A novel non-line-of-sight target detection method and system

Abstract

The application discloses a novel non-line-of-sight target detection method and system, and the non-line-of-sight target detection method comprises the following steps: a ground radar transmits a signal to an airborne relay system; the relay system receives and amplifies the transmission signal of the radar, and transmits the enhanced transmission signal to a target to be detected; the target to be detected receives the enhanced transmission signal and generates a return signal; the relay system receives and amplifies the target return signal, and transmits the enhanced return signal to the ground radar; and the ground radar processes the received enhanced target return signal, so that the non-line-of-sight target is detected. The non-line-of-sight target detection system comprises the ground radar, the airborne relay system and the target to be detected. The application amplifies the radar transmission signal and the target scattered return signal by using the airborne relay system, expands the radar detection range, and can detect the non-line-of-sight target which is blocked by high-rise buildings in a city environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of radar signal processing, and relates to a novel non-line-of-sight target detection method and system. BACKGROUND

[0002] The traditional radar detection method is for line-of-sight targets, that is, there is no obstruction between the radar and the target. For non-line-of-sight targets, electromagnetic waves are difficult to penetrate multiple layers of obstacles to obtain target information, resulting in the failure of the traditional line-of-sight target detection method. In urban environments, due to the obstruction of buildings, radar signals cannot propagate along a straight line to the target, resulting in the fact that unmanned aerial vehicle targets and ground vehicle targets behind the buildings cannot be effectively detected by the radar. Therefore, for the obstructed non-line-of-sight targets, how to accurately obtain target information and realize non-line-of-sight target detection has become one of the technical problems to be solved at present.

[0003] Existing non-line-of-sight target detection technologies mainly include penetration detection technology and multipath detection technology. The penetration detection technology utilizes the transmission characteristics of electromagnetic waves to obtain the information of non-line-of-sight targets by processing radar echoes that penetrate through obstacles. The multipath detection technology utilizes the reflection, diffraction and other multipath components of electromagnetic waves to realize the detection of hidden targets in corner non-line-of-sight scenes. When electromagnetic waves penetrate multiple layers of obstacles or thick buildings, the energy of the electromagnetic waves is severely attenuated, resulting in poor detection effect. In the multipath detection technology, the energy of the electromagnetic waves is also attenuated after being reflected by the wall, and the detection result is disturbed by multiple reflection signals between the walls, resulting in the appearance of false targets in the detection result. Whether it is the transmission detection technology or the multipath detection technology, the energy of the electromagnetic waves is greatly attenuated in the process of propagation, resulting in a limited non-line-of-sight detection range.

[0004] The non-line-of-sight target detection technology is mainly applied to specific non-line-of-sight scenes, and due to the energy attenuation of electromagnetic waves in the transmission, reflection and diffraction processes, the application scene of the current non-line-of-sight detection technology is small. For the obstructed far distance aerial unmanned aerial vehicle target and ground vehicle target, the signal-to-noise ratio of the echo signal received by the radar in the penetration detection technology and the multipath detection technology is very small, and effective non-line-of-sight target detection cannot be realized. SUMMARY

[0005] The present application aims to solve the technical problem of the severe energy attenuation of electromagnetic waves in the transmission, reflection and diffraction processes in the prior art, which results in a limited detection range. The present application provides a novel non-line-of-sight target detection method and system, and the technical scheme adopted is as follows:

[0006] A novel non-line-of-sight target detection method, comprising the steps of:

[0007] S1, a ground radar transmits a signal to an airborne relay system;

[0008] S2, the relay system receives and amplifies the transmitted signal, and forwards the enhanced transmitted signal to the target to be detected;

[0009] S3, the target to be detected receives the enhanced transmitted signal, and generates a target echo signal;

[0010] S4, the relay system receives and amplifies the target echo signal, and forwards the enhanced target echo signal to the ground radar;

[0011] S5, the ground radar processes the received enhanced target echo signal, thereby realizing the detection of the non-line-of-sight target.

[0012] In an embodiment of the present application, the step S1 comprises:

[0013] The ground radar transmits a linear frequency modulation pulse signal, denoted as:

[0014]

[0015] In formula (1), rect[] is a rectangular function, K is a frequency modulation slope and has K=B w / T p , where B w is the signal bandwidth, T p is the pulse duration of the linear frequency modulation pulse signal, and f c is the carrier frequency of the signal.

[0016] In an embodiment of the present application, the step S2 comprises:

[0017] The relay system receives the transmitted signal, denoted as:

[0018]

[0019] In formula (2), P t is the transmission power of the ground radar, is the transmission antenna gain of the ground radar in the direction, is the receiving antenna gain of the airborne relay system from the direction, is the azimuth angle and the elevation angle of the airborne relay system relative to the ground radar, L p1 is the power propagation loss from the ground radar to the airborne relay system, λ is the wavelength of the radar signal, and Δτ1 is the time delay corresponding to the transmission of the radar signal to the airborne relay system;

[0020] The transmitted signal forwarded by the relay system to the target to be detected is denoted as:

[0021]

[0022] In formula (3), η represents a power amplification coefficient of the airborne relay system, is the power transmitted by the relay system is the transmission gain of the direction signal, is the azimuth angle and the elevation angle of the target relative to the airborne relay system, L p2 is the power propagation loss from the airborne relay system to the target, Δτ2 is the time delay corresponding to the transmission of the relay amplified signal from the airborne relay system to the target.

[0023] In one embodiment of the present application, the step S3 comprises:

[0024] The echo signal generated by the target to be detected is represented as:

[0025]

[0026] In formula (4), σ is the scattering cross section area of the target.

[0027] In one embodiment of the present application, the step S4 comprises:

[0028] The reception of the echo signal by the relay system is represented as:

[0029]

[0030] In formula (5), L p3 is the power propagation loss from the target to the airborne relay system, Δτ3 is the time delay corresponding to the transmission of the target scattering signal to the airborne relay system;

[0031] The reception of the echo signal by the ground radar is represented as:

[0032]

[0033] In formula (6), L p4 is the power propagation loss from the airborne relay system to the ground radar, Δτ4 is the time delay corresponding to the transmission of the enhanced target echo signal by the airborne relay system to the ground radar;

[0034] Therefore, the reception of the echo signal of the target to be detected by the ground radar is represented as:

[0035]

[0036] In formula (7), P r is the target echo power received by the ground radar, R1 is the slant range between the ground radar and the airborne relay system, R2 is the slant range between the airborne relay system and the target, and c is the speed of light;

[0037] The echo of the target after removing the carrier frequency is represented as:

[0038]

[0039] The echo power of the non-line-of-sight target received by the ground radar is represented as:

[0040]

[0041] In the formulas (8) and (9), P t is the radar transmitting power, is the radar antenna gain, is the antenna gain of the relay receiving the radar signal, is the antenna gain of the relay transmitting the signal to the target, σ is the scattering coefficient of the target, η is the power amplification coefficient of the relay, λ is the wavelength, R1 is the radial distance from the radar to the airborne relay, and R2 is the radial distance from the airborne relay to the target.

[0042] In one embodiment of the present application, in the step S5, a pulse Doppler radar processing method is used for target detection.

[0043] The pulse Doppler radar echo signal processing process includes echo data preprocessing, pulse compression, moving target display, Doppler filtering, target detection, and target parameter estimation.

[0044] In one embodiment of the present application, the target Doppler frequency obtained in the target parameter estimation is composed of the Doppler frequency of the relay system relative to the ground radar and the Doppler frequency of the target to be detected relative to the relay system.

[0045] In one embodiment of the present application, the Doppler frequency of the target to be detected received by the ground radar is f d , and f d is represented as:

[0046] f d = f d1 + f d2 (14)

[0047] In the formula (14), f d1 and f d2 are the Doppler frequencies of the airborne relay system relative to the ground radar and the non-line-of-sight target relative to the airborne relay platform, respectively, and f d1 and f d2 are represented as:

[0048]

[0049]

[0050] where v plat and v target are the velocity vector of the airborne relay system and the velocity vector of the non-line-of-sight target, respectively, and k1 and k2 are the beam vector of the ground radar to the airborne relay platform and the beam vector of the airborne relay platform to the non-line-of-sight target, respectively, and k1 and k2 are expressed as:

[0051]

[0052]

[0053] v plat and v target are expressed as:

[0054] v plat = [v plat_x , v plat_y , v plat_z ] T (19)

[0055] v target = [v target_x , v target_y , v target_z ] T (20)

[0056] [v plat_x , v plat_y , v plat_z ] are the velocity components of the velocity vector of the airborne relay system on the x, y, z axes, respectively, and [v target_x , v target_y , v target_z ] are the velocity components of the velocity vector of the non-line-of-sight target on the x, y, z axes, respectively.

[0057] A novel non-line-of-sight target detection system, comprising: a ground radar, an airborne relay system and a target to be detected;

[0058] The ground radar is configured to transmit a signal to the airborne relay system;

[0059] The airborne relay system is configured to receive the transmitted signal, enhance the transmitted signal, and forward the enhanced transmitted signal to the target to be detected;

[0060] The target to be detected is configured to receive the enhanced transmitted signal and generate a target echo signal;

[0061] The relay system is configured to receive the target echo signal, enhance the target echo signal, and forward the enhanced target echo signal to the ground radar;

[0062] The ground radar is used for processing the received enhanced target echo signal.

[0063] In one embodiment of the present application, the airborne relay system is composed of a transmitting antenna, a receiving antenna and a power amplifier module.

[0064] The relay system receives the transmitting signal of the ground radar, amplifies the received transmitting signal through the power amplifier, and transmits the enhanced transmitting signal to the target to be detected through the transmitting antenna.

[0065] The present application has the following advantages:

[0066] 1. The non-line-of-sight target detection method of the present application uses the airborne relay system to enhance the radar transmitting signal and the echo signal scattered by the target, can specify the irradiation area to enhance the non-line-of-sight target echo signal and expand the radar detection range, and can detect the non-line-of-sight target (unmanned aerial vehicle target and vehicle target) blocked by high-rise buildings in urban environment.

[0067] 2. The non-line-of-sight target detection system of the present application can make the radar signal not propagate through the obstacle by deploying the airborne relay platform between the ground radar and the non-line-of-sight target, enhance the coverage area of the radar signal, reduce the signal attenuation, and improve the overall detection capability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 is a flowchart of the novel non-line-of-sight target detection method provided by the embodiment of the present application;

[0069] Figure 2 is a non-line-of-sight scene schematic diagram provided by the embodiment of the present application;

[0070] Figure 3 is a non-line-of-sight scene mathematical model schematic diagram provided by the embodiment of the present application;

[0071] Figure 4 is a pulse Doppler radar signal processing flowchart provided by the embodiment of the present application;

[0072] Figure 5 is a schematic diagram of the novel non-line-of-sight target detection system provided by the embodiment of the present application. DETAILED DESCRIPTION

[0073] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0074] In the urban environment, due to the existence of complex terrain such as buildings, roads and the like, the traditional line-of-sight target detection technology often faces problems such as signal being blocked by obstacles, signal energy attenuation, signal interference and the like, resulting in that the non-line-of-sight target cannot be effectively detected. The present application mainly aims at the non-line-of-sight target detection in the urban environment, and proposes a new non-line-of-sight target detection method, which can expand the detection range of the ground radar, enhance the target echo signal, and realize the detection of the unmanned aerial vehicle target and the vehicle target blocked by the building.

[0075] Referring to the drawings Figure 1 The non-line-of-sight target detection method comprises the following steps:

[0076] S1, the ground radar transmits a signal to an airborne relay system;

[0077] S2, the relay system receives and amplifies the transmitted signal, and transmits the enhanced transmitted signal to the target to be detected;

[0078] S3, the target to be detected receives the enhanced transmitted signal and generates a target echo signal;

[0079] S4, the relay system receives and amplifies the target echo signal, and transmits the enhanced target echo signal to the ground radar;

[0080] S5, the ground radar processes the received enhanced target echo signal, thereby realizing the detection of the non-line-of-sight target.

[0081] The present application proposes to use the airborne relay system to enhance and transmit the radar transmitted signal and the target scattered echo signal, and the scene schematic diagram is shown in the accompanying Figure 2 .

[0082] Specifically, the method first transmits a signal to the airborne relay system through the ground radar, the relay system receives the transmitted signal of the ground radar and amplifies the received radar transmitted signal through the power amplifier in the relay system, and the enhanced radar transmitted signal is irradiated to the detection area through the transmitting antenna of the relay system. After the target to be detected receives the radar signal transmitted by the relay system, a scattered echo is generated, the relay system receives the scattered echo signal of the target, enhances it and transmits it to the ground radar receiver, and the detection of the non-line-of-sight target can be realized by processing the target echo signal received by the radar receiver.

[0083] The relay system can provide an effective solution in these complex environments and has shown a wide application prospect. In the present application, by deploying the airborne relay platform between the ground radar and the non-line-of-sight target, the radar signal can be transmitted without passing through the obstacles, the coverage area of the radar signal can be enhanced, the signal attenuation can be reduced, and the overall detection capability of the system can be improved.

[0084] Attachment Figure 2 The corresponding three-dimensional mathematical model is established for the scene, as shown in the attached Figure 3 As shown, it is easy to analyze the specific representation of the target echo received by the ground radar.

[0085] In one embodiment of the present invention, it is assumed that a ground radar transmits a linear frequency modulation pulse signal, which is expressed as:

[0086]

[0087] In formula (1), rect[·] is a rectangular function, K is the frequency modulation slope and K=B w / T p , where B w is the signal bandwidth, T p is the pulse duration of the linear frequency modulated pulse signal, f c is the carrier frequency of the signal.

[0088] The transmitted signal received by the relay system can be expressed as:

[0089]

[0090] In formula (2), P t is the transmitting power of the ground radar, For ground radar The transmitting antenna gain in the direction, For the airborne relay system to receive Directional receiving antenna gain, is the azimuth and elevation angle of the airborne relay system relative to the ground radar, L p1 is the power propagation loss from the ground radar to the airborne relay system, λ is the wavelength of the radar signal, and Δτ1 is the time delay corresponding to the transmission of the radar signal to the airborne relay system.

[0091] The transmission signal forwarded by the relay system to the target to be detected can be expressed as:

[0092]

[0093] In formula (3), η represents the power amplification factor of the airborne relay system, Transmit for the relay system The transmission gain of the directional signal, is the azimuth and elevation angle of the target relative to the airborne relay system, L p2 is the power transmission loss from the airborne relay system to the target, and Δτ2 is the delay corresponding to the relay amplified signal being transmitted from the airborne relay system to the target.

[0094] The echo signal generated by the target to be detected can be expressed as:

[0095]

[0096] In formula (4), σ is the scattering cross section of the target.

[0097] The relay system receiving the echo signal can be expressed as:

[0098]

[0099] In formula (5), L p3 is the power propagation loss from the target to the airborne relay system, and Δτ3 is the time delay corresponding to the transmission of the target scattering signal to the airborne relay system.

[0100] The ground radar receiving the echo signal relayed by the relay system can be expressed as:

[0101]

[0102] In formula (6), L p4 is the power propagation loss from the airborne relay system to the ground radar, and Δτ4 is the time delay corresponding to the transmission of the enhanced target echo signal of the airborne relay system to the ground radar.

[0103] Therefore, the ground radar receiving the echo signal of the target to be detected can be expressed as:

[0104]

[0105] In formula (7), P r is the target echo power received by the ground radar, R1 is the slant range between the ground radar and the airborne relay system, R2 is the slant range between the airborne relay system and the target, and c is the speed of light.

[0106] The target echo after removing the carrier frequency can be expressed as:

[0107]

[0108] The target echo power received by the ground radar can be expressed as:

[0109]

[0110] In formulas (8) and (9), P t is the radar transmitting power, is the radar antenna gain, is the antenna gain of the relay receiving the radar signal, is the antenna gain of the relay transmitting the signal to the target, σ is the scattering coefficient of the target, η is the power amplification coefficient of the relay, λ is the wavelength, R1 is the radial distance from the radar to the airborne relay, and R2 is the radial distance from the airborne relay to the target.

[0111] The propagation delays from the ground radar to the airborne relay system and from the airborne relay system to the target to be detected are expressed as:

[0112] Δτ1=Δτ4=R1 / c (10)

[0113] Δτ2=Δτ3=R2 / c (11)

[0114] The power transmission loss coefficients from the ground radar to the airborne relay system and from the airborne relay system to the target to be detected are expressed as:

[0115]

[0116]

[0117] By processing the echo signals received by the ground radar receiver, targets in non-line-of-sight areas can be detected and their parameters estimated. The present invention uses pulse Doppler radar for target detection. Pulse Doppler radar uses the Doppler effect to estimate target parameters from the echo signals received by the radar. Pulse Doppler radar uses the Doppler frequency information in the echo signals to distinguish targets from clutter in the Doppler frequency domain.

[0118] The pulse Doppler radar echo signal processing process includes: echo data preprocessing, pulse compression, moving target display, Doppler filtering, target detection, and target parameter estimation. The specific signal processing process is shown in the attached figure. Figure 4 shown.

[0119] Formula (8) shows that the time delay between the radar receiving the target echo signal and the radar transmitting signal consists of two parts: the time delay corresponding to the distance between the radar and the airborne relay platform, and the time delay corresponding to the distance between the airborne relay platform and the target. The target distance obtained in target parameter estimation is also composed of these two distances. In practice, the distance between the ground radar and the airborne relay platform is known. The distance of the target relative to the airborne relay platform can be obtained by subtracting the distance between the radar and the relay platform from the target distance obtained in target parameter estimation.

[0120] In the present invention, the target Doppler frequency obtained in the target parameter estimation is composed of the Doppler frequency of the relay system relative to the ground radar and the Doppler frequency of the target to be detected relative to the relay system.

[0121] Assume that the Doppler frequency of the target to be detected received by the ground radar is f d , f d Expressed as:

[0122] f d =f d1 +f d2 (14)

[0123] f d1 and f d2 are respectively expressed as:

[0124]

[0125]

[0126] k1and k2in formula (14) and formula (15) are respectively expressed as:

[0127]

[0128]

[0129] v plat and v target are respectively expressed as:

[0130] v plat = [v plat_x , v plat_y , v plat_z ] T (19)

[0131] v target = [v target_x , v target_y , v target_z ] T (20)

[0132] In practical application, since the geometric relation of the airborne relay platform relative to the ground radar is known, the angle of the target relative to the airborne relay platform can be obtained after the target parameter estimation, and the actual motion speed of the target can be calculated.

[0133] Under the complex terrain of the city, buildings are easy to cause shielding and form non-line-of-sight conditions, and the airborne relay system can expand the radar detection range, break through the traditional line-of-sight limit, and improve the detection ability of various targets hidden in the city buildings, such as vehicles and special facilities. At the same time, the airborne relay system has mobility and can flexibly cover different areas of the city, and compared with the detection method of fixed stations, it can continuously and dynamically monitor non-line-of-sight targets in a more flexible and efficient way, and obtain the information of the target in time. In the urban combat scene, the airborne relay system can assist in detecting the enemy's hidden forces, unmanned aerial vehicles and the like, enhance the situation awareness capability, and better develop the combat strategy to ensure the effective development of military operations in the complex urban environment. There are many types of targets in the city environment, and the airborne relay system can improve the recognition ability of the radar to small targets or low reflection targets by enhancing the signal quality. The deployment of the airborne relay system can help the radar system to capture more reflection signals and improve the clarity of target recognition, avoiding the loss of targets caused by signal attenuation or shielding.

[0134] The non-line-of-sight target detection method provided by the present application can overcome the detection obstacles caused by high-rise buildings and the like in the city, and can effectively enhance signal propagation, improve detection range and enhance target recognition capability. At the same time, the detection method provided by the present application is not affected by the detection scene, and the detection range is large. With the increasing requirements of the city environment on radar detection, the radar technology combined with the airborne relay system will provide more reliable solutions for the fields of city safety, city combat, traffic management, unmanned driving and the like.

[0135] The present application also provides a new non-line-of-sight target detection system, referring to the accompanying drawings Figure 5 The non-line-of-sight target detection system comprises a ground radar, an airborne relay system and a target to be detected.

[0136] The ground radar is used for transmitting signals to the airborne relay system; the airborne relay system is used for receiving the transmitted signals, enhancing the transmitted signals, and forwarding the enhanced transmitted signals to the target to be detected; the relay system is used for receiving echo signals, enhancing the echo signals and forwarding the enhanced echo signals to the ground radar; the relay system is used for processing the echo signals received by the ground radar; and the target to be detected is used for receiving the enhanced transmitted signals and generating echo signals.

[0137] In the present application, the airborne relay system is composed of a transmitting antenna, a receiving antenna and a power amplifier module. The relay system receives the transmitted signals of the ground radar, amplifies the received transmitted signals through the power amplifier, and the enhanced transmitted signals are forwarded to the target to be detected through the transmitting antenna.

[0138] The application can expand the detection range of the ground radar by enhancing the signal of the radar irradiation to the target and the echo signal of the target scattering through the airborne relay system. In the urban environment, the radar signal cannot directly propagate to the target to be detected due to the shielding of the building. At present, the reflection, diffraction and transmission of electromagnetic waves on the building surface are mainly used to realize the non-line-of-sight target detection. However, the reflection, diffraction and transmission of electromagnetic waves on the building surface will cause the attenuation of electromagnetic wave energy, resulting in small radar detectable range, and the detection scene is mostly limited to indoor or fixed building distribution scene, and the target behind the multi-storey building cannot be effectively detected. At the same time, the non-line-of-sight detection method based on multipath detection technology will produce multipath ghost interference, affecting the detection of the real target. The method proposed in the application realizes the enhancement and forwarding of the signal between the radar and the target by using the airborne relay system, solves the problem of limited detection range caused by energy loss of electromagnetic waves due to reflection and transmission, and realizes the detection of unmanned aerial vehicle targets and vehicle targets blocked by buildings.

[0139] The above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, any modification, equivalent replacement and improvement made by those skilled in the art within the technical range disclosed by the application and within the spirit and principle of the application shall be covered within the protection scope of the application.

Claims

1. A novel non-line-of-sight target detection method, characterized by, The method comprises the steps of: S1, the ground radar transmits a signal to the airborne relay system; S2, the airborne relay system receives and amplifies the transmitted signal, and transmits the enhanced signal to the target to be detected; S3, the target to be detected receives the enhanced signal and generates a target echo signal; S4, the airborne relay system receives and amplifies the target echo signal, and transmits the enhanced target echo signal to the ground radar; S5, the ground radar processes the received enhanced target echo signal, thereby realizing the detection of the non-line-of-sight target; The step S1 comprises: The ground radar transmits a linear frequency modulation pulse signal, which is represented as: (1) In equation (1), is a rectangular function, is a frequency modulation slope and has where is the signal bandwidth, is the pulse duration of the linear frequency modulated pulse signal, is the carrier frequency of the signal; The step S2 comprises: The airborne relay system receives the transmitted signal, which is represented as: (2) in Equation (2), is the transmitting power of the ground radar, is the transmitting antenna gain of the ground radar in is the receiving antenna gain of the airborne relay system in is the power propagation loss from the ground radar to the airborne relay system, is the power propagation loss from the ground radar to the airborne relay system, is the azimuth and elevation angle of the airborne relay system relative to the ground radar, is the power propagation loss from the ground radar to the airborne relay system, is the wavelength of the radar signal, is the time delay corresponding to the transmission of the radar signal to the airborne relay system; The airborne relay system transmits the transmitted signal to the target to be detected, which is represented as: (3) In formula (3), a power amplification coefficient of the airborne relay system, a transmission power of the airborne relay system, a transmission gain of the directional signal, an azimuth angle and an elevation angle of the target relative to the airborne relay system, a power propagation loss of the airborne relay system to the target, a time delay corresponding to the relay amplification signal transmitted by the airborne relay system to the target. The step S3 comprises: The echo signal generated by the target to be detected is represented as: (4) In equation (4), The scattering cross section targeted; The step S4 comprises: The airborne relay system receives the echo signal, which is represented as: (5) In equation (5), is the power propagation loss from the target to the airborne relay system, is the time delay for the target scattering signal to arrive at the corresponding airborne relay system. The ground radar receives the echo signal transmitted by the airborne relay system, which is represented as: (6) In equation (6), is the power propagation loss of the airborne relay system to the ground radar, is the enhanced target echo signal transfer delay of the airborne relay system to the corresponding ground radar. Therefore, the ground radar receives the echo signal of the target to be detected, which is represented as: (7) In equation (7), is the target echo power received by the ground radar, is the slant range between the ground radar and the airborne relay system, is the slant range between the airborne relay system and the target, is the speed of light; The target echo signal without the carrier frequency is represented as: (8) The ground radar receives the echo power of the non-line-of-sight target, which is represented as: (9)。 2. A novel non-line of sight target detection method as claimed in claim 1, wherein, In the step S5, the pulse Doppler radar processing method is used for target detection; The processing process of the enhanced target echo signal comprises echo data preprocessing, pulse compression, moving target display, Doppler filtering, target detection, and target parameter estimation.

3. A novel non-line-of-sight target detection method according to claim 2, characterized in that, The target Doppler frequency obtained in the target parameter estimation is composed of the Doppler frequency of the airborne relay system relative to the ground radar and the Doppler frequency of the target to be detected relative to the airborne relay system.

4. A novel non-line-of-sight target detection method according to claim 3, characterized by, The ground radar receives the Doppler frequency of the target to be detected , is represented as: (14) In equation (14), and are the Doppler frequencies of the airborne relay system with respect to the ground radar and the non-line-of-sight target with respect to the airborne relay platform, respectively, and are expressed as: (15) (16) Equations (15) and (16) in which and are the velocity vector of the airborne relay system and the velocity vector of the non-line-of-sight target, respectively, and are the beam vector of the ground-to-airborne relay platform and the airborne relay platform-to-non-line-of-sight target, respectively, and are represented as: (17) (18) and are represented by: (19) (20) the velocity vector of the airborne relay system in the x and y axes, respectively, the velocity component of the airborne relay system in the x axis, the velocity vector of the non-line-of-sight target in the x and y axes, respectively, the velocity component of the non-line-of-sight target in the x axis.

5. A novel non-line-of-sight target detection system characterized by, It comprises: a ground radar, an airborne relay system, and a target to be detected; The ground radar is used for transmitting a signal to the airborne relay system; The airborne relay system is used for receiving the transmitted signal, enhancing the transmitted signal, and transmitting the enhanced transmitted signal to the target to be detected; The target to be detected is used for receiving the enhanced transmitted signal and generating a target echo signal; The airborne relay system is used for receiving the target echo signal, enhancing the target echo signal, and transmitting the enhanced target echo signal to the ground radar; The ground radar is used for processing the received enhanced target echo signal; The ground radar is used for transmitting a signal to the airborne relay system, which comprises: The ground radar transmits a linear frequency modulation pulse signal, which is represented as: (1) In equation (1), is a rectangular function, is a frequency modulation slope and has where is the signal bandwidth, is the pulse duration of the chirp signal, is the carrier frequency of the signal; The airborne relay system is used for receiving the transmitted signal, which is represented as: (2) in Equation (2), is a transmit power of the ground radar, is a distance between the ground radar and the airborne relay system, is a transmit antenna gain of the ground radar in a direction, is a receive antenna gain of the airborne relay system from a direction, is a receive antenna gain of the airborne relay system from a direction, is an azimuth angle and an elevation angle of the airborne relay system relative to the ground radar, is a power propagation loss of the ground radar to the airborne relay system, is a wavelength of the radar signal, is a time delay corresponding to a transmission of the radar signal to the airborne relay system; The airborne relay system transmits the transmitted signal to the target to be detected, which is represented as: (3) In formula (3), denotes a power amplification coefficient of the airborne relay system, denotes a transmission power of the airborne relay system, denotes a transmission gain of the directional signal, denotes an azimuth angle and an elevation angle of the target relative to the airborne relay system, denotes a power propagation loss of the airborne relay system to the target, denotes a time delay corresponding to the relay amplification signal transmitted by the airborne relay system to the target. The target to be detected generates an echo signal, which is represented as: (4) In equation (4), The scattering cross section targeted; The airborne relay system receives the echo signal, which is represented as: (5) In equation (5), is the power propagation loss from the target to the airborne relay system, is the time delay for the target scattering signal to arrive at the corresponding airborne relay system. The ground radar receives the echo signal transmitted by the airborne relay system, which is represented as: (6) In equation (6), is the power propagation loss of the airborne relay system to the ground radar, is the time delay corresponding to the enhanced target echo signal transfer of the airborne relay system to the ground radar. Therefore, the ground radar receives the echo signal of the target to be detected, which is represented as: (7) In equation (7), is the target echo power received by the ground radar, is the slant range between the ground radar and the airborne relay system, is the slant range between the airborne relay system and the target, is the speed of light; The target echo signal without the carrier frequency is represented as: (8) The ground radar receives the echo power of the non-line-of-sight target, which is represented as: (9)。 6. A novel non-line of sight target detection system as claimed in claim 5, wherein, The airborne relay system is composed of a transmitting antenna, a receiving antenna and a power amplifier module; The airborne relay system receives the transmitting signal of a ground radar, amplifies the received transmitting signal through the power amplifier module, and transmits the enhanced transmitting signal to a target to be detected through the transmitting antenna.

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