JP2013195167A - Radar signal processing apparatus and radar signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an output of a rainfall intensity estimation value far from a reality even when a change rate of a phase difference between polarized waves is locally changed.SOLUTION: A phase difference calculation section 19 calculates a phase difference between polarized waves of a horizontal polarization reception signal and a vertical polarization reception signal, and a reflected wave intensity calculation section 18 calculates reflected wave intensity from at least one of the horizontal polarization reception signal and the vertical polarization reception signal. A phase difference rainfall intensity calculation section 21 calculates phase difference rainfall intensity which is a rainfall intensity estimation value on the basis of a distance change rate of the phase difference, and a reflective factor rainfall intensity calculation section 20 calculates reflective factor rainfall intensity which is the rainfall intensity estimation value on the basis of the reflected wave intensity. A synthesis section 22 selects the phase difference rainfall intensity when the phase difference rainfall intensity and the reflective factor rainfall intensity satisfy a predetermined condition, and select the reflective factor rainfall intensity and outputs it as a rainfall intensity estimation value R when the phase difference rainfall intensity and the reflective factor rainfall intensity do not satisfy a predetermined condition.

Description

  The present invention relates to a radar signal processing device and a radar signal processing method. More specifically, the present invention relates to a radar signal processing apparatus and a radar signal processing method for estimating rainfall intensity using two radio waves of horizontal polarization and vertical polarization.

  In a widely used single-polarization weather radar, the rainfall intensity is estimated using a relational expression established between the echo intensity and the rainfall intensity (see, for example, Patent Document 1). However, since this relational expression changes greatly depending on the particle size distribution of raindrops, it is difficult to obtain an accurate rainfall intensity with a single-polarization weather radar.

  In general, raindrops have a shape close to a spheroid obtained by squashing a sphere in the vertical direction. Raindrops with a large particle size have a large flatness, and raindrops with a small particle size have a small flatness and are almost spherical. Therefore, if dual-polarization radar observation using horizontal and vertical polarization is performed, information on the shape of the raindrop, that is, information corresponding to the particle size distribution can be obtained, which enables highly accurate rainfall intensity measurement. Become. The amount of change per unit distance in the phase difference between polarized waves that occurs during the passage of radio waves through the rainfall region is effective in improving the accuracy of rainfall intensity measurement. The inter-polarization phase difference is the difference between the horizontal polarization and the vertical polarization phase of the received signal, and the rainfall intensity is estimated from the amount of change per unit distance of the inter-polarization phase difference.

  In Patent Literature 2, a distance differential section D for calculating the distance differential of the inter-polarization phase difference φdp is set using a provisional estimated value of the rainfall intensity calculated from the echo intensity, and the position using the distance differential section D is set. A radar signal processing device is described that calculates a rainfall intensity estimated value R from a phase difference distance differential value Kdp obtained by differentiating the phase difference φdp with respect to distance. In the meteorological radar system of Patent Document 3, precipitation intensity calculation processing is performed based on the received power of horizontal polarization, received power of vertical polarization, and phase difference between polarizations, and smoothing processing is performed to obtain precipitation intensity.

JP 2003-344556 A JP 2005-17082 A JP 2011-27545 A

  When calculating the estimated value of the rainfall intensity with the dual polarization radar, the rainfall intensity can be calculated without much influence of the rain attenuation by using the polarization phase difference change rate Kdp. However, there is a problem that the value of the polarization phase difference change rate Kdp is not stable, and the calculated rainfall intensity may be larger than the actual rainfall intensity.

  The present invention has been made in view of the above-described situation, and suppresses outputting an estimated value of rainfall intensity far from the actual value even when the rate of change in phase difference between polarizations locally changes. Objective.

  In order to achieve the above-described object, the radar signal processing apparatus according to the present invention radiates two radio waves of horizontal polarization and vertical polarization into space, and converts the radio waves reflected by an object existing in the space into two polarizations. A radar signal processing device that receives dual-polarized measurement values by receiving signals as horizontal polarization reception signals and vertical polarization reception signals and processing the horizontal polarization reception signals and vertical polarization reception signals. The phase difference calculation unit calculates a phase difference between the polarizations of the horizontal polarization reception signal and the vertical polarization reception signal, and the reflected wave intensity calculation unit calculates the horizontal polarization reception signal and the vertical polarization reception signal. The reflected wave intensity is calculated from at least one. The phase difference rainfall intensity calculation unit calculates the phase difference rainfall intensity, which is a rainfall intensity estimation value based on the distance change rate of the phase difference, and the reflection factor rainfall intensity calculation unit is a reflection, which is the rainfall intensity estimation value based on the reflected wave intensity. Calculate factor rainfall intensity. The combining unit selects the phase difference rainfall intensity when the phase difference rainfall intensity and the reflection factor rainfall intensity satisfy the predetermined condition, and selects the reflection factor rainfall intensity when the predetermined condition is not satisfied. And output as an estimated rainfall intensity.

  According to the present invention, even when the rate of change in phase difference between polarizations obtained from received signals of horizontal polarization and vertical polarization changes locally, an estimated value of rainfall intensity far from the actual is output. Can be suppressed.

It is a block diagram which shows the structural example of the radar signal processing apparatus which concerns on embodiment of this invention. It is a figure which shows the distance division of the observation area | region of the radar signal processing apparatus which concerns on embodiment. It is a figure explaining the calculation method of the rainfall intensity which concerns on embodiment. It is a flowchart which shows an example of the process of the rainfall estimation which concerns on embodiment.

(Embodiment)
FIG. 1 is a block diagram showing a configuration example of a radar signal processing apparatus according to an embodiment of the present invention. The radar signal processing apparatus includes a transmission signal generation unit 11, a transmission unit 12, a division unit 13, a transmission / reception switching unit 14H, a transmission / reception switching unit 14V, an antenna 15, a reception unit 16H, a reception unit 16V, an A-D conversion unit 17H, and an A-. A D conversion unit 17V, a reflected wave intensity calculation unit 18, a phase difference calculation unit 19, a reflection factor rainfall intensity calculation unit 20, a phase difference rainfall intensity calculation unit 21, and a synthesis unit 22 are provided.

  In the embodiment, in order to facilitate understanding, an example is given in which the radar signal processing device includes the transmission signal generation unit 11 to the A-D conversion units 17H and 17V. However, the reception signal is obtained by radiating radio waves. A configuration in which the radar device is independent and the radar signal processing device obtains a reception signal from the radar device may be employed. In that case, the radar signal processing apparatus includes a reflected wave intensity calculation unit 18, a phase difference calculation unit 19, a reflection factor rainfall intensity calculation unit 20, a phase difference rainfall intensity calculation unit 21, and a synthesis unit 22.

  Furthermore, it is also possible to provide a configuration in which one radar signal processing device is provided for a plurality of radar devices, and each received signal is transmitted from the plurality of radar devices to the radar signal processing device.

  The transmission signal generator 11 generates a transmission signal that is a source of a transmission wave that the radar radiates into the air. This transmission signal is processed by the transmission unit 12, and as a result, a transmission wave is output from the transmission unit 12. The transmission signal is amplified by the transmission unit 12 into a high power signal. The transmitter 12 further modulates the transmission wave as necessary. Usually, in order to obtain the distance resolution of the radar, pulse modulation is performed.

  The division unit 13 divides the transmission wave output from the transmission unit 12 into two and outputs the divided waves to the transmission / reception switching unit 14H and the transmission / reception switching unit 14V, respectively. The transmission / reception switching unit 14H and the transmission / reception switching unit 14V transmit the transmission wave output from the dividing unit 13 to the antenna 15 at the transmission timing of the radar apparatus. Also, at the reception timing of the radar device, the received wave received by the antenna 15 is transmitted to the receiving unit 16H and the receiving unit 16V, respectively.

  The antenna 15 receives two transmission waves, the transmission wave transmitted from the transmission / reception switching unit 14H and the transmission wave transmitted from the transmission / reception switching unit 14V. In the antenna 15, the transmission wave transmitted from the transmission / reception switching unit 14H is radiated into the atmosphere with horizontal polarization, and the transmission wave transmitted from the transmission / reception switching unit 14V is radiated into the atmosphere with vertical polarization.

  The reflected radio wave reflected by the atmosphere is received by the antenna 15. The horizontally polarized wave component of the reflected radio wave is transmitted from the antenna 15 to the receiving unit 16H via the transmission / reception switching unit 14H. Further, the vertically polarized wave component of the reflected radio wave is transmitted from the antenna 15 to the receiving unit 16V via the transmission / reception switching unit 14V. The receiving unit 16H and the receiving unit 16V perform amplification and frequency conversion on the input horizontal polarization reception signal and vertical polarization reception signal, respectively.

  The frequency-converted received signals output from the receiving unit 16H and the receiving unit 16V are converted from analog signals to digital signals by the AD converting units 17H and 17V, respectively. The converted signals are hereinafter simply referred to as horizontal polarization reception signals and vertical polarization reception signals.

  As a configuration of the radar signal processing apparatus, in FIG. 1, a transmission wave generated by one transmission unit 12 is divided into two by a division unit 13 so that horizontal polarization and vertical polarization are transmitted simultaneously. Some radar signal processing apparatuses have other configurations. For example, there is a technique in which horizontal polarization and vertical polarization are alternately observed by switching both polarizations with a switch, instead of simultaneously transmitting horizontal polarization and vertical polarization.

  The A-D converter 17H sends the horizontally polarized wave reception signal to the reflected wave intensity calculator 18 and the phase difference calculator 19. The AD conversion unit 17V sends the vertically polarized wave reception signal to the phase difference calculation unit 19.

  The reflected wave intensity calculator 18 calculates the reflected wave intensity, which is the power value of the received signal, from the horizontally polarized wave received signal. In general, since raindrops that are radar targets are randomly distributed in space, the received signal also has random characteristics. Therefore, in the calculation of the reflected wave intensity, the estimated value of the reflected wave intensity is calculated by averaging (that is, integrating) a plurality of statistically independent received signals obtained by a plurality of radar pulse transmissions. The accuracy of reflected wave intensity is improved by suppressing fluctuations. The reflected wave intensity is calculated for each azimuth and distance section (grid) of the observation region.

  Here, the reflected wave intensity is calculated based on the horizontal polarization reception signal, but may be calculated based on the vertical polarization reception signal, or the horizontal polarization reception signal and the vertical polarization reception signal may be calculated. You may calculate based on both.

The reflection factor rainfall intensity calculation unit 20 calculates the radar reflection factor of the rain from the reflected wave intensity using the weather radar equation, and further based on the radar reflection factor using the relational expression between the radar reflection factor and the rainfall intensity. is an estimate of the rain intensity is converted into the reflection factor rainfall intensity R _Z. The relationship between the radar reflectivity factor Z and the reflection factor rainfall R _Z, for example, the following equation (1) is used.
R _Z = B · Z ^β (1)
In Equation (1), R _Z is the rainfall intensity [mm / h], and B and β are constants. Z is a radar reflection factor [mm ⁶ / m ³ ], which corresponds to the radar reflectance per unit volume of rainfall. Although the constants B and β differ depending on the type of rainfall, values of B = 200 and β = 1.6 are often used as standard. The reflection factor Z and the reflection factor rainfall intensity R _Z are calculated for each azimuth and distance category (grid) of the observation region.

On the other hand, the phase difference calculation unit 19 calculates an inter-polarization phase difference (hereinafter also simply referred to as a phase difference) φdp between the horizontal polarization reception signal and the vertical polarization reception signal. The phase difference φdp is calculated by calculating the phase (deflection angle) of the cross-correlation coefficient between the horizontally polarized wave received signal and the vertically polarized wave received signal, and is expressed as the following equation (2).
φdp = arg (<s ^* hh · svv>) (2)
In Expression (2), shh is a received signal obtained by transmitting horizontal polarization and receiving horizontal polarization, and * on the right shoulder represents a complex conjugate. svv is a received signal obtained by transmitting vertical polarization and receiving vertical polarization. <> Represents a set average, and arg represents a declination.

  In actual signal processing, assuming the ergodic nature of the signal, collective averaging is realized by time averaging or time integration. That is, it is an average process or an integration process of signals obtained by a plurality of pulse transmissions. Here, the number of data used for the averaging process or the integration process is referred to as an integration number. The phase difference φdp is calculated for each azimuth and distance section (grid) of the observation region.

The phase difference rainfall intensity calculation unit 21 calculates a phase difference change rate Kdp that is a rate of change of the phase difference φdp in the distance direction, and a phase difference rainfall intensity R _Kdp that is an estimated value of the rainfall intensity based on the phase difference change rate _Kdp. Is calculated. The phase difference change rate Kdp is the change rate in the distance direction of the inter-polarization phase difference φdp between the horizontal polarization and the vertical polarization obtained from the radar observation data, and is expressed by the following equation (3). The
Kdp = (φdp (r1) −φdp (r2)) / 2 (r1−r2) (3)
In Expression (3), φdp (r1) and φdp (r2) are phase differences between the horizontally polarized wave reception signal and the vertically polarized wave reception signal at distances r1 and r2, respectively. The phase difference change rate Kdp is calculated for each azimuth and distance section (grid) of the observation region.

The following formula (4) is given as an expression for converting the phase difference change rate Kdp into the phase difference rainfall intensity _RKdp (for example, “Richard J. Doviak and Dusan S. Zrnic, Doppler Radar and Weather Observations, Second Edition”). Academic Press, Inc., 1993, p. 234).
R _Kdp = 5.1 (Kdp · λ) ^0.866 [mm / h] (4)
In Equation (4), R _Kdp is the rainfall intensity [mm / h], λ is the wavelength [cm] of the radar radio wave, and the unit of the phase difference change rate Kdp is [deg / km]. The phase difference rainfall intensity R _Kdp is calculated for each azimuth angle and distance section (grid) of the observation region.

  The synthesizer 22 calculates an estimated rainfall intensity value R for each azimuth and distance category (grid) from the reflection factor rainfall intensity and the phase difference rainfall intensity. Specifically, depending on whether or not the reflection factor rainfall intensity and the phase difference rainfall intensity satisfy the conditions defined for each grid, select the reflection factor rainfall intensity or phase difference rainfall intensity for that grid and estimate the rainfall intensity of that grid. Output as value R.

  FIG. 2 is a diagram illustrating distance sections of observation regions of the radar signal processing device according to the embodiment. For each azimuth angle of the observation area, division numbers are assigned in ascending order from the radar device. The interval between sections is represented by Δx.

In the first determination condition for calculating the rainfall intensity estimated value R, for each azimuth angle, the number of the grid distance section is i,
(| R _Kdp (i + 1) −R _Z (i + 1) | − | R _Kdp (i−1) −R _Z (i−1) |) / 2Δx <α
In this case, the phase difference rainfall intensity R _Kdp is adopted as the rainfall intensity estimated value R of the grid (determination 1). Here, i + 1 and i-1 indicate the numbers of the distance sections one after and one before the same azimuth as the lattice of interest. Δx is an interval between distance sections, and α is a constant.

Speaking judgment 1 in reverse,
(| R _Kdp (i + 1) −R _Z (i + 1) | − | R _Kdp (i−1) −R _Z (i−1) |) / 2Δx ≧ α
In this case, the reflection factor rainfall intensity of the distance section i is adopted as the rainfall intensity estimated value R of the distance section i. That is, the absolute value of the difference between the phase difference rainfall intensity and the reflection factor rainfall intensity in the section i + 1 immediately after the section i, and the phase difference rainfall intensity and the reflection factor rainfall intensity in the section i-1 immediately before the section i. When the difference from the absolute value of the difference is equal to or greater than a predetermined value, the reflection factor rainfall intensity of the section i is selected as the rainfall intensity estimated value R of the section i.

The second determination condition is as follows:
R _Kdp <R _Z * β
In this case, the phase difference rainfall intensity R _Kdp is adopted as the rainfall intensity estimated value R of the grid (determination 2). β is a constant.

Speaking of decision 2 in reverse,
R _Kdp ≧ R _Z * β
In this case, the reflection factor rainfall intensity is adopted as the rainfall intensity estimation value R of the grid. That is, for each grid, when the phase difference rainfall intensity is greater than or equal to a constant multiple of the reflection factor rainfall intensity, the reflection factor rainfall intensity of the grid is selected as the rainfall intensity estimation value R for the grid.

  FIG. 3 is a diagram for explaining a method of calculating rainfall intensity according to the embodiment. The reflected wave intensity does not fluctuate greatly depending on the distance, but the phase difference may fluctuate. At a distance where the change is large, the absolute value of the phase difference change rate becomes large, and the phase difference rainfall intensity is greater than the actual one. May be larger. When the absolute value of the difference between the phase difference rainfall intensity and the reflection factor rainfall intensity changes before and after the section i, the decision 1 is to reject the phase difference rainfall intensity of the section i. Further, in the case where the phase difference rainfall intensity of the section i of interest is equal to or larger than a constant multiple of the reflection factor rainfall intensity, the judgment 2 is to reject the phase difference rainfall intensity of the section i. In FIG. 3, the case where the phase difference rainfall intensity is rejected in the determination 2 is shown. The constant α for determination 1 and the constant β for determination 2 can be set based on actual observation.

The determination 1 and the determination 2 may be used independently to output the rainfall intensity estimated value R for each grid. Alternatively, the logical product of the determination 1 and the determination 2 may be determined as one condition. That is,
(| R _Kdp (i + 1) −R _Z (i + 1) | − | R _Kdp (i−1) −R _Z (i−1) |) / 2Δx <α
And
R _Kdp <R _Z * β
In this case, the phase difference rainfall intensity R _Kdp is adopted as the rainfall intensity estimated value R of the grid. In other cases, the reflection factor rainfall intensity is adopted as the rainfall intensity estimation value R of the grid.

  FIG. 4 is a flowchart illustrating an example of a rainfall estimation process according to the embodiment. The flowchart of FIG. 4 shows a case where the determination is performed using the logical product of the above-described determination 1 and determination 2 as a condition. The reflected wave intensity calculator 18 receives the received signal (step S01), performs an averaging process for each grating, and calculates the reflected wave intensity (step S02). Then, the reflection factor rainfall intensity calculation unit 20 calculates the radar reflection factor from the reflected wave intensity, and calculates the reflection factor rainfall intensity for each lattice (step S03).

  In parallel with the calculation of the reflection factor rainfall intensity, the phase difference calculation unit 19 inputs the horizontal polarization reception signal and the vertical polarization reception signal (step S11), averages the difference, and performs the phase difference between the polarizations. Is calculated (step S12). And the phase difference rainfall intensity calculation part 21 calculates the distance change rate of the phase difference between polarized waves, and calculates the phase difference rainfall intensity for every grating | lattice (step S13).

The combining unit 22 determines the condition for determination 1 from the reflection factor rainfall intensity and the phase difference rainfall intensity for each grid.
(| R _Kdp (i + 1) −R _Z (i + 1) | − | R _Kdp (i−1) −R _Z (i−1) |) / 2Δx <α
Is satisfied (step S21; YES) and the condition R _Kdp <R _Z * β of determination 2 is satisfied (step S22; YES), the phase difference rainfall intensity of the grid is selected as the rainfall intensity estimated value R. And output (step S23).

  When the condition of determination 1 is not satisfied (step S21; NO), or when the condition of determination 2 is not satisfied (step S22; NO), the reflection factor rainfall intensity of the grid is selected as the rainfall intensity estimated value R. Output (step S24).

  As described above, according to the radar signal processing apparatus of the present embodiment, even if the polarization phase difference change rate obtained from the horizontally polarized wave and vertically polarized wave received signals is locally changed, It can suppress outputting the estimated value of the rainfall intensity far from.

11 Transmission signal generator
12 Transmitter
13 Dividing unit 14H, 14V Transmission / reception switching unit
15 Antenna 16H, 16V Receiver 17H, 17V A-D converter
18 Reflected wave intensity calculator
19 Phase difference calculator
20 Reflection factor rainfall intensity calculator
21 Phase difference rainfall intensity calculation part
22 Synthesizer

Claims (6)

Two radio waves of horizontal polarization and vertical polarization are radiated into space, and radio waves reflected by objects existing in the space are received as horizontal polarization reception signals and vertical polarization reception signals with two polarizations, A radar signal processing device for obtaining a dual polarization measurement value by performing processing on a horizontal polarization reception signal and the vertical polarization reception signal,
A phase difference calculation unit that calculates a phase difference between the polarizations of the horizontal polarization reception signal and the vertical polarization reception signal;
A reflected wave intensity calculator that calculates a reflected wave intensity from at least one of the horizontal polarization reception signal and the vertical polarization reception signal;
A phase difference rainfall intensity calculation unit for calculating a phase difference rainfall intensity that is a rainfall intensity estimation value based on a distance change rate of the phase difference;
A reflection factor rainfall intensity calculating unit for calculating a reflection factor rainfall intensity that is an estimated rainfall intensity value based on the reflected wave intensity;
When the phase difference rainfall intensity and the reflection factor rainfall intensity satisfy a predetermined condition, the phase difference rainfall intensity is selected, and when the predetermined condition is not satisfied, the reflection factor rainfall intensity is selected. A synthesis unit that outputs the estimated rainfall intensity;
A radar signal processing apparatus comprising: The phase difference rainfall intensity calculating unit calculates the phase difference rainfall intensity for each segment of the observation area distance,
The reflection factor rainfall intensity calculating unit calculates the reflection factor rainfall intensity for each of the segments of the distance of the observation area,
The combining unit includes an absolute value of a difference between the phase difference rainfall intensity and the reflection factor rainfall intensity in the section immediately after the one section, and the position in the section immediately before the one section. When the difference between the absolute value of the difference between the phase difference rainfall intensity and the reflection factor rainfall intensity is equal to or greater than a predetermined value, the reflection factor rainfall intensity of the one category is selected as the rainfall intensity estimate value of the category.
The radar signal processing apparatus according to claim 1.   3. The radar signal processing according to claim 1, wherein the combining unit selects the reflection factor rainfall intensity as the rainfall intensity estimated value when the phase difference rainfall intensity is equal to or larger than a constant multiple of the reflection factor rainfall intensity. apparatus. Two radio waves of horizontal polarization and vertical polarization are radiated into space, and radio waves reflected by objects existing in the space are received as horizontal polarization reception signals and vertical polarization reception signals with two polarizations, A radar signal processing method performed by a radar signal processing device that acquires a dual polarization measurement value by performing processing on a horizontal polarization reception signal and the vertical polarization reception signal,
A phase difference calculating step for calculating a phase difference between the polarizations of the horizontal polarization reception signal and the vertical polarization reception signal;
A reflected wave intensity calculating step for calculating a reflected wave intensity from at least one of the horizontal polarization reception signal and the vertical polarization reception signal;
A phase difference rainfall intensity calculating step for calculating a phase difference rainfall intensity which is a rainfall intensity estimated value based on a distance change rate of the phase difference;
A reflection factor rainfall intensity calculating step for calculating a reflection factor rainfall intensity which is a rainfall intensity estimated value based on the reflected wave intensity;
When the phase difference rainfall intensity and the reflection factor rainfall intensity satisfy a predetermined condition, the phase difference rainfall intensity is selected, and when the predetermined condition is not satisfied, the reflection factor rainfall intensity is selected. A synthesis step to output as a rainfall intensity estimate;
A radar signal processing method comprising: In the phase difference rainfall intensity calculating step, the phase difference rainfall intensity is calculated for each segment of the observation area distance,
In the reflection factor rainfall intensity calculating step, the reflection factor rainfall intensity for each of the sections of the distance of the observation area is calculated,
In the synthesis step, an absolute value of a difference between the phase difference rainfall intensity and the reflection factor rainfall intensity in the section immediately after the one section, and the position in the section immediately before the one section. When the difference between the absolute value of the difference between the phase difference rainfall intensity and the reflection factor rainfall intensity is equal to or greater than a predetermined value, the reflection factor rainfall intensity of the one category is selected as the rainfall intensity estimate value of the category.
The radar signal processing method according to claim 4.   The radar signal processing according to claim 4 or 5, wherein, in the synthesis step, the reflection factor rainfall intensity is selected as the rainfall intensity estimation value when the phase difference rainfall intensity is equal to or larger than a constant multiple of the reflection factor rainfall intensity. Method.

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