An Adaptive STC Control Method Based on Accurate Estimation of Unit Clutter Spectrum

Abstract

The present invention discloses an adaptive STC control method based on accurate estimation of unit clutter spectrum, belonging to the field of radar technology, which includes the following steps: First, estimate the clutter power of each range unit in the current scan cycle of the radar; Second, correlate the clutter power of each range unit in the current scan cycle with the clutter map of the previous scan cycle to construct the clutter map of the current scan cycle; Then, on the basis of constructing the clutter map, estimate the clutter attenuation distance and attenuation depth; Finally, fit the time sensitivity control curves under four clutter environments, and select the time sensitivity control curve for the next scan cycle of the radar by using the minimum variance method.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar. Background Art

[0002] The targets detected by radar are usually moving objects (such as airplanes, ships, etc.), but there are often various stationary or slow-moving backgrounds around the targets, such as ground objects, sea surfaces, etc., and the echoes of these backgrounds constitute the clutter background of the targets. When the clutter and the targets are simultaneously displayed on the video, it will make the observation of the targets difficult. Especially in the near zone of the radar, the strong clutter power will also cause the automatic detection and data processing systems of the radar to be overloaded. Therefore, whether it is to prevent the radar from being overloaded or to improve the target detection performance of the radar, clutter suppression is required. This method starts from the original Sensitivity Time Control (STC) and studies the adaptive STC control method.

[0003] For clutter radar cross-sections subject to different distributions, the variation curve of STC with distance is different. For the sea clutter background at low grazing angles, the variation of the STC curve with distance is shown by the following formula:

[0004] stc_db(r) = -30log10(r) + 30log10(R g ) (1)

[0005] In the formula, R g is the maximum distance at which STC starts to control. For sea clutter at low grazing angles, STC is inversely proportional to R 3 .

[0006] When the clutter is cloud and rain clutter, the variation curve of STC with distance is:

[0007] stc_db(r) = -20log10(r) + 20log10(R g ) (2)

[0008] For cloud and rain clutter, STC is inversely proportional to R 2 .

[0009] When the clutter is volume clutter such as insects and bird flocks, the curve of STC varying with distance is as follows:

[0010] stc_db(r) = -10log10(r) + 10log10(R g ) (3)

[0011] When the clutter is various volume clutter, STC is inversely proportional to R.

[0012] For the case where the clutter amplitude does not vary with distance, the STC has a fixed attenuation at this time, and the curve of STC varying with distance is as follows:

[0013] stc_db(r) = C (4)

[0014] In the formula, C is a constant. At this time, the STC does not vary with distance.

[0015] When the radar is working, since the clutter environment faced by the radar changes continuously with time, the traditional manual selection of the STC curve has many limitations. It not only wastes human resources but also is difficult to select a suitable STC curve. Summary of the Invention

[0016] To solve the current STC control problem of radar receivers, the present invention proposes an adaptive STC control method based on accurate estimation of the clutter spectrum of cells. By constructing the clutter amplitude spectrum in the current background environment of the radar, the STC curves in different azimuths of the radar are adaptively selected through the clutter spectrum information.

[0017] To achieve the above technical objectives, the adaptive STC control method based on accurate estimation of the clutter spectrum of cells proposed by the present invention includes the following steps:

[0018] Step 1: Clutter environment perception, perceiving the strength of the clutter background faced by the current radar and accurately estimating the clutter power C of each range cell in the current scan period l , and constructing the clutter map C of the current scan period i ;

[0019] Step 2: Based on the clutter amplitude estimation, estimate the attenuation distance R required for fitting the STC curve in each azimuth max and the attenuation depth C max ;

[0020] Step 3: Based on the estimation of the attenuation distance and the attenuation depth, respectively generate:

[0021] The STC curve corresponding to the sea clutter background at low grazing angles: stc_db(r) = -30log10(r) + 30log10(R g );

[0022] The STC curve under the cloud and rain clutter background: stc_db(r) = -20log10(r) + 20log10(R g );

[0023] The STC curve under the volume clutter: stc_db(r) = -10log10(r) + 10log10(R g );

[0024] STC curve with fixed attenuation: stc_db(r) = C;

[0025] where R g is the maximum distance at which STC starts to act; The four fitted STC curves are respectively used as the sensitivity gain control curves of the radar receiver in the current azimuth to control the clutter attenuation of the radar echo z in . At this time, the output is:

[0026] z out (r) = 20log10(z in (r)) - stc_db(r)

[0027] Statistical variance is calculated for the output result, and the STC curve corresponding to the minimum variance is used as the sensitivity gain control curve of the radar receiver in the next scan cycle.

[0028] Furthermore, the clutter environment perception described in step 1 above includes adaptive threshold estimation, target echo filtering, and clutter map power calculation.

[0029] Adaptive threshold generation; For each range cell in a certain azimuth, the number of sliding window cells is set to m, and the number of guard cells is set to n. For the l-th range cell, the corresponding threshold estimate is:

[0030]

[0031] where z i is the amplitude corresponding to the i-th range cell;

[0032] Target echo filtering; Based on the threshold estimation, the clutter amplitude estimate of the l-th range cell is:

[0033]

[0034] Furthermore, clutter map power calculation: Assume that the amplitude of the i-th clutter cell in the clutter map estimated during the n-th scan of the radar is C k , and the clutter amplitude estimate of the i-th range cell during the (n + 1)-th scan of the radar is C l . Then the amplitude estimate of the i-th clutter cell in the clutter map during the (n + 1)-th scan of the radar is where α = C l / C k .

[0035] Even further, the attenuation distance R max and attenuation depth C max in fitting and estimation: Clutter attenuation distance R max Estimation: In order to estimate the clutter attenuation distance R max, it is necessary to estimate the background noise power of the radar first, and select the mean value of the n distance units at the tail of the clutter distribution curve in a certain direction as the estimate of the noise floor, recorded as N0; taking the clutter distribution curve in a certain direction as an example, the clutter-to-noise ratio in this direction can be recorded as C / N0, then the maximum clutter suppression distance of the radar is Clutter attenuation depth C max Estimation; Based on the estimation of the noise floor N0, the maximum clutter amplitude at a certain direction can be estimated by the average of n distance units after zero adjustment. At this time, the maximum clutter amplitude estimate is recorded as C0, and the attenuation depth C max =20log10(C0 / N0).

[0036] Compared with the existing methods, the present invention has the following advantages:

[0037] 1. In clutter power estimation, the target echo power is filtered out through adaptive thresholding, reducing the impact of the target echo power on clutter power estimation.

[0038] 2. In the construction of clutter map, the influence of outliers on the clutter map is reduced through clutter map association.

[0039] 3. The adaptive time sensitivity control method based on accurate estimation of unit clutter reduces the subjectivity and uncertainty of human selection factors and has stronger robustness and adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The specific implementation process of the adaptive STC control method of the present invention;

[0041] Figure 2 A radar echo of a certain direction of the present invention, and an adaptive threshold for suppressing target echo generated according to the radar echo;

[0042] Figure 3 The figure shows the comparison of radar echoes before and after clutter suppression according to the present invention. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further explained below in conjunction with the accompanying drawings and embodiments.

[0044] Taking a certain shore-based sea radar as an example, during the detection process, it will be affected by sea clutter, cloud and rain clutter, etc. The present invention is explained by taking the sea clutter echo of the radar under the third level sea condition as an example.

[0045] The first step is clutter environment perception. First, an adaptive threshold is generated based on the video echo obtained by the radar through matched filtering. The influence of the large target echo is filtered out based on the estimation. On this basis, the accurate range and azimuth unit clutter amplitude spectrum estimation is obtained through clutter map association and clutter map update.

[0046] In the second step, according to the accurate estimation result of the clutter amplitude spectrum obtained and the corresponding azimuth radar noise estimation result, estimate the clutter attenuation distance and attenuation depth;

[0047] In the third step, according to the estimated clutter attenuation distance and attenuation depth, use the four fitted STC curves as the radar receiver sensitivity gain control curves at the current azimuth respectively to control the clutter attenuation of the radar echo z in At this time, the output is:

[0048] z out (r) = 20log10(z in (r)) - stc_db(r);

[0049] Perform statistics on the output result to calculate the variance, and use the STC curve corresponding to the minimum variance as the sensitivity gain control curve of the radar receiver in the next scan cycle.

[0050] Figure 2 is the original radar video echo at a certain azimuth, and the power difference between the proximal clutter and the distant clutter in the original echo is about 70 dB, Figure 3 is the radar video echo after adaptive time sensitivity control (STC) is adaptively generated by using the adaptive time sensitivity control method based on the accurate estimation of the cell clutter spectrum.

[0051] As can be seen from the above embodiments, the feature of the present invention is that the adaptive sensitivity control method designed by using the accurate estimation of the clutter amplitude spectrum and the attenuation curve fitting can adaptively suppress the clutter entering the radar receiver proximally, avoid the oversaturation of the receiver, and improve the environmental adaptability of radar detection.

Claims

1. An adaptive STC control method based on accurate estimation of unit clutter spectrum, characterized in that: Step 1: Clutter environment perception, perceiving the strength of the clutter background faced by the current radar, and accurately estimating the clutter power C of each range cell in the current scan period, and constructing a clutter map C of the current scan period l , i ; Step 2: Based on the clutter amplitude estimation, estimate the attenuation distance R required for STC curve fitting in each azimuth max and the attenuation depth C max ; Step 3: On the basis of estimating the attenuation distance and attenuation depth, respectively generate: STC curve corresponding to sea clutter background at low grazing angle: stc_db(r) = -30log10(r) + 30log10(R g ) STC curve under the background of rain and cloud clutter: stc_db(r) = -20log10(r) + 20log10(R g ) STC curve under body clutter: stc_db(r) = -10log10(r) + 10log10(R g ) STC curve with fixed attenuation: stc_db(r) = C; where R g is the maximum distance for STC to start; the four fitted STC curves are respectively used as the radar receiver sensitivity gain control curves in the current azimuth to control the clutter attenuation of the radar echo Z in , and the output at this time is: z out (r) = 20 log10(z in (r)) - stc_db(r); Statistically calculate the variance of the output result, and use the STC curve corresponding to the minimum variance as the sensitivity gain control curve of the radar receiver in the next scan period.

2. The adaptive STC control method based on accurate estimation of unit clutter spectrum according to claim 1, characterized in that: Estimation of the clutter power C for each range cell in the current scan period l includes the following steps: Step 1: Generate an adaptive threshold; for each range cell in a certain azimuth, the number of sliding window cells is set to m, and the number of guard cells is set to n. For the l-th range cell, the corresponding threshold estimate is: where Z i is the amplitude corresponding to the i-th range cell; Step 2: Filter out the target echo; on the basis of threshold estimation, the clutter amplitude estimate of the l-th range cell is:

3. The adaptive STC control method based on accurate estimation of unit clutter spectrum according to claim 1 or 2, characterized in that: The estimation of the clutter power C of each range cell in the clutter map i includes: Suppose the amplitude of the $i$-th clutter cell in the clutter map estimated during the $n$-th scan of the radar is $C$. k The estimated clutter amplitude for the $i$-th range cell during the $(n + 1)$-th scan of the radar is $C$. l Then, the estimated amplitude of the $i$-th clutter cell in the clutter map during the $(n + 1)$-th scan of the radar is where $\alpha = C$. l $ / C$. k .

4. The adaptive STC control method based on accurate estimation of unit clutter spectrum according to claim 3, wherein: For the clutter attenuation distance R max and the attenuation depth C max The estimation includes: Step 1: Clutter attenuation distance R max Estimation: To estimate the clutter attenuation distance R max , it is necessary to first estimate the background noise power of the radar. Select the mean value of n range cells at the tail of the clutter distribution curve in a certain azimuth as the estimate of the noise floor, denoted as N0; assume the clutter-to-noise ratio in a certain azimuth is C / N0, then the maximum clutter suppression distance of the radar is Step 2: Clutter attenuation depth C max Estimation; based on the estimation of the noise floor N0, the maximum clutter amplitude in a certain azimuth can be estimated by the mean value of n range cells after zeroing the range. At this time, the estimated value of the maximum clutter amplitude is denoted as C0, and the attenuation depth C max = 20log10(C0 / N0).

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