CN107422308B

CN107422308B - Frequency domain ground object suppression method for weather radar

Info

Publication number: CN107422308B
Application number: CN201710478968.9A
Authority: CN
Inventors: 金哲媛; 崔扬; 杨琳
Original assignee: Anhui Sun Create Electronic Co Ltd
Current assignee: Anhui Sun Create Electronic Co Ltd
Priority date: 2017-06-22
Filing date: 2017-06-22
Publication date: 2020-02-18
Anticipated expiration: 2037-06-22
Also published as: CN107422308A

Abstract

The invention belongs to the field of signal processing of weather radars, and particularly relates to a frequency domain ground object suppression method of a weather radar. The invention calculates the CSR value through the clutter power and the signal power, selects the added window type through calculating the CSR value, and suppresses the frequency spectrum leakage of the ground clutter by adopting a high and low threshold judgment mode for selecting the window type. The invention can greatly reduce the situation that two adjacent banks select completely different window types at two sides of the threshold because a single threshold is over sensitive at the threshold. The invention can effectively control the frequency spectrum leakage, can better inhibit the frequency spectrum leakage of ground clutter, and effectively filter the ground residue, thereby improving the data quality of the radar.

Description

Frequency domain ground object suppression method for weather radar

Technical Field

The invention belongs to the field of signal processing of weather radars, and particularly relates to a frequency domain ground object suppression method of a weather radar.

Background

The weather radar can effectively monitor the occurrence and the change of a weather system, and is one of powerful methods for forecasting the disastrous weather. The ground clutter may contaminate the echo data of the meteorological target and even mask the detected weather signal information of the radar, which is the echo generated by the ground or buildings, etc. surrounding the radar station.

The current mainstream ground feature filter comprises an adaptive spectrum filter and an elliptic filter, which are calculated based on data in a radar coherent accumulation period, but the signal processing theory can know that the leakage of frequency spectrum can be caused by the limited sampling point number, the frequency spectrum leakage can pollute the data of other frequency points, and even when the energy of a main lobe is very strong, the pollution can spread into the whole frequency spectrum. However, at present, there is no method for effectively controlling the spectrum leakage, so that even the data subjected to the ground object filtering still has strong clutter signal residue.

Disclosure of Invention

The invention provides a frequency domain ground object suppression method of a weather radar, aiming at overcoming the defects of the prior art, and the method can effectively control frequency spectrum leakage, thereby suppressing the frequency spectrum leakage of ground object clutter and effectively filtering ground object residue.

In order to achieve the purpose, the invention adopts the following technical measures:

a frequency domain ground object suppression method of a weather radar comprises the following steps:

s1, calculating a power spectrum of a certain distance library in a coherent accumulation repetition period through FFT (fast Fourier transform), respectively searching spectral lines of which the power values start to rise towards the two sides, namely positive and negative channels, of the power spectrum by taking a zero-frequency component of the power spectrum as a start, taking the spectral lines of which the found power values start to rise as boundaries, taking the spectral lines of which the boundaries do not include the boundaries as clutter intervals, adding and summing the power values of the spectral lines in the clutter intervals, and averaging the sum of the power values of the spectral lines to obtain clutter power C;

s2, removing spectral lines in clutter intervals of the power spectrum, linearly interpolating the clutter intervals to obtain a new power spectrum, and obtaining a new power spectrum according to a formula

Wherein N represents the number of points collected in the phase-coherent accumulation repetition period, P_N(k) Representing the power spectrum result of the N points, wherein the value range of k is 0,1,2.. N-1, and calculating the power value of the new power spectrum to obtain signal power S;

s3, judging whether the current distance library finishes the selection of the window type, if so, finishing the data processing of the current distance library; otherwise, according to the formula of the miscellaneous signal ratio

Obtaining a CSR value, wherein C represents clutter power, S represents signal power, and the window type selection module adaptively selects a window type corresponding to the CSR value according to the CSR value;

and S4, after the window type is selected, windowing is carried out on the time domain data in the coherent accumulation repetition period, and the operation of the steps S1-S3 is repeated.

Preferably, the specific operation step of the window type selection module adaptively selecting the window type corresponding to the CSR value according to the CSR value includes:

s31, judging whether the current distance library is the first distance library, if so, turning to the operation of S36, and if not, turning to the operation of S32;

s32, judging whether the window type added to the previous distance library of the current distance library is a rectangular window, if so, judging whether the CSR value is less than or equal to 5dB, if not, selecting the added rectangular window to the current distance library, and finishing the selection of the window type of the distance library; if the value is greater than 5dB, the operation is shifted to step S36; if not, the operation proceeds to step S33;

s33, judging whether the window type added by the previous distance library is a rounding window, if so, judging whether the CSR value is larger than-30 dB and smaller than or equal to 15dB, if so, selecting the rounding window by the current distance library, and finishing the window type selection of the distance library; if the value is less than or equal to-30 dB or more than 15dB, the operation is switched to the step S36; if not, the operation is shifted to step S34;

s34, judging whether the window type added by the previous distance library is a blackman window, if so, judging whether the CSR value is more than 5dB and less than or equal to 30dB, if so, selecting the blackman window added by the current distance library, and finishing the selection of the window type of the distance library; if the value is less than or equal to 5dB or greater than 30dB, the operation is shifted to step S36; if not, the operation proceeds to step S35;

s35, deducing that the window type added by the previous distance library is a nuttally window, judging whether the CSR value is more than or equal to 15dB, if so, selecting the nuttally window added by the current distance library, and finishing the selection of the window type of the distance library; if the value is less than 15dB, the operation is shifted to step S36;

s36, judging whether the CSR value is larger than-27 dB and less than or equal to 10dB, if so, selecting a enhancing window from the current distance library, and finishing the window type selection of the distance library; if the value is less than or equal to-27 dB or more than 10dB, the operation is switched to the step S37;

s37, judging whether the CSR value is more than 10dB and less than or equal to 24dB, if so, selecting a blackman window in the current distance library, and finishing the window type selection of the distance library; if the value is less than or equal to 10dB or greater than 24dB, the operation is shifted to step S38;

s38, judging whether the CSR value is larger than 24dB, if so, selecting a nuttall window in the current distance library, and finishing the window type selection of the distance library; if the value is less than or equal to 24dB, the operation is shifted to step S39;

and S39, selecting a rectangular window from the current distance library, and finishing the selection of the window type of the distance library.

The invention has the beneficial effects that: the invention selects the added window type by calculating the CSR value, and the window type selection adopts a high and low threshold judgment mode to inhibit the frequency spectrum leakage of the ground clutter. The method can greatly reduce the condition that the single threshold is too sensitive at the critical position, so that two adjacent libraries select completely different window types at two sides of the threshold critical position, thereby effectively controlling the frequency spectrum leakage, better inhibiting the frequency spectrum leakage of ground clutter, effectively filtering the ground residue and improving the data quality of the radar.

Drawings

FIG. 1 is a work flow diagram of one embodiment of the present invention;

FIG. 2 is a power spectrum of a library according to an embodiment of the present invention;

FIG. 3 is a graph of a power spectrum of a library after linear interpolation near zero frequency according to an embodiment of the present invention;

FIG. 4 is a flow diagram of the operation of the window type selection module of one embodiment of the present invention;

FIG. 5 is a high and low threshold illustration of one embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, S1, calculating a power spectrum psd (f) of a kth distance bin in the coherent accumulation repetition period CPI by FFT, starting from a zero frequency component of the power spectrum psd (f), searching spectral lines on two sides of the power spectrum psd (f), i.e. positive and negative channels, respectively for which the power value starts to rise, and dividing the spectral lines on which the power value starts to rise, the spectral lines in the division and the spectral lines not including the division are used as boundariesIs clutter interval A ═ (psd (f)₁)，psd(f₂) Solving the sum of the power values of the spectral lines in the clutter interval A, and averaging the sum of the power values of the spectral lines to obtain clutter power C;

fig. 2 is a power spectrogram of a certain library, and frequency points with rising spectral lines are searched from zero frequency to two sides, as shown in fig. 2, S1> S2 on the left side of zero frequency, and S3< S4 on the right side of zero frequency, so that a clutter interval is a spectral line from S2 to S3, but S2 and S3 are not included, and clutter power C is obtained by averaging the sum of power values of the spectral lines.

S2, removing spectral lines in clutter intervals of the power spectrum, linearly interpolating the clutter intervals A to obtain new power spectrums psd '(f), and obtaining the new power spectrums psd' (f) according to a formula

as shown in fig. 3, the spectral lines from S2 to S3 are linearly interpolated to obtain a new power spectrum, and the power value of the new power spectrum is calculated to obtain the signal power S.

S3, judging whether the current distance library finishes the selection of the window type, if so, finishing the data processing of the current distance library; otherwise, according to the formula of the miscellaneous signal ratioObtaining a CSR value, wherein C represents clutter power, S represents signal power, and the window type selection module adaptively selects a window type corresponding to the CSR value according to the CSR value;

Windowing is a means to effectively suppress spectral leakage, especially when the main lobe strength is strong. If only the spectral lines near the zero frequency are processed at this time, the influence of the power leakage of the ground objects on the signals cannot be suppressed, at this time, a window with strong suppression degree is needed to control the leakage of the frequency spectrum, but if the strength of the ground objects is weak and the leakage of the frequency spectrum is not serious, the window with strong suppression degree is added, the loss of the signals is caused, and meanwhile, the signal spectral width is increased. Therefore, it is necessary to balance the choice of the added window type by determining the magnitude of the CSR value.

And windowing the time domain data in the coherent accumulation repetition period CPI, and selecting a corresponding window by judging the CSR value by adopting a window type selection module.

On the basis of the window type selection module, high and low threshold value comparison is added, the mode can greatly reduce the situation that two adjacent libraries select completely different window types because a single threshold value is too sensitive at a critical position and two adjacent libraries are on two sides of the threshold value, and the situation can cause that the two adjacent libraries have similar signal intensity values, but different suppression degrees and very large intensity difference are obtained through calculation because the windowing types are different. Table 1 shows the suppression effect of various windows. FIG. 4 is a flow diagram of the operation of the window type selection module according to one embodiment of the present invention, the window type selection module comprising:

Table 1 shows the suppression effect of rectangular windows, hanning windows, blackman windows, nuttall windows.

Table 1:

window function	Side lobe peak amplitude (dB)	Side lobe reduction rate (dB/octave)
			Rectangular window	-13	-6
hang ning window	-31	-18
			Blackman window	-57	-18
nut window	-98	-18

On the basis of the window type selection module, the benefits of high and low threshold comparison are added, for example, as follows:

if the CSR values of two neighboring range bins with similar intensity values are 9.98dB and 10.25dB, respectively, the CSR value of the previous range bin is 9.98dB, and the CSR value of the next range bin is 10.25dB, if only a single threshold is used for the window type selection, i.e. only the operations of steps S36 to S39 are performed, the previous range bin selects the added window as a rounding window, and the added window of the next range bin is a blackman window, which results in a large intensity difference between the intensity values of the two neighboring range bins after windowing. In fact, we have implemented a single threshold approach, which is quite obvious on the noise floor, making the variance of the noise floor much larger.

If the window type selection module in the invention is adopted, after the previous distance library is judged and selected, the operation of step S33 is executed, and the condition that the CSR value is more than-30 dB and less than or equal to 15dB is satisfied, so the hanning window is still selected, thus the problem that the intensity difference is large after the intensity values of two adjacent libraries are windowed is avoided.

Fig. 5 illustrates the high and low threshold determinations using a rectangular window selection as an example, if the previous distance bin is a rectangular window, the CSR value exceeds 5dB to select other window types, and the window type applied by the previous distance bin is other window types than the non-rectangular window (except for the hanning window), the CSR value is less than-27 dB (the hanning window is less than-30 dB) to select the rectangular window.

In summary, the invention selects the added window type by calculating the CSR value to suppress the frequency spectrum leakage of the clutter of the ground objects, thereby achieving a better suppression degree and effectively filtering the residual of the ground objects.

In addition, the window type selection adopts a high threshold value and low threshold value judgment mode, so that the condition that two adjacent libraries select completely different window types because the single threshold value is too sensitive at the critical position is greatly reduced.

Claims

1. A frequency domain ground object suppression method of a weather radar is characterized by comprising the following steps:

s4, after selecting the window type, windowing the time domain data in the coherent accumulation repetition period, and repeating the operation of the steps S1-S3;

the specific operation steps of the window type selection module for adaptively selecting the window type corresponding to the CSR value according to the CSR value comprise: