Sea peak identification method, device and equipment based on multi-polarization Doppler characteristic

Abstract

The invention discloses a sea peak identification method, device and equipment based on a multi-polarization Doppler characteristic. The method comprises the following steps: acquiring an echo signal of a radar; performing adaptive coherent detection on the echo signals in the plurality of polarization channels to obtain a detection result set of the plurality of polarization channels; fusing the detection result sets of the plurality of polarization channels to obtain a fusion result set; for each detection result in the fusion result set, calculating Doppler shift of the detection result in each polarization channel in the plurality of polarization channels; calculating a Doppler offset difference according to the Doppler offset of each polarization channel in the plurality of polarization channels according to the detection result; and determining whether the detection result is a sea peak or a target according to the magnitude relationship between the Doppler offset difference and the identification threshold. According to the method, the sea peak can be effectively identified in a short time.

Description

Technical Field

[0001] The present invention belongs to the technical field of radar, and particularly relates to a sea spike discrimination method, device and equipment based on multi-polarization Doppler characteristics. Background Art

[0002] The sea radar is the eye for ocean surveillance. It can search, track, identify and classify targets in the surveillance area by transmitting and receiving electromagnetic waves, and has the potential to work all-weather and all-day. The effective utilization of marine resources and the practical guarantee of maritime safety are inseparable from the marine environmental perception ability and the maritime target surveillance ability. At present, sea radars have been carried on various platforms such as land, sea, air and space, and meet different mission requirements through targeted system design. The effective detection of radar targets is not only an important prerequisite for subsequent target classification and recognition, but also an important guarantee to avoid the false alarms from background clutter occupying system resources.

[0003] The sea radar needs to detect various targets on the sea surface and at low altitude, such as sea ships, cargo ships, fishing boats, speedboats, icebergs, periscopes and various floating objects, as well as helicopters, sea-skimming missiles and unmanned aerial vehicles flying at low altitude over the sea. Fast targets can be effectively detected by relying on the speed difference between the target and the background clutter, and large targets can be effectively detected by relying on the intensity difference between the target echo and the background clutter echo. Therefore, the difficulty and key point of sea radar target detection have always been the detection problem of small targets on the sea surface at low altitude. Under the development trend of miniaturization, unmanned and stealth, these small sea surface targets at low altitude with small physical size and low echo intensity pose a serious threat to the safety of important civilian and military facilities such as coastal areas, shipping lanes and naval formations. Studying the detection method for sea surface small targets is of great significance for improving the target surveillance ability of radar.

[0004] The sea radar will inevitably receive the backscattering signal from the sea surface, which is usually called sea clutter. From the perspective of electromagnetic scattering mechanism, the sea surface backscattering signal is composed of a low-power, low HH / VV polarization ratio, low-speed, discrete and widely existing tilted modulation Bragg scattering component and a high-power, high HH / VV polarization ratio, high-speed, discrete and occasionally occurring sea spike. In the X-band radar data with a small grazing angle, the maximum radar cross-sectional (RCS) of the sea spike can reach the square meter level, or even be greater than the RCS of some small targets, which will inevitably cause false alarms during the radar detection process. At the same time, the sea spike has a long duration, ranging from sub-second level to second level, and has a long decorrelation time, which will have a certain impact on the performance of the radar.

[0005] Since the radar echoes of sea spikes and low-speed small targets on the sea surface are too similar, differentiating between the two has always been a difficult point for high-resolution marine radars, and the resulting false alarms of sea spikes are also a major problem for high-resolution marine radars. Summary of the Invention

[0006] To solve the above problems existing in the prior art, the present invention provides a method, device and equipment for identifying sea spikes based on multi-polarization Doppler characteristics.

[0007] The technical problems to be solved by the present invention are realized through the following technical solutions:

[0008] The present invention provides a method for identifying sea spikes based on multi-polarization Doppler characteristics, including:

[0009] Obtaining the echo signal of the radar;

[0010] Performing adaptive coherent detection on the echo signals in multiple polarization channels to obtain a detection result set for multiple polarization channels;

[0011] Fusing the detection result sets of the multiple polarization channels to obtain a fused result set;

[0012] For each detection result in the fused result set, calculating the Doppler shift of the detection result in each polarization channel among the multiple polarization channels;

[0013] Calculating the Doppler shift difference according to the Doppler shifts of the detection result in each polarization channel among the multiple polarization channels;

[0014] Determining whether the detection result is a sea spike or a target according to the magnitude relationship between the Doppler shift difference and the discrimination threshold.

[0015] The present invention provides a device for identifying sea spikes based on multi-polarization Doppler characteristics, including:

[0016] An acquisition module for acquiring the echo signal of the radar;

[0017] A detection module for performing adaptive coherent detection on the echo signals in multiple polarization channels to obtain a detection result set for multiple polarization channels;

[0018] A fusion module for fusing the detection result sets of the multiple polarization channels to obtain a fused result set;

[0019] A calculation unit for, for each detection result in the fused result set, calculating the Doppler shift of the detection result in each polarization channel among the multiple polarization channels; calculating the Doppler shift difference according to the Doppler shifts of the detection result in each polarization channel among the multiple polarization channels;

[0020] An identification unit, configured to determine whether the detection result is a sea spike or a target according to the magnitude relationship between the Doppler shift difference and the discrimination threshold.

[0021] The present invention further provides an electronic device, including a processor, a communication interface, a memory, and a communication bus. The processor, the communication interface, and the memory complete communication with each other through the communication bus; the memory is used to store a computer program; when the processor executes the program stored on the memory, the steps of the above-mentioned sea spike discrimination method based on multi-polarization Doppler characteristics are implemented.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The sea spike filtering method from scan to scan adopted by the past single-polarization radar requires an observation time of up to several seconds or even more than ten seconds, which is unacceptable in many practical applications and limits the application of the radar. The present invention proposes a sea spike discrimination method based on multi-polarization Doppler characteristics. This method utilizes the difference in Doppler shift of sea spikes and low-speed small targets on the sea surface in different polarization channels of a full-polarization radar, and can effectively discriminate sea spikes and eliminate the false alarms brought by them within a short time (for example, sub-second level), significantly improving the detection performance of the radar on the sea surface for low-speed small targets.

[0024] The following will further describe the present invention in detail with reference to the accompanying drawings and specific embodiments. Description of the Drawings

[0025] Figure 1 It is a schematic flowchart of the sea spike discrimination method based on multi-polarization Doppler characteristics provided by an embodiment of the present invention;

[0026] Figure 2 It is a schematic flowchart of the sea spike discrimination method based on multi-polarization Doppler characteristics provided by an embodiment of the present invention when the multiple polarization channels are the three polarization channels of HH, HV, and VV. Detailed Embodiments

[0027] The following further describes the present invention in detail with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0028] Most of the existing technologies focus on single-polarization radars and ignore the application of multi-polarization radars. For a single-polarization high-resolution sea radar operating in a fast-scanning mode, to eliminate sea spike false alarms, it is necessary to perform joint detection through multiple scans. In an actual clutter environment, sea spikes usually exhibit characteristics such as high power, a duration of seconds, and random distribution. Since the duration of sea spikes can be up to several seconds, multiple-scan joint processing requires an observation time of up to several seconds. The excessive processing time will affect the radar performance and limit the application of the radar.

[0029] The sea spike discrimination method based on multi-polarization Doppler characteristics proposed by the present invention makes full use of the polarization characteristics of the radar, can effectively discriminate sea spikes and eliminate the false alarms they bring in a short time (for example, sub-second time), and significantly improves the detection performance of the sea radar for low-speed small targets on the sea surface, which is a major improvement over the existing technologies.

[0030] Figure 1 It is a schematic flow diagram of a sea spike discrimination method based on multi-polarization Doppler characteristics provided by an embodiment of the present invention. As Figure 1 shown, the method includes:

[0031] S101. Obtain the echo signal of the radar.

[0032] S102. Perform adaptive coherent detection on the echo signals in multiple polarization channels to obtain a detection result set for multiple polarization channels.

[0033] In some embodiments, the multiple polarization channels are any two polarization channels among the HH polarization channel, the HV polarization channel, the VH polarization channel, and the VV polarization channel, that is, dual-polarization channels. Note that the VH polarization channel and the HV polarization channel cannot be selected simultaneously because, according to the reciprocity theorem in electromagnetic scattering theory, if the receiver noise is ignored, the data of the HV and VH polarization channels are the same. Among them, HH polarization represents horizontal-horizontal polarization, VV polarization represents vertical-vertical polarization, and HV polarization represents horizontal-vertical polarization.

[0034] In some embodiments, the multiple polarization channels are the HH polarization channel, the HV polarization channel, and the VV polarization channel, or the HH polarization channel, the VH polarization channel, and the VV polarization channel, that is, triple-polarization channels.

[0035] In some embodiments, the multiple polarization channels are the HH polarization channel, the HV polarization channel, the VV polarization channel, and the VH polarization channel, that is, full-polarization channels. Among them, VH polarization represents vertical-horizontal polarization.

[0036] S103. Fuse the detection result sets of multiple polarization channels to obtain a fused result set.

[0037] S104. For each detection result in the fusion result set, calculate the Doppler shift of each polarization channel in multiple polarization channels for the detection result.

[0038] S105. Calculate the Doppler shift difference according to the Doppler shifts of each polarization channel in multiple polarization channels for the detection result.

[0039] S106. Determine whether the detection result is a sea spike or a target according to the magnitude relationship between the Doppler shift difference and the discrimination threshold.

[0040] Exemplarily, Figure 2 when the above-mentioned multiple polarization channels are the three polarization channels of HH, HV, and VV, it is a schematic flowchart of a sea spike discrimination method based on multi-polarization Doppler characteristics. As Figure 2 shown, first perform long-time adaptive coherent detection on the echo signals in the three polarization channels of HH, HV, and VV to obtain the detection result sets of each polarization channel. Then, fuse the detection result sets, and then perform detection according to the fused detection result set, and eliminate sea spike false alarms according to multi-polarization detection data to obtain the target detection result.

[0041] In some embodiments, the above S102 can be implemented as: performing cell median constant false alarm rate moving target detection (CM-MTD) on the echo signals of each polarization channel in multiple polarization channels to obtain the detection result sets of each polarization channel. In some embodiments, other methods can also be used for detection to initially find possible sea spikes and targets in each polarization channel. It should be noted that considering the reciprocity theorem in electromagnetic scattering theory, if receiver noise is ignored, the HV and VH polarization data are the same. Therefore, when both HV and VH polarization channels exist in multiple polarization channels, only the echo data of the HV polarization channel needs to be detected.

[0042] For example, taking the HH polarization channel as an example, the formula for CM-MTD is:

[0043]

[0044] where ξ HH (f d ) is the test statistic of the Doppler cell with a Doppler shift of f d , the vectors x HH and x HH,p are the radar echo vectors received by the cell under test (CUT) and the reference cell respectively, and p(f d ) is the Doppler shift of f dThe Doppler steering vector, median{.} represents the median operation, P fa is the desired false alarm rate, H represents the conjugate transpose, T D is the decision threshold. P represents the number of reference cells, υ HH represents the shape parameter. The above formula means that when ξ HH (f d ) is greater than T D , the H1 hypothesis holds, that is, the target is detected. When ξ HH (f d ) is less than T D , the H0 hypothesis holds, that is, the target is not detected.

[0045] When the radar is in the scanning mode, the detection results are marked with range-azimuth cells, and when the radar is in the staring mode like the IPIX radar, they are marked with range-time cells. Taking the staring mode as an example, assume that an echo signal contains M consecutive range cells, and each range cell has Q pulses, then it can be divided into K×M range-time cells, where K is the largest integer not exceeding Q / N, and N is the number of accumulated pulses. Using the above detector CM-MTD to detect in these K×M range-time cells, detection results will be generated in each cell. It should be noted that the detection results concentrated in the detection results of each polarization channel are all range-time cells corresponding to the test statistics greater than the decision threshold. For example, for the echo signal of the HH polarization channel, the detection result set of the HH polarization channel consists of range-time cells that meet the following conditions:

[0046]

[0047] In the above formula, CD HH is the detection result set of the HH polarization channel, Θ is all the range-time cells to be detected in the clutter background, f r is the pulse repetition frequency, ξ HH (f d ; k,m) is the test statistic of the range-time cell at (k,m), k = 1,2,...,K; m = 1,2,...,M, and the Doppler shift of this cell is f d , T D is the decision threshold, and the cell false alarm rate can be approximated as NP fa .

[0048] In some embodiments, the above S103 can be implemented as: using the detection result sets of multiple polarization channels to form a set, and using this set as the fusion result set. That is to say, the detection result sets of multiple polarization channels can be fused according to the "or" rule to obtain the fusion result set.

[0049] For example, when there are three polarization channels, namely HH, HV, and VV, the obtained fused result set CD can be expressed by the following formula:

[0050] Where T represents the decision threshold. The detection results in the fused result set may come from small targets, sea spike false alarms, or false alarms caused by Bragg scattering. Since sea spikes have a large radar cross section (RCS), a long duration, and strong temporal correlation, most false alarms are caused by sea spikes.

[0051] In some embodiments, the above S104 can be implemented as follows: for each detection result in the fused result set, determine the radar echo signals of the distance-time unit corresponding to the detection result in each polarization channel among the multiple polarization channels; for each polarization channel among the multiple polarization channels, perform peak search on the normalized Doppler spectrum of the radar echo signal of the distance-time unit corresponding to the detection result in this polarization channel to obtain the Doppler shift of the detection result in this polarization channel.

[0052] Full-polarization sea spikes have different Doppler shifts in the three polarization channels of HH, HV, and VV. Different from this, the Doppler shift of a target is independent of polarization. Based on this characteristic, it is possible to determine whether the detection result in the fused result set is a small target or a sea spike. Specifically, for each detection result in the fused result set, the calculation formula for the Doppler shift of the detection result in each polarization channel is as follows:

[0053]

[0054] Where * represents the *th polarization channel, * ∈ {HH, HV, VV, VH}, is the radar echo signal of the distance-time unit corresponding to the detection result in the *th polarization channel, and the vector x * and x *,p are the radar echo vectors received by the cell under test (CUT) and the reference cell respectively, p(f d ) is the Doppler steering vector with a Doppler shift of f d , median{·} represents the median operation, arg represents the phase angle operation, and max represents the maximum operation.

[0055] In radar signal processing, the Doppler shift of sea spikes is different under different polarizations, while the Doppler shift of a target is independent of polarization. Therefore, this difference can be used to construct corresponding Doppler statistics for their discrimination.

[0056] In some embodiments, when there are two polarization channels among the multiple polarization channels, S105 above can be implemented as: taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels, and using the obtained modulus value as the Doppler shift difference of the detection result in the two polarization channels.

[0057] In some embodiments, when there are three polarization channels, namely HH, HV, and VV, among the multiple polarization channels, S105 above can be implemented as: taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels of HH and HV, taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels of HH and VV, taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels of HV and VV, and using the sum of the obtained modulus values as the Doppler shift difference of the detection result in these three polarization channels.

[0058] In some embodiments, when there are four polarization channels, namely HH, HV, VV, and VH, among the multiple polarization channels, S105 above can be implemented as: taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels of HH and HV, taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels of HH and VV, taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels of HV and VV, taking the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels of HV and VH, and using the sum of the obtained modulus values as the Doppler shift difference of the detection result in these three polarization channels.

[0059] Exemplarily, when there are three polarization channels, namely HH, HV, and VV, the expression of the Doppler shift difference η(x) of each detection result in these three polarization channels is as follows:

[0060]

[0061] where are the Doppler shifts of the detection result in the three polarization channels of HH, HV, and VV respectively, and |.| represents the modulus operation.

[0062] Exemplarily, when there are four polarization channels, namely HH, HV, VV, and VH, the expression of the Doppler shift difference η(x) of each detection result in these four polarization channels is as follows:

[0063]

[0064] where is the Doppler shift of the detection result in the VH polarization channel.

[0065] In some embodiments, S106 above can be implemented as follows: when the Doppler shift difference is greater than the discrimination threshold, the detection result is discriminated as a sea spike; when the Doppler shift difference is less than or equal to the discrimination threshold, the detection result is discriminated as a target.

[0066] Here, for each detection result, when the Doppler shift difference of the detection result is greater than the discrimination threshold δ, the detection result is discriminated as a sea spike; otherwise, the detection result is discriminated as a small low-speed target on the sea surface. The discrimination threshold δ is a trade-off value that needs to balance between eliminating false alarms of sea spikes and ensuring the detection performance of small targets, so as to effectively discriminate sea spikes and targets. The discrimination threshold δ can be set according to experience.

[0067] The detection method of the present invention has low complexity. The detection time depends on the time for adaptive coherent detection of the echo signal, and the time for adaptive coherent detection of the echo signal depends on the time length of the unit to be detected. Usually, the time length of the unit to be detected is in the sub-second level. Therefore, the present invention can effectively discriminate sea spikes and eliminate the false alarms brought by them within the time of the sub-second level.

[0068] The present invention utilizes the difference in Doppler shift of sea spikes and small low-speed targets on the sea surface in different polarization channels of a full-polarization radar, and can effectively discriminate sea spikes and eliminate the false alarms brought by them in a short time, significantly improving the detection performance of a sea radar for small low-speed targets on the sea surface. The past method of filtering sea spikes from scan to scan used in single-polarization radars requires an observation time of up to several seconds or even more than ten seconds, which is unacceptable in many practical applications and limits the application of the radar. However, the method proposed by the present invention can effectively eliminate false alarms of sea spikes in a short time, for example, within the time scale of the sub-second level, providing the possibility for target detection of a sea radar in a more complex sea clutter background.

[0069] The present invention also provides a sea spike discrimination device based on multi-polarization Doppler characteristics, including: an acquisition module for acquiring the echo signal of the radar; a detection module for performing adaptive coherent detection on the echo signals in multiple polarization channels to obtain a detection result set of multiple polarization channels; a fusion module for fusing the detection result set of multiple polarization channels to obtain a fusion result set; a calculation unit for calculating, for each detection result in the fusion result set, the Doppler shift of the detection result in each polarization channel among multiple polarization channels; calculating the Doppler shift difference according to the Doppler shift of the detection result in each polarization channel among multiple polarization channels; and an identification unit for determining whether the detection result is a sea spike or a target according to the magnitude relationship between the Doppler shift difference and the discrimination threshold.

[0070] The present invention further provides an electronic device, comprising a processor, a communication interface, a memory, and a communication bus. The processor, the communication interface, and the memory complete communication with each other through the communication bus. The memory is used for storing a computer program. When the processor executes the program stored in the memory, the steps of the above-mentioned method for identifying sea spikes based on multi-polarization Doppler characteristics are implemented.

[0071] It should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined.

[0072] In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0073] In the specification, the term "comprising" does not exclude other components or steps, and "a" or "one" does not exclude a plurality. Certain measures are described in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0074] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A sea spike discrimination method based on multi-polarization Doppler characteristics, characterized in that Including: Obtain the echo signal of the radar; Perform adaptive coherent detection on the echo signals in multiple polarization channels to obtain a set of detection results for the multiple polarization channels; Fuse the set of detection results of the multiple polarization channels to obtain a fused result set; For each detection result in the fused result set, calculate the Doppler shift of the detection result in each polarization channel among the multiple polarization channels; Calculate the Doppler shift difference according to the Doppler shifts of the detection result in each polarization channel among the multiple polarization channels; Determine whether the detection result is a sea spike or a target according to the magnitude relationship between the Doppler shift difference and the discrimination threshold; 2. The method according to claim 1, characterized in that, The multiple polarization channels are any two of the HH polarization channel, HV polarization channel, VH polarization channel, and VV polarization channel, and the multiple polarization channels do not simultaneously include the HV polarization channel and the VH polarization channel.

3. The method according to claim 1, wherein The multiple polarization channels are the HH polarization channel, HV polarization channel, VV polarization channel, and VH polarization channel.

4. The method according to claim 1, characterized in that, The fusing the set of detection results of the multiple polarization channels to obtain a fused result set includes: Use the set of detection results of the multiple polarization channels to form a set, and use the set as the fused result set.

5. The method according to claim 1, wherein The calculating the Doppler shift of the detection result in each polarization channel among the multiple polarization channels includes: Determine the radar echo signals of each polarization channel in the multiple polarization channels corresponding to the range-time unit of the detection result; For each polarization channel among the multiple polarization channels, perform peak search on the normalized Doppler spectrum of the radar echo signal of the range-time unit corresponding to the detection result in this polarization channel to obtain the Doppler shift of the detection result in this polarization channel.

6. The method according to claim 1, wherein When the multiple polarization channels are two polarization channels, the calculating the Doppler shift difference according to the Doppler shifts of the detection result in each polarization channel among the multiple polarization channels includes: Take the modulus value after subtracting the Doppler shifts of the detection result in the two polarization channels, and use the obtained modulus value as the Doppler shift difference of the detection result in the two polarization channels.

7. The method according to claim 1, wherein The determining whether the detection result is a sea spike or a target according to the magnitude relationship between the Doppler shift difference and the discrimination threshold includes: When the Doppler shift difference is greater than the discrimination threshold, identify the detection result as a sea spike; When the Doppler shift difference is less than or equal to the discrimination threshold, identify the detection result as a target.

8. The method according to claim 1, wherein The performing adaptive coherent detection on the echo signals in multiple polarization channels to obtain a set of detection results for the multiple polarization channels includes: Perform CM-MTD detection on the echo signals of each polarization channel in multiple polarization channels to obtain a set of detection results for each polarization channel.

9. A sea spike discrimination device based on multi-polarization Doppler characteristics, characterized in that, Including: An acquisition module for acquiring the echo signal of the radar; A detection module for performing adaptive coherent detection on the echo signals in multiple polarization channels to obtain a set of detection results for the multiple polarization channels; A fusion module for fusing the set of detection results of the multiple polarization channels to obtain a fused result set; A calculation unit for calculating, for each detection result in the fusion result set, the Doppler shift of each polarization channel in the plurality of polarization channels for the detection result; Calculating a Doppler shift difference according to the Doppler shifts of each polarization channel in the plurality of polarization channels for the detection result; An identification unit for determining whether the detection result is a sea spike or a target according to the magnitude relationship between the Doppler shift difference and a discrimination threshold.

10. An electronic device, comprising a processor, a communication interface, a memory, and a communication bus, characterized in that The processor, the communication interface, and the memory complete communication with each other through the communication bus; The memory is used for storing a computer program; When the processor executes the program stored on the memory, it implements the method steps described in any one of claims 1-8.

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