CN114002673A - Satellite-borne passive SAR non-cooperative signal sensing system and multi-dimensional parameter estimation method - Google Patents
Satellite-borne passive SAR non-cooperative signal sensing system and multi-dimensional parameter estimation method Download PDFInfo
- Publication number
- CN114002673A CN114002673A CN202110960781.9A CN202110960781A CN114002673A CN 114002673 A CN114002673 A CN 114002673A CN 202110960781 A CN202110960781 A CN 202110960781A CN 114002673 A CN114002673 A CN 114002673A
- Authority
- CN
- China
- Prior art keywords
- sar
- cooperative
- signal
- antenna
- frequency
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9021—SAR image post-processing techniques
- G01S13/9023—SAR image post-processing techniques combined with interferometric techniques
Landscapes
- Engineering & Computer Science (AREA)
- Remote Sensing (AREA)
- Radar, Positioning & Navigation (AREA)
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Radar Systems Or Details Thereof (AREA)
Abstract
A satellite-borne passive SAR non-cooperative signal sensing system and a multi-dimensional parameter estimation method belong to the technical field of radar. The method comprises a non-cooperative SAR signal sensing system and a non-cooperative SAR signal multi-dimensional parameter estimation method, wherein the non-cooperative SAR signal sensing system comprises a zenith sensing antenna, a direct signal array receiving unit, a ground detection antenna and an echo signal array receiving unit, and reception of a non-cooperative SAR direct signal and an echo signal is realized; the non-cooperative SAR signal multi-dimensional parameter estimation method comprises a direct signal time-frequency space characteristic estimation unit and an antenna beam pointing parameter estimation unit, and multi-dimensional parameter estimation and antenna pointing estimation of the non-cooperative SAR signal are achieved. Compared with the traditional satellite-borne SAR system, the satellite-borne passive SAR does not need to transmit any signal, can sense and capture the available non-cooperative SAR signal source in the space in real time, and utilizes the non-cooperative SAR signal source to carry out the double-station SAR imaging detection.
Description
Technical Field
The invention relates to a satellite-borne passive SAR non-cooperative signal sensing system and a multi-dimensional parameter estimation method, and belongs to the technical field of radars.
Background
International SAR satellites have evolved over 40 years and the number of SAR satellites in orbit has exceeded 40. In recent years, with the maturity of commercial miniaturized SAR satellite technology, there will be nearly thousands of miniaturized SAR satellites operating in orbit in the next 5 to 10 years. Limited by legal operating frequencies, large-scale miniaturized SAR satellites will necessarily suffer from certain electromagnetic interference problems. A new SAR technology, namely a satellite-borne passive SAR system technology, needs to be researched. The satellite-borne passive SAR system can realize imaging observation on the ground by only sensing and utilizing signals of other SAR satellites without actively transmitting high-power broadband signals.
Most of the existing satellite-borne passive SAR systems are cooperative detection, such as multi-satellite formation (one-shot multi-receiving or multi-shot one-receiving), medium and high orbit satellite transmission and low orbit satellite reception, and the like, enough prior information and time-frequency space synchronization information exist between the receiving and transmitting SAR satellites, so that the complexity and the technical difficulty of the satellite-borne SAR system can be simplified. However, the cooperative detection system can only sense and utilize a limited number of SAR satellite signals, and cannot sense and utilize all the SAR satellite information in orbit, which results in a low imaging duty ratio of the system.
Disclosure of Invention
The technical problem solved by the invention is as follows: the method overcomes the defects of the prior art, provides a satellite-borne passive SAR non-cooperative signal sensing system and a multi-dimensional parameter estimation method, designs a hardware system consisting of a satellite-borne passive SAR non-cooperative signal sensing subsystem and a ground imaging detection subsystem for realizing imaging detection by utilizing a space non-cooperative SAR signal, and provides the multi-dimensional parameter estimation method for realizing passive imaging. In the space non-cooperative SAR signal sensing stage, a non-cooperative SAR signal of a corresponding detection frequency band is received through a zenith sensing antenna; because the signal parameters of the non-cooperative SAR cannot be predicted, a direct signal array receiving unit is needed to carry out rapid time-frequency two-dimensional estimation on the direct non-cooperative SAR signals, solve the space position and flight trajectory of the non-cooperative SAR satellites, and input the available direct signal characteristic parameters into a radar ground-to-ground imaging detection subsystem through signal availability analysis. In order to realize imaging detection to the ground, a planar multi-channel antenna is arranged at the lower part of the passive SAR satellite and is used for receiving echo signals of non-cooperative SAR signals detected to the ground; the beam direction of the non-cooperative SAR satellite during the ground observation is obtained through the echo signal intensity analysis, so that the main lobe footprint of the beam of the non-cooperative SAR antenna is determined, and the complete satellite multi-dimensional parameter estimation is obtained. On the basis, the earth detection antenna can realize earth observation imaging through DBF rapid beam alignment.
The technical solution of the invention is as follows:
the non-cooperative signal sensing system of the satellite-borne passive SAR comprises a zenith sensing antenna, a direct signal array receiving unit, a ground detection antenna and an echo signal array receiving unit;
the zenith sensing antenna is used for receiving a non-cooperative SAR satellite antenna side lobe transmitting signal, generating a four-channel direct signal through a sum-difference network and sending the four-channel direct signal to a direct signal array receiving unit;
the direct signal array receiving unit is used for carrying out sum and difference beam angle measurement, difference Doppler positioning and time-frequency parameter search processing on direct signals, generating non-cooperative SAR signal time-frequency estimation parameters and sending the non-cooperative SAR signal time-frequency estimation parameters to the echo signal array receiving unit;
the ground detection antenna is used for receiving echo signals of a ground search area, generating echo signals of a beam pointing area through DBF multi-channel processing and sending the echo signals to the echo signal array receiving unit;
the echo signal array receiving unit is used for performing parallel pulse compression and azimuth coherent accumulation processing on ground echo signals, generating an echo energy distribution model and generating a non-cooperative SAR antenna beam direction, and finally finishing sensing of the non-cooperative signals.
Furthermore, the zenith sensing antenna adopts a two-dimensional planar array antenna with an X wave band, is symmetrically divided into four-quadrant distribution sub-arrays, and realizes amplitude measurement of sum and difference wave beams in a digital or analog mode.
Furthermore, the direct signal array receiving unit comprises four independent down-conversion receiving channels, and each down-conversion receiving channel comprises a radio frequency band-pass filter, a variable gain amplifier, a mixer, an intermediate frequency band-pass filter, an intermediate frequency low noise amplifier and an analog-to-digital converter and is used for inputting the sampled digital signal into the processor module;
the processor module is used for finishing signal parameter estimation and then feeding back the center frequency to the programmable local oscillator source to generate a more matched local oscillator frequency, so that the intermediate frequency direct signal after frequency mixing is easier to sample by the analog-to-digital converter, and the sampling frequency and the data rate are reduced; the estimated parameters include center frequency, bandwidth, time width of the uncooperative SAR signal.
Further, the ground detection antenna adopts an X-waveband two-dimensional multi-channel array antenna.
Further, the aperture of the ground detection antenna is L multiplied by W, wherein L is larger than 6m, and W is larger than 1 m.
Furthermore, the number of channels of the ground probing antenna is P × Q, and the number of subarray units corresponding to each channel is Mp×MqP is 1,2, …, P, Q is 1,2, …, Q, azimuth is realized by sub-array level digital beam forming
Two-dimensional beam scanning to a distance of + -theta, wherein,
θ∈[10°～30°]the side lobe of the antenna directional diagram is better than-13 dB and the grating lobe is better than-15 dB during scanning.
Furthermore, the echo signal array receiving unit comprises P × Q independent receiving channels, each channel comprises a radio frequency band-pass filter, a variable gain amplifier, a mixer, an intermediate frequency band-pass filter, an intermediate frequency low noise amplifier, and an analog-to-digital converter, and is used for inputting the sampled digital signals to the processor module;
the processor module completes I/Q demodulation, DBF, range direction pulse compression and azimuth direction incoherent accumulation of the intermediate frequency echo signals to obtain echo signals with high signal-to-noise ratio, and the echo signals are used for carrying out two-dimensional search and estimation on beam directions of the non-cooperative SAR antenna.
The satellite-borne passive SAR non-cooperative signal multi-dimensional parameter estimation method comprises the following steps:
1) direct signals received by the zenith sensing antenna are fed into a direct signal array receiving unit after passing through a sum-difference network, a programmable local array source is adopted to mix with direct sum signals, and the time width of non-cooperative signals
Rough estimation; a frequency bandwidth of
Having a center frequency of
Doppler frequency
Real-time estimation of multidimensional parameters;
2) constructing an optimization model aiming at optimizing the performance of an Impact Response Width (IRW), a Peak Side Lobe Ratio (PSLR) and an Integral Side Lobe Ratio (ISLR) after signal pulse compression, and quickly searching in a time-frequency two-dimensional support domain by utilizing global optimization means such as a particle swarm algorithm and the like to obtain the optimal estimation of time-frequency parameters of the non-cooperative SAR signal;
3) in a direct signal array receiving unit, according to a time-frequency parameter estimation result of a non-cooperative SAR signal, amplitude comparison angle measurement and differential Doppler calculation are carried out on a sum-difference beam channel direct signal to obtain a relative space position estimation of a non-cooperative SAR satellite and a passive SAR, and an improved Extended Kalman Filter (EKF) tracking algorithm is adopted to fit a non-cooperative SAR operation track;
4) the direct signal array receiving unit sends the non-cooperative SAR time frequency estimation parameters to the echo signal array receiving unit;
5) according to the spatial position relation of the passive SAR and the non-cooperative SAR, the ground detection antenna conducts search by enabling a multi-channel antenna to be subjected to DBF weighted synthesis to form narrow beams pointing to a potential ground imaging area, and echo signals are received;
6) in an echo signal array receiving unit, processing such as I/Q demodulation, DBF beam scanning, range direction pulse compression, azimuth direction coherent accumulation and the like is realized on echo signals through a parallel FPGA platform, and the power distribution of the echo signals in a ground imaging area is obtained;
7) the echo signal array receiving unit corrects an echo power distribution model obtained by DBF beam scanning, and compensates power attenuation difference values of echoes generated due to different paths in a pitching plane to obtain corrected echo power distribution of a search area; selecting the center of the imaging area of the non-cooperative SAR with the strongest power point, thereby solving the azimuth direction and range direction beam pointing estimation of the non-cooperative SAR
8) Thus, time-frequency space parameter estimation of the non-cooperative SAR signals is completed, and the ground detection antenna points the wave beams to the corresponding areas to realize the double-station passive SAR imaging; the whole process is carried out in real time in an on-orbit mode, and continuous estimation and imaging processing are completed.
A computer readable storage medium storing a computer program which, when executed by a processor, implements the steps of the non-cooperative signal sensing system and the multi-dimensional parameter estimation method of the satellite-borne passive SAR.
The non-cooperative signal perception system and the multidimensional parameter estimation device of the satellite-borne passive SAR comprise a memory, a processor and a computer program which is stored in the memory and can run on the processor, and are characterized in that: and the processor realizes the steps of the non-cooperative signal perception system of the satellite-borne passive SAR and the multi-dimensional parameter estimation method when executing the computer program.
Compared with the prior art, the invention has the advantages that:
1) according to the space non-cooperative SAR signal self-sensing system, radar signal parameters are not required to be predicted, the space non-cooperative SAR signal can be automatically sensed only by adding one zenith array antenna, all in-orbit SAR satellite signals can be fully utilized for imaging detection to the ground, and the flexibility and the imaging duty ratio are high;
2) the invention does not need to transmit high-power signals, omits a large-scale power amplifier, greatly reduces the system cost and has very good concealment;
3) the invention adopts parallel fast search optimization processing in the signal parameter estimation process, thereby not only ensuring the parameter estimation precision, but also considering the real-time property of signal processing.
Drawings
FIG. 1 is a schematic diagram of a space-borne passive SAR to space non-cooperative SAR sensing and joint imaging scene;
FIG. 2 is a block diagram of a spaceborne passive SAR non-cooperative signal intelligent sensing system designed by the invention;
FIG. 3 is a block diagram of a parameter estimation process of a satellite-borne passive SAR non-cooperative signal designed by the invention;
FIG. 4 is a diagram of a satellite-borne passive SAR zenith sensing antenna subsystem structure;
FIG. 5 is a schematic diagram of time-frequency-space parameter estimation of a non-cooperative SAR signal;
FIG. 6 is a block diagram of a non-cooperative SAR direct signal array receiving unit structure;
FIG. 7 is a schematic diagram of non-cooperative SAR antenna beam pointing parameter estimation;
fig. 8 is a block diagram of a non-cooperative SAR echo signal array receiving unit.
Detailed Description
In order to better understand the technical solutions, the technical solutions of the present application are described in detail below with reference to the drawings and specific embodiments, and it should be understood that the specific features in the embodiments and examples of the present application are detailed descriptions of the technical solutions of the present application, and are not limitations of the technical solutions of the present application, and the technical features in the embodiments and examples of the present application may be combined with each other without conflict.
The non-cooperative signal sensing system and the multidimensional parameter estimation method of the satellite-borne passive SAR provided by the embodiment of the present application are further described in detail below with reference to the drawings of the specification, and specific implementation manners may include (as shown in fig. 1 to 8):
in the solution provided in the embodiments of the present application,
a. in an exemplary embodiment of the invention, a non-cooperative signal sensing system and a multi-dimensional parameter estimation method of a satellite-borne passive SAR are provided.
Fig. 1 is a schematic diagram of a combined imaging and detection scene of a satellite-borne passive SAR and a spatial non-cooperative SAR, including:
a main lobe of a non-cooperative SAR satellite antenna operating in space points to a ground observation area, and simultaneously, a signal is radiated and leaked through a side lobe and is transmitted to a satellite-borne passive SAR; the satellite-borne passive SAR zenith antenna of the low orbit receives and senses a direct signal, and the position and signal parameters of a non-cooperative SAR satellite are obtained through time-frequency space multi-dimensional parameter analysis; and the main lobe footprint of the antenna is determined by scanning and searching the distance of the earth observation antenna to the beam, and then the main lobe of the antenna is aligned to the area to realize passive imaging detection.
Fig. 2 is a satellite-borne passive SAR non-cooperative signal intelligent sensing system according to an embodiment of the present invention, including:
the zenith sensing antenna subsystem 10 and the direct signal array receiving unit 20 receive and process the direct signal of the non-cooperative SAR to realize the receiving of the space available signal and the intelligent sensing of the multidimensional information, input the signal to the echo signal array receiving unit 30, receive and process the echo of the irradiation area of the non-cooperative SAR beam through the multi-channel ground-to-ground detection antenna subsystem 40, and realize the non-cooperative SAR beam pointing estimation and the ground-to-ground imaging detection.
Fig. 3 is a processing flow diagram of a satellite-borne passive SAR non-cooperative signal parameter estimation technique according to an embodiment of the present invention, including:
the lateral leakage signal of the space non-cooperative SAR antenna is received by a four-subarray zenith antenna 100, time-frequency parameter rough estimation 101 of the signal is obtained through rapid time-domain analysis, and the signal availability is determined according to the time-frequency characteristic of the signal; obtaining a space angle estimation 102 of the non-cooperative SAR through four-channel digital sum-difference receiving processing, estimating a space distance 103 of the non-cooperative SAR through a Doppler change rate of a sum beam receiving signal, realizing space positioning by combining signal angle estimation, and fitting a satellite motion track 104 by adopting an improved EKF algorithm; and determining the working mode of the non-cooperative SAR satellite according to the orbit characteristics of the non-cooperative SAR satellite. The conventional SAR antenna has poor azimuth scanning capability, and according to the non-cooperative SAR working mode obtained by the judgment, the azimuth scanning boundary of the antenna beam of the non-cooperative SAR can be determined, namely the non-cooperative SAR signal azimuth estimation 105 is realized.
The passive SAR earth observation antenna rapidly forms a high-resolution narrow beam in a corresponding scanning area through DBF processing, and beam scanning is carried out 106 along the distance direction in the estimated azimuth range; and reconstructing a footprint of the uncooperative SAR antenna according to the echo signal power model, and determining a two-dimensional pointing angle of a beam of the uncooperative SAR antenna, so as to estimate an incident angle 107 of the uncooperative SAR signal. According to the relative positions of the passive SAR satellite and the non-cooperative SAR satellite, the DBF weighting is adopted to align the beam center to the non-cooperative SAR antenna pointing area, and the double-station radar imaging detection 108 based on the non-cooperative external radiation source is realized.
Referring to fig. 4, the zenith sensing antenna subsystem 10 includes: the four-subarray zenith antenna 101 divides a two-dimensional plane antenna into four-quadrant symmetrical subarrays by utilizing a single pulse sum and difference angle measurement principle, realizes a sum and difference directional diagram with low side lobes through amplitude and phase weighting, and ensures that sum beams of the four subarrays can scan in a 120-degree cone angle of an airspace without generating grating lobes; in order to improve the searching efficiency of available signals in space and keep the beam width at 8-12 degrees; the four-channel broadband signal receiver 102 is used for effectively receiving the space non-cooperative SAR signals, and the receiving channel passband is 9-10.2 GHz; the sum and difference beam former 103 is used for forming a sum signal channel and a two-dimensional difference signal channel in a digital or analog mode, performing down-conversion, filtering, amplification and normalization to realize the sum and difference amplitude of the four sub-array channels, and obtaining the azimuth and the pitch angle 104 of the incident non-cooperative SAR signal through an angle identification curve; and the signal processor 105 is used for extracting sum signal channel data and used for the time-frequency parameter accurate estimation, the distance estimation and the flight path correlation processing of the non-cooperative SAR signal.
Referring to fig. 5, the spatial parameter estimation process of the spatial non-cooperative SAR includes: zenith antenna and difference beam receiving signals can be used for estimating azimuth and pitch angle of the non-cooperative SAR to realize angle tracking; the sum beam receiving signal can realize Doppler estimation and distance tracking of the non-cooperative SAR and further obtain the radial velocity component of the sum beam receiving signal; obtaining multiple groups of angles of non-cooperative SAR through continuous observation
And a distance r measured value, wherein the SAR satellite running in space has a relatively stable motion track, and the flight point track of the non-cooperative SAR satellite can be associated by adopting an improved EKF algorithm to fit the actual flight track of the non-cooperative SAR satellite, so that the satellite orbit determination is realized.
Referring to fig. 6, the multi-dimensional parameter estimation of the spatial non-cooperative SAR direct signal is completed by the direct signal array receiving unit 20, and the signal parameters 40 and the working mode 50 of the non-cooperative SAR are obtained by the FPGA processing according to the position 30 of the passive SAR satellite. Four paths of signals received by the four-subarray zenith antenna 10 are input into a direct signal array receiving unit 20, each path of signal comprises a radio frequency band-pass filter 201, and interference signals outside 9-10.2GHz are filtered; then a variable gain amplifier 202, a mixer 203, an intermediate frequency band-pass filter 204, an intermediate frequency low noise amplifier 205 and an ADC 206 are connected; the sampled signal is fed into an FPGA or other processor 207; the programmable local oscillator 208 outputs matched local oscillator signals under the signal frequency estimation parameters fed back by the FPGA, and the local oscillator signals are gated by the multi-way switch 209 to be sequentially mixed with the received signals to obtain the transmission characteristics of the four receiving channels, and amplitude-phase consistency correction is performed in the FPGA processor. Since spatially uncooperative SAR typically transmit chirp modulated (LFM) signals for imaging detection, it is possible to detect in the time domainProcessing to obtain a coarse estimate of the time width of the signal
Coarse estimation of signal center frequency and bandwidth by FFT
Meanwhile, Doppler frequency obtained by space position estimation is compensated, local oscillation signals with matched frequencies are output to four channels for down-conversion filtering processing, and the frequencies of the local oscillation sources are continuously received and fed back, so that intermediate frequency signals after down-conversion are easier to be sampled by an ADC (analog to digital converter), and the sampling rate is reduced; after the signal rough estimation parameters are obtained, a time-frequency two-dimensional fine search model is established, and the signal parameters are subjected to fast random search in a time-frequency two-dimensional domain by means of particle swarm optimization and the like, so that the optimal parameter estimation of the direct signals is realized.
Fourthly, referring to fig. 7(a), because the conventional SAR antenna has a limited scanning angle in the azimuth direction, the azimuth angle of the non-cooperative SAR emission signal can be determined according to the prior knowledge, and the beam earth-scan boundary of the non-cooperative SAR antenna is calculated by combining the fitted flight trajectory and the altitude thereof, so that the footprint of the non-cooperative SAR antenna is estimated; referring to fig. 7(b), the space-borne SAR ground-based detection antenna searches in a non-cooperative SAR antenna footprint area, and a DBF technology is adopted to quickly form a narrow beam to scan along a distance direction; the non-cooperative SAR signal is scattered to other directions when encountering a ground target, so that the actual irradiation area of the non-cooperative SAR antenna can be determined by adopting the ground detection antenna to receive scattered echoes and carrying out energy detection, and the beam pointing estimation of the non-cooperative SAR antenna is realized.
Fifthly, referring to fig. 8, the uncooperative SAR echo signal is received by the two-dimensional multi-channel ground detection antenna 10, fed into the echo signal array receiving unit 20, and processed by the FPGA 207 according to the passive SAR satellite position 30, the uncooperative SAR working mode 40 and the signal parameter 50 estimated by the direct signal array receiving unit, to obtain the estimation of the distance direction pointing direction 60 and the azimuth direction pointing direction 70 of the uncooperative SAR antenna beam. Inputting multiple paths of signals received by a ground detection antenna 10 into an echo signal array receiving unit 20, wherein each path of signals comprises a radio frequency band-pass filter 201 for filtering interference signals except for 9-10.2 GHz; the receive path includes, but is not limited to, a variable gain amplifier 202, a mixer 203, an intermediate frequency bandpass filter 204, an intermediate frequency low noise amplifier 205, and an ADC 206; the sampled signals are fed into an FPGA or other processor 207; the programmable local oscillator 208 outputs local oscillator signals with matched frequencies according to input non-cooperative SAR signal estimation parameters, sequentially gates through the switch 209, mixes with each path of received signals to obtain the transmission characteristics of multiple paths of receiving channels, and performs amplitude-phase consistency calibration in the FPGA processor. The multi-channel antenna beam is scanned on the ground along the distance direction, an echo power distribution model of the whole area is quickly obtained through multi-channel receiving and DBF processing, the point with the strongest power is selected as the irradiation center of the non-cooperative SAR beam and is associated with the non-cooperative SAR space position, and the distance direction 60 and the azimuth direction 70 of the beam pointing direction are estimated through calculation.
b. Non-cooperative signal time-frequency two-dimensional parameter fast estimation method
In this embodiment, in order to quickly obtain the time-frequency two-dimensional parameter estimation of the non-cooperative SAR signal, a two-step estimation strategy combining coarse estimation and local fine search is adopted. Firstly, obtaining rough estimation of parameters such as signal time width, center frequency, bandwidth and the like according to a time domain sampling signal and an FFT (fast Fourier transform) technology; because the signal frequency may be superposed with instantaneous velocity Doppler components and other error factors, the particle swarm optimization algorithm is adopted to quickly and randomly search the signal parameters in a time-frequency two-dimensional domain, and an optimal estimation of the signal parameters is established by matching an optimization model.
Referring to fig. 4, the satellite-borne passive SAR first senses the spatially available X-band signals. Compared with a ground system, the space transmission signal is not easily subjected to clutter and multipath interference, the high-power signal transmitted by the non-cooperative SAR generates lateral leakage through the antenna side lobe, and a relatively pure direct wave of the non-cooperative SAR signal can be obtained through airspace search. The satellite-borne passive SAR is provided with a zenith sensing antenna, the four-channel zenith antenna 101 forms a single-pulse array, the antenna and the wave beam scan in a 120-degree cone angle range in an airspace in the flight process of the passive SAR, and non-cooperative SAR signals in an X wave band are searched and received; the received signal is fed into a four-channel wideband signal receiver 102 for processingFiltering down-conversion processing, and estimating the pulse duration of the down-converted sampling signal
A frequency bandwidth of
Having a center frequency of
The spatial relative position estimation of the incident SAR signal is done via the sum and difference beamformer 103: including azimuth and pitch angles
Distance between two adjacent plates
Wherein, the satellite angle information is obtained by comparing the sum and difference beams and measuring the angle,
and representing antenna directional diagrams corresponding to the four sub-arrays, the zenith antenna and the beam directional diagram are represented as follows:
the azimuth difference beam direction diagram is shown as:
the elevation difference beam direction diagram is shown as:
according to the echo amplitude ratio of different receiving beams, a corresponding two-dimensional space angle can be obtained through an angle identification curve:
spatial range of uncooperative SAR satellites
Obtained by the doppler frequency rate of change of the direct wave signal. The Doppler frequency due to the relative motion of passive SAR and uncooperative SAR is roughly estimated
The change rate of Doppler frequency is easily obtained during continuous observation
Wherein the space coordinate of the non-cooperative SAR is (x)0,y0,z0) Passive SAR observation point spatial position (x)i,yi,zi)，
Representing the space distance vector of the two; at the space position of the passive SAR,Speed of movement
And acceleration
Under the known condition, dynamic measurement is carried out within a period of time, and fuzzy-free positioning can be realized on the non-cooperative SAR satellite according to the space angle measurement value. Continuously receiving the direct wave signals, and fitting the non-cooperative SAR track by adopting an EKF algorithm.
Referring to fig. 6, the direct signal array receiving unit 20 is composed of a down-conversion rf receiving channel (including an rf band pass filter 201, a variable gain amplifier 202, a mixer 203, an if band pass filter 204, an if low noise amplifier 205, and an ADC 206) and an FPGA processor 207. The channel signals are mixed with a programmable local oscillator 208 during the down-conversion process, wherein the passband of the radio frequency band-pass filter is 9-10.2 GHz. Programmable local oscillator initial frequency set to fLOThe pulse duration of the down-converted sampled signal is estimated as
A frequency bandwidth of
Having a center frequency of
The instantaneous Doppler frequency obtained by the filtering process is
The center frequency of the incident signal is corrected to
Updating the output frequency of the programmable local vibration source, and sampling and analyzing the signal after down-conversion; repeating the steps to obtainTo sets of estimates of signal frequency parameters for continuously updating the spatial location of the target.
And thirdly, because the parameters of the non-cooperative SAR signal are unknown, the spatial measurement error cannot be avoided, and on the basis of the time-frequency parameter estimation result, two-dimensional local fine search needs to be carried out in an estimation neighborhood. The invention provides a signal time-frequency two-dimensional parameter fast searching method based on particle swarm optimization. Establishing an optimization model, and using a time unit delta t in the time and frequency two-dimensional support domain with the plurality of groups of estimation parameters openedpAnd randomly searching the two-dimensional parameters by taking the frequency unit delta f as a unit. Establishing an optimization objective function, and taking a signal rough estimation result as a received signal
Signal of random search parameter configuration
As a reference signal, performing matched filtering on a received direct signal:
calculating the impulse response width IRW, the peak sidelobe ratio PSLR and the integral sidelobe ratio ISLR of the signal after pulse compression, and constructing a multi-objective optimization model:
wherein, w1～w3The weight is optimized for multiple targets, and can be specified according to prior knowledge or dynamically adjusted; the calculation speed of two-dimensional parameter optimization can be accelerated by utilizing the parallelism of the particle swarm optimization algorithm, and the method is easy to realize in an FPGA processor; the frequency domain pulse compression only has multiplication and addition operation and is simple in calculation; the two random parameters a and b are updated within the specified iteration times, and the optimized variable dimension is low, so that the optimal estimation 50 of the signal time-frequency parameters can be quickly obtained.
c. Non-cooperative SAR antenna beam pointing estimation method
In the embodiment, in order to quickly obtain the beam pointing direction of the non-cooperative SAR antenna, the earth detection search combining the multi-channel receiving and DBF technology is adopted, and the azimuth angle of the non-cooperative SAR emission signal and the central pointing direction of the main lobe of the antenna are determined according to the estimated working state of the satellite; because the pitch scanning angle of the general satellite-borne SAR is 20-60 degrees, distance dimensional beam scanning is carried out in the corresponding direction, and the beam direction of the non-cooperative SAR is determined according to the echo energy distribution.
Referring to fig. 7(a), the working mode of the non-cooperative SAR is determined according to the flight trajectory of the non-cooperative SAR obtained by the fitting, and the azimuth scanning capability of the satellite-borne SAR antenna beam is poor, so that the scanning range is generally the range
When there is
Thus the azimuth angle theta of the beamsThe interval is unambiguous; the distance direction scanning range is wider, when the scanning range is +/-theta, theta is less than or equal to 20 degrees, and therefore an actual imaging observation area needs to be determined through distance direction fine search. Firstly, determining the antenna footprint of the non-cooperative SAR in a ground area corresponding to the satellite flight track according to an azimuth-distance two-dimensional maximum area coverage principle.
Referring to fig. 7(b), the ground target in the non-cooperative SAR signal beam irradiation area scatters energy to other directions, the ground detection antenna beam of the passive SAR scans rapidly in the distance direction, and the actual beam pointing direction of the non-cooperative SAR antenna is determined by comparing the signal energy of the received echoes. The aperture of the satellite-borne passive SAR ground detection antenna is L multiplied by W, L is generally larger than 6m, W is larger than 1m, and the aperture is slightly larger than that of a conventional same-frequency-band satellite-borne SAR antenna, so that a narrow beam with higher resolution ratio can be formed; through DBF technology and multi-channel receiving, the scattered signal echo intensity of the beam scanning area can be rapidly detected.
Referring to FIG. 8, the echo signal array receiving unit 20 down-converts the RF receiving channel (including the RF band-pass filter 201, may beVariable gain amplifier 202, mixer 203, intermediate frequency bandpass filter 204, intermediate frequency low noise amplifier 205 and ADC 206) and FPGA processor 207. Mixing the channel signal with a programmable local oscillator 208 during down-conversion processing, configuring local oscillator parameters according to the estimated non-cooperative SAR signal parameters, and weighting the sampled multi-channel received echo signal by DBF to realize optimal reception in different scanning areas; according to the non-cooperative SAR signal parameters obtained by the reception and signal analysis of the zenith sensing antenna, a local reference signal s is constructedr(ii) a Pulse compression and azimuth coherent accumulation processing of multiple echoes are realized in parallel in an FPGA processor, and an echo power distribution model of the whole scanning area is established
Under the condition that the scattering characteristics of the ground target are distributed uniformly, the point with the strongest echo power is used as the pointing center of the non-cooperative SAR antenna beam, and therefore the distance direction 60 and the azimuth direction 70 of the non-cooperative SAR antenna beam are estimated.
Fourthly, when constructing the echo power distribution model F, in order to avoid estimation errors caused by inconsistent attenuation of echo energy at different distances, compensating the signal transmission path loss after the echo power of the target is obtained by azimuth accumulation: according to the radar equation, the signal-to-noise ratio of the scattered echo signal can be expressed as
Wherein the scattered echo energy of the non-cooperative SAR signal is caused by the transmission path rRIn order to accurately invert the actual irradiation region of the non-cooperative SAR beam, the scattering signal energy distribution model of the corresponding region needs to be modified into
Assume that the near-point slant distance of the scanning area of the earth-detecting antenna beam is r0When the beam is swept in the range direction, the pitch angle is
The satellite-borne passive SAR satellite has the height h, the echo energy obtained by the accumulation processing of the range direction pulse pressure and the azimuth direction is P, and the echo energy of the point is corrected into P after considering the path attenuation
In consideration of the scattering characteristic distribution of the ground target, in order to avoid misjudgment caused by receiving of a leakage signal echo by a ground detection antenna due to the existence of a strong scattering target outside a non-cooperative SAR irradiation region, the scanning region can be calibrated by a subarea scattering parameter, and the scattering sectional area parameter in the correction formula (10) is sigma'.
From the above description of the examples, it can be seen that the invention does not involve too complex computation, time-frequency two-dimensional fast estimation of the uncooperative SAR direct signal, and echo-based uncooperative SAR beam pointing estimation with high on-orbit processing efficiency. Compared with active double-base detection, the system can effectively utilize the existing non-cooperative SAR signal in the space to realize passive detection by introducing a zenith antenna sensing system, and has good concealment; meanwhile, the perception of the spatial multidimensional information relates to a multi-target particle swarm optimization algorithm, and the multi-target particle swarm optimization algorithm and subsequent spatial search and imaging processing can be realized in a parallel computing mode, so that the method has the advantages of high computing efficiency, good real-time performance and the like.
The novel intelligent sensing and multidimensional parameter estimation technology for the non-cooperative SAR satellite signals does not need any prior information, the space non-cooperative SAR signals are autonomously sensed by utilizing the zenith array antenna, the multidimensional characteristics of the non-cooperative SAR signals, such as time domain (including signal time width, pulse repetition period and the like), frequency domain (including central frequency, bandwidth and the like), airspace (including non-cooperative SAR satellite tracks, antenna beam pointing and the like), and the like, are accurately estimated, the ground detection antenna beams are guided to point to the antenna beam irradiation area of the non-cooperative SAR satellites, and echo signals are received and processed, so that ground imaging observation is realized. The invention can utilize all in-orbit SAR satellite signals, does not need to transmit high-power signals, greatly reduces the system cost and has good concealment.
A computer-readable storage medium having stored thereon computer instructions which, when executed on a computer, cause the computer to perform the method of fig. 3.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (10)
1. The non-cooperative signal sensing system of the satellite-borne passive SAR is characterized by comprising a zenith sensing antenna, a direct signal array receiving unit, a ground detection antenna and an echo signal array receiving unit;
the zenith sensing antenna is used for receiving a non-cooperative SAR satellite antenna side lobe transmitting signal, generating a four-channel direct signal through a sum-difference network and sending the four-channel direct signal to a direct signal array receiving unit;
the direct signal array receiving unit is used for carrying out sum and difference beam angle measurement, difference Doppler positioning and time-frequency parameter search processing on direct signals, generating non-cooperative SAR signal time-frequency estimation parameters and sending the non-cooperative SAR signal time-frequency estimation parameters to the echo signal array receiving unit;
the ground detection antenna is used for receiving echo signals of a ground search area, generating echo signals of a beam pointing area through DBF multi-channel processing and sending the echo signals to the echo signal array receiving unit;
the echo signal array receiving unit is used for performing parallel pulse compression and azimuth coherent accumulation processing on ground echo signals, generating an echo energy distribution model and generating a non-cooperative SAR antenna beam direction, and finally finishing sensing of the non-cooperative signals.
2. The non-cooperative signal sensing system of the passive SAR on board of claim 1, wherein: the zenith sensing antenna is a two-dimensional planar array antenna with an X wave band, is symmetrically divided into four-quadrant distribution sub-arrays, and realizes amplitude measurement of sum and difference wave beams in a digital or analog mode.
3. The non-cooperative signal sensing system of the passive SAR on board of claim 1, wherein: the direct signal array receiving unit comprises four independent down-conversion receiving channels, and each down-conversion receiving channel comprises a radio frequency band-pass filter, a variable gain amplifier, a mixer, an intermediate frequency band-pass filter, an intermediate frequency low noise amplifier and an analog-to-digital converter and is used for inputting sampled digital signals into the processor module;
the processor module is used for finishing signal parameter estimation and then feeding back the center frequency to the programmable local oscillator source to generate a more matched local oscillator frequency, so that the intermediate frequency direct signal after frequency mixing is easier to sample by the analog-to-digital converter, and the sampling frequency and the data rate are reduced; the estimated parameters include center frequency, bandwidth, time width of the uncooperative SAR signal.
4. The non-cooperative signal sensing system of the passive SAR on board of claim 1, wherein: the ground detection antenna adopts an X-waveband two-dimensional multi-channel array antenna.
5. The non-cooperative signal sensing system of the on-board passive SAR of claim 4, wherein: the aperture of the front surface of the ground detection antenna is L multiplied by W, wherein L is larger than 6m, and W is larger than 1 m.
6. The non-cooperative signal sensing system of the on-board passive SAR of claim 4, wherein: the number of channels of the ground detection antenna is P multiplied by Q, and the number of subarray units corresponding to each channel is Mp×MqP1, 2, and P, Q1, 2, and Q, azimuth is achieved by subarray-level digital beamforming
Two-dimensional beam scanning to a distance of + -theta, wherein,
θ∈[10°～30°]the side lobe of the antenna directional diagram is better than-13 dB and the grating lobe is better than-15 dB during scanning.
7. The non-cooperative signal sensing system of the passive SAR on board of claim 1, wherein: the echo signal array receiving unit comprises a P multiplied by Q independent receiving channel, each channel comprises a radio frequency band-pass filter, a variable gain amplifier, a mixer, an intermediate frequency band-pass filter, an intermediate frequency low noise amplifier and an analog-to-digital converter, and the echo signal array receiving unit is used for inputting sampled digital signals to a processor module;
the processor module completes I/Q demodulation, DBF, range direction pulse compression and azimuth direction incoherent accumulation of the intermediate frequency echo signals to obtain echo signals with high signal-to-noise ratio, and the echo signals are used for carrying out two-dimensional search and estimation on beam directions of the non-cooperative SAR antenna.
8. The satellite-borne passive SAR non-cooperative signal multi-dimensional parameter estimation method is characterized by comprising the following steps of:
1) direct signals received by the zenith sensing antenna are fed into a direct signal array receiving unit after passing through a sum-difference network, a programmable local array source is adopted to mix with direct sum signals, and the time width of non-cooperative signals
Rough estimation; a frequency bandwidth of
Having a center frequency of
Doppler frequency
Real-time estimation of multidimensional parameters;
2) constructing an optimization model aiming at optimizing the performance of an Impact Response Width (IRW), a Peak Side Lobe Ratio (PSLR) and an Integral Side Lobe Ratio (ISLR) after signal pulse compression, and quickly searching in a time-frequency two-dimensional support domain by utilizing global optimization means such as a particle swarm algorithm and the like to obtain the optimal estimation of time-frequency parameters of the non-cooperative SAR signal;
3) in a direct signal array receiving unit, according to a time-frequency parameter estimation result of a non-cooperative SAR signal, amplitude comparison angle measurement and differential Doppler calculation are carried out on a sum-difference beam channel direct signal to obtain a relative space position estimation of a non-cooperative SAR satellite and a passive SAR, and an improved Extended Kalman Filter (EKF) tracking algorithm is adopted to fit a non-cooperative SAR operation track;
4) the direct signal array receiving unit sends the non-cooperative SAR time frequency estimation parameters to the echo signal array receiving unit;
5) according to the spatial position relation of the passive SAR and the non-cooperative SAR, the ground detection antenna conducts search by enabling a multi-channel antenna to be subjected to DBF weighted synthesis to form narrow beams pointing to a potential ground imaging area, and echo signals are received;
6) in an echo signal array receiving unit, processing such as I/Q demodulation, DBF beam scanning, range direction pulse compression, azimuth direction coherent accumulation and the like is realized on echo signals through a parallel FPGA platform, and the power distribution of the echo signals in a ground imaging area is obtained;
7) the echo signal array receiving unit corrects an echo power distribution model obtained by DBF beam scanning, and compensates power attenuation difference values of echoes generated due to different paths in a pitching plane to obtain corrected echo power distribution of a search area; selecting the center of the imaging area of the non-cooperative SAR with the strongest power point, thereby solving the azimuth direction and range direction beam pointing estimation of the non-cooperative SAR
8) Thus, time-frequency space parameter estimation of the non-cooperative SAR signals is completed, and the ground detection antenna points the wave beams to the corresponding areas to realize the double-station passive SAR imaging; the whole process is carried out in real time in an on-orbit mode, and continuous estimation and imaging processing are completed.
9. A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the steps of the method as claimed in claim 8.
10. The non-cooperative signal perception system and the multidimensional parameter estimation device of the satellite-borne passive SAR comprise a memory, a processor and a computer program which is stored in the memory and can run on the processor, and are characterized in that: the processor, when executing the computer program, performs the steps of the method of claim 8.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110960781.9A CN114002673A (en) | 2021-08-20 | 2021-08-20 | Satellite-borne passive SAR non-cooperative signal sensing system and multi-dimensional parameter estimation method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202110960781.9A CN114002673A (en) | 2021-08-20 | 2021-08-20 | Satellite-borne passive SAR non-cooperative signal sensing system and multi-dimensional parameter estimation method |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN114002673A true CN114002673A (en) | 2022-02-01 |
Family
ID=79921080
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202110960781.9A Pending CN114002673A (en) | 2021-08-20 | 2021-08-20 | Satellite-borne passive SAR non-cooperative signal sensing system and multi-dimensional parameter estimation method |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN114002673A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114488133A (en) * | 2022-03-08 | 2022-05-13 | 北京卫星信息工程研究所 | Method for extracting and classifying multidimensional scattering characteristics of satellite-borne GNSS-S radar ship |
| CN114509754A (en) * | 2022-03-28 | 2022-05-17 | 北京卫星信息工程研究所 | Satellite-borne multi-channel GNSS-S radar mass data on-orbit processing system and method |
| CN114509752A (en) * | 2022-02-09 | 2022-05-17 | 北京卫星信息工程研究所 | Air target cooperative detection method and satellite-ground integrated multi-source radar system |
| CN114895338A (en) * | 2022-03-31 | 2022-08-12 | 北京卫星信息工程研究所 | Large-range sea surface wind field inversion system and method for satellite-borne GNSS-S radar multi-dimensional information |
| CN116500566A (en) * | 2023-06-28 | 2023-07-28 | 中国科学院空天信息创新研究院 | On-orbit SAR emission azimuth direction diagram testing device and performance evaluation method |
-
2021
- 2021-08-20 CN CN202110960781.9A patent/CN114002673A/en active Pending
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114509752A (en) * | 2022-02-09 | 2022-05-17 | 北京卫星信息工程研究所 | Air target cooperative detection method and satellite-ground integrated multi-source radar system |
| CN114488133A (en) * | 2022-03-08 | 2022-05-13 | 北京卫星信息工程研究所 | Method for extracting and classifying multidimensional scattering characteristics of satellite-borne GNSS-S radar ship |
| CN114488133B (en) * | 2022-03-08 | 2023-03-07 | 北京卫星信息工程研究所 | Method for extracting and classifying multidimensional scattering characteristics of satellite-borne GNSS-S radar ship |
| CN114509754A (en) * | 2022-03-28 | 2022-05-17 | 北京卫星信息工程研究所 | Satellite-borne multi-channel GNSS-S radar mass data on-orbit processing system and method |
| CN114895338A (en) * | 2022-03-31 | 2022-08-12 | 北京卫星信息工程研究所 | Large-range sea surface wind field inversion system and method for satellite-borne GNSS-S radar multi-dimensional information |
| CN116500566A (en) * | 2023-06-28 | 2023-07-28 | 中国科学院空天信息创新研究院 | On-orbit SAR emission azimuth direction diagram testing device and performance evaluation method |
| CN116500566B (en) * | 2023-06-28 | 2023-09-01 | 中国科学院空天信息创新研究院 | On-orbit SAR emission azimuth direction diagram testing device and performance evaluation method |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN114002673A (en) | Satellite-borne passive SAR non-cooperative signal sensing system and multi-dimensional parameter estimation method | |
| US7812759B2 (en) | Radar apparatus for detection position information of a target by receiving reflection signals reflected by the target with a plurality of reception antennas | |
| CN109581352B (en) | Super-resolution angle measurement system based on millimeter wave radar | |
| CN107976660B (en) | Missile-borne multi-channel radar ultra-low-altitude target analysis and multi-path echo modeling method | |
| CN111257878B (en) | Wave form design method based on pitching dimensional frequency intra-pulse scanning high-resolution wide-range SAR | |
| US10247815B1 (en) | Phased array radar system with specular multipath mitigation | |
| Wang et al. | Subarray-based frequency diverse array for target range-angle localization with monopulse processing | |
| CN111007503A (en) | Moving target focusing and positioning method and system based on frequency spectrum accurate positioning | |
| CN111413666A (en) | Design method of array frequency and direction measurement combined receiver | |
| CN111707996B (en) | GEO satellite-borne SAR moving target detection method based on improved GRFT-STAP | |
| CN109655819A (en) | A kind of clutter recognition three-D imaging method based on real aperture Doppler beam sharpening | |
| CN115015925A (en) | Airborne array radar super-resolution forward-looking imaging method and device based on improved matching pursuit | |
| Nickel | Fundamentals of signal processing for phased array radar | |
| Bai et al. | DOA Estimation Using Shipborne HFSWR Based on Virtual Synthetic Array | |
| Bordoni et al. | Performance investigation on scan-on-receive and adaptive digital beam-forming for high-resolution wide-swath synthetic aperture radar | |
| De et al. | Angle estimation using modified subarray level monopulse ratio algorithm and s-curve in digital phased array radar | |
| CN114325560A (en) | Super-resolution target direction finding method for beam scanning radar | |
| Gogineni et al. | Sounding and imaging of fast flowing glaciers and ice-sheet margins | |
| Ryndyk et al. | Estimation of coordinates of ground targets in multi-static forward scattering radar | |
| RU2692467C2 (en) | Radar method | |
| CN115877346B (en) | Unmanned aerial vehicle-mounted off-target vector detection method based on two-dimensional phased array radar | |
| Kassem et al. | BISAR mapping II Treatment, simulation and experimentation | |
| Thi et al. | A Proposed Algorithm for Range Ambiguities Suppression in Multi-Static Sar | |
| CN111257861B (en) | 24GHz continuous wave radar angle measurement method | |
| Cheung | Digital beamforming array phase calibration techniques for multi-pass interferometric SAR |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |