472 results about "Synthetic aperture sonar" patented technology

The invention discloses a large squint sliding spotlight SAR(synthetic aperture radar) imaging processing method, which belongs to the signal processing field. The processing method mainly comprises the following five parts, namely directional Deramp processing, two-dimensional phase compensation, interpolation processing, image coarse focusing and directional secondary focusing; the large squintsliding spotlight SAR imaging processing method has high accuracy and can realize accurate focusing in a full scene by using a secondary focus technology for compensating the spare-varying feature ofa Doppler parameter; in addition, the processing method has high efficiency, since distance migration induced by a reference slant distance in an echo signal is removed so as to greatly reduce data volume of the echo signal and improve the processing efficiency; moreover, the processing method has strong practicability and can realize the high-precision imaging process in a large squint angel mode; compared with the traditional imaging processing method, the large squint sliding spotlight SAR imaging processing method has better practicability.

The invention relates to a design method for the formation configuration of distributed satellites with synthetic aperture radars (SAR). The method comprises the following five operation steps: step 1: designing the formation configuration of the distributed satellites and conforming fly-by path equations; step 2: confirming an optimal base line length range of the distributed satellites in start time; step 3: confirming an optimal base line sequence of the distributed satellites in start time; step 4: confirming track parameters of the formed satellites forming a concentric circle configuration; and step 5: calculating effective base lines and vertical path base lines in a track period. The invention provides the concentric circle formation configuration, uses the optimal base line combined constraint conditions of multi-base line interference SARs as design input parameters and designs a control law of radar antenna visual angles to realize that a distributed satellite SAR system can satisfy the design requirements of the optimal base line combined constraint conditions in any time in a track operation period and a basis is provided for the distributed satellite SAR system to obtain high-precision DEM products by a multi-base line interference SAR treatment method.

The invention discloses an imaging method for a bistatic forward-looking synthetic aperture radar (SAR). Aiming at the defect existing when the existing method is used for the imaging process of the bistatic forward-looking synthetic aperture radar, the imaging method adopts a bistatic forward-looking SAR point target response two-dimensional frequency spectrum based on the least square polynomial fitting; the frequency spectrum is the least square approximation of the two-dimensional frequency spectrum with the accurate theory. According to the characteristics of bistatic forward-looking invariant SAR direction, variant range and nonlinear and variant Doppler centroid range of range cell migration in an RD (radar domain) domain, bistatic forward-looking SAR range migration correction, secondary-range compression and high-order phase compensation are realized by the frequency spectrum so as to accurately focus the bistatic forward-looking SAR. Compared with the traditional SAR imaging method and the bistatic forward-looking SAR imaging method, the method disclosed by the invention has higher imaging precision.

The invention provides a method for acquiring and imaging data of compressive sensing synthetic aperture radar. The method comprises the following steps of: 1, selecting an observation scene; 2, emitting a Chirp signal by a radar antenna; 3, receiving a distance direction signal of the synthetic aperture radar; 4, constructing a compressive sensing restoring matrix; 5, correcting distance compression and distance migration; 6, constructing an orientation direction filter matrix; and 7, compressing towards the orientation direction. By the method for acquiring and imaging the data, aiming at realizing great reduction of radar stored and transmitted data quantity in the special observation scene and synchronously realizing restoring of a distance direction pulse compression signal and correction of the distance migration, the problem that interpolation calculation cannot be performed on a compressive sensing restoring signal is solved.

The invention provides a compressed sensing synthetic aperture radar (SAR) imaging method based on fractional order fourier transformation, and belongs to the technical field of microwave imaging. For a sparse target scene, a system emits a linear frequency modulation pulse signal; by adopting a method for projecting an echo signal to a low-dimension measurement matrix, measurement data which are much smaller than those required by a Nyquist sampling principle are acquired; due to the echo signal, after a reconstruction matrix is constructed by a simplified fractional order fourier transformation domain sparse mode and a data acquisition mode, a calculated distance pulse pressure result is optimized by a compressed sensing signal reconstruction method and is subjected to distance migration correction and direction pulse pressure to obtain a target scene imaging result. By the imaging method, the measurement data amount of a target scene with a sparse characteristic can be greatly reduced; and pressure on data storage and data transmission can be effectively relieved.

The invention discloses an implementation method of a high resolution and wide swath spaceborne SAR (Synthetic Aperture Radar) system. The implementation method comprises adopting the sliding bunching mode that multiple-input and multiple-output are performed and N different carrier frequencies of linear frequency modulation signals are transmitted from N sub-apertures in the azimuth direction of a spaceborne SAR to enable sub-band echoes which are received by the plurality of sub-apertures to be separated, performing azimuth pretreatment on the separated sub-band echoes and eliminating the spectrum overlapping caused by the beam scanning and the antenna multi-channel structure; performing range sub-band composition on signals after the azimuth pretreatment to obtain a sub-band composition signal and obtain the range high resolution, wherein the bandwidth of the sub-band composition signal is N times of the bandwidth of the single linear frequency modulation signal; achieving residual focusing of the sub-band composition signal through an RMA (Range Migration Algorithm) to obtain a final high resolution radar image.

The invention relates to a waveform design for a formation flying satellites SAR (synthetic aperture radar), and provides an orthogonal waveform designing method which is used for carrying out phase encoding for linear frequency modulation (LFM) signals. The orthogonal waveform designing method includes generating a linear frequency modulation signal at first, dividing the linear frequency modulation signal into N parts according to equal time intervals to form N sub-pulses, carrying out random phase encoding for each sub-pulse by M times according to the number M of the formation flying satellites, establishing an ambiguity function expression, calculating cluster tolerance xi meeting formation flying satellite synthetic aperture radar Doppler mismatch, finding out a critical N value meeting requirements by the aid of a searching comparison method, finally selecting energy and functions which are in autocorrelation and cross-correlation as cost functions, namely fitness functions in genetic algorithm, searching code values of phase encoding of the various sub-pulses by the aid of the genetic algorithm, and finding out orthogonal waveforms after optimization at last. The waveforms have low autocorrelation side lobes, cross-correlation peak values, bandwidth occupation ratio and Doppler mismatch, and excellently suppress echo signal interferences among different space-borne SARs.

The invention discloses a small FMCW-based (frequency modulated continuous wave) SAR (synthetic aperture radar) imaging system by using an FPGA (field programmable gate array) to mainly overcome the disadvantages of large volume, heavy weight and high power consumption of the traditional SAR imaging system. The small FMCW-based SAR imaging system comprises a radar front end, an acquisition preprocessing unit, a signal processing unit and a receiving host, wherein the acquisition preprocessing unit comprises an instruction communication module, an A/D (analogue/digital) acquisition module, an FPGA control and calculation module and a data sending interface; the signal processing unit comprises a data receiving interface, an FPGA control module, a DSP (digital signal processor) calculation module and a data sending interface; the acquisition preprocessing unit and the FPGA of the signal processing unit are used for receiving back waves and inertial navigation parameters of the radar front end, feeding back the regulation instruction to the radar front end to perform distance pulse pressure, transmitting data to a DSP, receiving the calculation results of the DSP and transmitting thecalculation results of the DSP to the receiving host for display. According to the small FMCW-based SAR imaging system, one picture can be imaged in real time in one second under the airborne condition, the small FMCW-based SAR imaging system has the advantages of small size, light weight, small power consumption and good reliability and can be applied to the fields of radars, guided missile, remote sensing, etc.

A synthetic aperture three-dimensional fluid flow imaging apparatus is provided. The apparatus includes a plurality of cameras. At least two of the cameras are oriented to view a volume along mutually non-parallel directions. The cameras are connected to a programmable computer. The computer captures images from the cameras to generate three dimensional intensity fields. The computer can refocus the images on at least one refocus plane to generate reconstructed three dimensional intensity fields on a plane within the volume. Intensity field cross-correlation is performed on the reconstructed three dimensional intensity fields to extract velocity fields within the volume. The velocity fields represent velocities of objects or fluid phases within the volume. These velocity fields can be recorded for later use.

The invention discloses a circular synthetic aperture radar (CSAR) 3D microwave imaging method for an earth synchronous orbit. In the method, parameters of the earth synchronous orbit are designed to cause a synthetic aperture radar (SAR) satellite platform to make a flight with an annular track around a target zone and above the target zone, and an antenna beam is caused to irradiate the target zone all the time by a circular synthetic aperture radar mode, and a ground object target is subject to continuous large-area fixed point observation to acquire high-resolution 3D imaging information of the ground object target. A CSAR system of the earth synchronous orbit provided by the system can acquire high-resolution 3D images of the ground object, solves the problem that the existing space-borne SARs are hard to acquire the high-resolution 3D information of the ground object; and is applicable to areas with complex and steep terrains as elevation information does not interfere with phase ambiguity in the SAR. The CSAR system of the earth synchronous orbit can realize the fixed point continuous observation of large-area zones, and solve the problems that the existing space-borne SARs have small observation zones and long revisit period.

Method and apparatus for simultaneous synthetic aperture radar and moving target detection. A plurality of independent radio frequency signals are generated and applied to separate radiating, receiving antenna elements. Signals are generated as basis functions, such that moving target detection and synthetic aperture radar signals are constructed from individual waveform components in space, time, frequency, and coding. Waveform components are sorted and combined at reception. Received data is simultaneously processed to extract synthetic aperture radar images and moving target indication detections.

The invention discloses an SAR (synthetic aperture radar) real-time imaging method based on a frequency modulated continuous wave, and the problem that a conventional method cannot process the real-time echo data of the frequency modulated continuous wave is mainly solved. The SAR real-time imaging method comprises the following realization steps of: carrying out previous wave filtration on initial data; carrying out Doppler center estimation, walking correction and Doppler center translation on the data subjected to the previous wave filtration; carrying out inverse fast Fourier transform (IFFT) on the data subjected to the center translation along a distance direction; carrying out Doppler frequency modulation rate estimation on the data subjected to the IFFT to obtain a frequency modulation rate value; calculating the motion error parameter of a loader according to the frequency modulation rate value; carrying out motion compensation on the data subjected to the previous wave filtration according to the motion error parameter; carrying out the walking correction, the Doppler center translation and bending correction on the data subjected to the motion compensation; carrying outthe frequency modulation rate estimation on the data subjected to the bending correction; and carrying out focusing and imaging on the data along an azimuth direction according to the obtained frequency modulation rate value to obtain an SAR image. The SAR real-time imaging method has the advantage that the SAR imaging resolution is high, and can be applied to the processing of the real-time echodata of the frequency modulated continuous wave.

A method is provided for reducing quadratic phase errors in synthetic aperture radar signals from a plurality of range lines where each range line includes a plurality of azimuth positions. The method includes receiving a plurality of slow-time samples representing radar signals for a plurality of azimuth positions for a plurality of range lines. A plurality of corrected samples and an initial quadratic phase error coefficient are identified based upon the slow-time samples. The corrected samples are processed according to a superresolution signal processing technique to thereby obtain a plurality of estimated Doppler frequencies for a plurality of point scatterers at each range line, after which a true signal for each range line is reconstructed based upon the plurality of estimated Doppler frequencies. A correction to the initial quadratic phase error coefficient is then obtained based upon the corrected samples, the true signals and the initial quadratic phase error coefficient.

The invention discloses an SAR (synthetic aperture radar) tomography super-resolution imaging method. The SAR tomography super-resolution imaging method includes registering obtained two-dimensional imaging results of various SAR tomography baselines, creating height-direction signals pixel by pixel according to the sequence of the baselines, realizing frequency modulation correction and constructing a redundancy matrix; and modeling a height-direction imaging problem into a sparse signal reconstruction problem according to the characteristic of sparsity of height-direction scattering coefficients, computing a sparse solution of the spares signal reconstruction problem by means of iteration by the aid of the constraint condition of the minimum weighted norm, and realizing height-dimensional imaging of an object. The method is applied to SAR tomography height-dimensional imaging, and problems that the quantity of two-dimensional SAR images in the same area and (/or) trajectory distribution is uneven, and only a few parts of trajectory intervals (baselines) meet the Nyquist sampling theory are solved. In addition, by the aid of the method, energy of the object is more concentrated, namely, the resolution is improved, and the problem that the quantity of baselines is small is solved.

Methods and systems for detecting and mitigating DRFM-based interference in SAR images are provided. Embodiments include methods and systems for detecting and removing DRFM-based interference from SAR images by exploiting multi-channel SAR data. Embodiments provide an Electronic Counter Counter Measure (ECCM) technique that is effective against, among others, SAR DRFM-based repeater jamming, false target images, noise jamming, and vector multiplier jamming for false scene generation. When used, embodiments of the present invention reduce jammer effectiveness to a small range strip (a strip parallel to the range dimension) in the direction of the jammer. In addition, jammer mitigation is performed without losing SAR image data at the affected SAR pixels. Furthermore, embodiments of are compatible with time variable ECCM techniques, including orthogonal waveforms or pulse jitter techniques, for example.

The invention provides an SAR (synthetic aperture radar) echo simulating method based on GPU (graphics processing unit) parallel computing, overcomes defects on influencing SAR echo simulating speed and accuracy, and improves influencing SAR echo simulating speed. The method includes the steps of setting up scene scattering point mesh generation and making sure position relation of double antenna SAR and scene targets; building up backscattering coefficient model, and generating correlated backscattering coefficient pairs according to sight relation of double antenna SAR and ground scene so as to complete backscattering coefficient computing; calculating positioning echo signals in SAR irradiating area; performing convolution to positioning echo signals acquired in step 3 and transmitting signals to acquire current pulsing echo signals; and going through all positioning times to acquire SAR echo data influenced by double antenna in the whole scene.

The invention discloses an airborne SAR (synthetic aperture radar) imaging method suitable for a large squint angle. The method comprises the following steps of: (1) establishing an echo signal model; (2) performing signal imaging by the steps of: (2-1) performing distance fast Fourier transform and azimuth fast Fourier transform on a point target signal; (2-2) performing distance inverse Fouriertransform and performing accurate treatment on the phase of the signal; (2-3) multiplying the result by a Chirpscaling factor; (2-4) performing distance Fourier transform; (2-5) multiplying the result by a distance compensation factor; (2-6) performing distance inverse Fourier transform; (2-7) multiplying the result by an azimuth compensation factor; and (2-8) performing azimuth inverse Fourier transform to obtain a compressed SAR image signal. In the method, by imaging the point target under a large squint angle, a good peak-sidelobe ratio and an integral-sidelobe ratio can be obtained; a relatively high spatial resolution can be obtained in the distance direction and azimuth direction by use of the SAR pulse compression technology and the synthetic aperture technology; and moreover, themethod performs distance relocation correction in a time domain, simplifies an echo signal distance model, reduces the two-dimensional coupling quantity, adopts accurate phase unwrapping, realizes accurate correction of the signal and has a relatively high processing speed.

The invention discloses a synthetic aperture radar (SAR) imaging method based on field programmable gate array (FPGA). The SAR imaging method based on the FPGA mainly solves the problems that an existing system is complex in structure and slow in data processing speed. The SAR imaging method based on the FPGA comprises the following steps: calling a multiplying unit in the FPGA, conducting fast Fourier transform (FFT) operation after multiplying each array of distance direction data and hamming window data after quantification, finishing distance pulse pressure; calculating a scene central location of the distance direction by inertia parameters, intercepting the distance direction data; transposing acquired data by interception, realizing to store aperture data based on direction; estimating a Doppler central value and a Doppler frequency modulation rate based on inertia navigation parameters; constructing a Doppler frequency shift function, a Doppler frequency modulation function and a direction hamming window function based on the estimated Doppler central value and the Doppler frequency modulation rate; conducting FFT operation by multiplying each array of the direction data after finishing the distance impulse pressure with the Doppler frequency shift function, the Doppler frequency modulation function and the direction hamming window function, and acquiring final imaging data. The SAR imaging method based on the FPGA has the advantages of simplifying an SAR imaging system structure, improving processing speed, and capable of being used in the SAR imaging under a missile-borne module.

The invention discloses a side slope safety monitoring and prewarning method based on ground-based synthetic aperture radar. The side slope safety monitoring and prewarning method includes acquiring radar data, about continuous fixed point observation, of a side slope area by the ground-based synthetic aperture radar; subjecting the radar data which are acquired to imaging processing, differential interference processing and deformation information extracting; performing side slope slip analysis, prediction and automatic prewarning. By the side slope safety monitoring and prewarning method, all-time, all-weather, remote-distance, high-accuracy and fixed-point continuous monitoring of the large-range side slope area can be realized, and acoustic, optical and electric signal prewarning can be realized automatically.

The invention provides a hard threshold OMP (orthogonal matching pursuit)-based linear array SAR (synthetic aperture radar) sparse imaging method. A linear measurement matrix of original echo signals of a linear array SAR and scattering coefficients in a target space of an observed scene is established for the characteristic that main scattering targets are spatially sparse in the target space of the observed scene of the linear array SAR, and contrast between maximum and minimum target scattering coefficients and a target scattering coefficient change rate are used as iteration ending conditions for the iteration processing of a hard threshold OMP algorithm, so that the dependence of a conventional OMP algorithm on the number of the main scattering targets in linear array SAR sparse imaging is overcome. Compared with a conventional OMP algorithm-based linear array SAR sparse imaging method, so that the method has the advantages that the number of the main scattering targets in the target space of the observed scene is not required to be known, and the method is more applicable to the linear array SAR sparse imaging when the number of the main scattering targets is unknown under actual conditions; the imaging accuracy of the linear array SAR is improved. The method can be applied to the fields of SAR imaging, earth remote sensing and the like.

Method and apparatus for simultaneous synthetic aperture radar and moving target detection. A plurality, of independent radio frequency signals are generated and applied to separate radiating/receiving antenna elements. Signals are generated as basis functions, such that moving target detection and synthetic aperture radar signals are constructed from individual waveform components in space, time, frequency, and coding. Waveform components are sorted and combined at reception. Received data is simultaneously processed to extract synthetic aperture radar images and moving target indication detections.

Described is a system for synthetic aperture radar (SAR) imaging. The system is adapted to reconstruct a set of images to generate a set of reconstructed SAR images, wherein at least some of the reconstructed SIR images have noise and contain glint. The reconstructed SAR images are then stacked into a matrix D, in which each column of the matrix is a reconstructed SAR image. Using sparse and low-rank decomposition on the matrix D, the system then extracts a clean background from the reconstructed SAR images and separates the noise and glint. Based on that, the system is operable to detect moving targets in sparse part S and issuing a notification of such a moving target.