A Spatiotemporal Blind Synchronization Method for Underwater Acoustic Waves and Airborne Radar Waves

Abstract

The present invention discloses a spatio-temporal blind synchronization method for underwater acoustic waves and airborne radar waves, which relates to the field of radar detection. The method includes: a pulsed Doppler radar generates multiple detection pulses in the air to conduct a cruising search of the sea surface; the radar uses the PRF search of multiple phase channels to sample the echo of the water surface micro-motion signal; the signal processor of the radar processes the sampled signal according to the different radial velocities of the sea clutter and the water surface micro-motion signal relative to the detection direction of the pulsed Doppler radar to obtain the acoustic time-domain waveform of the underwater acoustic wave target; the radar is controlled to hover at the intensity center according to the position of the maximum echo amplitude of the acoustic time-domain waveform, and the radar PRF parameter is adjusted according to the echo amplitude until the acoustic time-domain waveform is synchronized with the radar detection pulse, realizing the spatio-temporal synchronization and time synchronization of the underwater acoustic wave and the airborne radar wave, and providing technical support for the actual combat application of cross-media detection.

Description

Technical Field

[0001] The present invention relates to the field of radar detection, and in particular to a method for spatio-temporal blind synchronization of underwater acoustic waves and airborne radar waves. Background Art

[0002] Radar systems involving spatio-temporal synchronization problems are mainly bistatic / multistatic radars. Bistatic / multistatic radars are mainly used for anti-stealth and anti-jamming, and usually work in a mode of matching a main station and a secondary station. By using the multi-baseline angle setting of stealth aircraft and the spaced layout of the multi-baseline secondary station and the main station. In addition to coating with radar-absorbing materials, stealth aircraft also use a smooth polyhedral fuselage to reduce the reflectivity in the direction of electromagnetic wave radiation while adsorbing electromagnetic waves, so that the electromagnetic waves are reflected to other areas. Usually, the reflection angle is about 120°. Bistatic radars utilize this characteristic to achieve anti-stealth by transmitting from the main station and receiving at the multi-baseline angle area of 120° at the secondary station. At the same time, when under attack by anti-radiation missiles, the main station stops transmitting, and the secondary station randomly alternates to transmit while the main station receives, realizing the anti-missile and anti-stealth working mode. The spatio-temporal synchronization of bistatic radars mainly lies in the time-phase-beam synchronization between the main and secondary stations. Among them, time-phase synchronization is completed by the synchronization antenna receiving system of the secondary station, and the clock signal of the main station is transmitted to the secondary station through the synchronization antenna to achieve time-phase synchronization. Beam synchronization is realized under the control of the main station according to the main station synchronization search and synchronization tracking instructions.

[0003] The concept of spatio-temporal synchronization of cross-media detection radars is different from that of bistatic / multistatic radars. It is a blind synchronization of handshake search based on prior knowledge between two unknown entities, or a blind synchronization of the search for the acoustic wave surface micro-motion signal of an unknown underwater target by a radar based on prior knowledge. Moreover, due to the limitation of the scene change from space to underwater in cross-media detection, it is impossible to effectively achieve wired or wireless direct synchronization. Therefore, it is necessary to study a spatio-temporal synchronization method that meets the actual requirements. Summary of the Invention

[0004] In view of the above problems and technical requirements, the inventor of the present invention has proposed a method for spatio-temporal blind synchronization of underwater acoustic waves and airborne radar waves. Through detection pulse scanning and PRF scanning, high-resolution micro-Doppler frequency detection of long-time coherent accumulation of signals in static and dynamic environments is realized, and the PRF is finely adjusted according to the echo amplitude of the signal echo to achieve beam synchronization and PRF synchronization of underwater acoustic waves and airborne radar waves.

[0005] The technical solution of the present invention is as follows:

[0006] A method for spatio-temporal blind synchronization of underwater acoustic waves and airborne radar waves, comprising the following steps:

[0007] The pulsed Doppler radar generates multiple detection pulses in the air through an airborne or unmanned aerial vehicle (UAV) carrier to conduct a cruising search of the sea surface;

[0008] When the pulsed Doppler radar receives the echo of the surface micro-motion signal caused by the underwater acoustic wave target, the echo of the surface micro-motion signal is sampled by using the PRF search of the multiple phase channels of the radar;

[0009] According to the different radial velocities of the sea clutter and the surface micro-motion signal relative to the detection direction of the pulsed Doppler radar, the signal processor of the radar processes the sampled signal to obtain the acoustic time-domain waveform of the underwater acoustic wave target;

[0010] Centering on the detection pulse corresponding to the maximum echo amplitude of the acoustic time-domain waveform during the cruise scan, the pulsed Doppler radar is controlled to hover at the intensity center to achieve the spatial synchronization of the underwater acoustic wave target and the airborne radar wave;

[0011] According to the echo amplitude of each phase channel of the acoustic time-domain waveform, the radar PRF parameter is adjusted until the maximum echo amplitude is determined to achieve the synchronization of the acoustic time-domain waveform and the radar detection pulse and generate a resonance phenomenon, so as to achieve the time synchronization of the underwater acoustic wave target and the airborne radar wave.

[0012] A further technical solution thereof is that the signal processor of the radar processes the sampled signal according to the different radial velocities of the sea clutter and the surface micro-motion signal relative to the detection direction of the pulsed Doppler radar, including:

[0013] The sea clutter consists of countless waves, with wave crests and wave troughs. The radial velocities of the wave crests and wave troughs relative to the detection direction of the pulsed Doppler radar are zero, and the Doppler frequency is zero;

[0014] The surface micro-motion signal caused by the underwater acoustic wave target at the water surface is a high-speed periodic vibration signal. The vibration frequency of the surface micro-motion signal is consistent with the frequency of the underwater acoustic wave target. The vibration frequency of the underwater acoustic wave target is in the range of 10 Hz - 300 Hz, the sound source level is 140 dB - 160 dB, the sound source depth is 1 - 5 meters, facing the detection direction of the pulsed Doppler radar, and the radial velocity of the surface micro-motion signal changes periodically at a high speed and the Doppler frequency is not zero.

[0015] A further technical solution thereof is that processing the sampled signal to obtain the acoustic time-domain waveform of the underwater acoustic wave target includes:

[0016] In a signal processor, after converting the sampled signal from analog to digital, the digital signal is successively subjected to digital down-conversion and Fourier transform, and then stored in a buffer zone by partition according to the order of transmitted detection pulses. Moving target detection and constant false alarm detection are performed on each partition in turn. After long-term coherent accumulation, sea clutter with a Doppler frequency of zero is finally filtered out from the sampled signal. The measured different Doppler frequencies and radar detection pulses respectively correspond to the sampling positions of the signal echo. Therefore, the acoustic time-domain waveform of the underwater acoustic target is obtained by fitting with the least squares method, and thus the high-resolution Doppler frequency information and echo amplitude information of the underwater acoustic target are obtained.

[0017] A further technical solution thereof is to sample the echo of the surface micro-motion signal by using the pulse repetition frequency search of multiple phase channels of the radar, including:

[0018] In the signal processor, a signal processing channel is established every 45 degrees, and a detection pulse is transmitted every 45 degrees. Eight sample points of the surface micro-motion signal echo are effectively collected within one acoustic vibration period. The eight-phase detection pulses correspond to different parts of the surface micro-motion signal echo, and the radar pulse repetition frequency parameter is finely adjusted by the echo amplitude fed back by each phase channel, so that the radar wave repetition frequency corresponding to the eight sample points is the same as the frequency of the underwater acoustic target. When the two are the same, the echo amplitude of the acoustic time-domain waveform corresponding to the eight-phase channel is the largest, and the signal-to-noise ratio of the micro-Doppler coherent accumulation is the largest.

[0019] A further technical solution thereof is that the high-resolution Doppler frequency information of the underwater acoustic target includes Doppler frequency and Doppler velocity, and different Doppler frequencies are presented according to different phases of the acoustic vibration period. The Doppler frequency is positive in the 0° - 90° interval of the acoustic wave. The Doppler velocity is the largest at 0°, and the Doppler velocity is zero and the corresponding Doppler frequency is zero at 90°. In the 90° - 180° interval, the polarity of the Doppler velocity becomes negative, the velocity gradually increases, and the Doppler frequency increases. The negative velocity is the largest at 180°, and then the negative velocity gradually decreases. The negative velocity is zero at 270°, and the corresponding Doppler frequency is zero. Starting from 270°, the velocity polarity becomes positive, the Doppler frequency becomes positive, and gradually increases until the positive velocity is the largest at 360°.

[0020] A further technical solution thereof is to adjust the radar pulse repetition frequency parameter according to the echo amplitude of each phase channel of the acoustic time-domain waveform, including:

[0021] Send the unified clock signal of the radar to the pulse width counter to obtain the width of the transmitted detection pulse, and input the width into the pulse dead time counter. When the echo amplitude does not reach the maximum value, coarsely adjust the pulse dead time counter through the FPGA, thereby changing the repetition frequency parameter of the radar detection pulse to achieve rough PRF search closed-loop tracking; when fine-tuning the frequency is required, connect the numerically controlled delay line chip to the FPGA, and through the picosecond-level control accuracy of the numerically controlled delay line chip, thereby changing the repetition frequency parameter of the radar detection pulse to achieve fine PRF search closed-loop tracking.

[0022] A further technical solution thereof is that if the underwater acoustic wave target is a cooperative target, the method for blind synchronization of space-time before sea surface cruise search further includes:

[0023] Set in advance the search area of the pulsed Doppler radar on the sea surface, and the search area covers the underwater acoustic wave target; and agree in advance that the frequency of the underwater acoustic wave target is the same as the radar wave repetition frequency and the phases are consistent;

[0024] Then the pulsed Doppler radar cruises over the search area in the air by an airborne or unmanned aerial vehicle (UAV) - borne manner, and generates multiple detection pulses to cover the search area during the cruise.

[0025] A further technical solution thereof is that the scanning mode of the pulsed Doppler radar is an electro - mechanical composite scanning. Horizontally, phased array multi - beam is adopted, and longitudinally, a servo system is used for scanning. The operating frequency is 92G - 95G, the bandwidth is 10MHz, the beam scanning range is 90°×90°, vertical polarization is used, the signal processing is eight - channel, the resolution bandwidth of the Doppler filter is 0.6Hz, and the clutter suppression ratio is 50dB.

[0026] A further technical solution thereof is that the coverage angle of the detection pulse is tgα = L / R, where L is the lateral coverage distance of the detection pulse, taking 10000m, R is the vertical distance from the radar to the sea surface, taking 8000m, then α = 32°, and the width of the detection pulse is taken as 2°*2°.

[0027] The beneficial technical effects of the present invention are:

[0028] This application studies the propagation of underwater acoustic signals in the form of pressure waves. When the pressure wave impacts the water-air boundary, it causes slight fluctuations on the water surface. By using the spatio-temporal blind synchronization method of underwater acoustic waves and airborne radar waves, underwater targets can shake hands and communicate with the airborne radar. Then, by demodulating the echo of the slight water surface movement signal and using the demodulated information for cross-media detection, the search and rescue of underwater targets can be realized. The spatio-temporal blind synchronization method lays the foundation for the coherent accumulation of micro-Doppler filtering in the Doppler radar system in a resonant manner for a long time. It controls the pulsed Doppler radar to hover at the center of the slight movement intensity, and during the sampling process, continuously adjusts the radar repetition frequency through closed-loop PRF search to make it the same as the frequency of the underwater acoustic target. Finally, the "spatio-temporal synchronization" of underwater acoustic waves and airborne radar waves is achieved, generating a resonant effect, effectively improving the efficiency of the radar detecting the slight water surface movement caused by underwater acoustic waves, increasing the detection range, and providing technical support for the practical application of cross-media detection. Description of the Drawings

[0029] Figure 1 is a flowchart of the spatio-temporal blind synchronization method provided by this application.

[0030] Figure 2 is the search timing diagram of the eight-phase channel provided by this application.

[0031] Figure 3 is the principle block diagram of the signal processor provided by this application.

[0032] Figure 4 is the principle diagram of the PRF adjustment of the transmitted detection pulse provided by this application.

[0033] Figure 5 is the processing result diagram of the radar detecting the echo of the slight water surface movement signal without using the spatio-temporal blind synchronization algorithm.

[0034] Figure 6 is the processing result diagram of the radar detecting the echo of the slight water surface movement signal using the spatio-temporal blind synchronization algorithm. Detailed Embodiments

[0035] The following further describes the detailed embodiments of the present invention with reference to the drawings.

[0036] As Figure 1 shown, this application provides a spatio-temporal blind synchronization method for underwater acoustic waves and airborne radar waves, including the following steps:

[0037] Step 1: The pulsed Doppler radar conducts a cruise search on the sea surface by generating multiple detection pulses in the air through an airborne or unmanned aerial vehicle (UAV) -borne method.

[0038] Optionally, if the underwater acoustic wave target is a cooperative target, before step 1, the search area of the pulsed Doppler radar on the sea surface is set in advance. The search area covers the underwater acoustic wave target. For example, the search area is controlled within a range of 10Km * 10Km. When it is necessary to expand the search range, several sub-areas are set with the set search area as a unit and searched in turn. It is also necessary to agree in advance that the frequency of the underwater acoustic wave target is the same as the radar wave repetition frequency and the phases are consistent. Then the pulsed Doppler radar cruises over the search area by air-borne or UAV-borne means, and generates multiple detection pulses to cover the search area during cruising.

[0039] Optionally, the scanning mode of the pulsed Doppler radar of the present application is electro-mechanical composite scanning. It uses phased array multi-beams horizontally and a servo system for scanning vertically. The operating frequency is 92G - 95G, the bandwidth is 10MHz, the beam scanning range is 90°×90°, the vertical polarization is used, the signal processing is eight-channel, the resolution bandwidth of the Doppler filter is 0.6Hz, and the clutter suppression ratio is 50dB.

[0040] Optionally, the coverage angle of the detection pulse is tgα = L / R, where L is the horizontal coverage distance of the detection pulse, taking 10000m, and R is the vertical distance from the radar to the sea surface, taking 8000m. Then α = 32°, and the width of the detection pulse is taken as 2°*2°.

[0041] Step 2: When the pulsed Doppler radar receives the surface micro-motion signal echo caused by the underwater acoustic wave target, sample the surface micro-motion signal echo using the repetition frequency search of the radar's multiple phase channels.

[0042] As Figure 2 shown, in the signal processor, a signal processing channel is established every 45 degrees, and a detection pulse A - H is emitted every 45 degrees. Therefore, eight sample points of the surface micro-motion signal echo can be effectively collected within one acoustic vibration period. The eight-phase detection pulses correspond to different parts of the surface micro-motion signal echo, and the radar repetition frequency parameter is finely adjusted through the echo amplitude fed back by each phase channel, so that the radar wave repetition frequency corresponding to the eight sample points is the same as the frequency of the underwater acoustic wave target (i.e., cycle synchronization). When the two are the same, the echo amplitude of the acoustic time-domain waveform corresponding to the eight-phase channel is the largest, and the signal-to-noise ratio of the micro-Doppler coherent accumulation is the largest.

[0043] Step 3: The signal processor of the radar processes the sampled signal according to the different radial velocities of the sea wave clutter and the surface micro-motion signal relative to the detection direction of the pulsed Doppler radar to obtain the acoustic time-domain waveform of the underwater acoustic wave target.

[0044] From the perspective of Doppler radar detection, when a surge quickly crawls to the wave crest, it will stagnate for 1 - 2 seconds, then quickly decline. When it reaches the wave trough, it will stagnate for another 1 - 2 seconds before starting the next cycle. Therefore, sea clutter consists of countless waves, with wave crests and wave troughs. The radial velocity of the wave crests and wave troughs relative to the detection direction of the multi-channel pulsed Doppler radar is zero, and the Doppler frequency is zero, which is the strongest component of sea clutter.

[0045] Different from sea clutter, the water surface micro-motion signal caused by an underwater acoustic target at the water surface is a vibration signal with high-speed periodic changes. The vibration frequency of the water surface micro-motion signal is consistent with the frequency of the underwater acoustic target. The vibration frequency of the underwater target sound source is between 10 Hz and 300 Hz, the sound source level is 140 dB - 160 dB, and the sound source depth is 1 - 5 meters. Facing the detection direction of the multi-channel pulsed Doppler radar, the radial velocity of the water surface micro-motion signal changes periodically at high speed, and the Doppler frequency is not zero.

[0046] Based on the above analysis, the conclusion is drawn that there are substantial differences in the radial velocities of sea clutter and water surface micro-motion signals relative to the detection direction of the pulsed Doppler radar.

[0047] Therefore, based on the above conclusion, the following processing is performed on the sampled signal in the signal processor, as Figure 3 shown. After converting the sampled signal from analog to digital, the digital signal is sequentially subjected to digital down-conversion DDC, Fourier transform FFT, and then stored in the buffer area in partitions according to the order of the transmitted detection pulses. Moving target detection MTD and constant false alarm rate detection CFAR are performed on each partition in turn. After long-time coherent integration, finally, the sea clutter with a Doppler frequency of zero is filtered out from the sampled signal. By increasing the radar transmission frequency and long-time coherent integration, the target Doppler frequency and the radar Doppler resolution are improved, which can ensure the correct identification of underwater acoustic signals and filter out other Doppler interferences, sound source interferences, and strong water surface clutter, etc.

[0048] Present different Doppler frequencies according to different phases of the acoustic wave vibration period. In the range of 0° to 90° of the acoustic wave, the Doppler frequency is positive. The Doppler velocity is the largest at 0°, and the Doppler velocity is zero and the corresponding Doppler frequency is zero at 90°. In the range of 90° to 180°, the polarity of the Doppler velocity becomes negative, the velocity gradually increases, and the Doppler frequency increases. The negative velocity is the largest at 180°, and then the negative velocity gradually decreases. The negative velocity is zero at 270°, and the corresponding Doppler frequency is zero. Starting from 270°, the polarity of the velocity becomes positive, the Doppler frequency becomes positive, and gradually increases until the positive velocity is the largest at 360°. Since the different measured Doppler frequencies and radar detection pulses correspond to the sampling positions of the signal echo respectively, the time-domain waveform of the underwater acoustic wave target is obtained by least squares fitting, and thus the high-resolution Doppler frequency information and echo amplitude information of the underwater acoustic wave target are obtained, where the high-resolution Doppler frequency information includes Doppler frequency and Doppler velocity.

[0049] Step 4: With the detection pulse corresponding to the maximum echo amplitude of the time-domain waveform of the acoustic wave during the cruise scan as the center, control the pulsed Doppler radar to hover at the intensity center to achieve the spatial synchronization of the underwater acoustic wave target and the airborne radar wave.

[0050] At the same time, adjust the radar PRF parameter according to the echo amplitude of each phase channel of the time-domain waveform of the acoustic wave until the echo amplitude is the largest, determine the synchronization of the time-domain waveform of the acoustic wave and the radar detection pulse, and generate a resonance phenomenon to achieve the time synchronization of the underwater acoustic wave target and the airborne radar wave. This application utilizes the high time-base accuracy of the pulsed Doppler radar to accurately achieve underwater and airborne time synchronization. The spatial synchronization is achieved by the signal processor controlling the beam scanning to make the beam track the strongest area of the acoustic wave.

[0051] As Figure 4 shown, adjusting the radar PRF parameter according to the echo amplitude specifically includes:

[0052] Send the unified clock signal of the radar to the pulse width counter to obtain the width of the transmitted detection pulse, and input this width to the pulse cut-off period counter. When the echo amplitude has not reached the maximum value, roughly adjust the pulse cut-off period counter through the FPGA, thereby changing the repetition frequency parameter of the radar detection pulse to achieve rough PRF search closed-loop tracking. When fine frequency adjustment is required, connect the numerically controlled delay line chip to the FPGA, and through the picosecond-level control accuracy of the numerically controlled delay line chip, change the repetition frequency parameter of the radar detection pulse to achieve fine PRF search closed-loop tracking.

[0053] It should be noted that if the underwater acoustic wave target is a non-cooperative target, then according to the above PRF search process of the radar, the repetition frequency of the radar wave is closed-loop adjusted to be the same as the frequency of the underwater acoustic wave target and the phases are consistent. Combining Figure 5 、 Figure 6As shown in the figure, when the radar detects the surface micro-motion signal without the time-space blind synchronization algorithm, the echo signal is submerged in the noise and the surface micro-motion signal cannot be distinguished; after the echo signal collected by the pulse Doppler radar with the time-space blind synchronization algorithm is processed, the radar detection pulse is synchronized with the surface micro-motion signal, resulting in a resonance phenomenon, indicating that the underwater acoustic target has successfully shaken hands with the aerial radar, and information can be transmitted through frequency coding subsequently, realizing the search and rescue of underwater targets by surface and aerial reconnaissance means.

[0054] The above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be determined to be included in the protection scope of the present invention.

Claims

1. An underwater acoustic wave and airborne radar wave spatio-temporal blind synchronization method, characterized in that, The described spatio-temporal blind synchronization method includes: The pulsed Doppler radar generates multiple detection pulses in the air by airborne or unmanned aerial vehicle (UAV) - borne means to conduct a cruise search over the sea surface; When the pulsed Doppler radar receives the surface micro - motion signal echo caused by the underwater acoustic target, it samples the surface micro - motion signal echo using the repetition frequency search of the radar's multiple phase channels; The signal processor of the radar processes the sampled signal according to the different radial velocities of the sea clutter and the surface micro - motion signal relative to the detection direction of the pulsed Doppler radar to obtain the acoustic time - domain waveform of the underwater acoustic target; Centering on the detection pulse corresponding to the maximum echo amplitude of the acoustic time - domain waveform during the cruise scan, the pulsed Doppler radar is controlled to hover at the center to achieve the spatial synchronization of the underwater acoustic target and the airborne radar wave; The radar repetition frequency parameter is adjusted according to the echo amplitude of each phase channel of the acoustic time - domain waveform until the maximum echo amplitude is determined, at which time the acoustic time - domain waveform is synchronized with the radar detection pulse and a resonance phenomenon occurs, achieving the time synchronization of the underwater acoustic target and the airborne radar wave.

2. The spatio-temporal blind synchronization method according to claim 1, wherein The signal processor of the radar processes the sampled signal according to the different radial velocities of the sea clutter and the surface micro - motion signal relative to the detection direction of the pulsed Doppler radar, including: The sea clutter consists of countless sea waves with crests and troughs. The radial velocities of the crests and troughs relative to the detection direction of the pulsed Doppler radar are zero, and the Doppler frequencies are zero; The surface micro - motion signal caused by the underwater acoustic target at the water surface is a high - speed periodically varying vibration signal. The vibration frequency of the surface micro - motion signal is consistent with the frequency of the underwater acoustic target. The vibration frequency of the underwater acoustic target is in the range of 10 Hz - 300 Hz, the source level is 140 dB - 160 dB, the source depth is 1 - 5 meters, facing the detection direction of the pulsed Doppler radar. The radial velocity of the surface micro - motion signal changes periodically at a high speed and the Doppler frequency is non - zero.

3. The spatio-temporal blind synchronization method according to claim 2, wherein The processing of the sampled signal to obtain the acoustic time - domain waveform of the underwater acoustic target includes: In the signal processor, after converting the sampled signal from analog to digital, the digital signal is successively subjected to digital down - conversion, Fourier transform, and then stored in the buffer area in partitions according to the order of the transmitted detection pulses. Moving target detection and constant false alarm detection are performed on each partition in turn. After long - time coherent integration, finally, the sea clutter with zero Doppler frequency is filtered out from the sampled signal. The measured different Doppler frequencies and radar detection pulses correspond to the sampling positions of the signal echo respectively. Therefore, the acoustic time - domain waveform of the underwater acoustic target is obtained by least - squares fitting, thereby obtaining the high - resolution Doppler frequency information and echo amplitude information of the underwater acoustic target.

4. The spatio-temporal blind synchronization method according to claim 3, characterized in that, The sampling of the surface micro - motion signal echo using the repetition frequency search of the radar's multiple phase channels includes: In the signal processor, a signal processing channel is established every 45 degrees, and a detection pulse is emitted every 45 degrees. Eight sample points of the echo of the water surface micro-motion signal are effectively collected within one acoustic wave vibration cycle. The eight-phase detection pulses correspond to different parts of the echo of the water surface micro-motion signal, and the radar PRF parameter is finely adjusted through the echo amplitude fed back by each phase channel, so that the radar wave repetition frequency corresponding to the eight sample points is the same as the frequency of the underwater acoustic target. When they are the same, the echo amplitude of the acoustic wave time-domain waveform corresponding to the eight-phase channel is the largest, and the signal-to-noise ratio of the micro-Doppler coherent accumulation is the largest.

5. The spatio-temporal blind synchronization method according to claim 3, wherein The high-resolution Doppler frequency information of the underwater acoustic target includes Doppler frequency and Doppler velocity, which presents different Doppler frequencies according to different phases of the acoustic wave vibration cycle. The Doppler frequency is positive in the range of 0° to 90° of the acoustic wave. The Doppler velocity is the largest at 0°, and the Doppler velocity is zero and the corresponding Doppler frequency is zero at 90°. In the range of 90° to 180°, the polarity of the Doppler velocity becomes negative, the velocity gradually increases, and the Doppler frequency increases. The negative velocity is the largest at 180°, and then the negative velocity gradually decreases. The negative velocity is zero at 270°, and the corresponding Doppler frequency is zero. Starting from 270°, the velocity polarity becomes positive, the Doppler frequency becomes positive, and gradually increases until the positive velocity is the largest at 360°.

6. The spatio-temporal blind synchronization method according to claim 1, wherein The adjustment of the radar PRF parameter according to the echo amplitude of each phase channel of the acoustic wave time-domain waveform includes: Sending the unified clock signal of the radar to the pulse width counter to obtain the width of the emitted detection pulse, and inputting the width into the pulse off-period counter. When the echo amplitude does not reach the maximum value, the pulse off-period counter is roughly adjusted through the FPGA, so as to change the repetition frequency parameter of the radar detection pulse and realize the closed-loop tracking of the rough PRF search. When fine frequency adjustment is required, the digital controlled delay line chip is connected to the FPGA, and through the picosecond-level control accuracy of the digital controlled delay line chip, the repetition frequency parameter of the radar detection pulse is changed, so as to realize the closed-loop tracking of the fine PRF search.

7. The spatio-temporal blind synchronization method according to claim 1, wherein If the underwater acoustic target is a cooperative target, then before the sea surface cruise search, the space-time blind synchronization method further includes: Pre-setting the search area of the pulse Doppler radar on the sea surface, and the search area covers the underwater acoustic target; and pre-agreeing that the frequency of the underwater acoustic target is the same as the radar wave repetition frequency and the phases are consistent; Then the pulse Doppler radar cruises over the search area in the air by an airborne or unmanned aerial vehicle (UAV) -borne method, and generates multiple detection pulses to cover the search area during the cruise.

8. The spatio-temporal blind synchronization method according to any one of claims 1-7, characterized in that The scanning mode of the pulse Doppler radar is an electro-mechanical composite scanning. Horizontally, it uses a phased array multi-beam, and vertically, it uses a servo system for scanning. The operating frequency is 92G - 95G, the bandwidth is 10MHz, the beam scanning range is 90°×90°, the vertical polarization is used, the signal processing is eight-channel, the resolution bandwidth of the Doppler filter is 0.6Hz, and the clutter suppression ratio is 50dB.

9. The spatio-temporal blind synchronization method according to any one of claims 1-7, characterized in that, The coverage angle of the detection pulse is tgα = L / R, where L is the lateral coverage distance of the detection pulse, taken as 10,000 m, and R is the vertical distance from the radar to the sea surface, taken as 8,000 m. Then α = 32°, and the width of the detection pulse is taken as 2° * 2°.

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