CN104678369A - Dual-polarization weather radar calibration method based on non-fixed metal ball - Google Patents

Abstract

The invention discloses a dual-polarization weather radar calibration method based on non-fixed metal balls, which comprises the following steps: according to the radar position, determining the calibration site, recording the radar position and the longitude and latitude of the calibration position; according to the longitude and latitude and the height of the radar station, Calculate the possible azimuth, elevation angle and distance of the metal ball relative to the radar in the calibration state, set the scanning elevation angle and scanning mode of the radar; raise the metal ball in the calibration area, set a high-precision GPS module at the bottom of the metal ball, and control the radar according to Work in the preset scanning mode, record the IQ data and basic data of the radar; analyze the data, find the metal ball target detected by the radar, compare it with the theoretical value, calculate the error between the measured value and the theoretical value, and correct it according to the error. The method of the invention is simple and easy to implement, solves the problem of calibration of radar parameters when the metal ball moves, and can perform calibration of all detection parameters of the polarization radar.

Description

A Calibration Method for Dual-polarization Weather Radar Based on Unfixed Metal Ball

technical field

The invention relates to a system calibration method for a dual-polarization radar, in particular to a method for system calibration of a dual-polarization radar by using a non-fixed metal ball, which belongs to the field of radar signal processing research.

Background technique

In the field of modern meteorology, weather radar is widely used in various aspects such as real-time weather monitoring and human shadow operation command. For the weather radar system, system calibration is an essential work, and the uncalibrated radar cannot express the current weather conditions with correct parameters. For single-polarization radar, only one channel needs to be calibrated; for dual-polarization radar, since it has two horizontal and vertical channels, the two channels must be calibrated separately, including the consistency of amplitude and phase Calibration etc.

There are many methods of radar calibration, generally divided into online calibration and offline calibration. Online calibration uses the signal source, noise source and other devices integrated in the radar to generate signals by itself, and after the radar receiving and processing, the receiving channel, transmitting channel and other parts are calibrated and calibrated. The principle of offline calibration is basically the same as that of online calibration, except that the integrated signal source and other devices are replaced by external instruments. Wang Zhijun (1996) proposed a method to calibrate the radar gain by using a metal sphere. This method uses the characteristic that the sphere has zero depolarization effect on the incident wave, and calculates the radar gain by the power returned by the radar according to the meteorological equation of the point target. At the same time, it is also proposed that if only the gain difference between the horizontal and vertical channels needs to be measured, it can be calibrated by small raindrops. Li Xiangying et al. (2002) used radar RCS (Radar Cross Section) target characteristics to calibrate the radar. Li Yongxin et al. (2007) also carried out RCS measurement of radar calibration error. They used a balloon to hang a standard metal ball as a standard calibration body to calibrate the radar. They found that the RCS of the balloon had a great influence on the radar calibration results. Earle Williams et al. (2012) used metal balls to calibrate the ZDR of KOUN radar and WSR-88D radar, and found the deviation of these two radars.

Consistent calibration of horizontal and vertical channels is essential for polarimetric radars. Although the method of using light rain to calibrate radar is simple, the calibration accuracy cannot be accurately quantified due to the uncertainty of precipitation itself. With the method of hanging metal balls by balloons, the calibration accuracy is not easy to grasp because the balloon RCS has an impact on the calibration results. At the same time, the polarization radar has multiple polarization parameters, all of which need to be calibrated, and it is not enough to calibrate only one or a few.

Contents of the invention

The present invention aims at the deficiencies of the current technology. On the basis of RCS calibration based on the metal ball, the high-precision GPS module is used to record the position of the metal ball, and the radar is analyzed from two aspects of the time domain and the frequency domain. The calculation method of multi-point fusion ensures the accuracy of radar calculation results. The invention calibrates all parameters of the dual-polarization weather radar, and can still be used normally when the metal ball is in motion.

In order to solve the above-mentioned technical problems, the technical scheme of the dual-polarization weather radar calibration method based on non-fixed metal balls of the present invention is:

Determine the calibration location according to the location of the radar, and record the radar location and the latitude and longitude of the calibration location;

According to the obtained latitude and longitude and the height of the radar station, calculate the possible azimuth, elevation angle and distance of the metal ball relative to the radar in the calibration state, and set the scanning elevation angle and scanning mode of the radar;

Use the equipment to raise the metal ball in the calibration area, set a high-precision GPS module at the bottom of the metal ball, and at the same time control the radar to work according to the preset scanning mode, record the IQ data and basic data of the radar; the equipment used to raise the metal ball can be Using traditional balloons, drones can also be used, and the best use is a kite. Because the kite basically has no impact on the endurance, and the kite can maintain its position well in the air without significant drift. In the actual test, it is found that the kite has no effect on the RCS of the metal ball, which solves the problem that the balloon has a greater impact on the radar calibration. It is more accurate to test the accuracy with the high-precision GPS module.

Analyze the IQ data and base data, find the metal ball target detected by the radar, compare it with the theoretical value, calculate the error between the measured value and the theoretical value, and correct the radar according to the error result.

Compared with the method of the prior art, the beneficial effect of the method of the present invention is that it is simple and easy to implement, and can accurately calibrate the whole radar machine; it improves the calculation accuracy, solves the problem of radar parameter calibration when the metal ball moves, and can calibrate the polarized radar All detection parameters are calibrated.

Instructions attached

Figure 1 is the calculation of the azimuth and elevation angle of the metal ball relative to the radar;

Figure 2 is the FFT spectrum of the distance unit where the metal ball is located;

Figure 3 is the radar base data of several adjacent elevation angles where the metal ball is located;

Figure 4 is a comparison between the metal ball reflectivity factor detected by radar and the theoretical value;

Figure 5 is the differential reflectivity of multiple volume-scanning metal balls detected by radar;

Figure 6 is the correlation coefficient of multiple volume-scanning metal balls detected by radar;

Figure 7 is the differential propagation phase shift of multiple volume-scanning metal balls detected by radar.

Detailed ways

A detailed description of a dual-polarization weather radar calibration scheme based on a non-fixed metal ball of the present invention specifically includes the following steps:

According to the latitude, longitude and altitude of the radar, select a suitable calibration location, which requires no obvious object obstruction and not far from the radar station. The selection of the calibration position is crucial to the success of the radar calibration. If the calibration position is too far away from the radar, since the metal ball can only rise to a certain height, the radar will observe at a very low elevation angle, which is not conducive to Target determination. At the same time, it is required that there are not many obstacles near the calibration location, such as woods, iron towers, hills and other objects. After the area is determined, the possible azimuth, elevation and distance of the metal ball can be calculated based on the position and the position of the radar, and the data can be used to set the scanning mode and signal processing mode of the radar.

Calculate the possible azimuth, elevation angle and distance of the position relative to the radar according to the possible maximum height of the metal ball, and set the working mode and scanning mode of the radar accordingly; after calculating the possible position of the metal ball relative to the radar, it is The scanning method and signal processing method of the radar can be set according to the location. If conditions permit, it is best to use the sector scanning mode, which can reduce unnecessary data recording.

Raise the metal ball with a kite in the calibration area, and add a high-precision GPS module to the bottom of the ball to record the position of the metal ball and control the radar to work in a predetermined scanning mode.

Observe the calibration area, and after finding the target, record the IQ data and basic data stably for a period of time; when performing calibration, first raise the metal ball in the calibration area, turn on the radar at the same time, and scan according to the preset mode. After the metal ball is raised, it is easy to observe the metal ball target on the radar. At this time, make sure that the radar base data and IQ data are stored normally. The IQ data can be used to confirm the position and strength of the metal ball from the spectrum, and the base data is used to compare the results calculated by the radar with the theoretical value of the metal ball itself, and calculate the error between the two.

Analyze the results recorded by the radar, compare with the theoretical value calculated by the metal ball, calculate the measurement error of the radar, and calibrate the radar according to the error value. In this step, the calculation of the theoretical value of the reflectivity factor of the metal ball is a very critical step. Assume that the radius of the metal ball is r (m), the peak power of the radar transmitter is Pt (Kw), the antenna gain is G, and the noise figure of the receiver is NF(dB), the bandwidth of the receiver is BW(MHz), the radar wavelength is λ(m), the feeder loss is L(dB), the detectable intensity at 1Km of the radar is dBZ0, and the distance between the metal ball and the radar is R (Km), the reflectivity of the metal ball is calculated according to the following formula:

RCS=π×r ²

$\mathrm{<span\; class="notranslate">\; PR</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Pt</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; G</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; RCS</span>}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{\frac{\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; 10</span>}}}}{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 4</span>}}}$

SNR＝10×log(Pr*1000)-(-114+NF+10×log BW)

$\mathrm{<span\; class="notranslate">\; dBZ</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; dBZ</span>}\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; SNR</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 20</span>}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; log</span>}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; R</span>}}{\mathrm{<span\; class="notranslate">\; 1000</span>}}<span\; class="notranslate">\; )</span>$

Among them, RCS is the radar reflection cross section of the metal ball, Pr is the power received by the radar receiver, and dBZ is the final calculation result of the reflectivity factor. When analyzing the data, since the metal ball will move, the data is processed from both the time domain and the frequency domain to solve the matching problem between the data and the target point.

After the data recording is completed, it is necessary to analyze the calibration data. The reflectivity factor of the metal sphere itself can be calculated by the formula described above, while for other polarization parameters, since the metal sphere is a sphere, the theoretical value of differential reflectivity and differential propagation phase shift is 0, and the theoretical value of its correlation coefficient is 1. Since the metal ball will move, it can be analyzed from the frequency domain. Figure 2 calculates the frequency spectrum at the position of the metal ball detected by the radar. The abscissa is the number of channels of the FFT, and the ordinate is the amplitude, from which the position of the metal ball can be obtained. Figure 3 shows the basic data of several elevation angles near the position of the metal ball, the abscissa is the azimuth, and the ordinate is the distance. Figures 4 to 7 respectively represent the comparison between the measured and theoretical values of reflectivity factors of metal balls detected by multi-volume scanning radars, as well as the measured differential reflectivity, correlation coefficient and differential propagation phase shift. The abscissa is volume The number of sweeps, the ordinates are the respective parameters. Through analysis, the error of radar measurement parameters can be known.

Claims (3)

1., based on a dual-polarization weather radar Calibration Method for on-fixed Metal Ball, it is characterized in that comprising following steps:

According to radar position, determine calibration place, record radar site and the longitude and latitude of calibration position;

According to the longitude and latitude obtained and radar station height, calculating Metal Ball relative to the possible orientation of radar, the elevation angle and distance, arranges the scanning elevation angle and the scan mode of radar when calibration state;

Utilize in calibration region equipment to rise Metal Ball, arrange high-precision GPS module bottom Metal Ball, control radar carries out work according to the scan mode preset simultaneously, the I/Q data of record radar and base data;

Analyze I/Q data and base data, find the Metal Ball target of radar detection, compare with theoretical value, calculate the error of measured value and theoretical value, according to error result, radar is revised.

2. a kind of dual-polarization weather radar Calibration Method based on on-fixed Metal Ball as claimed in claim 1, is characterized in that described scan mode is fan sweeping pattern.

3. a kind of dual-polarization weather radar Calibration Method based on on-fixed Metal Ball as claimed in claim 1 or 2, is characterized in that described rise Metal Ball equipment is unmanned plane or balloon or kite.