CN115792995A - Target detection system and method based on satellite-borne GNSS-S - Google Patents
Target detection system and method based on satellite-borne GNSS-S Download PDFInfo
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Abstract
The invention relates to a target detection system and a method based on satellite-borne GNSS-S, comprising the following steps: the system comprises an opposite GNSS direct signal processing unit, a satellite-to-satellite GNSS direct signal processing unit and a satellite-to-satellite GNSS direct signal processing unit, wherein the opposite GNSS direct signal processing unit is used for receiving a direct signal of a navigation satellite, outputting platform parameter information of the opposite GNSS direct signal processing unit and outputting corresponding navigation satellite information according to the direct signal, and the navigation satellite information comprises telegraph text bit information; the sea GNSS scattered signal processing unit is used for receiving scattered signals of the direct signals passing through a sea surface target area and determining information of the target area; the direct-scattered signal synchronous conversion unit is used for determining time synchronization information required by time synchronization between a direct signal and a scattered signal, a reference signal required by distance direction compression and a phase compensation factor required by azimuth coherent accumulation according to the navigation satellite information and the platform parameter information and outputting the time synchronization information, the reference signal and the phase compensation factor to the sea GNSS scattered signal processing unit; the sea GNSS scattered signal processing unit determines information of a target area according to output information of the direct scattered signal synchronous conversion unit. The signal-to-noise ratio of the target echo signal can be effectively improved.
Description
Technical Field
The invention relates to the technical field of radars, in particular to a target detection system and method based on satellite-borne GNSS-S.
Background
The GNSS-S target detection system detects the sea surface target by utilizing the signal of the GNSS navigation satellite scattered by the sea surface, and has the advantages of abundant signal sources, all-time and all-weather detection, radio silence and radar stealth resistance, low load power consumption, easy low-orbit satellite carrying and the like. The technology can be complemented with electronic reconnaissance, radar, optical reconnaissance and other means, improves the sensing capability of the battlefield of our army, and is an important means for marine reconnaissance and monitoring. In recent years, the development of sea surface target detection based on GNSS-S signals becomes a hot point of scientific research.
However, the GNSS navigation satellite has a high height above the ground, the signal emission power is small, the signal power reaching the ground is usually about-130 dBm, and the scattered satellite signal is weaker, so that the satellite-borne GNSS-S target detection system has high difficulty in realizing sea surface target detection. In order to realize the detection of the extremely weak GNSS-S signal, the signal needs to be accumulated for a long time, however, the length of the integration time is limited by the random inversion of navigation message bits and the signal frequency shift, so that the accumulation time in the azimuth coherent processing process cannot exceed the length of the message bits.
Disclosure of Invention
In view of this, embodiments of the present invention provide a target detection system and method based on a satellite-borne GNSS-S, which break through the limitation of random inversion of a text bit during processing of a target echo signal, and can implement long-term coherent accumulation processing.
In a first aspect, a first embodiment of the present invention provides a target detection system based on an on-board GNSS-S, where the system includes: the system comprises a sky GNSS direct signal processing unit, a navigation satellite system and a satellite navigation system, wherein the sky GNSS direct signal processing unit is used for receiving a direct signal of a navigation satellite, outputting platform parameter information of the sky GNSS direct signal and outputting corresponding navigation satellite information according to the direct signal, and the navigation satellite information comprises telegraph text bit information; the sea GNSS scattered signal processing unit is used for receiving scattered signals of the direct signals passing through a sea surface target area and determining information of the target area; the direct-scattered signal synchronous conversion unit is used for determining time synchronization information required by time synchronization between the direct signal and the scattered signal, a reference signal required by range-direction compression and a phase compensation factor required by azimuth coherent accumulation according to the navigation satellite information and the platform parameter information and outputting the time synchronization information, the reference signal required by range-direction compression and the phase compensation factor to the sea-to-sea GNSS scattered signal processing unit; and the sea-to-sea GNSS scattered signal processing unit determines the information of a target area according to the output information of the scattered signal synchronous conversion unit.
Further, the pair of sky GNSS receiving units includes: the sky GNSS receiver is used for receiving the direct signal; the time information output module is used for outputting time synchronization information to the scattered signal synchronization conversion unit; the GNSS satellite information output module is used for outputting the navigation satellite information according to the direct signal; and the platform information module is used for outputting the platform parameter information.
Further, the sea GNSS scattering reception unit includes: a radar antenna for receiving the scattered signal; the scattering signal preprocessing module is used for amplifying, filtering and down-converting the scattering signal and converting the scattering signal into an analog intermediate frequency signal; the digital sampling module is used for carrying out digital sampling on the analog intermediate frequency signal; the distance direction matched filtering module is used for performing matched filtering and compression processing on the sampling signal output by the digital sampling module; the phase compensation module is used for carrying out phase correction on the output signal of the distance direction matched filtering module; the azimuth accumulation module is used for carrying out azimuth accumulation on the output signal of the phase compensation module; and the target information module is used for determining the information of the sea surface target area according to the accumulation result output by the azimuth accumulation module.
Further, the scattered signal synchronous conversion unit includes: the synchronous signal generating module is used for receiving the time synchronous information of the time information output module, converting the time synchronous information into the control information of the digital sampling module and outputting the control information to the digital sampling module; the reference signal generating module is used for receiving the output information of the GNSS satellite information output module, generating a reference signal matched and filtered with the scattering signal and outputting the reference signal to the distance direction matched and filtered module; and the phase compensation factor calculation module is used for receiving the output information of the GNSS satellite information output module and the satellite platform information module, calculating a phase compensation factor during azimuth accumulation and outputting the phase compensation factor to the phase compensation module.
Further, the platform parameter information includes position coordinates and speed information of a platform where the sky-to-sky GNSS direct signal processing unit is located, the platform is a low-orbit satellite platform, and the system shares a GNSS receiving unit on the low-orbit satellite platform as the sky-to-sky GNSS direct signal processing unit; the navigation satellite information also includes pseudo code, doppler shift, and code phase information.
In a second aspect, a second embodiment of the present invention provides a method for detecting a target based on an on-board GNSS-S, which is applied to the system for detecting a target based on an on-board GNSS-S according to any one of the first aspect, and the method includes: according to the reference signal, performing range compression on the scattering signal; synchronously sampling the scattering signals according to the time synchronization information; according to the phase compensation factor, performing azimuth coherent processing on the scattering signals after range direction compression and synchronous sampling; and determining the information of the sea surface target area according to the scattering signals subjected to distance direction compression, synchronous sampling and azimuth direction coherent processing.
Further, performing range-wise compression on the scattered signals, comprising: and acquiring the reference signal from the direct scattering signal synchronous conversion unit, carrying out carrier frequency mixing and pseudo code operation on the scattering signal to obtain a one-dimensional accumulated value of the scattering signal, and carrying out range compression on the scattering signal according to the one-dimensional accumulated value.
Further, synchronously sampling the scattered signal comprises: and taking the pulse-per-second signal of the direct signal as a trigger signal of digital sampling of the scattered signal, selecting a 1ms time length acquisition data packet, adding the time information of the navigation satellite to the acquired data packet, adding a timestamp, and synchronously sampling the scattered signal.
Further, the azimuth coherent processing is performed on the scattering signals after the distance direction compression and synchronous sampling, and the azimuth coherent processing includes: calculating the time delay deltat of the scattering signal and the direct signal for a target area i According to Δ t i Calculating the phase difference delta xi caused by the path i B is the textual bit information of the direct signal, and the phase correction factor Delta theta of the target area i Comprises the following steps:
Δθ i ＝Δξ i +bπ；
the formula of the azimuth coherent processing is as follows:
and qi is echo energy information of the sea surface target area obtained on the ith square point.
And further, according to the telegraph text bit information in the direct signal, carrying out phase correction on the telegraph text bit information at the telegraph text bit overturning moment to obtain a phase compensation factor at the corresponding moment.
According to the target detection system and method based on the satellite-borne GNSS-S, a GNSS receiver of a low-earth orbit satellite platform and a direct signal receiver required by GNSS-S target detection are shared, the GNSS receiver of the satellite platform provides positioning information for a satellite, and also outputs signal characteristic information of Doppler, code phase, telegraph bit and the like of the direct satellite signal, additional transmitting equipment is not needed, the system is simple, and the GNSS-S load and the satellite platform are deeply fused, so that system redundancy is reduced, structure complexity is reduced, and system cost is reduced. The embodiment of the invention also provides a direct and scattered signal synchronous conversion unit which is used for converting the direct and scattered signal into a local reference signal required by radar detection according to the characteristic information of the direct navigation satellite signal output by the low-earth orbit satellite platform GNSS receiver and synchronizing the second pulse signal with the GNSS target scattered signal. The embodiment also provides an echo signal long-time coherent accumulation method for eliminating the influence of random turning of GNSS telegraph text bits, solves the technical problem that the accumulation time cannot exceed the length of the telegraph text bits in the azimuth coherent processing process, realizes the coherent processing time of the second level, and improves the signal-to-noise ratio.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a target detection system based on an on-board GNSS-S according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a synchronization signal generation module according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a reference signal generating module according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a phase compensation factor calculation module according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of the distance direction signal compression of an embodiment of the present invention;
FIG. 6 is a timing diagram of synchronous sampling of scattered signals according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a direct scattering signal geometry according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of the principle of azimuthal coherent accumulation for an embodiment of the present invention;
FIG. 9 is a schematic diagram illustrating the calculation of phase correction factors according to an embodiment of the present invention;
FIG. 10 is a diagram of a target area detection matrix according to an embodiment of the present invention.
Detailed Description
The description of the embodiments of this specification should be taken in conjunction with the accompanying drawings, which are to be considered part of the entire written description. In the drawings, the shape or thickness of the embodiments may be exaggerated and simplified or conveniently indicated. Further, the components of the structures in the drawings are described separately, and it should be noted that the components not shown or described in the drawings are in a form known to those skilled in the art.
Any reference to directions and orientations in the description of the embodiments herein is merely for convenience of description and should not be construed as limiting the scope of the present invention in any way. The following description of the preferred embodiments refers to combinations of features which may be present independently or in combination, and the present invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.
Fig. 1 is a schematic structural diagram of a target detection system based on a satellite-borne GNSS-S according to a first embodiment of the present invention, where the system includes: and the opposite-to-sky GNSS direct signal processing unit 10 is used for receiving a direct signal of a navigation satellite, outputting platform parameter information of the opposite-to-sky GNSS direct signal, and outputting corresponding navigation satellite information according to the direct signal, wherein the navigation satellite information comprises telegraph text bit information. And the sea-to-sea GNSS scattered signal processing unit 20 is used for receiving the scattered signals of the direct signals passing through the sea surface target area and determining the information of the target area. And the direct scattering signal synchronous conversion unit 30 is configured to determine time synchronization information required for time synchronization between the direct signal and the scattering signal, a reference signal required for range-direction compression, and a phase compensation factor required for azimuth coherent accumulation according to the navigation satellite information and the platform parameter information, and output the phase compensation factor to the sea GNSS scattering signal processing unit 20. The sea-to-sea GNSS scattered signal processing unit 20 determines information of the target area according to the output information of the direct scattered signal synchronous conversion unit.
The platform parameter information includes position coordinates and speed information of a platform where the inter-sky GNSS direct signal processing unit 10 is located, the platform is a low-earth satellite platform, and the system shares a GNSS receiving unit on the low-earth satellite platform as the inter-sky GNSS direct signal processing unit 10. The navigation satellite information also includes pseudo code, doppler shift, and code phase information.
As shown in fig. 1, in the present embodiment, the GNSS receiver unit includes: an opposite-sky GNSS receiver 101 for receiving a direct signal; a time information output module 102, configured to output time synchronization information to the scattered signal synchronization conversion unit 30, where the time synchronization information includes a pulse per second signal and absolute time information of a navigation satellite direct signal; the GNSS satellite information output module 103 is configured to output navigation satellite information according to the direct signal; and a platform information module 104 for outputting platform parameter information, such as position (X, Y, Z) coordinates and velocity (Vx, vy, vz) of the satellite platform.
As shown in fig. 1, in the present embodiment, the sea-to-sea GNSS scattering signal processing unit 20 includes: a radar antenna 201 for receiving the scattered signal, wherein the radar antenna 201 is preferably a large-aperture high-gain antenna; the scattering signal preprocessing module 202 is configured to amplify, filter, and downconvert the scattering signal, and convert the scattering signal into an analog intermediate frequency signal; the digital sampling module 203 is used for performing digital sampling on the analog intermediate frequency signal under the control of the synchronous signal generating module 301; the distance direction matched filtering module 204 is used for performing matched filtering and compression processing on the sampling signal output by the digital sampling module 203 under the control of the reference signal generating module 302; a phase compensation module 205, configured to perform phase correction on the output signal of the distance direction matched filter module 204 under the control of the phase compensation factor calculation module 303; an azimuth accumulation module 206, configured to perform azimuth accumulation on the output signal of the phase compensation module 205; and an object information module 207 for determining information of the sea surface object region according to the accumulation result output from the azimuth accumulation module 206.
As shown in fig. 1, in the present embodiment, the direct dispersion signal synchronous conversion unit 30 includes: a synchronization signal generating module 301, configured to receive the time synchronization information from the time information output module 102, convert the time synchronization information into control information of the digital sampling module 203, and output the control information to the digital sampling module 203; a reference signal generating module 302, configured to receive the output information of the GNSS satellite information output module 103, generate a reference signal matched and filtered with the scattered signal, and output the reference signal to the distance direction matched and filtered module 204; the phase compensation factor calculation module 303 is configured to receive the output information of the GNSS satellite information output module 103 and the satellite platform information module 104, calculate a phase compensation factor during azimuth accumulation, and output the phase compensation factor to the phase compensation module 205.
As shown in fig. 2, in the present embodiment, the synchronization signal generation module 301 inputs a PPS (pulse per second) signal of a direct navigation signal and GNSS time (e.g., GPS week, intra-week second), converts the PPS signal into a trigger signal output of AD (digital) sampling, and converts the GNSS time into time stamp information to be added to data of the AD sampling.
As shown in fig. 3, in the present embodiment, the input signal of the reference signal generating module 302 includes: satellite system information (e.g., GPS, beidou), PRN number of the current visible satellite, satellite doppler, satellite code phase, carrier location information. And calculating the delay time of the target area, and generating local reference signals of all visible satellites required for matched filtering.
As shown in fig. 4, in the present embodiment, the input signal of the phase compensation factor calculation module 303 includes: PRN number of the current visible satellite, navigation satellite position, satellite platform position, target area coordinate and navigation message bit information. And calculating the delay time and navigation message information of the target area, and outputting the phase compensation factor of each coordinate point.
According to the target detection system based on the satellite-borne GNSS-S, the GNSS receiver sharing the satellite platform receives the sky signal, the large gain antenna is adopted to receive the GNSS signal scattered by the sea surface target, the working frequency band of the antenna is the navigation satellite frequency band (such as 1.575GHz and 1.268 GHz), the sea antenna receives the GNSS signal scattered by the sea surface, and the GNSS signal is amplified, filtered, subjected to down-conversion mixing processing and converted into the intermediate frequency signal to be output. And a DSC unit is adopted to realize the synchronization of the direct signal and the scattered signal and the conversion processing of information. A matching filter for performing pulse compression of a scattered GNSS signal and phase correction information of azimuth coherent are generated by a DSC unit. Distance direction compression and azimuth direction coherence of extremely weak GNSS scattering signals are achieved on a low-earth-orbit satellite platform, signal to noise ratio is improved, a scattering energy matrix diagram of a large-range sea surface target is obtained, and detection of the sea surface target is achieved. Compared with a traditional satellite-borne radar system, the system does not need to emit signals, utilizes ubiquitous GNSS signals to realize sea surface target detection, simultaneously reuses the existing GNSS receiver of a satellite platform, is simple in system architecture and low in cost, is convenient to realize low-orbit small satellite networking application, and realizes global-range passive detection of sea surface targets.
As shown in fig. 5 to 10, a second embodiment of the present invention further provides a target detection method based on a satellite-borne GNSS-S, which applies the target detection system based on a satellite-borne GNSS-S according to the first embodiment to realize sea surface target detection, and improves the signal-to-noise ratio of the target scattered GNSS signals by adopting distance direction compression and azimuth direction coherence to the sea surface extremely weak GNSS-S scattered signals. The embodiment comprises the steps of generating a local reference signal by using information such as satellite Doppler, code phase and the like obtained by a sky GNSS receiver 101, and performing range compression on a scattered signal; meanwhile, PPS synchronous signals are provided for the sky GNSS receiver, synchronous sampling is carried out on the scattered signals, and the message turning of the scattered signals is predicted according to navigation message bit information provided for the sky GNSS receiver, so that the problem of message random turning when the extremely weak scattered signals are subjected to azimuth coherent is solved, azimuth coherent accumulation processing across bit lengths is realized, and the signal-to-noise ratio of the sea surface target scattered signals is improved.
As shown in fig. 5, in the present embodiment, the process of compressing the distance of the GNSS-S target scattering signal includes:
a1, selecting a visible navigation satellite;
a2, acquiring a local reference signal from a DSC unit (a scattered signal synchronous conversion unit);
a3, carrying out carrier frequency mixing on the signals obtained in the a 2;
a4, performing pseudo code correlation operation on the signals obtained in the a 3;
and a5, obtaining a one-dimensional accumulated value of the signal according to the calculation result of the a 4.
As shown in fig. 6, in the present embodiment, the flow of the synchronous sampling timing of the scattering signal is as follows: receiving a navigation satellite PPS signal of a DSC unit as a trigger signal of sampling of a scattered signal ADC (digital), selecting 1ms to collect a packet of data, and adding the time of the navigation satellite to the packet of data to be stamped to be used as original data of subsequent signal processing. Taking PPS of a direct satellite signal as a synchronous signal, starting data acquisition by each pulse, and adding timestamp information to the acquired data according to GNSS time; performing range-direction pulse compression on a GNSS signal which is received by a sea scattering receiving system and scattered by the sea surface and a local reference signal generated by a DSC unit; and the DSC unit receives the telegraph text bit information directly reaching the navigation satellite, corrects the signal phase at the telegraph text bit overturning moment and increases the accumulated gain when carrying out azimuth coherent accumulation processing.
As shown in fig. 7, in the present embodiment, the propagation time delay of the direct signal and the scattered signal is calculated by the following method: receiving a navigation satellite of a DSC unitSatellite PRN number, doppler shift fd i Code phase c i And the coordinates of the navigation satellite are (X) s ，Y s ，Z s ) Position coordinates (X) of the satellite platform u ，Y u ，Z u ) The coordinates of the target search area are (X) d ，Y d ，Z d ) And calculating the direct signal propagation distance d according to the geometric relation as follows:
the scattering signal propagation distance D is:
the propagation delay time Δ t of the scattered signal and the direct signal is shown as follows:
wherein c is the speed of light of 3 x 108m/s;
and the formula of the matched filter for obtaining the scattering signal by the above formula is as follows:
s(t)＝A D(t+Δt)C(t+Δt)cos[2π(f+f d )(t+Δt)]；
wherein, A is signal amplitude, D () is telegraph text data, C () is navigation pseudo code sequence, f is signal carrier frequency.
As shown in fig. 8, in the present embodiment, the phase correction factor is calculated by the following method: calculating the time delay delta t of the scattering signal and the direct signal for the target detection area i A phase difference Δ ξ caused by the delay time calculation path i Then the phase correction factor Δ θ of the detection area i Comprises the following steps:
Δθ i ＝Δξ i +bπ；
wherein b is the telegraph text bit information (the value of b is 0 or 1) of the navigation satellite direct signal received by the DSC unit, and the phase is corrected according to the telegraph text bit.
The DSC unit outputs digital text bit information by adopting a serial port; the message bit information is synchronous with the PPS pulse time, and a group of message bit information is output at 1 PPS pulse interval; the azimuth coherent processing time is t milliseconds, and t is far longer than the telegraph text bit time (for example, the GPS bit duration is 20 ms).
As shown in fig. 9, in the present embodiment, the azimuth coherence is accumulated by the following method: after distance compression and time synchronous sampling, echo energy information q of a group of target areas is obtained at each square position point i Along with the flight of the low orbit satellite, a series of target point echoes are obtained in the azimuth direction, as the GNSS-S echo energy is very weak, the echo energy in the azimuth direction needs to be further accumulated for realizing target detection, and in order to eliminate the influence of telegraph text bits and range migration, the phase correction is carried out on azimuth direction coherent signals, and the accumulation formula after correction is as follows:
wherein, delta theta i Is a phase correction factor.
The DSC unit calculates the time delay td of the ground echo region according to the position of the low-orbit satellite, the position of the navigation satellite and the position of the target region, and generates a local signal; and calculating a local carrier and a code phase according to the echo time delay td and the code phase and Doppler information of the direct satellite signal, and generating a local reference signal of matched filtering according to the pseudo code of the navigation satellite.
As shown in fig. 10, in this embodiment, a target region is scanned point by point to obtain an echo energy matrix map of the target region, and when there is a target, the echo energy at the target region is greater than background noise, and target detection can be achieved through the map.
The target detection method based on the satellite-borne GNSS-S utilizes navigation information received by a satellite platform to generate a local reference signal, performs distance direction compression processing on a scattered navigation signal received by a sea scattering receiving antenna, and generates phase information of azimuth direction coherent processing by combining navigation message bit information to realize long-time azimuth direction coherent processing of the length of an ultra-message bit. The GNSS receiver of the low-earth-orbit satellite platform is shared with a direct signal receiver required by GNSS-S target detection, and the GNSS receiver of the satellite platform provides positioning information for a satellite and also outputs signal characteristic information such as Doppler, code phase, telegraph text bit and the like of direct satellite signals. The invention provides a DSC unit which is used for converting a characteristic information of a direct navigation satellite signal output by a GNSS receiver of a low earth orbit satellite platform into a local signal required by radar detection and synchronizing a PPS pulse signal and a GNSS target scattering signal. The invention provides a long-time coherent accumulation method for echo signals, which is used for eliminating the random overturning influence of GNSS telegraph text bits. The technical problem that the accumulated time cannot exceed the bit length of the telegraph text in the azimuth coherent processing process is solved, the second-level coherent processing time is realized, and the signal-to-noise ratio is improved. Compared with the prior art, the invention has the following advantages: the target is detected by adopting the signals transmitted by the navigation satellite, the global coverage of the navigation satellite signals is realized, no additional transmitting equipment is needed, and the system is simple; the satellite-borne GNSS-S target detection system shares a GNSS receiver of a low-orbit satellite platform with a direct processing receiver, and the GNSS-S load and the satellite platform are deeply fused, so that system redundancy is reduced, structure complexity is reduced, and system cost is reduced; the processing of the target echo signal breaks through the limit of random turning of the telegraph text bit, can realize long-time coherent accumulation processing, and has high signal-to-noise ratio.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. An on-board GNSS-S based target detection system, comprising:
the system comprises an opposite GNSS direct signal processing unit (10) for receiving a direct signal of a navigation satellite, outputting platform parameter information of the opposite GNSS direct signal and outputting corresponding navigation satellite information according to the direct signal, wherein the navigation satellite information comprises telegraph text bit information;
the sea GNSS scattered signal processing unit (20) is used for receiving scattered signals of the direct signals passing through a sea surface target area and determining information of the target area;
the direct-scattered signal synchronous conversion unit (30) is used for determining time synchronization information required by time synchronization between the direct signal and the scattered signal, a reference signal required by range-direction compression and a phase compensation factor required by azimuth coherent accumulation according to the navigation satellite information and the platform parameter information and outputting the time synchronization information, the reference signal and the phase compensation factor to the sea GNSS scattered signal processing unit (20);
the sea-to-sea GNSS scattered signal processing unit (20) determines information of a target area according to the output information of the scattered signal synchronous conversion unit.
2. The on-board GNSS-S based target detection system of claim 1, wherein the sky-to-GNSS receiving unit comprises:
-a sky GNSS receiver (101) for receiving the direct signal;
a time information output module (102) for outputting time synchronization information to the scattered signal synchronization conversion unit (30);
the GNSS satellite information output module (103) is used for outputting the navigation satellite information according to the direct signal;
a platform information module (104) for outputting the platform parameter information.
3. The satellite-based GNSS-S target detection system of claim 2, wherein the sea-to-sea GNSS scattered signal processing unit (20) comprises:
a radar antenna (201) for receiving the scattered signal;
the scattering signal preprocessing module (202) is used for amplifying, filtering and down-converting the scattering signal and converting the scattering signal into an analog intermediate frequency signal;
a digital sampling module (203) for digitally sampling the analog intermediate frequency signal;
the distance direction matched filtering module (204) is used for carrying out matched filtering and compression processing on the sampling signal output by the digital sampling module (203);
a phase compensation module (205) for phase correcting the output signal of the distance to matched filter module (204);
an azimuth accumulation module (206) for performing azimuth accumulation on the output signal of the phase compensation module (205);
and the target information module (207) is used for determining the information of the sea surface target area according to the accumulation result output by the azimuth accumulation module (206).
4. The satellite-based GNSS-S target detection system according to claim 3, wherein the direct-scattered signal synchronous conversion unit (30) comprises:
a synchronization signal generating module (301) for receiving the time synchronization information of the time information output module (102), converting the time synchronization information into the control information of the digital sampling module (203), and outputting the control information to the digital sampling module (203);
a reference signal generating module (302) for receiving the output information of the GNSS satellite information output module (103), generating a reference signal matched and filtered with the scattered signal and outputting the reference signal to the distance matching and filtering module (204);
and the phase compensation factor calculation module (303) is used for receiving the output information of the GNSS satellite information output module (103) and the satellite platform information module (104), calculating a phase compensation factor during azimuth accumulation and outputting the phase compensation factor to the phase compensation module (205).
5. The on-board GNSS-S based target detection system according to any of the claims 1-4, wherein the platform parameter information comprises position coordinates and velocity information of the platform where the on-day GNSS direct signal processing unit (10) is located, the platform is a low-orbit satellite platform, the system shares a GNSS receiving unit on the low-orbit satellite platform as the on-day GNSS direct signal processing unit (10);
the navigation satellite information also includes pseudo-code, doppler shift, and code phase information.
6. An on-board GNSS-S based target detection method applying the on-board GNSS-S based target detection system according to any one of claims 1 to 5, the method comprising:
according to the reference signal, performing range compression on the scattering signal;
according to the time synchronization information, synchronously sampling the scattering signals;
according to the phase compensation factor, carrying out azimuth coherent processing on the scattering signal after distance direction compression and synchronous sampling;
and determining the information of the sea surface target area according to the scattering signals after the distance direction compression, the synchronous sampling and the azimuth direction coherent processing.
7. The method as claimed in claim 6, wherein the step of performing range-wise compression on the scattered signals comprises:
and acquiring the reference signal from the direct scattering signal synchronous conversion unit (30), carrying out carrier frequency mixing and pseudo code operation on the scattering signal to obtain a one-dimensional accumulated value of the scattering signal, and carrying out distance compression on the scattering signal according to the one-dimensional accumulated value.
8. The method for target detection based on GNSS-S on board a satellite according to claim 6, wherein the synchronous sampling of the scattered signals comprises:
and taking the pulse-per-second signal of the direct signal as a trigger signal of digital sampling of the scattered signal, selecting a 1ms time length acquisition data packet, adding the time information of the navigation satellite to the acquired data packet, adding a timestamp, and synchronously sampling the scattered signal.
9. The method for target detection based on the GNSS-S on board the satellite according to any of the claims 6 to 8, wherein the performing the azimuth coherent processing on the scattering signals after the range direction compression and synchronous sampling comprises:
calculating the time delay deltat of the scattering signal and the direct signal for a target area i According to Δ t i Calculating the phase difference delta xi caused by the path i B is the textual bit information of the direct signal, and the phase correction factor Delta theta of the target area i Comprises the following steps:
Δθ i ＝Δξ i +bπ；
the formula of the azimuth coherent processing is as follows:
wherein q is i And obtaining echo energy information of the sea surface target area on the ith azimuth point.
10. The method as claimed in claim 9, wherein the phase of the message bit information is corrected at a message bit flipping time according to the message bit information in the direct signal, so as to obtain a phase compensation factor at the corresponding time.
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| CN114488132A (en) * | 2022-02-22 | 2022-05-13 | 北京卫星信息工程研究所 | Target detection method of satellite-borne GNSS-S radar |
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| CN114637004A (en) * | 2022-03-14 | 2022-06-17 | 北京卫星信息工程研究所 | Satellite-borne GNSS-S multi-station radar on-orbit processing and ship information fusion system and method |
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| FR2972806A1 (en) * | 2011-03-16 | 2012-09-21 | Centre Nat Etd Spatiales | Method for detection and localization of ship within oceanic surface, involves associating accumulated signal strength with each partition, and implementing image processing step to isolate one or multiple objects in image |
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