CN115792995B - 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 method based on a satellite-borne GNSS-S, comprising the following steps: the on-sky GNSS direct signal processing unit is used for receiving direct signals of navigation satellites, outputting platform parameter information of the on-sky GNSS direct signal processing unit and outputting corresponding navigation satellite information according to the direct signals, wherein the navigation satellite information comprises text bit information; the sea GNSS scattering signal processing unit is used for receiving the scattering signal of the direct signal passing through the sea surface target area and determining the 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, reference signals required by distance direction compression and phase compensation factors required by azimuth coherent accumulation according to navigation satellite information and platform parameter information, and outputting the phase compensation factors to the sea GNSS scattered signal processing unit; and determining the information of the target area by the sea GNSS scattering signal processing unit according to the output information of the direct scattering 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 a satellite-borne GNSS-S.
Background
The GNSS-S target detection system detects sea surface targets by utilizing signals of GNSS navigation satellites scattered by the sea surface, and has the advantages of rich signal sources, full-day and all-weather detection, capability of resisting radio silence and radar stealth, low load power consumption, easiness in carrying low-orbit satellites and the like. The technology can be complemented with means such as electronic reconnaissance, radar, optical reconnaissance and the like, improves the battlefield sensing capability of the army, and is an important means for ocean reconnaissance and monitoring. In recent years, the development of sea surface target detection based on GNSS-S signals is a hot spot for scientific research.
However, the GNSS navigation satellites are higher from the ground, the signal transmitting power is low, the signal power reaching the ground is typically about-130 dBm, and the scattered satellite signals are weaker, which makes it difficult for the satellite-borne GNSS-S target detection system to realize sea surface target detection. In order to realize the detection of the extremely weak GNSS-S signal, the signals need to be accumulated for a long time, however, the random overturn of the navigation message bits and the frequency shift of the signals can limit the length of the integration time, so that the accumulated time cannot exceed the length of the navigation message bits in the azimuth coherent processing process.
Disclosure of Invention
Therefore, the embodiment of the invention aims to provide a target detection system and method based on a satellite-borne GNSS-S, which break through the limitation of random overturn of text bits during target echo signal processing and can realize long-time coherent accumulation processing.
In a first aspect, a first embodiment of the present invention provides an on-board GNSS-S based object detection system, the system comprising: the system comprises a GNSS direct signal processing unit, a navigation satellite receiving unit and a navigation satellite receiving unit, wherein the GNSS direct signal processing unit is used for receiving direct signals of navigation satellites, outputting platform parameter information of the GNSS direct signal processing unit and corresponding navigation satellite information according to the direct signals, and the navigation satellite information comprises text bit information; the sea GNSS scattering signal processing unit is used for receiving the scattering signal of the direct signal passing through the sea surface target area and determining the 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, reference signals required by distance direction compression and phase compensation factors required by azimuth coherent accumulation according to the navigation satellite information and the platform parameter information, and outputting the phase compensation factors to the sea GNSS scattered signal processing unit; and the sea GNSS scattering signal processing unit determines the information of the target area according to the output information of the direct scattering signal synchronous conversion unit.
Further, the pair of the sky GNSS receiving units includes: a pair of GNSS receivers for receiving the direct signal; the time information output module is used for outputting time synchronization information to the direct dispersion signal synchronous 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 pair of sea GNSS scattering receiving units includes: a radar antenna for receiving the scattered signal; the scattered signal preprocessing module is used for amplifying, filtering and down-converting the scattered signal and converting the scattered signal into an analog intermediate frequency signal; the digital sampling module is used for digitally sampling the analog intermediate frequency signal; the distance direction matched filtering module is used for carrying out matched filtering and compression processing on the sampling signals output by the digital sampling module; the phase compensation module is used for carrying out phase correction on the output signal of the distance matching filtering module; the azimuth accumulating module is used for accumulating the azimuth of 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 direct-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 control information of the digital sampling module and outputting the control information to the digital sampling module; the reference signal generation 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 matching and filtering 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 the phase compensation factor when the azimuth direction is accumulated and outputting the phase compensation factor to the phase compensation module.
Further, the platform parameter information comprises position coordinates and speed information of a platform where the pair of the acquired GNSS direct signal processing units are 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 pair of the acquired GNSS direct signal processing units; 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 an object based on a satellite-borne GNSS-S, using the object detection system based on a satellite-borne GNSS-S according to any of the first aspect, the method comprising: according to the reference signal, compressing the scattering signal in a distance direction; according to the time synchronization information, synchronously sampling the scattering signals; carrying out azimuth coherent processing on the scattered signals after distance compressing and synchronous sampling according to the phase compensation factors; and determining the information of the sea surface target area according to the scattering signals subjected to distance compression, synchronous sampling and azimuth coherent processing.
Further, performing distance-wise compression on the scattered signal includes: and acquiring the reference signal from the direct scattered signal synchronous conversion unit, carrying out carrier frequency mixing and pseudo code operation on the scattered signal to obtain a one-dimensional accumulated value of the scattered signal, and carrying out distance direction compression on the scattered signal according to the one-dimensional accumulated value.
Further, synchronously sampling the scattered signal includes: taking the second pulse signal of the direct signal as a trigger signal of the digital sampling of the scattering signal, selecting a 1ms time length to collect a data packet, adding time information of a navigation satellite to the collected data packet, adding a time stamp on the collected data packet, and synchronously sampling the scattering signal.
Further, performing azimuth coherent processing on the scattered signals after distance compressing and synchronous sampling, including: calculating a time delay deltat of the scattered signal and the direct signal for a target area i According to Deltat i Calculating the path-induced phase difference Δζ i If the text bit information of the direct signal is b, the phase correction factor delta theta of the target area i The method 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.
Further, according to the text bit information in the direct signal, the text bit information is subjected to phase correction at the 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, the GNSS receiver of the low-orbit satellite platform and the direct signal receiver required by GNSS-S target detection are shared, the GNSS receiver of the satellite platform not only provides positioning information for satellites, but also outputs signal characteristic information such as Doppler, code phase and text bits of direct satellite signals, and the like, no additional transmitting equipment is needed, the system is simple, and the GNSS-S load and the satellite platform are subjected to deep fusion, so that the system redundancy is reduced, the structural complexity is reduced, and the system cost is reduced. The embodiment of the invention also provides a direct scattered signal synchronous conversion unit which converts the direct navigation satellite signal into a local reference signal required by radar detection according to the characteristic information of the direct navigation satellite signal output by the GNSS receiver of the low-orbit satellite platform, and synchronizes the second pulse signal with the GNSS target scattered signal. The embodiment also provides a long-time coherent accumulation method for eliminating the echo signals influenced by random overturn of the GNSS text bits, solves the technical problem that the accumulation time cannot exceed the text bit length in the azimuthal coherent processing process, realizes the coherent processing time of second level, and improves the signal to noise ratio.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are 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 other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a target detection system based on a satellite-borne 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 distance signal compression according to 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 graph of direct dispersion signal geometry according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of the principle of azimuthal coherent accumulation according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of phase correction factor calculation 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 a complete description of the embodiments. In the drawings, the shape or thickness of the embodiments may be enlarged and indicated simply or conveniently. Furthermore, portions of the structures in the drawings will be described in terms of separate descriptions, and it should be noted that elements not shown or described in the drawings are in a form known to those of ordinary skill in the art.
Any references to directions and orientations in the description of the embodiments herein are for convenience only and should not be construed as limiting the scope of the invention in any way. The following description of the preferred embodiments will refer to combinations of features, which may be present alone or in combination, and the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.
As shown in fig. 1, a schematic structural diagram of an object detection system based on an on-board GNSS-S according to a first embodiment of the present invention, the system includes: the on-sky GNSS direct signal processing unit 10 is used for receiving direct signals of navigation satellites, outputting platform parameter information of the on-sky GNSS direct signal processing unit and outputting corresponding navigation satellite information according to the direct signals, wherein the navigation satellite information comprises text bit information. The sea GNSS scattered signal processing unit 20 is configured to receive the scattered signal of the direct signal passing through the sea surface target area and determine the information of the target area. The direct scattered signal synchronous conversion unit 30 is configured to determine time synchronization information required for time synchronization between the direct signal and the scattered signal, reference signals required for distance direction compression, and phase compensation factors required for azimuth phase coherent accumulation according to the navigation satellite information and the platform parameter information, and output the phase compensation factors to the marine GNSS scattered signal processing unit 20. The 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 on-sky GNSS direct signal processing unit 10 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 on-sky GNSS direct signal processing unit 10. The navigation satellite information also includes pseudocode, doppler shift, and code phase information.
As shown in fig. 1, in the present embodiment, the paired GNSS receiving unit includes: a pair of GNSS receivers 101 for receiving the direct signal; a time information output module 102, configured to output time synchronization information to the direct scattered signal synchronous conversion unit 30, where the time synchronization information includes a second pulse signal and absolute time information of the direct signal of the navigation satellite; the GNSS satellite information output module 103 is configured to output navigation satellite information according to the direct signal; the platform information module 104 is configured to output 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 marine GNSS scatter signal processing unit 20 includes: a radar antenna 201 for receiving the scattered signal, the radar antenna 201 preferably being a large-caliber high-gain antenna; the scattered signal preprocessing module 202 is configured to amplify, filter and downconvert the scattered signal, and convert the scattered signal into an analog intermediate frequency signal; the digital sampling module 203 is configured to digitally sample the analog intermediate frequency signal under the control of the synchronization signal generating module 301; the distance direction matching filtering module 204 is configured to perform matching 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 matching filter module 204 under the control of the phase compensation factor calculation module 303; an azimuth accumulating module 206, configured to accumulate the output signal of the phase compensating module 205 in azimuth; the target information module 207 is configured to determine information of a sea surface target area according to the accumulation result output by the azimuth accumulating module 206.
As shown in fig. 1, in the present embodiment, the direct-scattered signal synchronous converting unit 30 includes: the synchronization signal generation module 301 is configured to receive the time synchronization information of 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; the reference signal generating module 302 is configured to receive the output information of the GNSS satellite information output module 103, generate a reference signal matched and filtered with the scattering signal, and output the reference signal to the distance matching and filtering 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 when the azimuth is accumulated, 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 PPS (pulse per second) signals of the direct navigation signal and GNSS time (e.g., GPS week, intra-week seconds), converts the PPS signals into trigger signal output of AD (digital) samples, and simultaneously converts the GNSS time into time stamp information to be added to the data of the AD samples.
As shown in fig. 3, in the present embodiment, the input signals of the reference signal generating module 302 include: satellite system information (e.g., GPS, beidou), PRN number of currently visible satellites, satellite doppler, satellite code phase, carrier location information. The delay time of the target area is calculated, and local reference signals of all visible satellites required for matched filtering are generated.
As shown in fig. 4, in the present embodiment, the input signals of the phase compensation factor calculation module 303 include: PRN number of the current visible satellite, navigation satellite position, satellite platform position, target area coordinates, and navigation message bit information. And calculating the delay time and navigation message information of the target area, and outputting phase compensation factors of all coordinate points.
According to the target detection system based on the satellite-borne GNSS-S, a GNSS receiver of a common satellite platform receives the sky signals, a large-gain antenna is adopted to receive the sea surface target scattering GNSS signals, the working frequency band of the antenna is a navigation satellite frequency band (such as 1.575GHz and 1.268 GHz), the sea surface scattering GNSS signals received by the sea antenna are amplified and filtered, then the down-conversion mixing processing is carried out, and the signals are converted into intermediate frequency signals to be output. And a DSC unit is adopted to realize synchronization of the direct signal and the scattered signal and conversion processing of information. The DSC unit generates phase correction information of the phase correlation of the azimuth phase and the matched filter for performing scattered GNSS signal pulse compression. The distance direction compression and azimuth direction correlation of extremely weak GNSS scattering signals are realized on a low orbit satellite platform, the signal to noise ratio of the signals is improved, a scattering energy matrix diagram of a large-range sea surface target is obtained, and the detection of the sea surface target is realized. Compared with the traditional satellite-borne radar system, the system has the advantages that no signal is required to be transmitted, the ubiquitous GNSS signal is utilized to realize sea surface target detection, meanwhile, the existing GNSS receiver of the satellite platform is multiplexed, the system architecture is simple, the cost is low, the networking application of low-orbit satellites is convenient to realize, and the global sea surface target passive detection is realized.
As shown in fig. 5 to 10, the second embodiment of the present invention further provides a target detection method based on a satellite-borne GNSS-S, which is implemented by applying the target detection system based on a satellite-borne GNSS-S according to the first embodiment, and improves the signal-to-noise ratio of the target scattered GNSS signal by adopting distance-direction compression and azimuth-direction correlation to the extremely weak GNSS-S scattered signal of the sea surface. The embodiment includes generating a local reference signal by using information such as satellite Doppler, code phase and the like obtained by the GNSS receiver 101, and performing distance compression on a scattered signal; meanwhile, a PPS synchronous signal is provided for the space GNSS receiver, synchronous sampling is carried out on the scattered signals, text inversion of the scattered signals is predicted by navigation text bit information provided for the space GNSS receiver, the problem of random text inversion during azimuth phase-coherent of extremely weak scattered signals is solved, azimuth phase-coherent accumulation processing of cross-bit length is realized, and the signal to noise ratio of sea surface target scattered signals is improved.
As shown in fig. 5, in the present embodiment, the flow of distance-to-compression of the GNSS-S target scattered signal is as follows:
a1, selecting a visible navigation satellite;
a2, acquiring a local reference signal from a DSC unit (direct scattered signal synchronous conversion unit);
a3, carrying out carrier frequency mixing on the signals obtained in the step a 2;
a4, performing pseudo code correlation operation on the signals obtained in the step a 3;
a5, obtaining a one-dimensional accumulated value of the signal according to the calculation result of a 4.
As shown in fig. 6, in the present embodiment, the scattering signal synchronous sampling timing flow is as follows: and receiving a navigation satellite PPS signal of the DSC unit as a trigger signal of a scattering signal ADC (digital) sampling, selecting 1ms to collect one packet of data, and adding the time of the navigation satellite to the data packet to be used as the original data of subsequent signal processing by adding a time stamp. Taking PPS of direct satellite signals as synchronous signals, starting data acquisition by each pulse, and adding time stamp information to acquired data according to GNSS time; performing distance pulse compression on GNSS signals received by a sea surface scattering receiving system and local reference signals generated by a DSC unit; and the DSC unit receives the text bit information of the direct navigation satellite, and corrects the signal phase at the text bit overturning moment when carrying out azimuth coherent accumulation processing, so as to increase the accumulation gain.
As shown in fig. 7, in the present embodiment, the transmission time delay of the direct signal and the scattered signal is calculated by the following method: navigation satellite PRN number, doppler shift fd of receiving DSC unit i Code phase c i The coordinates of the navigation satellite are (X) s ，Y s ，Z s ) The position coordinates (X u ，Y u ，Z u ) The coordinates of the target search area are (X d ，Y d ，Z d ) The direct signal propagation distance d is calculated according to the geometric relation as follows:
the scattered signal propagation distance D is:
the transmission delay time Δt of the scattered signal and the direct signal is as follows:
wherein, c is the light speed of 3X 108m/s;
the formula of the matched filter for obtaining the scattered signal from 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 text data, C (-) is navigation pseudo code sequence, and 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 scattered signal and the direct signal for the target detection area i Phase difference Δζ caused by the delay time calculation path i The phase correction factor delta theta of the detection zone i The method comprises the following steps:
Δθ i ＝Δξ i +bπ；
b is text bit information (b is 0 or 1) of the direct signal of the navigation satellite received by the DSC unit, and the phase is corrected according to the text bit.
The DSC unit outputs digital text bit information by adopting a serial port; the message bit information is synchronous with PPS second pulse time, and a group of message bit information is output at 1 PPS pulse interval; the azimuthal-phase processing time takes t milliseconds, which is much greater than the text bit time (e.g., GPS bit duration 20 ms).
As shown in fig. 9, in the present embodiment, the azimuth phase correlation is accumulated by the following method: after distance-wise compression and time-synchronous sampling, echo energy information q of a set of target areas is obtained at each square point i Along with the flight of the low orbit satellite, a series of target point echoes are obtained in the azimuth direction, because the GNSS-S echo energy is very weak, the echo energy in the azimuth direction is further accumulated for realizing target detection, the influence of text bits and range migration is eliminated, phase correction is carried out on the azimuth phase-coherent signal, and the accumulated 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 low orbit satellite position, the navigation satellite position and the target region position, and generates a local signal; and calculating a local carrier wave 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 matched and filtered local reference signal according to the pseudo code of the navigation satellite.
As shown in fig. 10, in this embodiment, a point-by-point scanning is performed on a target area, so as to obtain an echo energy matrix diagram of the target area, where the echo energy is greater than background noise when there is a target, and target detection can be achieved through the diagram.
According to the target detection method based on the satellite-borne GNSS-S, the local reference signal is generated by utilizing navigation information received by the satellite platform, the distance direction compression processing is carried out on the scattered navigation signal received by the sea scattering receiving antenna, and then the phase information of the azimuth direction phase-coherent processing is generated by combining the navigation message bit information, so that the long-time azimuth direction phase-coherent processing of the super-message bit length is realized. The invention provides a method for sharing a GNSS receiver of a low-orbit satellite platform with a direct signal receiver required by GNSS-S target detection, wherein the GNSS receiver of the satellite platform not only provides positioning information for satellites, but also outputs signal characteristic information such as Doppler, code phase, text bits and the like of direct satellite signals. The invention provides a DSC unit, which converts the characteristic information of a direct navigation satellite signal output by a GNSS receiver of a low-orbit satellite platform into a local signal required by radar detection, and synchronizes a GNSS target scattering signal by adopting a PPS pulse signal. The invention provides a long-time coherent accumulation method for echo signals, which eliminates the influence of random overturn of GNSS text bits. The technical problem that the accumulated time cannot exceed the text bit length in the azimuth coherent processing process is solved, the coherent processing time of second level 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 satellites, 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 the GNSS receiver of the low-orbit satellite platform with the direct processing receiver, and the GNSS-S load and the satellite platform are subjected to deep fusion, so that the system redundancy is reduced, the structural complexity is reduced, and the system cost is reduced; the target echo signal processing breaks through the limitation of random upset of the text bits, and long-time coherent accumulation processing can be realized, so that the signal to noise ratio is high.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (9)
1. An on-board GNSS-S based object detection system, the system comprising:
the GNSS direct signal processing unit (10) is used for receiving direct signals of navigation satellites, outputting platform parameter information of the GNSS direct signal processing unit and corresponding navigation satellite information according to the direct signals, wherein the navigation satellite information comprises text bit information;
a sea GNSS scattering signal processing unit (20) for receiving the direct signal via the scattering signal of the sea surface target area and determining the information of the target area;
a direct scattered signal synchronous conversion unit (30) for determining time synchronization information required by time synchronization between the direct signal and the scattered signal, reference signals required by distance direction compression and phase compensation factors required by azimuth coherent accumulation according to the navigation satellite information and the platform parameter information, and outputting the phase compensation factors to the sea GNSS scattered signal processing unit (20);
the sea GNSS scattering signal processing unit (20) determines information of a target area according to the output information of the direct scattering signal synchronous conversion unit;
the pair of sea GNSS scattered signal processing units (20) comprises:
a radar antenna (201) for receiving the scattered signal;
a scattered signal preprocessing module (202) for amplifying, filtering and down-converting the scattered signal and converting the scattered signal into an analog intermediate frequency signal;
a digital sampling module (203) for digitally sampling the analog intermediate frequency signal;
the distance matching filtering module (204) is used for performing matching filtering and compression processing on the sampling signals output by the digital sampling module (203);
a phase compensation module (205) for performing phase correction on the output signal of the distance matching filter module (204);
an azimuth accumulating module (206) for accumulating azimuth of the output signal of the phase compensating module (205);
a target information module (207) for determining information of the sea surface target area according to the accumulation result output by the azimuth accumulating module (206);
the on-sky GNSS direct signal processing unit (10) comprises an on-sky GNSS receiver (101), wherein the on-sky GNSS receiver (101) provides a PPS synchronous signal, synchronously samples a scattering signal, and predicts the text inversion of the scattering signal by using navigation text bit information provided by the on-sky GNSS receiver (101).
2. The satellite-borne GNSS-S based object detection system according to claim 1, wherein the pair of GNSS direct signal processing units (10) further comprises:
a time information output module (102) for outputting time synchronization information to the direct-scattered signal synchronization conversion unit (30);
a GNSS satellite information output module (103) for outputting the navigation satellite information according to the direct signal;
and the platform information module (104) is used for outputting the platform parameter information.
3. The satellite-borne GNSS-S based object detection system according to claim 2, wherein the direct scattered signal synchronization conversion unit (30) comprises:
the synchronous signal generation module (301) is used for receiving the time synchronous information of the time information output module (102), converting the time synchronous information into control information of the digital sampling module (203) and outputting the control information to the digital sampling module (203);
the reference signal generation module (302) is used for receiving the output information of the GNSS satellite information output module (103), generating a reference signal matched and filtered with the scattering 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 the phase compensation factor when the azimuth direction is accumulated and outputting the phase compensation factor to the phase compensation module (205).
4. A satellite-borne GNSS-S based object detection system according to any of the claims 1-3, characterised in that the platform parameter information comprises position coordinates and velocity information of a platform where the pair of GNSS direct signal processing units (10) is located, the platform being a low-earth satellite platform, the system sharing a GNSS receiving unit on the low-earth satellite platform as the pair of GNSS direct signal processing units (10);
the navigation satellite information also includes pseudo code, doppler shift, and code phase information.
5. A method of on-board GNSS-S based object detection, applying an on-board GNSS-S based object detection system according to any of the claims 1-4, the method comprising:
according to the reference signal, compressing the scattering signal in a distance direction;
according to the time synchronization information, synchronously sampling the scattering signals;
carrying out azimuth coherent processing on the scattered signals after distance compressing and synchronous sampling according to the phase compensation factors;
and determining the information of the sea surface target area according to the scattering signals subjected to distance compression, synchronous sampling and azimuth coherent processing.
6. The method of claim 5, wherein the performing range compression on the scattered signal comprises:
and acquiring the reference signal from the direct scattered signal synchronous conversion unit (30) unit, carrying out carrier frequency mixing and pseudo code operation on the scattered signal to obtain a one-dimensional accumulated value of the scattered signal, and carrying out distance direction compression on the scattered signal according to the one-dimensional accumulated value.
7. The method of claim 5, wherein synchronously sampling the scattered signals comprises:
taking the second pulse signal of the direct signal as a trigger signal of the digital sampling of the scattering signal, selecting a 1ms time length to collect a data packet, adding time information of a navigation satellite to the collected data packet, adding a time stamp on the collected data packet, and synchronously sampling the scattering signal.
8. The method for detecting an object based on a satellite-borne GNSS-S according to claim 5, wherein performing an azimuthal correlation on the scattered signal after the distance-wise compression and the synchronous sampling comprises:
calculating a time delay deltat of the scattered signal and the direct signal for a target area i According to Deltat i Calculating the path-induced phase difference Δζ i If the text bit information of the direct signal is b, the phase correction factor delta theta of the target area i The method comprises the following steps:
Δθ i ＝Δξ i +bπ；
the formula of the azimuth coherent processing is as follows:
wherein q i And the echo energy information of the sea surface target area obtained at the ith square point.
9. The method for detecting targets based on-board GNSS-S according to claim 8, wherein the phase correction is performed on the text bit information at the text bit flip time according to the text bit information in the direct signal, so as to obtain the 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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| CN114545448A (en) * | 2022-02-17 | 2022-05-27 | 北京卫星信息工程研究所 | Satellite-borne GNSS-R/S integrated receiving system and ocean intelligent detection method |
| 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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