JP2008014837A - Radar system and its signal processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the performance of topographic echo cancellation processing, and compute a Doppler speed with high precision. <P>SOLUTION: After A/D conversion of a received signal received by an antenna is performed, its quadrature detection is performed. A signal processing part finds speed spectra at each predetermined time duration by converting the quadraturely detected I/Q signals in a time region into a frequency region, by applying FFT processing to them. From the individual speed spectra found at each predetermined time duration, components appearing near zero speed are removed respectively as topographic echoes. The speed spectra from which the topographic echoes have been removed are integrated, and based on the integrated speed spectra the Doppler speed is computed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radar apparatus used in a Doppler radar such as a wind profiler for observing wind direction and wind speed in the sky, and a signal processing method therefor.

  A radar apparatus (such as a wind profiler) that observes clear-sky turbulent echoes has a weak SN ratio (signal-to-noise ratio) because it targets weak reflected waves scattered by atmospheric turbulence and the like. . In order to cope with this, for example, coherent integration is performed on the received signal in the time domain, or incoherent integration (spectrum integration) is performed in which a plurality of velocity spectra are added in the frequency domain. After these signal-to-noise ratio improvement processes, a terrain echo removal process is performed. The terrain echo is an echo returned from an object (such as a mountain or a building) on the ground, and its Doppler velocity becomes zero, so that it can be distinguished from a desired atmospheric echo and removed (for example, see Patent Document 1). .)

However, when the wind speed on the ground is high, the shape of the terrain echo fluctuates and changes in each spectrum due to the influence of the fluctuation of leaves. For this reason, when the terrain echo removal process is performed after spectrum integration, the width of the terrain echo is widened, and the weather echo is partially removed together with the terrain echo.
Japanese Patent No. 3702347

  As described above, in the terrain echo removal process in the conventional radar signal processing method, the shape of the terrain echo in each spectrum differs due to wind fluctuations, etc., so that the terrain echo can be accurately removed after spectrum integration. Can not.

  The present invention has been made paying attention to the above circumstances, and an object thereof is to provide a radar apparatus capable of improving the performance of terrain echo removal processing and accurately calculating the Doppler velocity, and a signal processing method thereof. There is to do.

  In order to achieve the above object, a radar apparatus according to the present invention includes a transmission / reception unit that repeatedly transmits a radar pulse and receives a radar echo, and converts the received signal of the radar echo into a frequency domain to obtain a velocity spectrum at a constant time interval. Conversion means for obtaining the above, a removing means for removing a component appearing in the vicinity of zero speed from each of the velocity spectra for each fixed time as a terrain echo, and an integrating means for integrating the velocity spectrum for each fixed time from which the terrain echo is removed, And calculating means for calculating the Doppler velocity of the target based on the accumulated velocity spectrum.

  The signal processing method according to the present invention is a signal processing method used in a radar apparatus that repeatedly transmits radar pulses and receives radar echoes, and converts the received signals of the radar echoes into a frequency domain at regular intervals. The velocity spectrum of the constant time is obtained, components appearing near the velocity zero are removed as terrain echoes from each of the velocity spectra for each fixed time, the velocity spectrum for each fixed time from which the terrain echo is removed is integrated, and the integrated velocity The Doppler velocity of the target is calculated based on the spectrum.

  In the radar apparatus and the signal processing method thereof having the above-described configuration, the terrain echo removal process is performed before spectrum integration for each velocity spectrum obtained at regular time intervals. As a result, even when the shape of the terrain echo in each spectrum differs due to wind fluctuation or the like, the terrain echo can be accurately removed, and a highly reliable Doppler velocity can be calculated.

  Therefore, according to the present invention, it is possible to provide a radar apparatus capable of improving the performance of the terrain echo removal process and calculating the Doppler speed with high accuracy and a signal processing method thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a functional block diagram showing an embodiment of a radar apparatus according to the present invention.
The modulation unit 12 generates a digital value of an intermediate frequency signal of a designated modulation system under the control given from the signal processing unit 11 via the interface (I / F). This digital value is converted into an analog value by the D / A converter 13 to generate a transmission intermediate frequency signal (fi). The generated transmission intermediate frequency signal is up-converted to the transmission frequency of the radar pulse in the transmission / reception unit 14, and after power amplification, is transmitted from the antenna 15 to the space.

  The radar pulse with the frequency f0 transmitted from the antenna 15 is reflected by a target such as raindrops, and the radar echo returns. This radar echo is accompanied by a Doppler frequency (fd) reflecting the moving speed of the target, and the reception frequency is represented as (f0 + fd). The radar echo arrives at the transmitting / receiving unit 14 via the antenna 15 and is amplified and then down-converted to generate a reception intermediate frequency signal of (fi + fd). The received intermediate frequency signal is converted into a digital value by the A / D converter 16 and then quadrature detected by the demodulator 17.

  Further, the quadrature-detected signal is demodulated by the demodulation unit 17 by a plurality of modulation methods. The received data of the I component (in-phase component) and Q component (quadrature phase component) obtained in this way is given to the signal processing unit 11 via the interface (I / F). The signal processing unit 11 calculates observation data such as echo reflection intensity, target velocity and velocity width from the received data. In particular, the target Doppler velocity can be calculated from the velocity spectrum obtained by performing the FFT process on the received data.

  FIG. 2 is a flowchart showing a processing procedure of the radar apparatus of FIG. The received signal is A / D converted and then subjected to quadrature detection, and I component (in-phase component) and Q component (quadrature phase component) signals are output. Further, the signal processing unit 11 performs FFT processing on the output I / Q signal. In this FFT processing, a velocity spectrum is obtained by converting a time domain I / Q signal into a frequency domain.

Here, the terrain echo removal process for the velocity spectrum obtained at regular intervals by the FFT process will be described with reference to FIG.
The terrain echo observed by the radar device has a velocity component in the vicinity of the Doppler velocity of zero due to the influence of the leaves of the tree fluctuating with the wind. As shown in FIG. 3, if the terrain echo removal process is performed after spectrum integration, this fluctuation component is included, so that the terrain echo component has a large width centering on a Doppler velocity of zero. For this reason, if the terrain echo is to be removed from the integrated spectrum, the desired weather echo may be partially removed together with the terrain echo.

  Therefore, in the present invention, terrain echo removal processing is performed on each velocity spectrum obtained at regular intervals before spectrum integration. Before integration, since it is easy to detect the fluctuation component of the terrain echo in each spectrum, only the terrain echo can be accurately removed. After performing the topographic echo removal processing for each spectrum, the spectrum is accumulated and the Doppler velocity of the target is calculated based on the accumulated spectrum.

  As described above, in the above embodiment, the received signal received by the antenna is A / D converted and then subjected to quadrature detection. The signal processing unit obtains a velocity spectrum by converting the time-domain I / Q signal subjected to quadrature detection into the frequency domain by FFT processing. A terrain echo removal process is performed on each of the obtained velocity spectra. Then, the velocity spectra from which the topographic echoes are removed are integrated, and the Doppler velocity is calculated based on the integrated velocity spectrum.

  In this way, by performing terrain echo removal processing on each spectrum before integrating the velocity spectrum, even if the shape of the terrain echo in each spectrum differs due to wind fluctuations, etc., the terrain echo can be accurately removed. It is possible to calculate the Doppler speed with high reliability.

  The present invention is not limited to the above embodiment. For example, in FIG. 1, the functions of the D / A conversion unit 13 and the A / D conversion unit 16 can be combined with other functional blocks. The present invention is not limited to a weather radar but can be applied to other Doppler radars.

  In short, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

The functional block diagram which shows one Embodiment of the radar apparatus concerning this invention. The flowchart which shows the process sequence of the radar apparatus of FIG. The figure which shows the topographic echo removal process with respect to a velocity spectrum.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Signal processing part, 12 ... Modulation part, 13 ... D / A conversion part, 14 ... Transmission / reception part, 15 ... Antenna apparatus, 16 ... A / D conversion part, 17 ... Demodulation part

Claims (2)

A transmission / reception unit that repeatedly transmits radar pulses and receives radar echoes;
Conversion means for converting the received signal of the radar echo into a frequency domain to obtain a velocity spectrum at a constant time;
Removing means for removing a component appearing near velocity zero from each velocity spectrum for each predetermined time as a terrain echo;
An accumulating means for accumulating a velocity spectrum every fixed time from which the terrain echo is removed;
A radar apparatus comprising: a calculation unit that calculates a Doppler velocity of a target based on the accumulated velocity spectrum. A signal processing method used in a radar device that repeatedly transmits radar pulses and receives radar echoes,
Convert the received signal of the radar echo into the frequency domain to obtain a velocity spectrum for every fixed time,
Removing the component appearing near the velocity zero from each velocity spectrum for each predetermined time as a terrain echo,
Accumulate the velocity spectrum every fixed time from which the terrain echo is removed,
A signal processing method characterized in that a Doppler velocity of a target is calculated based on the accumulated velocity spectrum.

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