CN104133198A - Ionized-layer interference suppression method used in high frequency ground wave radar - Google Patents

Abstract

The invention relates to the technical field of radar anti-jamming, in particular to a method for suppressing ionospheric interference in high-frequency ground wave radar. The invention adopts the time-frequency analysis method, utilizes the characteristics of the ionospheric interference in the space domain, time domain and Doppler domain, detects and eliminates the data segment (time and distance element) interfered by the ionosphere. First, the FFT transformation with large coherent accumulation time is used to detect the range element of interference, and then the time-frequency analysis of short-term accumulation is performed on the range element echo that may have interference, and the constant false alarm rate (CFAR) detection method is used to determine the ionospheric The distance element and time period of the interference, and zero-set suppression of the disturbed ocean echo data in the echo, redo the second FFT, and the range Doppler spectrum that suppresses the ionospheric interference can be obtained. The invention has good suppression effect, simple algorithm structure, good real-time performance and low false alarm rate, and is a robust algorithm that can be applied in real time.

Description

Ionospheric Interference Suppression Method in High Frequency Ground Wave Radar

technical field

The invention relates to the technical field of radar anti-jamming, in particular to a method for suppressing ionospheric interference in high-frequency ground wave radar.

Background technique

HF Ground Wave Radar (HF Ground Wave Radar) utilizes the characteristics of small attenuation of vertically polarized high-frequency electromagnetic waves on the conductive ocean surface and the first-order and second-order scattering mechanisms of the ocean surface for radio waves, which can detect wind fields beyond the horizon , wave field, current field and other ocean dynamic parameters and ships, aircraft and other maritime moving targets. The transmitted wave mainly propagates through the surface of the ocean. In actual work, due to reasons such as hardware and the site of the transmitting array, some electromagnetic waves will also propagate upwards and enter the receiver after being reflected by the ionosphere. The ionosphere generally refers to the atmosphere above 60km containing free electrons. The concentration of various charged particles in this layer varies with height. At the height of the E layer, there is an irregular Es layer, generally at 90 to 120km. Ionospheric interference mainly refers to the high-frequency radio waves that are reflected by ionized clouds in the Es layer and reach the radar receiving end. As long as the ionospheric Es layer exists, no matter what frequency the radar works in, ionospheric interference will generally occur.

Ground-wave radar ionospheric interference has the following main characteristics: (1) Ionospheric interference is mainly generated by the reflection and scattering of transmitted radio waves through the ionosphere, and its energy is much stronger than that of sea clutter and target echoes. (2) During the accumulation period, the incident direction of the ionospheric disturbance is stable, and it can be considered as stable in space; (3) Generally, the ionospheric disturbance stabilizes within 300- About 500ms, which is shorter than the pulse repetition period, so it fluctuates in time and space, and has certain random non-stationary characteristics.

At present, the existing high-frequency radar anti-jamming methods mainly include: airspace adaptive beamforming, polarization filtering method, characteristic subspace method for filtering in time domain and frequency domain, adaptive filtering cancellation method, and so on. Wherein the adaptive beam forming ionosphere suppression method needs to configure two-dimensional arrays on the horizontal plane (Gao Huotao, Qin Chenqing, Yang Zijie: Anti-jamming method for high-frequency ground wave radar based on antenna subarray, CN100380135C), and the polarization filtering method needs to set up an occupied area Larger horizontal antennas (H leong:'Adaptive nulling of skywaveinterference using horizontal dipole antennas in a coastal surface HF waveradar system', Radar 97, 14-16 October 1997, Publication No.49:26-30), the two methods It is relatively complicated to implement, but the characteristic subspace method for filtering in the time domain and frequency domain or their joint domain (Xiong Xinnong, Wan Xianrong, Ke Hengyu, Xiao Huaiguo, Ionospheric clutter suppression for high frequency ground wave radar based on time-frequency analysis, System Engineering and Electronic Technology, No. 8, 2008) due to the need for orthogonal decomposition of the signal, there are clutter residues and certain signal loss. For the method of adaptive filtering cancellation of portable high-frequency ground wave radar (Zhou Hao, Wen Biyang, Wu Shicai, Shi Zhenhua, method for suppressing ionospheric clutter in portable high-frequency ground wave radar, CN101581782A) to realize ionospheric interference Inhibition, due to the existence of the signal receiving structure of its reference channel, increases the complexity of the system.

Contents of the invention

Aiming at the problems existing in the background technology, the present invention adopts the time-frequency analysis method, and utilizes the characteristics of the ionospheric interference in the space domain, the time domain and the Doppler domain to detect the data segment (on time and on the distance element) interfered by the ionosphere and eliminate.

The technical scheme provided by the invention is:

(1) The N receiving channels of the high-frequency ground wave radar are sampled to obtain the original sampling data, and the first FFT processing (FT1 transformation) is performed to realize distance separation, and the sampling data X _i (r, t) on each distance element is obtained t=1...L, r=1...R, L is the number of FT1 frames, R is the distance metadata; then perform a second FFT on each distance metadata of each channel (the coherence time is 10-20 minutes), and obtain The range Doppler spectrum of each channel S _i (r, f)i=1...N, r=1...R, N is the number of channels, R is the range element, f is the Doppler frequency, where N>4 ;

(2) Perform energy averaging on the range Doppler spectra of N channels: is the range Doppler spectrum after multi-channel energy averaging after long-time FFT;

(3) Using the characteristic that ionospheric interference only appears in a certain discrete distance unit, its energy is much stronger than that of sea clutter and target echo. Interference position detection, determine the echo distance element that may have ionospheric interference;

3.1) Determine the frequency interval Δf to be detected, based on the maximum Doppler frequency shift of the ocean current, take 0.3f _B , where f _B is the Bragg scattering frequency corresponding to the current radar operating frequency. Calculate the power sum of all distance elements in the frequency interval to be detected:

For the negative first-order current region: $J_{\mathrm{nf}}\left(r\right)=\underset{f_k}{\mathrm{\Σ}}{S}_0^2(r,f_k),f_k\∈\left[\begin{array}{cc}-f_B-\mathrm{\Δf}& {-f}_B+\mathrm{\Δf}\end{array}\right]$

For the positive first-order current region: $J_{\mathrm{pf}}\left(r\right)=\underset{f_k}{\mathrm{\Σ}}{S}_0^2(r,f_k),f_k\∈\left[\begin{array}{cc}{f}_B-\mathrm{\Δ\; f}& f_B+\mathrm{\Δ\; f}\end{array}\right]$

J _nf and J _pf represent the echo power at the negative and positive first-order bragg frequencies, respectively. Considering that the maximum detection range of high-frequency ground wave radar is about 200 km, and the ionospheric interference generally appears in local features beyond 50 km, it is only necessary to Detect the J _nf and J _pf data from 50km to 200km.

3.2) The maximum value detection method is used to detect the range element sequence R _e that may have interference. If the kth distance element satisfies:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; nf</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; nf</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; pf</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; pf</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; k</span>}$

Then it is considered that the echo on the distance element k is affected by ionospheric interference, and k'=k-1 represents the distance element adjacent to the radar at the detection position.

(4) Carry out time-frequency analysis on the FT1 data corresponding to the range element R'∈Re _e that may have ionospheric interference, specifically by using short-term coherent accumulation sliding window FFT processing to obtain low frequency resolution and high time resolution The time-frequency diagram of , that is, the time Doppler spectrum S _i (t _j ,f'), f' is the spectral frequency under short-time FFT, i=1...N, j=1...L, L is the sliding window snapshot That is time, _Re represents the range element position sequence that actually has ionospheric interference; ; FFT points are 32 or 64, and the step size is less than 16.

(5) Perform energy averaging of N channels to remove the influence of random noise on different channels:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Indicates the time Doppler spectrum under multi-channel energy averaging of a single range element echo after short-time FFT.

(6) Using the short-term broadband characteristics of the ionospheric echo, the interference time detection is performed on the snapshot data at the Bragg frequency in the first-order current Doppler frequency range.

For the negative first-order current region: $S_{R^{\&prime;}}^2(t,f_k),f_k\&Element;\left[\begin{array}{cc}-f_B-\mathrm{\&Delta;}{f}^{\&prime;}& -f_B+\mathrm{\&Delta;}{f}^{\&prime;}\end{array}\right]$

For the positive first-order current region: $S_{R^{\&prime;}}^2(t,f_k),f_k\&Element;\left[\begin{array}{cc}{f}_B-\mathrm{\&Delta;}{f}^{\&prime;}& f_B+\mathrm{\&Delta;}{f}^{\&prime;}\end{array}\right]$

In order to redo the time Doppler spectrum after the energy average of each channel after the second FFT, Δf′ is the frequency interval to be detected, which is taken as 0.3f _B ; the snapshot position t _e of the interference effect is obtained for different frequency points, where The detection adopts the constant false alarm rate (CFAR) detection method. In order to reduce the probability of false alarm, the threshold adopts E[] represents the statistical mean, σ _S is The standard deviation of , λ takes a value between 1 and 2. For the ocean echo, due to its obvious short-term stationary characteristics, it can be completely preserved under detection. However, for ionospheric disturbances with obvious fluctuations in time, effective detection can be achieved.

(7) Perform zero-setting processing on the detected disturbed distance element and the FT1 echo data on the frame number t, where the determination of the frame number is determined by the snapshot position t _e and the time-frequency analysis parameters. For the snapshot t _e ′, the corresponding FT1 frame is:

t _c =[1+(t _e ′-1)p 2+(t _e ′-1)p…s+(t _e ′-1)p]

Among them, s is the number of short-time Fourier transform points, and p is the sliding window interval; for two-dimensional data _Xi (r,t)t=1...L if r∈R _e and t∈t _c , then _Xi ( r,t)=0.

(8) Redo the second FFT, that is, perform a second FFT on each range metadata of each channel to obtain the range Doppler spectrum S _i (r,f)i=1...N of each channel, r=1...R, N is the number of channels, r is the distance element, f is the Doppler frequency, and the ionospheric interference has been suppressed at this time.

Compared with the prior art, the present invention has the following advantages and effects:

1. The algorithm of the present invention uses time-frequency analysis means with different time resolutions and frequency resolutions to detect interference distance elements and time at different scales. When determining the distance elements where the interference occurs, the FFT transformation with a large coherent accumulation time is adopted. When determining the period of ionospheric interference, the sliding window FFT time-frequency analysis method with short accumulation time and low step size is used to improve the time resolution of detection.

2. The present invention detects and processes based on the space and time characteristics of ionospheric interference. First, it uses the strong signal characteristics on the finite distance element within the range of 50-200km, and uses the maximum value detection method to determine the occurrence of interference in the distance element dimension. distance element. Then, using its short-term large fluctuation characteristics in time and wide-band characteristics in frequency domain, the short-time time-frequency method with low frequency resolution and high time resolution is used to detect the period of interference occurrence, and the suppression effect is good.

3. The statistical characteristics of the ocean echo are stable under short-term time-frequency processing, which can be considered as a stable signal. When performing CFAR detection, the false alarm rate is low.

4. The present invention does not consider the influence of the incoming wave direction of the interference, and only suppresses it in the field of signal energy. Compared with other filtering methods, the algorithm has a simple structure and good real-time performance.

Description of drawings

Fig. 1 is the algorithm flowchart that the present invention proposes;

Fig. 2 is the FT1 data with ionospheric interference in actual reception;

Figure 3 is the Doppler spectrum before and after interference suppression.

Detailed ways

The high-frequency ground wave radar adopts the frequency-modulated interrupted continuous wave (FMICW) system. Under this waveform system, after the ocean echo enters the receiver, the distance element separation of the ocean echo data can be realized through intermediate frequency sampling, digital down-mixing and the first FFT transformation (FT1 transformation) to obtain the FT1 echo data X _i ( r, t) t=1...L, r=1...R, L is the number of FT1 transform frames, and R is the distance element. FT1 data is a two-dimensional matrix, each value of which represents the time-domain echo received at time t at distance element r. When ionospheric interference occurs, there will be high-intensity, wide-frequency domain, and short-duration interference in several distance elements in the actual received data. Figure 2 shows the situation of ionospheric interference in FT1 data. The ocean echo corresponding to the distance element and time period cannot be used for subsequent sea state parameter inversion due to the interference of the ionosphere. It is the main purpose of the present invention to detect it, determine the interference period and suppress it, as shown in Figure 1 As shown, the specific steps are as follows:

(1) Perform the first FFT processing (FT1 transformation) on the original echoes obtained by sampling the N receiving channels of the radar system to obtain the FT1 echo data X _i (r,t)t=1...L,r on each range element =1...R, L is the number of FT1 frames, R is the distance element, and then the second FFT is performed on the echoes of each channel to obtain the range Doppler spectrum S _i (r , f) i=1...N, r=1...R, N is the number of channels, R is the distance element, f is the Doppler frequency, where N>4;

(2) Perform energy averaging on the range Doppler spectra of N channels: is the range Doppler spectrum after multi-channel energy averaging after long-term FFT;

(3) Using the characteristic that ionospheric interference only appears in a certain discrete distance unit, its energy is much stronger than that of sea clutter and target echo. Interference distance element position detection, determine the echo distance element that may have ionospheric interference;

3.1) Determine the frequency interval Δf to be detected, based on the maximum Doppler frequency shift of the ocean current, take 0.3f _B , where f _B is the Bragg scattering frequency corresponding to the current radar operating frequency. Calculate the power sum of all distance elements in the frequency interval to be detected:

For the negative first-order current region: $J_{\mathrm{nf}}\left(r\right)=\underset{f_k}{\mathrm{\&Sigma;}}{S}_0^2(r,f_k),f_k\&Element;\left[\begin{array}{cc}-f_B-\mathrm{\&Delta;f}& {-f}_B+\mathrm{\&Delta;f}\end{array}\right]$

For the positive first-order current region: $J_{\mathrm{pf}}\left(r\right)=\underset{f_k}{\mathrm{\&Sigma;}}{S}_0^2(r,f_k),f_k\&Element;\left[\begin{array}{cc}{f}_B-\mathrm{\&Delta;f}& f_B+\mathrm{\&Delta;f}\end{array}\right]$

J _nf and J _pf represent the echo power at the negative and positive first-order bragg frequencies, respectively. Considering that the maximum detection range of high-frequency ground wave radar is about 200 km, and the ionospheric interference generally appears in local features beyond 50 km, it is only necessary to Detect the J _nf and J _pf interval data from 50km to 200km.

3.2) Since the echoes of each range element do not have uniform gain and statistical characteristics, but for the particularity that the echo energy of the range element where ionospheric interference occurs will be greater than the energy of sea clutter, the maximum value detection method is adopted. The detection output is the range element sequence R _e that may have interference. If the kth distance element satisfies:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; nf</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; nf</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\\ {\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; pf</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>{<span\; class="notranslate">\; ></span>\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; pf</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; )</span>\end{array}\right.<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; k</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; k</span>}$

Then it is considered that the echo on the distance element k is affected by ionospheric interference, and k'=k-1 represents the distance element adjacent to the radar at the detection position.

(4) Carry out time-frequency analysis on the FT1 data corresponding to the range element R'∈Re _e that may have ionospheric interference, specifically by using short-term coherent accumulation sliding window FFT processing to obtain low frequency resolution and high time resolution The time-frequency diagram of , that is, the time Doppler spectrum S _i (t _j , f'), the spectral frequency under the short-time FFT of f', i=1...N, j=1...L, L is the sliding window snapshot, namely Time, _Re represents the range element position sequence where ionospheric interference actually exists.

(5) Perform energy averaging of N channels to remove the influence of random noise on different channels:

${\mathrm{<span\; class="notranslate">\; S</span>}}_{{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; |</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

Indicates the time Doppler spectrum under multi-channel energy averaging of a single range element echo after short-time FFT.

(6) Using the short-term broadband characteristics of the ionospheric echo, the interference time detection is performed on the snapshot data at the relevant Bragg frequency in the first-order current Doppler frequency interval.

For the negative first-order current region: $S_{R^{\&prime;}}^2(t,f_k),f_k\&Element;\left[\begin{array}{cc}-f_B-\mathrm{\&Delta;}{f}^{\&prime;}& -f_B+\mathrm{\&Delta;}{f}^{\&prime;}\end{array}\right]$

For the positive first-order current region: $S_{R^{\&prime;}}^2(t,f_k),f_k\&Element;\left[\begin{array}{cc}{f}_B-\mathrm{\&Delta;}{f}^{\&prime;}& f_B+\mathrm{\&Delta;}{f}^{\&prime;}\end{array}\right]$

In order to redo the time Doppler spectrum after the energy average of each channel after the second FFT, Δf′ is the frequency interval to be detected, generally 0.3f _B ; for different frequency points to obtain the snapshot position t _e affected by the interference, here The CFAR detection method was used for detection. In order to reduce the probability of false alarm, the threshold adopts λ takes a value between 1 and 2, and σ _S is standard deviation of . For the ocean echo, due to its obvious short-term stationary characteristics, it can be completely preserved under detection. However, for ionospheric disturbances with obvious fluctuations in time, effective detection can be achieved.

(7) Perform zero-setting processing on the detected disturbed distance element and the FT1 echo data on the frame number t, where the determination of the frame number is determined by the snapshot position t _e and the time-frequency analysis parameters. For the snapshot t _e ′, the corresponding FT1 frame is:

t _c =[1+(t _e ′-1)p 2+(t _e ′-1)p…s+(t _e ′-1)p]

Among them, s is the number of short-time Fourier transform points, and p is the sliding window interval.

(8) Redo the second FFT, that is, perform a second FFT on each range metadata of each channel to obtain the range Doppler spectrum S _i (r, f)i=1...N of each channel, r=1...R, N is the number of channels, r is the distance element, f is the Doppler frequency, and the ionospheric interference has been suppressed at this time.

Figure 2 is the measured range Doppler spectrum. It can be seen from the figure that there is obvious ionospheric interference at 100-130 km, and the ionospheric interference suppression is performed on the data with the algorithm of the present invention, and the suppression effect at 120 km is shown in Fig. 3 . It can be seen from Fig. 3 that after the Doppler spectrum at 120 km is suppressed by ionospheric interference, its positive first-order Bragg peak is obviously prominent, indicating that the algorithm of the present invention can greatly suppress ionospheric interference.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or supplements to the described specific embodiments or adopt similar methods to replace them, but they will not deviate from the spirit of the present invention or go beyond the definition of the appended claims range.

Claims (3)

1. ionospheric interference inhibition method in a high-frequency ground wave radar, is characterized in that: comprises the following steps,

N receiving cable of step (1), high-frequency ground wave radar obtains original sampling data through sampling, carries out FFT processing-FT1 conversion for the first time, realizes distance separated, obtains the sampled data X in each distance element _i(r, t) t=1 ... L, r=1 ... R, L is FT1 frame number, R is distance element number; Again each distance element data of each passage are carried out to FFT for the second time, obtain the range Doppler spectrum S of each passage _i(r, f) i=1 ... N, r=1 ... R, N is port number, and R is distance element number, and f is Doppler frequency, wherein, N>4;

Step (2), that the range Doppler spectrum of N passage is carried out to energy is average: during for length, after FFT, the range Doppler after hyperchannel energy is average is composed;

Step (3), in range Doppler spectrum, in surrounding's frequency band of First-order sea clutter, carry out ionospheric interference position probing, determine the echo distance element that may have ionospheric interference;

Step (4), to there is echo distance element R ' the ∈ R of ionospheric interference _ecorresponding FT1 data are carried out time frequency analysis, are specially and adopt the sliding window FFT of coherent accumulation in short-term to process, and obtain low frequency resolution, the time-frequency figure under high time resolution, i.e. time doppler spectral S _i(t _j, f'), the spectral frequency under f' short time FFT, i=1 ... N, j=1 ... L, L is the time for sliding window snap, R _ethe distance element position sequence that represents physical presence ionospheric interference;

Step (5), to carry out N channel energy average, removes the random noise impact occurring on different passages:

$S_{R^{\&prime;}}^2(t,f)=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{\left|\right|S_i(t,f)\left|\right|}^2$

represent that single distance element echo is after short time FFT, the time doppler spectral of hyperchannel energy under on average;

Step (6), utilize the feature of broadband in short-term of Ionospheric Echo, on single order ocean current Doppler frequency interval, the fast beat of data under Bragg frequency is carried out to detection interference time;

Step (7), the FT1 echo data being disturbed on distance element and frame number t detecting is carried out to zero setting processing, wherein frame number determines by snap position t _edetermine with time frequency analysis parameter; Be there is to the snap t disturbing in each _e', its corresponding FT1 frame is:

t _c＝［1＋(t _e′－1)p?2+(t _e′-1)p…s+(t _e′-1)p]

Wherein, what s was Short Time Fourier Transform counts, and p is sliding window interval;

Step (8), the FFT that reforms the 2nd time, carry out FFT for the second time to each distance element data of each passage again again, obtains the range Doppler spectrum S of each passage _i(r, f) i=1 ... N, r=1 ... R, N is port number, and r is distance element, and f is Doppler frequency, and now ionospheric interference is suppressed.

2. ionospheric interference inhibition method in a kind of high-frequency ground wave radar according to claim 1, is characterized in that: described step (3) detects and may exist the echo distance element of ionospheric interference to adopt with the following method to realize:

Step 3.1), determine frequency separation Δ f to be detected, with ocean current maximum doppler frequency, be as the criterion, get 0.3f _b, calculate all distance elements at the power of frequency separation to be detected and:

For negative single order ocean current, district has: $J_{\mathrm{nf}}\left(r\right)=\underset{f_k}{\mathrm{\&Sigma;}}{S}_0^2(r,f_k),f_k\&Element;\left[\begin{array}{cc}-f_B-\mathrm{\&Delta;f}& {-f}_B+\mathrm{\&Delta;f}\end{array}\right]$

For positive single order ocean current, district has: $J_{\mathrm{pf}}\left(r\right)=\underset{f_k}{\mathrm{\&Sigma;}}{S}_0^2(r,f_k),f_k\&Element;\left[\begin{array}{cc}{f}_B-\mathrm{\&Delta;f}& f_B+\mathrm{\&Delta;f}\end{array}\right]$

To J _nfand J _pfdata detect, J _nfand J _pfbe illustrated respectively in the echo power in negative, positive single order bragg frequency, f _bfor Prague bragg scattering frequency corresponding to current radar frequency of operation;

Step 3.2) adopting maximum value detection method, may there is the distance element sequence R of interference in detection _e; If k distance element meets:

$\left\{\begin{array}{c}{J}_{\mathrm{nf}}\left(k\right)>J_{\mathrm{nf}}\left(k^{\&prime;}\right)\\ J_{\mathrm{pf}}\left(k\right){>J}_{\mathrm{pf}}\left(k^{\&prime;}\right)\end{array}\right.,k^{\&prime;}<k$

Think that the echo on this distance element k exists ionospheric interference impact, k'=k-1 is illustrated in the distance element of the contiguous radar in detection position.

3. ionospheric interference inhibition method in a kind of high-frequency ground wave radar according to claim 1 and 2, is characterized in that: described step (6) comprises following content,

For negative single order ocean current, district has: $S_{R^{\&prime;}}^2(t,f_k),f_k\&Element;\left[\begin{array}{cc}-f_B-\mathrm{\&Delta;}{f}^{\&prime;}& -f_B+\mathrm{\&Delta;}{f}^{\&prime;}\end{array}\right]$

For positive single order ocean current, district has: $S_{R^{\&prime;}}^2(t,f_k),f_k\&Element;\left[\begin{array}{cc}{f}_B-\mathrm{\&Delta;}{f}^{\&prime;}& f_B+\mathrm{\&Delta;}{f}^{\&prime;}\end{array}\right]$

Different frequent points is obtained respectively to the snap position t of disturbing effect _e, for reforming after secondary FFT, the time doppler spectral after each channel energy is average, Δ f ' is frequency separation to be detected, gets 0.3f _b; Detect and adopt conventional CFAR detection method herein, Threshold is e ［ ］ represents average statistical, σ _sfor standard deviation, λ is value between 1 to 2.