Radar weather data signal processing method and signal processing module

Disclosed is a radar weather data signal processing module comprising: a pulse compression unit for pulse-compressing a received weather signal; a correlation coefficient calculation unit for calculating a correlation coefficient on the basis of the pulse-compressed weather signal; and a weather variable calculation unit for calculating a weather variable on the basis of the calculated correlation coefficient.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a National Stage Patent Application of PCT International Patent Application No. PCT/KR2014/003025 (filed on Apr. 8, 2014) under 35 U.S.C. §371, which claims priority to Korean Patent Application No. 10-2013-0043043 (filed on Apr. 18, 2013), which are all hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a radar weather data signal processing method and signal processing module, and more particularly, to a radar weather data signal processing method and signal processing module, whereby a weather variable is calculated from a weather signal.

BACKGROUND ART

A weather observation apparatus receives weather observation data from a weather radar or an antenna, properly signal-processes the received data, thereby displaying real time observation data or generating a weather product.

In order to precisely check or forecast weather, a capability for properly processing weather data is required. However, when a current signal processing technology is used, a burden occurs due to a high required amount of calculation, and resolution is lowered.

DETAILED DESCRIPTION OF THE INVENTION

Technical Problem

The present invention provides a radar weather data signal processing method and signal processing module, whereby pulse compression processing is used to implement high resolution.

Technical Solution

According to an aspect of the present invention, there is provided a radar weather data signal processing module including: a pulse compression unit that pulse-compresses a received weather signal; a correlation coefficient calculation unit that calculates a correlation coefficient based on the pulse-compressed weather signal; and a weather variable calculation unit that calculates a weather variable based on the calculated correlation coefficient.

The pulse compression unit may include: a format conversion unit that converts a horizontal polarized wave in-phase/quadrature-phase (I/Q) signal and a vertical polarized wave I/Q signal that are received weather signals, into a format of floating decimal point data; a linear frequency modulation (LFM) signal-applying unit that applies a reference LFM signal; a window application unit that applies window functions to the horizontal polarized wave I/Q signal and the vertical polarized wave I/Q signal that are converted by the format conversion unit and the reference LFM signal; a fast fourier transform (FFT) performance unit that performs FFT on the signals to which the window functions are applied; a convolution unit that performs convolution on the signals on which FFT is performed by the FFT performance unit; and an inverse FFT (IFFT) performance unit that generates a compressed horizontal polarized wave I/Q signal and a compressed vertical polarized wave I/Q signal by performing IFFT on the convoluted signals.

The correlation coefficient calculation unit may include: a mode selection unit that selects a time domain mode or a frequency domain mode; a time domain mode unit that calculates a single polarized wave correlation coefficient and a cross-polarized wave correlation coefficient by performing time domain clutter filtering on the compressed I/Q signal; and a frequency domain mode unit that calculates a single polarized wave correlation coefficient by performing frequency domain clutter filtering on the compressed I/Q signal.

The weather variable calculation unit may include: a threshold variable calculation unit that calculates a threshold variable based on the calculated correlation coefficient; a weather variable calculation unit that calculates a weather variable based on the calculated correlation coefficient; a threshold processing unit that removes a weather variable less than a threshold value and causes a weather variable that exceeds the threshold value to pass, based on the threshold variable and the weather variable; and a speckle removing unit that removes speckles from the weather variable that is threshold-processed by the threshold processing unit.

The weather variable calculation unit may further include a distance averaging unit that averages a distance of the calculated correlation coefficient.

According to another aspect of the present invention, there is provided a radar weather data signal processing method, whereby a weather signal is processed by a radar weather data signal processing module, the radar weather data signal processing method including: pulse-compressing a received weather signal using the radar weather data signal processing module; calculating a correlation coefficient based on the pulse-compressed weather signal using the radar weather data signal processing module; and calculating a weather variable based on the calculated correlation coefficient using the radar weather data signal processing module.

Effects of the Invention

According to the present invention, a pulse compression processing operation is adopted in a weather signal processing operation so that high resolution can be implemented, and a window function is applied to pulse compression so that a problem of the occurrence of side lobes can be solved.

MODE OF THE INVENTION

An exemplary embodiment of the present invention will be described in detail with reference to the attached drawings.

FIG. 1is a block diagram of a signal processing module according to an embodiment of the present invention.

Referring toFIG. 1, a signal processing module (hereinafter, referred to as a ‘signal processing apparatus100’) includes a communication controller110, a signal processing unit120, and a storing unit130. The communication controller110receives a horizontal polarized wave in-phase/quadrature-phase (I/Q) signal and a vertical polarized wave I/Q signal from a transmission/receiving unit (not shown) as light and transfers the received horizontal polarized wave I/Q signal and the received vertical polarized wave I/Q signal to the signal processing unit120through a peripheral component interconnect (PCI). The communication controller110includes an optical communication function based on a field programmable gate array (FPGA). The signal processing unit120generates a weather variable based on the horizontal polarized wave I/Q signal and the vertical polarized wave I/Q signal that are received from the communication controller110and transmits the generated weather variable to an operation control unit (not shown). The signal processing unit120will be described in detail below. The storing unit130stores temporary data that is processed by the signal processing unit120. The storing unit130may be implemented with a solid-state drive (SSD). Also, the storing unit130is an element that may be omitted in consideration of a burden of a load.

FIG. 2is a block diagram of a signal processing unit ofFIG. 1according to an embodiment of the present invention.

Referring toFIG. 2, a signal processing unit200includes a pulse compression unit210that receives a horizontal/vertical (H/V) polarized wave I/Q signal including fixed decimal point data of 20 bits from a communication controller through a PCI and converts the received H/V polarized wave I/Q signal into the format of a floating decimal point and pulse-compresses the converted H/V polarized wave I/Q signal, a correlation coefficient calculation unit220that calculates a correlation coefficient from the compressed H/V polarized wave I/Q signal, and a weather variable calculation unit230that calculates a weather variable from the correlation coefficient. The signal processing unit200outputs the calculated weather variable to the operation control unit (not shown). Although not shown, the signal processing unit200may further include a communication unit, such as a PCI that may communicate with the communication controller in the signal processing apparatus, and a communication unit, such as Ethernet that may communicate with the operation control unit or a display analysis unit. Elements of the signal processing unit200will be described in detail below.

FIG. 3is a block diagram of a pulse compression unit ofFIG. 2according to an embodiment of the present invention.

Referring toFIG. 3, a pulse compression unit300includes a format conversion unit310, a linear frequency modulation (LFM) signal-applying unit320, a window application unit330, a fast fourier transform (FFT) performance unit340, a convolution unit350, and an inverse FFT (IFFT) performance unit360.

The pulse compression unit300receives the horizontal/vertical (H/V) polarized wave I/Q signal including fixed decimal point data of 20 bits, and the format conversion unit310converts the received horizontal/vertical (H/V) polarized wave I/Q signal including fixed decimal point data of 20 bits into the format of a floating decimal point of 32 bits.

After that, the pulse compression unit300performs pulse compression. A pulse compression method includes a time domain method and a frequency domain method. The time domain method is a procedure for convoluting a received LFM (or chirp) signal and a reference LFM signal. In this case, since the amount of calculation is required in units of N2(N is the number of samples), when the number of samples is increased, the amount of calculation is exponentially increased. Thus, the frequency domain method using FFT is generally applied to pulse compression. In this case, the frequency domain method is mathematically the same as the time domain method. However, the amount of calculation is required in units of N log N, and as the number of samples is increased, the amount of calculation is greatly decreased compared to the time domain method. However, since FFT is used, the number of samples should correspond to a multiplier of 2.FIG. 3relates to a pulse compression method using the frequency domain method.

The LFM signal-applying unit320applies the reference LFM signal to the window application unit330. The window application unit330applies window functions to the applied reference LFM signal, the horizontal polarized wave I/Q signal, and the vertical polarized wave I/Q signal. Examples of window functions include a hamming function, a blackman function, and a Kaiser function. The window functions are not limited. When no window function is applied before FFT is performed, a large number of side lobes is generated in the pulse-compressed signal. In this case, the window function is applied before FFT is performed, so that the number of side lobes is greatly reduced. However, main lobes may be widened so that a proper window function should be applied according to circumstances.

FIG. 4Ais a view of a waveform of a reference LFM signal to which no window function is applied, andFIG. 4Bis a view of a waveform of a pulse-compressed signal to which no window function is applied.

FIGS. 4A and 4Bshow the result of application in a near distance mode. A pulse width in the time domain is 1 [μs], and a bandwidth in the frequency domain is 10 [MHz]. As illustrated inFIG. 4B, a large number of side lobes is generated in a compressed signal.

FIG. 5Ais a view of a waveform of a reference LFM signal to which no window function is applied, andFIG. 5Bis a view of a waveform of a pulse-compressed signal to which no window function is applied.

FIGS. 5A and 5Bshow the result of application in the near distance mode.FIGS. 5A and 5Bshow the result of applying a hamming function as a window function. A pulse width in the time domain is 1 [μs], and a bandwidth in the frequency domain is 10 [MHz]. As illustrated inFIG. 5B, the number of side lobes is reduced in a compressed signal.

The FFT performance unit340performs FFT on the reference LFM signal, the horizontal polarized wave I/Q signal, and the vertical polarized wave I/Q signal to which the window functions are applied. The convolution unit350convolutes the LFM signal and the horizontal polarized wave I/Q signal on which FFT is performed, and convolutes the LFM signal and the vertical polarized wave I/Q signal on which FFT is performed. After that, the IFFT performance unit performs IFFT on the convoluted signal, generates a compressed horizontal polarized wave complex pulse and a compressed vertical polarized wave complex pulse and transmits the generated compressed horizontal polarized wave complex pulse and a compressed vertical polarized wave complex pulse to the correlation coefficient calculation unit.

FIG. 6is a block diagram of the correlation coefficient calculation unit ofFIG. 2according to an embodiment of the present invention.

Referring toFIG. 6, the correlation coefficient calculation unit600includes a mode selection unit610, a pulse pair processing (PPP) mode calculation unit620, and a discret fourier transform/fast fourier transform (DFT/FFT) mode calculation unit630. The PPP mode calculation unit620includes a clutter filtering unit622, a T0calculation unit624, a time domain correlation coefficient calculation unit626, and a dual polarized wave cross-correlation coefficient calculation unit628. The DFT/FFT mode calculation unit630includes a power spectrum calculation unit632, a clutter filtering unit634, and an IDFT/IFFT performance unit636.

The correlation coefficient calculation unit600receives the compressed horizontal polarized wave complex pulse and the compressed vertical polarized wave complex pulse, calculates a correlation coefficient thereof and performs clutter filtering. Clutter filtering is applied to calculation of R0, R1, and R2that are single polarized wave correlation coefficients so that R0, R1, and R2are calculated. A procedure of obtaining the single polarized wave correlation coefficients is classified into a PPP mode that is a time domain calculation method and a DFT/FFT mode that is a frequency domain calculation method. The FFT mode is applied to reduce the amount of calculation when the number of pulses is a multiplier of 2 in a DFT mode. Time domain clutter filtering is applied to clutter filtering in the PPP mode, and frequency domain clutter filtering is applied to clutter filtering in the DFT/FFT mode. Time domain clutter filtering has a small amount of calculation and may be applied regardless of an operation mode and the type of a weather variable. However, when a clutter and weather data overlap each other, the clutter and the weather data cannot be distinguished from each other so that the weather data is damaged. An adaptive filtering technique may be applied to frequency domain clutter filtering. Thus, when the clutter and the weather data overlap each other, damage of the weather data is minimized. However, frequency domain clutter filtering has a large amount of calculation and may be applied only when a distance between pulses is uniform. Thus, frequency domain clutter filtering is not applied to calculate a partial dual polarized wave weather variable. In these days, due to the development of hardware performance, there is no problem in performing the frequency domain clutter filtering. Thus, only frequency domain clutter filtering is applied to single polarized wave calculation, and time domain clutter filtering is used to calculate a dual polarized wave correlation coefficient or when the distance between pulses is not uniform.

The mode selection unit610determines whether to calculate the correlation coefficient in the PPP mode or to calculate the correlation coefficient in the DFT/FFT mode so as to calculate R0, R1, and R2that are single polarized wave correlation coefficients.

When the PPP mode calculation unit620is selected, in order to calculate R0, R1, and R2, the clutter filtering unit622performs clutter filtering on the received horizontal/vertical polarized wave complex pulse. An infinite impulse response (IIR) time domain clutter filter is used in the clutter filtering unit622in the PPP mode. A −40 dB filter or −50 dB filter is used as the IIR time domain clutter filter according to a clutter removing capability. These are selectively applied according to a clutter width.

FIG. 7is a view of a structure of an IIR time domain clutter filter according to an embodiment of the present invention.

Referring toFIG. 7, s is a received complex pulse, and s′ is a filtered complex pulse. Here, B0to B4and C1to C4are filter coefficients. An equation for obtaining s′ is as shown in the following Equation 1.
s′n=B0sn+B1sn−1+B2sn−2+B3sn−3+B4sn−4−C1s′n−1+C2s′n−2+C3s′n−3+C4s′n−4[Equation 1]

As known from characteristics of the IIR time domain clutter filter, the IIR time domain clutter filter suppresses all signals around zero-velocity to a predetermined size on an assumption that the velocity of a clutter is 0, so that a weather signal adjacent to the clutter is damaged.

The time domain correlation coefficient calculation unit626calculates R0, R1, and R2using the clutter-filtered horizontal/vertical polarized wave complex pulse. R0is a zerothlag autocorrelation of the filtered complex pulse, and R1is a first lag autocorrelation of the filtered complex pulse, and R2is a second lag autocorrelation of the filtered complex pulse.

Calculation equations of R0, R1, and R2are as shown in the following Equations 2, 3, and 4.

In the case of R0, R1, and R2, R0h, R1h, and R2hrelated to horizontal polarized wave and R0v, R1v, and R2vrelated to vertical polarized wave are calculated.

When the DFT/FFT mode calculation unit630is selected, the power spectrum calculation unit632calculates a power spectrum of each horizontal/vertical polarized wave in the frequency domain from the received complex pulse. A calculation equation for obtaining the power spectrum is as shown in the following Equation 5.

Since fourier transform is used in the frequency domain, the window function may be used to calculate the power spectrum so as to reduce the number of side lobes. In Equation 5, w is a window function.

The clutter filtering unit634obtains a power spectrum of each polarized wave component and then frequency domain clutter filters the power spectrum. The clutter filtering unit634distinguishes a spectrum of a clutter portion from the frequency domain, removes data of the clutter portion around zero velocity and then estimates weather data of the removed portion using an adjacent value. A method of restoring a weather signal of the removed portion includes linear interpolation and a Gaussian model adaptive processing (GMAP) method.

The IDFT/IFFT performance unit636performs IDFT/IFFT on the filtered power spectrum of each polarized wave component. In this case, first three coefficients of an IDFT/IFFTed coefficient, i.e., zeroth, first, and second coefficients are R0h, R0v, R1h, R1v, R2h, and R2v.

T0and a dual polarized wave cross-correlation coefficient ρhvare calculated in the PPP mode.

The T0calculation unit624calculates T0hand T0from the horizontal/vertical polarized wave complex pulse. T0is a zerothlag autocorrelation of the unfiltered complex pulse, and T0his horizontal polarized wave T0, and T0is vertical polarized wave T0. T0is calculated from each of horizontal polarized wave and vertical polarized wave, and a calculation equation thereof is as shown in the following Equation 6.

In Equation 6, M is the number of pulses, and s is a received complex pulse.

The dual polarized wave cross-correlation coefficient calculation unit628calculates the dual polarized wave cross-correlation coefficient ρhvfrom the received complex pulse. ρhv(0) is a zerothlag cross-correlation coefficient of an unfiltered vertical polarized wave complex pulse and horizontal polarized wave complex pulse. A calculation equation of ρhv(0) is as shown in the following Equation 7.

Clutter filtering is not basically performed on ρhv(0), but clutter filtering may be selectively performed on ρhv(0).

The correlation coefficient calculation unit600transmits the calculated correlation coefficients to a weather variable calculation unit.

FIG. 8is a block diagram of a weather variable calculation unit according to an embodiment of the present invention.

Referring toFIG. 8, a weather variable calculation unit800includes a distance averaging unit810, a threshold variable calculation unit820, a weather variable calculation unit830, a threshold processing unit840, and a speckle removing unit850.

The distance averaging unit810actually averages a correlation coefficient that corresponds to n distances. Advantages of a distance averaging procedure include a reduction in the amount of calculation and suppressing noise and a local non-weather echo. However, since the n distances are averaged, distance resolution is lowered. The distance averaging procedure is a procedure that is selectively applied to a case where noise needs to be suppressed in a situation in which resolution is not significant. Thus, the distance averaging unit810is an element that is selectively applied.

The threshold variable calculation unit820calculates a threshold variable that is a variable for threshold processing. Types of the threshold variable include LOG, SQI, CCOR, and SIG. Equations for obtaining LOG, SQI, CCOR, and SIG are as shown in Equations 8 through 11.

In Equation 8, N is noise power.

The weather variable calculation unit830calculates Z, V, W, and ZDR that are weather variables for each polarized wave using the received correlation coefficient and calculates ρHV, φDP, and KDP that are dual polarized wave cross-correlation weather variables.

Equations for obtaining Z, V, W, ZDR, ρHV, and φDP that are weather variables are as shown in the following Equations 12 through 17.

In Equations 12 through 17, a is atmospheric attenuation, and r is a distance, and N is noise power. Also, values dBZ0and ZDRoffsetare received from the operation control unit.

A specific difference phase (KDP) among the weather variables is not directly calculated from the correlation coefficient but is secondarily calculated. The KDP is calculated using a variation amount (differential value) over time of φDP, as shown in Equation 18.

Velocity V among the weather variables may be velocity unfolding processed. Velocity unfolding is a procedure of increasing the range of observation velocity by increasing the range of unambiguous velocity using dual PRF.

The threshold processing unit840removes weather variables less than a threshold value, i.e., causes only weather variables that exceed the threshold value to pass, so as to improve quality of the calculated weather variables.

Table 1 shows applied threshold variables caused by weather variables.

Table 2 shows an example of the range of a threshold value.

TABLE 2Threshold valuesRangesLOGthresh0 to 40dBSQIthresh0 to 1CCORthresh0 to −100dBSIGthresh0 to 100dBρHVthresh0 to 1

The applied threshold variables and the threshold value range are not limited to the above tables and are determined after signal quality analysis is performed using an external display analysis unit.

The speckle removing unit850interpolates or removes isolated data after threshold processing is performed, based on peripheral data so as to manage the quality of the weather variables. The speckle removing unit850examines n effectiveness of a neighbor value of isolated variables. If n or more peripheral data are effective, the data removed by the threshold processing is interpolated as peripheral effective values. If n or less peripheral data are effective, the data passed by the threshold processing is removed. The weather variables are finally calculated after speckles are removed.

FIG. 9is a flowchart illustrating a weather signal processing method according to an embodiment of the present invention.

Referring toFIG. 9, in Operation910, the signal processing apparatus pulse-compresses a weather data signal received from radar. The signal processing apparatus receives a horizontal/vertical (H/V) polarized wave I/Q signal including fixed decimal point of 20 bits and converts the received horizontal/vertical (H/V) polarized wave I/Q signal into the format of a floating decimal point of 32 bits and then pulse-compresses the converted horizontal/vertical (H/V) polarized wave I/Q signal.

In Operation920, the signal processing apparatus calculates a correlation coefficient based on the pulse-compressed weather signal. The signal processing apparatus calculates single polarized wave and dual polarized wave correlation coefficients from the compressed H/V polarized wave I/Q signal.

In Operation930, the signal processing apparatus calculates a weather variable based on the calculated correlation coefficient. The signal processing apparatus calculates a threshold variable and the weather variable based on the correlation coefficient, threshold processes the calculated threshold variable and weather variable, removes speckles, thereby calculating a final weather variable.

FIG. 10is a flowchart illustrating a pulse compression operation910ofFIG. 9according to an embodiment of the present invention.

A pulse compression method includes a time domain method and a frequency domain method. The time domain method is a procedure of convoluting a received LFM (or chirp) signal and a reference LFM signal. In this case, since the amount of calculation is required in units of N2(N is the number of samples), when the number of samples is increased, the amount of calculation is exponentially increased. Thus, the frequency domain method using FFT is generally applied to pulse compression. In this case, the frequency domain method is mathematically the same as the time domain method. However, the amount of calculation is required in units of N log N, and as the number of samples is increased, the amount of calculation is greatly decreased compared to the time domain method. However, since FFT is used, the number of samples should correspond to a multiplier of 2.FIG. 10relates to a pulse compression method using the frequency domain method.

Referring toFIG. 10, in Operation1010, the signal processing apparatus converts a horizontal polarized wave I/Q signal and a vertical polarized wave I/Q signal of 20 bits that are received weather signals into floating decimal point data of 32 bits.

In Operation1020, the signal processing apparatus applies a window function to the format-converted horizontal polarized wave I/Q signal and vertical polarized wave I/Q signal and the reference LFM signal. An example of the window function includes a hamming function, a blackman function, or a Kaiser function. The window function is not limited. When no window function is applied before FFT is performed, a large number of side lobes is generated in the pulse-compressed signal. In this case, the window function is applied before FFT is performed, so that the number of side lobes is greatly reduced. However, a main lobe may be widened so that a proper window function should be applied according to circumstances.

In Operation1030, the signal processing apparatus performs FFT on the reference LFM signal, the horizontal polarized wave I/Q signal and the vertical polarized wave I/Q signal to which the window functions are applied.

In Operation1040, the signal processing apparatus performs convolution on signals on which FFT is performed. The signal processing apparatus convolutes the FFTed LFM signal and horizontal polarized wave I/Q signal and convolutes the FFTed LFM signal and the vertical polarized wave I/Q signal.

In Operation1050, the signal processing apparatus generates a compressed horizontal polarized wave I/Q signal and a compressed vertical polarized wave I/Q signal by performing IFFT on the convoluted signals.

FIG. 11is a flowchart illustrating a correlation coefficient calculation operation920ofFIG. 9according to an embodiment of the present invention.

Referring toFIG. 11, in Operation1110, the signal processing apparatus selects a time domain mode or a frequency domain mode. A procedure of obtaining a single polarized wave correlation coefficient is classified into a PPP mode that is a time domain calculation method and a DFT/FFT mode that is a frequency domain calculation method. The FFT mode is a method applied to reduce the amount of calculation when the number of pulses is a multiplier of 2 in a DFT mode. Time domain clutter filtering is applied to clutter filtering in the PPP mode, and frequency domain clutter filtering is applied to clutter filtering in the DFT/FFT mode. Time domain clutter filtering has a small amount of calculation and may be applied regardless of an operation mode and the type of the weather variable. However, when a clutter and weather data overlap each other, the clutter and the weather data cannot be distinguished from each other so that weather data is damaged. An adaptive filtering technique may be applied to frequency domain clutter filtering. Thus, when the clutter and the weather data overlap each other, damage of the weather data is minimized. However, frequency domain clutter filtering has a large amount of calculation and may be applied only when a distance between pulses is uniform. Thus, frequency domain clutter filtering is not applied to calculate a partial dual polarized wave weather variable. In these days, due to the development of hardware performance, there is no problem in performing the frequency domain clutter filtering. Thus, only frequency domain clutter filtering is applied to single polarized wave calculation, and time domain clutter filtering is used to calculate a dual polarized wave correlation coefficient or when the distance between pulses is not uniform. The signal processing apparatus determines whether to calculate the correlation coefficient in the PPP mode or to calculate the correlation coefficient in the DFT/FFT mode so as to calculate R0, R1, and R2that are single polarized wave correlation coefficients.

In Operation1120, the signal processing apparatus performs time domain clutter filtering on the compressed I/Q signal in the time domain mode and calculates a single polarized wave correlation coefficient and a cross-polarized wave correlation coefficient. The signal processing apparatus performs clutter filtering on received horizontal/vertical polarized wave complex pulse so as to calculate R0, R1, and R2. An IIR time domain clutter filter is used as a clutter filter in the time domain mode. A −40 dB filter or −50 dB filter is used as the IIR time domain clutter filter according to a clutter removing capability. These are selectively applied according to a clutter width. An example of the IIR time domain clutter filter is previously shown inFIG. 7. As known from characteristics of the IIR time domain clutter filter, the IIR time domain clutter filter suppresses all signals around zero-velocity to a predetermined size on an assumption that the velocity of a clutter is 0, so that a weather signal adjacent to the clutter is damaged. The signal processing apparatus calculates R0, R1, and R2using the clutter-filtered horizontal/vertical polarized wave complex pulse. R0is a zerothlag autocorrelation of the filtered complex pulse, and R1is a first lag autocorrelation of the filtered complex pulse, and R2is a second lag autocorrelation of the filtered complex pulse. Calculation equations of R0, R1, and R2are as shown in the following Equations 2, 3, and 4. In the case of R0, R1, and R2, R0h, R1h, and R2hrelated to horizontal polarized wave and R0v, R1v, and R2vrelated to vertical polarized wave are calculated.

T0and a dual polarized wave cross-correlation coefficient ρhvare calculated in the time domain mode. The signal processing apparatus calculates T0hand T0vfrom the horizontal/vertical polarized wave complex pulse. T0is a zerothlag autocorrelation of the unfiltered complex pulse, and T0his horizontal polarized wave T0, and T0vis vertical polarized wave T0. T0is calculated from each of horizontal polarized wave and vertical polarized wave, and a calculation equation thereof is as shown in the following Equation 6. The dual polarized wave cross-correlation coefficient ρhvis calculated from the received complex pulse. ρhv(0) is a zerothlag cross-correlation coefficient of an unfiltered vertical polarized wave complex pulse and horizontal polarized wave complex pulse. A calculation equation of ρhv(0) is as shown in the following Equation 7. Clutter filtering is not basically performed on ρhv(0), but clutter filtering may be selectively performed on ρhv(0).

In Operation1130, the signal processing apparatus performs frequency domain clutter filtering on the compressed I/Q signal in the frequency domain mode and calculates a single polarized wave correlation coefficient. When the frequency domain mode, i.e., the DFT/FFT mode is selected, the signal processing apparatus calculates a power spectrum of each horizontal/vertical polarized wave in the frequency domain from the received complex pulse. A calculation equation for obtaining the power spectrum is as shown in the following Equation 5. Since fourier transform is used in the frequency domain, the window function may be used to calculate the power spectrum so as to reduce the number of side lobes. After that, the signal processing apparatus obtains a power spectrum of each polarized wave component and then frequency domain clutter filters the power spectrum. The signal processing apparatus distinguishes a spectrum of a clutter portion from the frequency domain, removes data of the clutter portion around zero velocity and then estimates weather data of the removed portion using an adjacent value. A method of restoring a weather signal of the removed portion includes linear interpolation and a Gaussian model adaptive processing (GMAP) method. After that, the signal processing apparatus performs IDFT/IFFT on the filtered power spectrum of each polarized wave component. In this case, first three coefficients of an IDFT/IFFTed coefficient, i.e., zeroth, first, and second coefficients are R0h, R0v, R1h, R1v, R2h, and R2v.

FIG. 12is a flowchart illustrating a weather variable calculation operation930ofFIG. 9according to an embodiment of the present invention.

Referring toFIG. 12, in Operation1210, the signal processing apparatus calculates a threshold variable based on the calculated correlation coefficient. Types of the threshold variable include LOG, SQI, CCOR, and SIG. Equations for obtaining LOG, SQI, CCOR, and SIG are as shown in Equations 8 through 11.

In Operation1220, the signal processing apparatus calculates weather variables based on the calculated correlation coefficient. The signal processing apparatus calculates Z, V, W, and ZDR that are weather variables for each polarized wave using the received correlation coefficient and calculates ρHV, φDP, and KDP that are dual polarized wave cross-correlation weather variables. Equations for obtaining Z, V, W, ZDR, ρHV, and φDP that are weather variables are as shown in the following Equations 12 through 17. A KDP among the weather variables is not directly calculated from the correlation coefficient but is secondarily calculated. The KDP is calculated using a variation amount (differential value) over time of φDP, as shown in Equation 18. Also, velocity V among the weather variables may be velocity unfolding processed. Velocity unfolding is a procedure of increasing the range of observation velocity by increasing the range of unambiguous velocity using dual PRF.

In Operation1230, the signal processing apparatus removes weather variables less than a threshold value, i.e., causes only weather variables that exceed the threshold value to pass, based on the threshold variable and the weather variable.

In Operation1240, the signal processing apparatus removes speckles from the threshold-processed weather variable. The signal processing apparatus interpolates or removes isolated data after threshold processing is performed, based on peripheral data so as to manage the quality of the weather variables. In detail, the signal processing apparatus examines n effectiveness of a neighbor value of isolated variables. If n or more peripheral data are effective, the data removed by the threshold processing is interpolated as peripheral effective values. If n or less peripheral data are effective, the data passed by the threshold processing is removed. The weather variables are finally calculated after speckles are removed.

Although not shown, prior to Operation1210ofFIG. 12, the signal processing apparatus may average a distance of the calculated correlation coefficient. Advantages of a distance averaging procedure include a reduction in the amount of calculation and suppressing noise and a local non-weather echo. However, since distances are averaged, distance resolution is lowered. The distance averaging procedure is a procedure that is selectively applied to a case where noise needs to be suppressed in a situation in which resolution is not significant.

INDUSTRIAL APPLICABILITY

According to the present invention, a radar weather data signal processing method and signal processing module, whereby high resolution can be implemented and a window function is applied to pulse compression so that a problem of the occurrence of side lobes can be solved, can be configured.