Spaceborne Ship Monitoring Radar Detection Methods and Systems

Abstract

This invention provides a method and system for detecting ships using spaceborne ship monitoring radar, comprising: setting the pulse repetition frequency of the sea-penetrating radar on a zebra map; setting the sea-penetrating radar transmission signal; transmitting the signal and acquiring the sea-penetrating echo according to the settings; calculating the range ambiguity set where the main ambiguity energy is located; suppressing land ambiguity for the range ambiguity in the range ambiguity set; and detecting ships in the effective observation area of ​​the sea-penetrating echo after land ambiguity suppression. This invention noise-enhances the echo signal, solving the problem of false alarm detection and effectively improving the observation performance of space-based sea-surface detection radar; by using signal encoding and existing SAR image databases for range ambiguity suppression techniques, and by using a matched filter corresponding to the effective observation area to achieve range focusing in the effective observation area, it solves the problem of high range ambiguity requirements and realizes a spaceborne radar system for ship monitoring with low false alarm rates.

Description

Technical Field

[0001] This invention belongs to the field of spaceborne radar technology, specifically, it relates to a spaceborne ship monitoring radar detection method and system, and more specifically, it relates to a spaceborne ship monitoring radar system and method based on signal encoding and an external SAR image database. Background Technology

[0002] Spaceborne ship monitoring technology monitors a vessel's position and status in real time, enabling timely detection of potential hazards, preventing accidents, providing global ship dynamic information, and maintaining maritime safety and order. Simultaneously, monitoring vessel emissions and pollution helps in the timely detection and response to marine pollution incidents, and precise ship monitoring allows for better management of marine resources, including fisheries resources. Therefore, spaceborne ship monitoring technology not only improves the safety of maritime navigation but also plays a vital role in combating illegal activities, protecting the marine environment, and promoting marine resource management.

[0003] The main methods for spaceborne ship monitoring include spaceborne AIS (Airborne Identification System), spaceborne SAR (Synthetic Aperture Radar), and detection radar systems. Among these, spaceborne SAR and detection radar offer all-weather, all-day, wide-area ship detection capabilities, making them powerful methods for detecting ships even when they are silent. The core difference between the two lies in their imaging mechanisms and resolution requirements, necessitating different algorithms and system architectures for data processing. Similar to spaceborne SAR, spaceborne ship detection radar systems face the challenge of minimizing antenna area for wide-area sea observations, making it impossible to simultaneously address radar range and azimuth ambiguity, thus introducing false ship targets into the effective observation area. Therefore, effectively suppressing ambiguity in spaceborne ship detection radar becomes a significant challenge in system design.

[0004] Currently, improving range ambiguity in spaceborne radar systems is mainly achieved through techniques such as waveform design optimization, phase coding, positive and negative frequency modulation, and digital beamforming. Patent document "A Spaceborne SAR Range Ambiguity Suppression Method Based on Transmit / Receive Pointer Separation" (CN117233765A) discloses a method that reduces the main lobe width of the radiation pattern by separating the antenna range from the transmit / receive pattern, thus moving the first ambiguity region outside the antenna main lobe and suppressing range ambiguity. However, this method sacrifices observation swath width and is not suitable for wide-area detection by spaceborne ship detection radar.

[0005] The paper "A Method for Suppressing Narrative Point and Range Ambiguity Based on Real-Time Beamforming of Spaceborne SAR" (Han Xiaodong, Song Hongjun, Xu Wei, et al. Journal of Electronics and Information Technology, 2013(12):2823-2828.) proposes a method for suppressing narrative point and range ambiguity. This method can suppress ambiguity signals to the greatest extent without affecting the reception of useful signals. It has a wide beam selection range and reduces the difficulty of beam selection in the design of spaceborne SAR systems. However, it requires the system to be a pitch-oriented multi-channel system, which results in relatively high system complexity.

[0006] The patent document "A Real-Time Echo Recovery Method for High Repetition Rate Coding Synthetic Aperture Radar" (CN116299461A) discloses a method that uses periodic phase coding sequences to transmit to the ground, constructs a phase coding guidance matrix, and derives an echo recovery weight vector from the phase coding guidance matrix to achieve real-time and accurate unambiguous signal recovery of multiple sub-mapped areas. However, it can only be used in SAR imaging systems and requires a high repetition rate.

[0007] The patent "A method for suppressing range ambiguity in spaceborne synthetic aperture radar" (CN112698329A) discloses a method that uses positive and negative frequency modulation slopes to transmit linear frequency modulation signals, and then compresses the received signals twice to complete two-dimensional focusing imaging. This method can effectively reduce the interference of target signals in the main ambiguity area and maintain the focusing effect and energy of the target in the main lobe area. However, it is difficult to suppress the ambiguity in the area that differs from the observation area by an even number of ambiguity numbers.

[0008] The patent document "A Spaceborne SAR Range Ambiguity Suppression Method Based on Two-Dimensional Waveform Coding" discloses a method that segments the bandwidth of a linear frequency modulated (LFM) signal and uses a particle swarm optimization (PSO) algorithm to alternately optimize two segmented LFM signals. This yields two orthogonal nonlinear LFM signals with reduced cross-correlation energy and low peak-to-end sidelobe ratios and integral sidelobe ratios, aiming to enable normal imaging of the scene's echoes and suppress range ambiguity energy of multiple consecutive orders to varying degrees. However, this method only noise-enhances the range ambiguity, and in land-sea interface areas, land ambiguity can lead to a decrease in ship detection performance.

[0009] In summary, there is an urgent need for a spaceborne ship monitoring radar detection method and system that can detect and suppress ambiguous land areas, noise-encode ship echo signals in ambiguous distance areas, and effectively reduce the false alarm rate of ship detection in the observation area caused by distance ambiguity. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for detecting satellite-borne ship monitoring radar.

[0011] The present invention provides a detection method for a spaceborne ship monitoring radar system, comprising:

[0012] Step S1: Set the sea-penetrating radar transmission signal;

[0013] Step S2: Set the transmission and reception timing of the marine radar, including the pulse repetition frequency and the signal transmission-reception window;

[0014] Step S3: Transmit a signal to the sea and obtain the radar echo of the sea detection according to the transmission and reception timing settings;

[0015] Step S4: Select the set of range ambiguities where the main lobe of the radar range-direction pattern is located, and generate a land scattering energy map;

[0016] Step S5: Suppress land ambiguity in the land scattering energy map for the distance ambiguity in the distance ambiguity number set;

[0017] Step S6: Detect ships in the effective observation area of ​​the radar echo after land ambiguity suppression.

[0018] Preferably, the pulse repetition frequency is set according to the functional relationship curve between the incident angle or the distance from the ground to the sub-satellite point and the pulse repetition frequency, so as to receive the original echo of the main lobe receiving area of ​​the entire antenna and meet the Nyquist sampling requirements in the azimuth direction.

[0019] The transmitted signal is encoded in the form of an orthogonal encoded pulse sequence, in which any two pulses are orthogonal in the time domain.

[0020] The pulse sequence transmission method is to periodically repeat the transmission with the number of pulses in the pulse sequence as the period.

[0021] The length of the pulse sequence is greater than the difference between the distance ambiguity number of the nadir echo and the distance ambiguity number of the farthest echo from Earth plus one.

[0022] Preferably, step S4 includes:

[0023] Step S4.1: Using an external SAR image database, transmit / receive timing settings, and range-direction antenna pattern, reconstruct the land scattering energy map of the range-ambiguous region.

[0024] Step S4.2: Compare the land scattering energy map and select the distance fuzzy number set of the top N fuzzy energies by sorting.

[0025] Step S4.1 includes:

[0026] Step S4.1.1: Input satellite position and velocity, pulse repetition frequency, sampling detection, and gate opening and closing times;

[0027] Step S4.1.2: Set the distance ambiguity number and use the range Doppler equation to perform spatial positioning for all azimuth and distance ambiguity cells;

[0028] Step S4.1.3: Read the ground object scattering intensity map at the spatial location of the location from the external SAR image database, and construct the land scattering intensity map of the distance-ambiguous area;

[0029] Step S4.1.4: Use the radar range-direction antenna pattern to weight the ground object scattering intensity map to obtain the land scattering energy map of the range-ambiguous region.

[0030] Preferably, step S5 includes:

[0031] Step S5.1: Determine the transmitted signal corresponding to the main lobe of the radar range pattern.

[0032] Step S5.2: For the main lobe region of the radar range pattern, use the transmitted signal as a matched filter to compress the range of the original echo and perform azimuth focusing.

[0033] Step S5.3: Based on the land scattering energy map, suppress strong points with energy greater than the average energy in the distance ambiguity region.

[0034] Step S5.4: Defocus the land scattering energy map of the range ambiguity area after strong point suppression, and use the transmitted signal for inverse matched filtering to obtain the suppressed radar echo.

[0035] Preferably, step S6 includes:

[0036] Step S6.1: Determine the transmitted signal corresponding to the effective observation area.

[0037] Step S6.2: Use the transmitted signal as a matched filter to compress the range of the radar echo after land ambiguity suppression and perform azimuth focusing processing.

[0038] Step S6.3: Use the constant false alarm rate (CFAR) detection method to detect the selected sea surface area and obtain the ship detection results.

[0039] The present invention provides a detection system for a spaceborne ship monitoring radar system, comprising:

[0040] Module M1: Set the sea-penetrating radar transmission signal;

[0041] Module M2 sets the transmission and reception timing of the marine radar, including the pulse repetition frequency and the signal transmission-reception window;

[0042] Module M3 transmits signals to the sea and acquires radar echoes for sea detection according to the transmission and reception timing settings;

[0043] Module M4 selects the set of range ambiguities where the main lobe of the radar range-direction pattern is located, and generates a land scattering energy map;

[0044] Module M5: Suppresses land ambiguity in the land scattering energy map to address distance ambiguity in the distance ambiguity data set;

[0045] Module M6 performs effective observation area ship detection on radar echoes after land ambiguity suppression.

[0046] Preferably, the pulse repetition frequency is set according to the functional relationship curve between the incident angle or the distance from the ground to the sub-satellite point and the pulse repetition frequency, so as to receive the original echo of the main lobe receiving area of ​​the entire antenna and meet the Nyquist sampling requirements in the azimuth direction.

[0047] The transmitted signal is encoded in the form of an orthogonal encoded pulse sequence, in which any two pulses are orthogonal in the time domain.

[0048] The pulse sequence transmission method is to periodically repeat the transmission with the number of pulses in the pulse sequence as the period.

[0049] The length of the pulse sequence is greater than the difference between the distance ambiguity number of the nadir echo and the distance ambiguity number of the farthest echo from Earth plus one.

[0050] Preferably, the module M4 includes:

[0051] Module M4.1: Reconstructs the land scattering energy map of the range-ambiguous region using an external SAR image database, transmit and receive timing settings, and range-direction antenna pattern.

[0052] Module M4.2: By comparing the land scattering energy map, select the set of distance fuzzy numbers where the top N fuzzy energies are located by sorting.

[0053] The module M4.1 includes:

[0054] Module M4.1.1: Input satellite position and velocity, pulse repetition frequency, sampling detection, and gate opening and closing times;

[0055] Module M4.1.2: Set the distance ambiguity number and use the range Doppler equation to perform spatial positioning for all azimuth and distance ambiguity cells;

[0056] Module M4.1.3: Reads the scattering intensity map of ground objects at the spatial location from an external SAR image database and constructs the land scattering intensity map of the distance-ambiguous area;

[0057] Module M4.1.4: Uses the radar's range-direction antenna pattern to weight the ground object scattering intensity map to obtain the land scattering energy map of the range-ambiguous region.

[0058] Preferably, module M5 includes:

[0059] Module M5.1: Determines the transmitted signal corresponding to the main lobe of the radar range pattern.

[0060] Module M5.2: For the main lobe region of the radar range pattern, the transmitted signal is used as a matched filter to compress the range of the original echo and perform azimuth focusing.

[0061] Module M5.3: Based on the land scattering energy map, it suppresses strong points with energy greater than the average energy in the range ambiguity region.

[0062] Module M5.4: Defocuses the land scattering energy map of the range ambiguity area after strong point suppression, and uses the transmitted signal for inverse matched filtering to obtain the suppressed radar echo.

[0063] Preferably, module M6 includes:

[0064] Module M6.1: Determines the transmitted signal corresponding to the effective observation area.

[0065] Module M6.2: Uses the transmitted signal as a matched filter to compress the range of the radar echo after land ambiguity suppression and performs azimuth focusing.

[0066] Module M6.3: Uses constant false alarm rate (CFAR) detection method to detect selected sea surface areas and obtain ship detection results.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] 1. This invention noises the ship echo signal in the distance ambiguity zone, solving the problem of false alarms caused by distance ambiguity in traditional sea surface ship detection radar, and effectively improving the observation performance of space-based sea surface detection radar.

[0069] 2. This invention solves the problem of high range ambiguity requirements in sea surface ship detection by using signal encoding and existing SAR image database for range ambiguity suppression technology, and achieves low false alarm detection of sea surface ships.

[0070] 3. This invention utilizes signal coding and existing SAR image database inversion technology to achieve distance focusing of the effective observation area through matched filters corresponding to the effective observation area, breaking through the problem of high false alarm rate in traditional sea surface ship detection and realizing a spaceborne radar system for low false alarm ship monitoring. Attached Figure Description

[0071] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0072] Figure 1 A schematic diagram of the detection method of a spaceborne ship monitoring radar system;

[0073] Figure 2 This is a schematic diagram of the echo signals in the effective observation area and the ambiguity area of ​​the simulation.

[0074] Figure 3 This is a schematic diagram of the imaging results in the distance-blurred area;

[0075] Figure 4 This is a schematic diagram of the radar detection intensity distribution in the effective observation area before range ambiguity suppression;

[0076] Figure 5 This is a schematic diagram of the effective detection intensity distribution of radar after range ambiguity suppression. Detailed Implementation

[0077] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0078] A detection method for a spaceborne ship monitoring radar system according to the present invention includes:

[0079] Step S1: Set the sea-penetrating radar to transmit signals and receive the raw echoes from the main lobe receiving area of ​​the entire antenna.

[0080] Step S2: Set the transmission and reception timing of the sea exploration radar.

[0081] Specifically, the transmission and reception timing includes the pulse repetition frequency and the signal transmission-reception window.

[0082] The pulse repetition frequency (PRF) is set by plotting a function curve of the incident angle or the distance from the ground point to the nadir versus the PRF, i.e., on a zebra plot. The set PRF ensures that the azimuth direction satisfies Nyquist sampling and covers the effective observation area.

[0083] PRF>B a

[0084] Where PRF is the pulse repetition frequency, B a This refers to the Doppler bandwidth.

[0085] The signal transmission-reception window is such that the signal transmission and echo reception times do not overlap, and the length of the pulse length superposition reception window is less than the pulse transmission repetition time.

[0086] A periodic coded signal pulse sequence is used, meaning that the signal is periodically repeated with the number of pulses in the sequence as the period, and any pulses in the coded signal pulse sequence are orthogonal to each other.

[0087] s k (t r ) = s k+N (t r )

[0088]

[0089] Among them, s k (t r ) represents the k-th transmitted pulse in azimuth, t r For distance in time, T p Where is the pulse width, and N is the pulse sequence length (repetition period), s n (t r ) represents the nth transmitted pulse in azimuth, s m (t r ) represents the m-th transmitted pulse in azimuth, with the superscript "*" indicating the conjugate operator. Here, N should satisfy:

[0090]

[0091] Among them, R far To determine the slant range corresponding to the farthest echo from Earth, R nadir denoted by slant distance α, c is the speed of light, and PRF is the pulse repetition frequency. This is the floor operator.

[0092] In more preferred embodiments, the signal encoding form is an orthogonal encoded pulse sequence, wherein any two pulses in the sequence are orthogonal in the time domain;

[0093] The pulse sequence transmission method is to periodically repeat the transmission with the number of pulses in the pulse sequence as the period.

[0094] The length of the pulse sequence must be greater than the difference between the distance ambiguity number of the nadir echo and the distance ambiguity number of the farthest echo from Earth plus one.

[0095] Step S3: Transmit signal and acquire echo: Based on the setting of the encoded signal pulse sequence and the setting of the pulse repetition interval described in step S2, that is, the transmission and reception timing is set, the sea detection echo is acquired.

[0096] Step S4: Calculate the set of range ambiguities where the main lobe of the radar range pattern is located;

[0097] Specifically, step S4, calculating the set of range ambiguities where the main lobe of the radar range-direction pattern is located, includes:

[0098] Step S4.1: Using the external SAR image database, the radar operating timing used in step S3 (i.e., the setting of the coded signal pulse sequence and pulse repetition interval, and the range antenna pattern), reconstruct the land scattering energy map of the range-ambiguous area.

[0099] Specifically, step S4.1 includes:

[0100] Step S4.1.1: Input satellite position and velocity, pulse repetition frequency, sampling detection, gate opening time and closing time;

[0101] Step S4.1.2: Set the distance ambiguity number and use the range Doppler equation to perform spatial positioning for all azimuth and distance ambiguity cells;

[0102]

[0103] Where, p t For the target location, p s (t a ), v s (t a ) represent the azimuth and time t, respectively. a The radar antenna center position and velocity are given by: c (speed of light), τ (gate time of the target), k (range ambiguity number), PRF (pulse repetition frequency), λ (radar wavelength), and f. dc For the Doppler center, D DEM Represents an external digital elevation model (DEM) database.

[0104] Step S4.1.3: Read the scattering intensity of ground objects at this spatial location from the external SAR image database (set to zero if it is water area) and construct a land scattering intensity map of the fuzzy area;

[0105] Step S4.1.4: Use the radar range-direction pattern to weight the ground object scattering intensity map to obtain the land scattering energy map of the fuzzy area.

[0106] Step S4.2: Compare different land energy maps and select the distance fuzzy numbers of the top N fuzzy energies as the distance fuzzy number set.

[0107] Step S5, Land Blur Suppression: For the distance ambiguity in the set of distance ambiguity numbers determined in Step S4, different matched filters are used to suppress the land ambiguity of the original echo sequence;

[0108] Specifically, for any major distance ambiguity region determined in step S4, step S5 specifically includes:

[0109] Step S5.1: Determine the transmitted signal corresponding to the main range ambiguity region;

[0110] Step S5.2: For this major range ambiguity area, the transmitted signal is used as a matched filter to compress the range of the original echo and perform azimuth focusing processing;

[0111] The echo signal received by the radar is represented as follows:

[0112]

[0113] Wherein s(t) a ,t r ) represents radar echo, s amb,k (t a ,t r ) represents radar echoes in the ambiguous region, s obs (t a ,t r ) represents the echo from the observation area, t a For azimuth time, t r For radar fast time. Assume the radar echo in the k0th ambiguity region. The corresponding transmission signal is Using this signal to s(t) a ,t r Pulse compression

[0114]

[0115] in, The signal after compression of the echo pulse in the k0 ambiguity region, s' obs,cmp (t a ,t r ) represents the compressed signal of the echo in the observation area, s' amb,cmp,k (t a ,t r () represents the compressed signal of the echo pulse in the k-th ambiguity region. This represents the k-th transmitted pulse in azimuth, with the superscript "*" indicating the conjugate operator.

[0116] By separating the transmit and receive directions of the antenna pattern along the range, the main lobe beamwidth is narrowed, and the ambiguous area is moved out of the main lobe, thus suppressing range ambiguity.

[0117] Step S5.3: Based on the land scattering energy map of the fuzzy region generated in step S4, suppress strong points with energy greater than the average energy within the fuzzy region.

[0118] Step S5.4: Defocus the image of the blurred area after strong point suppression, and use the transmitted signal of the blurred area for inverse matched filtering to obtain the radar echo after suppressing the strong points of the blurred area.

[0119] Step S6, Ship Detection in Effective Observation Area: Ship detection processing is performed on the sea-penetrating radar echo after land ambiguity suppression.

[0120] Specifically, step S6 includes:

[0121] Step S6.1: Determine the transmitted signal corresponding to the effective observation area;

[0122] Step S6.2: Use the transmitted signal as a matched filter to perform range compression on the radar echo after land ambiguity suppression obtained in step S5.4, and perform azimuth focusing processing;

[0123] Step S6.3: Use the constant false alarm rate (CFAR) detection method to detect the sea surface area and obtain the ship detection results.

[0124] The effectiveness of the present invention was verified using simulation data, and the simulation parameters are shown in Table 1.

[0125] Table 1. Simulation parameters of the spaceborne marine radar system:

[0126]

[0127] Assume the encoded signal uses the following short-offset orthogonal waveform:

[0128]

[0129] Among them, K r To adjust the frequency of the transmitted signal, T p B is the pulse width. r The signal bandwidth is given by , and the subscript n indicates the nth transmitted pulse. j represents the imaginary part, and t represents time.

[0130] by Figure 2 The simulation of echo signals in the effective observation area and the ambiguous area is used as an example. Figure 3 For example, the energy difference between the strong points in the blurred region and the target is -20dB, and 111 near-end blurred strong points are evenly distributed around the target point. Figure 4 It is evident that traditional signal coding and processing techniques, by failing to suppress near-range blurring, will result in increased noise floor. Figure 5 It is evident that by employing periodic coded signals as the transmission signals of the sea-penetrating radar, utilizing an external SAR image database to detect and suppress ambiguous land areas, and using a matched filter corresponding to the effective observation area to achieve distance focusing in the effective observation area, as well as achieving high defocusing of ships on the sea surface in the ambiguous observation area, the echo signals of ships in the distance-ambiguous area are noise-reduced, effectively reducing the false alarm rate of ship detection in the observation area caused by distance ambiguity and improving the probability of ship detection in the effective observation area.

[0131] The present invention also provides a detection system for a spaceborne ship monitoring radar system. The detection system can be implemented by executing the process steps of the spaceborne ship monitoring radar system detection method. That is, those skilled in the art can understand the spaceborne ship monitoring radar system detection method as a preferred embodiment of the detection system.

[0132] The present invention provides a detection system for a spaceborne ship monitoring radar system, comprising:

[0133] Module M1: Set the sea-penetrating radar to transmit signals and receive raw echoes;

[0134] Module M2 sets the transmission and reception timing of the marine radar, including the pulse repetition frequency and the signal transmission-reception window;

[0135] Module M3 transmits signals to the sea and acquires radar echoes for sea detection according to the transmission and reception timing settings;

[0136] Module M4 selects the set of range ambiguities where the main lobe of the radar range-direction pattern is located, and generates a land scattering energy map;

[0137] Module M5: Suppresses land ambiguity in the land scattering energy map to address distance ambiguity in the distance ambiguity data set;

[0138] Module M6 performs effective observation area ship detection on radar echoes after land ambiguity suppression.

[0139] In more preferred embodiments, the pulse repetition frequency is set according to the functional relationship curve between the incident angle or the distance from the ground to the sub-satellite point and the pulse repetition frequency, so as to receive the original echo of the main lobe receiving area of ​​the entire antenna, and the azimuth direction meets the Nyquist sampling requirements.

[0140] The transmitted signal is encoded in the form of an orthogonal encoded pulse sequence, in which any two pulses are orthogonal in the time domain.

[0141] The pulse sequence transmission method is to periodically repeat the transmission with the number of pulses in the pulse sequence as the period.

[0142] The length of the pulse sequence is greater than the difference between the distance ambiguity number of the nadir echo and the distance ambiguity number of the farthest echo from Earth plus one.

[0143] The signal transmission and reception timing in module M3 is set based on the interval of repeated transmission of the coded signal pulse sequence to obtain radar echoes.

[0144] In more preferred embodiments, module M4 includes:

[0145] Module M4.1: Reconstructs the land scattering energy map of the range-ambiguous region using an external SAR image database, transmit and receive timing settings, and range-direction antenna pattern.

[0146] Module M4.2: By comparing the land scattering energy map, select the set of distance fuzzy numbers where the top N fuzzy energies are located by sorting.

[0147] The module M4.1 includes:

[0148] Module M4.1.1: Input satellite position and velocity, pulse repetition frequency, sampling detection, and gate opening and closing times;

[0149] Module M4.1.2: Set the distance ambiguity number and use the range Doppler equation to perform spatial positioning for all azimuth and distance ambiguity cells;

[0150] Module M4.1.3: Reads the scattering intensity map of ground objects at the spatial location from an external SAR image database and constructs the land scattering intensity map of the distance-ambiguous area;

[0151] Module M4.1.4: Uses the radar's range-direction antenna pattern to weight the ground object scattering intensity map to obtain the land scattering energy map of the range-ambiguous region.

[0152] In more preferred embodiments, module M5 includes:

[0153] Module M5.1: Determines the transmitted signal corresponding to the main lobe of the radar range pattern.

[0154] Module M5.2: For the main lobe region of the radar range pattern, the transmitted signal is used as a matched filter to compress the range of the original echo and perform azimuth focusing.

[0155] Module M5.3: Based on the land scattering energy map, it suppresses strong points with energy greater than the average energy in the range ambiguity region.

[0156] Module M5.4: Defocuses the land scattering energy map of the range ambiguity area after strong point suppression, and uses the transmitted signal for inverse matched filtering to obtain the suppressed radar echo.

[0157] In more preferred embodiments, module M6 includes:

[0158] Module M6.1: Determines the transmitted signal corresponding to the effective observation area.

[0159] Module M6.2: Uses the transmitted signal as a matched filter to compress the range of the radar echo after land ambiguity suppression and performs azimuth focusing.

[0160] Module M6.3: Uses constant false alarm rate (CFAR) detection method to detect selected sea surface areas and obtain ship detection results.

[0161] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0162] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method of detecting by a spaceborne vessel monitoring radar system, characterized in that, include: Step S1: Set the sea-penetrating radar transmission signal; Step S2: Set the transmission and reception timing of the marine radar, including the pulse repetition frequency and the signal transmission-reception window; Step S3: Transmit a signal to the sea and obtain the radar echo of the sea detection according to the transmission and reception timing settings; Step S4: Select the set of range ambiguities where the main lobe of the radar range-direction pattern is located, and generate a land scattering energy map; Step S5: Suppress land ambiguity in the land scattering energy map for the distance ambiguity in the distance ambiguity number set; Step S6: Detect ships in the effective observation area of ​​the radar echo after land ambiguity suppression; The pulse repetition frequency is set according to the functional relationship curve between the incident angle or the distance from the ground to the sub-satellite point and the pulse repetition frequency, and the original echo of the main lobe receiving area of ​​the entire antenna is received, and the azimuth direction meets the Nyquist sampling requirements. The transmitted signal is encoded in the form of an orthogonal coded pulse sequence, wherein any two pulses in the sequence are orthogonal in the time domain; The pulse sequence transmission method is to periodically repeat the transmission with the number of pulses in the pulse sequence as the period. The length of the pulse sequence is greater than the difference between the distance ambiguity number of the nadir echo and the distance ambiguity number of the farthest echo from Earth plus one. Step S4 includes: Step S4.1: Using an external SAR image database, transmit / receive timing settings, and range-direction antenna pattern, reconstruct the land scattering energy map of the range-ambiguous region; Step S4.2: Compare the land scattering energy map and select the distance fuzzy number set of the top N fuzzy energies by sorting; Step S4.1 includes: Step S4.1.1: Input satellite position and velocity, pulse repetition frequency, sampling detection, and gate opening and closing times; Step S4.1.2: Set the distance ambiguity number and use the range Doppler equation to perform spatial positioning for all azimuth and distance ambiguity cells; Step S4.1.3: Read the ground object scattering intensity map at the spatial location of the location from the external SAR image database, and construct the land scattering intensity map of the distance-ambiguous area; Step S4.1.4: Use the radar range-direction antenna pattern to weight the ground object scattering intensity map to obtain the land scattering energy map of the range-ambiguous region; Step S5 includes: Step S5.1: Determine the transmitted signal corresponding to the main lobe of the radar range pattern; Step S5.2: For the main lobe region of the radar range pattern, use the transmitted signal as a matched filter to compress the range of the original echo and perform azimuth focusing. Step S5.3: Based on the land scattering energy map, suppress strong points with energy greater than the average energy in the range ambiguity region; Step S5.4: Defocus the land scattering energy map of the range ambiguity area after strong point suppression, and use the transmitted signal for inverse matched filtering to obtain the suppressed radar echo.

2. The method of claim 1, wherein the method further comprises: Step S6 includes: Step S6.1: Determine the transmitted signal corresponding to the effective observation area; Step S6.2: Use the transmitted signal as a matched filter to compress the range of the radar echo after land ambiguity suppression and perform azimuth focusing processing; Step S6.3: Use the constant false alarm rate (CFAR) detection method to detect the selected sea surface area and obtain the ship detection results.

3. A detection system for a spaceborne ship monitoring radar system, characterized in that, include: Module M1: Set the sea-penetrating radar transmission signal; Module M2 sets the transmission and reception timing of the marine radar, including the pulse repetition frequency and the signal transmission-reception window; Module M3 transmits signals to the sea and acquires radar echoes for sea detection according to the transmission and reception timing settings; Module M4 selects the set of range ambiguities where the main lobe of the radar range-direction pattern is located, and generates a land scattering energy map; Module M5: Suppresses land ambiguity in the land scattering energy map to address distance ambiguity in the distance ambiguity data set; Module M6: Effectively detects ships in the observation area of ​​radar echoes after land ambiguity suppression; The pulse repetition frequency is set according to the functional relationship curve between the incident angle or the distance from the ground to the sub-satellite point and the pulse repetition frequency, and the original echo of the main lobe receiving area of ​​the entire antenna is received, and the azimuth direction meets the Nyquist sampling requirements. The transmitted signal is encoded in the form of an orthogonal coded pulse sequence, wherein any two pulses in the sequence are orthogonal in the time domain; The pulse sequence transmission method is to periodically repeat the transmission with the number of pulses in the pulse sequence as the period. The length of the pulse sequence is greater than the difference between the distance ambiguity number of the nadir echo and the distance ambiguity number of the farthest echo from Earth plus one. The module M4 includes: Module M4.1: Reconstructs the land scattering energy map of the range-ambiguous region using an external SAR image database, transmit / receive timing settings, and range-direction antenna pattern; Module M4.2: By comparing the land scattering energy map, select the set of distance fuzzy numbers where the top N fuzzy energies are located by sorting; The module M4.1 includes: Module M4.1.1: Input satellite position and velocity, pulse repetition frequency, sampling detection, and gate opening and closing times; Module M4.1.2: Set the distance ambiguity number and use the range Doppler equation to perform spatial positioning for all azimuth and distance ambiguity cells; Module M4.1.3: Reads the scattering intensity map of ground objects at the spatial location from an external SAR image database and constructs the land scattering intensity map for areas with ambiguous distances; Module M4.1.4: Uses the radar's range-to-antenna radiation pattern to weight the ground object scattering intensity map to obtain the land scattering energy map of the range-ambiguous region; The module M5 includes: Module M5.1: Determines the transmitted signal corresponding to the main lobe of the radar range pattern; Module M5.2: For the main lobe region of the radar range pattern, the transmitted signal is used as a matched filter to compress the range of the original echo and perform azimuth focusing. Module M5.3: Based on the land scattering energy map, suppress strong points with energy greater than the average energy in the range ambiguity region; Module M5.4: Defocuses the land scattering energy map of the range ambiguity area after strong point suppression, and uses the transmitted signal for inverse matched filtering to obtain the suppressed radar echo.

4. The detection system of the spaceborne ship monitoring radar system according to claim 3, characterized in that, The module M6 includes: Module M6.1: Determines the transmitted signal corresponding to the effective observation area; Module M6.2: Uses the transmitted signal as a matched filter to compress the range of the radar echo after land ambiguity suppression and performs azimuth focusing processing; Module M6.3: Uses constant false alarm rate (CFAR) detection method to detect selected sea surface areas and obtain ship detection results.

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