due to G s The change is equivalent for both signal and noise; in the signal-to-noise ratio, G... s The changes are canceled out, therefore the improved calculation method considers using the receiver output signal-to-noise ratio to calculate P. r This allows for the calculation of the reflectivity factor; the improved reflectivity factor calculation method is implemented as follows: Figure 1 As shown, the specific steps of the improved airborne weather radar reflectivity factor calculation method of this invention are as follows:

[0025] Step 1: Fitting the curve of the relationship between received power and output signal-to-noise ratio

[0026] (1) The receiver's linear amplification region [P] min ,P max Divide the power points into N (N≥100) equally spaced power points P i (1,2,...N);

[0027] (2) These powers, equal to P, are generated using a signal source. i A signal of (1,2,...,N) is fed into the receiver input, and the output signal-to-noise ratio is measured at the digital receiver. Among them AD s The ADC quantization value of the signal, AD n The noise ADC quantization values ​​are used to obtain N output signal-to-noise ratios (SNRs). o (1,2,...,N).

[0028] (3) Based on these data, {SNR} o (k),P i (k)}k=1,2,...,N, using the Matlab tool to calculate the coefficients a, b, c of the quadratic polynomial fitting curve, then the relationship between the two is:

[0029] P i (k)=aSNR o 2 (k)+bSNR o (k)+c (3)

[0030] Step 2: Calculate the output signal-to-noise ratio

[0031] (1) Calculate the receiver output noise floor (AD) at the digital receiver end. n The value can be calculated using the period of airborne weather radar, or it can be calculated using the average value of far-field echo signals.

[0032] (2) Calculate the receiver output signal-to-noise ratio. For each echo range cell, the echo signal magnitude within that range cell is quantized into an AD converter at the digital receiver. t Then the output signal-to-noise ratio is:

[0033]

[0034] Step 3: Calculate the received echo power

[0035] Calculate the received echo power using the following formula:

[0036] P r =aSNR 2+bSNR+c (5)

[0037] Step 4: Calculate the reflectivity factor

[0038] Calculate the reflectance factor using the following formula:

[0039] Z M P is the reflectivity factor. t τ is the peak power of the transmitter; G is the radar antenna gain; C is the speed of light; τ is the pulse width; and θ is the azimuth beamwidth. The pitch beamwidth; |K| 2 =0.93; λ is the radar operating wavelength; R is the target distance; L is atmospheric attenuation.

[0040] This invention first uses curve fitting to calculate the relationship between the output signal-to-noise ratio and the input power, and then estimates the received echo power P using the output signal-to-noise ratio. r This allows for the calculation of the emissivity factor without the need to add gain calibration devices to the receiving link, reducing the complexity of the airborne weather radar receiving link and also reducing the cost of the airborne weather radar system.

[0041] To verify the feasibility of the improved airborne weather radar reflectivity factor calculation method, a certain type of airborne weather radar was used as the experimental platform. First, curve fitting was performed using laboratory data. Then, actual radiating meteorological target echo data (reflectivity factor of 48 dBZ) was used for calculation. The calculated reflectivity factor was compared with the theoretical value. The specific implementation steps are as follows:

[0042] Step 1: Fitting the curve of the relationship between received power and output signal-to-noise ratio

[0043] (1) Divide the receiver's linear amplification region [-115dBm, -45dBm] into 100 equally spaced power points.

[0044] P i (1,2,...100)={-110dbm,-114.29dbm,-113.58dbm...,-45dbm};

[0045] (2) These powers, equal to P, are generated using a signal source. i A signal of (1,2,...,N) is fed into the receiver input, and the output signal-to-noise ratio is measured at the digital receiver. Among them AD s The ADC quantization value of the signal, AD n The noise ADC quantization values ​​yield N output signal-to-noise ratios:

[0046] SNR o(1,2,...,N)={0.496dB,1.167dB,...,65.9dB}.

[0047] (3) Based on these data, {SNR} o (k),P i (k)}k=1,2,...,N, using Matlab, the coefficients a=7.6*10 are calculated to fit the quadratic polynomial curve. -5 Given b = 0.994 and c = -110.4, the relationship between them is:

[0048] P r =7.6*10 -5 *SNR o 2 +0.994*SNR o -110.4.

[0049] Step 2: Calculate the output signal-to-noise ratio

[0050] (1) Calculate the receiver output noise floor (AD) at the digital receiver end. n The value AD is calculated using the periodic data from an airborne weather radar. n =35. (2) Calculate the receiver output signal-to-noise ratio. Select a range cell where the target echo is located, and quantize the magnitude of the echo signal in that range cell at the digital receiver to AD. t =5354, then the output signal-to-noise ratio is:

[0051] Step 3: Calculate the received echo power

[0052] Calculate the signal return power using the following formula:

[0053] P r =7.6*10 -5 *43.6922 2 +0.994*43.6922-110.4=-66.8249dBm

[0054] Step 4: Calculate the reflectivity factor

[0055] Calculate the reflectance factor using the following formula:

[0056] The inherent parameters of the system are shown in the table below:

[0057] Table 1: System Inherent Parameters

[0058]

[0059] Combine the parameters in the table above with P rSubstituting into the reflectivity factor calculation formula, Z is calculated. M =48.25dBz, close to the theoretical value; the error curve between the meteorological target reflectance factor measured from 50 consecutive samples and the actual value is shown in the figure. Figure 2 As shown, by Figure 2 It can be seen that the error in the calculation of the reflectivity factor is within an acceptable range, thus verifying the feasibility of the improved scheme.

[0060] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical solutions, and technical solutions in this invention can be freely combined and used.

Claims

1. An improved method for calculating the reflectivity factor of airborne weather radar, characterized in that, include: Fitting the curve of the relationship between received power and output signal-to-noise ratio; Linear amplification region of the receiver Divided into Equally spaced power points ; Power generated by a signal source equal to The signal is fed into the receiver input, and the output signal-to-noise ratio is measured at the digital receiver. And obtain N output signal-to-noise ratios. ,in The ADC quantization value of the signal. Quantization value for noise ADC; using Calculate the coefficients a, b, and c of the quadratic polynomial fitting curve; then the relationship between the measured output signal-to-noise ratio and the input power at the digital receiver is: ,in, ; Calculate the noise power and output signal power to obtain the signal-to-noise ratio; calculate the noise power using either the airborne weather radar periodic self-test method or the method of averaging far-field echo signals. For each echo range cell, the magnitude of the echo signal within that range cell is quantized at the digital receiver. Then the output signal-to-noise ratio is: Calculate the received echo power based on the signal-to-noise ratio value; based on... Calculate the received echo power, where To receive echo power The reflectivity factor is calculated based on the echo power.

2. The improved airborne weather radar reflectivity factor calculation method according to claim 1, characterized in that, according to Calculate the reflectivity factor, where It is the reflectivity factor; This refers to the transmitter's peak power. Radar antenna gain; The speed of light; Pulse width; These are the azimuth beamwidths; This refers to the pitch beamwidth; λ is the radar operating wavelength; The target distance; This is due to atmospheric attenuation.

Images