FMCW SAR Research Articles

A novel ground-track FMCW SAR imaging method based on modified wavenumber domain algorithm

A novel ground-track FMCW SAR imaging method based on modified wavenumber domain algorithm

Subaperture Imaging Algorithm for Squinted Automotive FMCW SAR Based on CLOSI-Omega-K

Subaperture Imaging Algorithm for Squinted Automotive FMCW SAR Based on CLOSI-Omega-K

Azimuth Interrupted FMCW SAR for High-Resolution Imaging

Azimuth interrupted frequency modulation continuous-wave synthetic aperture radar (AI-FMCW SAR) is a novel type of light and miniaturized sensor that works on satellites, which can transmit and receive signals with a single antenna. Different from conventional pulse SAR, the instantaneous duty cycle of pulse is close to 100%. Several pulses could not be transmitted and would be replaced by receiving echoes. There will be gaps in the received echoes. It is necessary to reconstruct the gapped data; otherwise, there will be ghosting with traditional imaging algorithms. The current algorithms for reconstructing the gapped data are computationally time-consuming and not suitable for high-resolution imaging. Therefore, a new imaging algorithm is proposed to focus on the AI-FMCW SAR raw data via subaperture processing, which is called subaperature sparse reconstructing technique (SSRT). It can significantly suppress ghost targets and has a high calculation speed. In this letter, the spaceborne AI-FMCW SAR signal model was proposed first. Then, SSRT was proposed to process the AI-FMCW SAR data, in which the generalized orthogonal matching pursuit (GOMP) algorithm was used to reconstruct the signals. Finally, the simulation experiments verified the effectiveness and rapidity of the proposed approach.

An improved range Doppler algorithm based on squint FMCW SAR imaging

An improved range Doppler algorithm based on squint FMCW SAR imaging

Sea Surface Imaging with a Shortened Delayed-Dechirp Process of Airborne FMCW SAR for Ocean Monitoring on Emergency

A sea surface imaging technique for an emergency response using a ready-made frequency modulated continuous wave–synthetic aperture radar (FMCW SAR) system and its experimental results are described in this paper. The optimal range of radiowave incidence angle for sea surface imaging was analyzed by a theoretical scattering model and measurement data, and it was properly applied to the FMCW SAR system by readjusting the delayed-dechirp process. Raw data acquired through flight experiments were reconstructed to SAR image by the range-doppler algorithm. To verify the performance of the reconstructed sea surface image, dual-channel images collected by the configuration of the along-track interferometry were used, and then performance indicators such as signal attenuation, coherence, and phase difference were analyzed. Through this experimental study, it was confirmed that the ready-made FMCW SAR system without a function of the incident angle control can also conduct limited missions for maritime observation. It is possible to be an alternative resource for emergency response, in which the cases are requiring urgent maritime disaster detection and analysis.

Moving Target Refocusing With the FMCW SAR System MIRANDA-35

Inverse synthetic aperture radar is a commonly adopted technique for producing high-resolution images of moving targets. This article investigates the imaging capabilities of high-frequency and high-bandwidth systems by means of two distinct experiments. The deployed sensor is the Fraunhofer FHR MIRANDA-35, a millimeter-wave synthetic aperture radar airborne system, which transmits frequency-modulated continuous-wave signals at the Ka-band and is capable of achieving centimeter resolution. The performances are assessed by comparing the derived estimates (e.g., radial velocity and acceleration, and dimensions) with independent ground measurements. The resulting accuracy can be summarized as follows: the mean value of the percent error is 2.05% and 2.11% for radial velocity and acceleration, respectively, and 4.27% for the target dimensions.

Sparse Scene Recovery for High-Resolution Automobile FMCW SAR via Scaled Compressed Sensing

This paper introduces a sparse scene reconstruction algorithm for automobile frequency-modulated continuous-wave synthetic aperture radar (FMCW SAR) through scaled compressed sensing (CS). An FMCW radar leads to low manufacturing cost, compact realization, and low transmission power. An automobile SAR is more economical and easier to implement than typical SAR platforms (e.g., satellites and aircraft). We apply CS to randomly subsampled raw data of automobile FMCW SAR for sparse reconstruction. We exploit the fact that the velocity of an automobile is significantly lower than that of the SAR platforms, which leads to a vastly narrow bandwidth of an azimuth-matched filter in the azimuth compression of the range-Doppler algorithm (RDA). Low-frequency azimuth data have a fundamental effect on azimuth compression. We propose a new reconstruction scheme, scaled CS, which specializes in low-frequency information recovery for automobile SAR. The scheme is based on basis pursuit denoising (BPDN). A Ku-band FMCW SAR system is developed to verify the performance of the proposed algorithm. We mount our system on an automobile and collect FMCW SAR raw data in the stripmap mode with a van maintained a constant speed on a highway. The proposed reconstruction algorithm shows improved recovery performance for automobile FMCW SAR, which is validated by processing a high-resolution real SAR image.

Краткий опыт создания и первые результаты практической съемки поверхности малогабаритной РЛС с синтезированием апертуры антенны с борта мультикоптера.

Краткий опыт создания и первые результаты практической съемки поверхности малогабаритной РЛС с синтезированием апертуры антенны с борта мультикоптера.

A New Distortion Correction Method for FMCW SAR Real-Time Imaging

A new and fast approach to correct distortion between the airborne frequency-modulated continuous wave synthetic aperture radar (FMCW SAR) real-time images is proposed in this letter. The main idea of the proposed method contains two parts. First, the rotation distortion, according to the adjacent subimages caused by the selection of the reference trajectory, is efficiently corrected by data reposition. Comparing with the conventional correction technique, the time consumption is dramatically reduced from 0.3 s to only 0.717 ms. Second, the residual offset error between the rotated subimages is analyzed and compensated in the first-step motion compensation. With the application of the proposed method, the distortion correction during FMCW SAR real-time imaging becomes realizable. The correction approach has been evaluated by an FMCW SAR system, and the obtained results verify the feasibility and effectiveness of the proposed method.

An analysis of Chosen Image Formation Algorithms for Synthetic Aperture Radar with FMCW

Abstract The modelling of FMCW SAR systems, due to long signal duration time, commonly used start-stop approximation for pulsed radars causes errors in the image. Continuous motion of the radar platform results in additional range-azimuth couplings and range walk term that should be considered in processing of signal from this type of radar. The paper presents an analysis of the following algorithms: Time Domain Correlation (TDC), Range Doppler Algorithm (RDA), and Range Migration Algorithm (RMA). The comparison of the algorithms is based on theoretical estimation of their computation complexity and the quality of images obtained on the basis of real signals of FMCW SAR systems.

Strong Spurious Noise Suppression for an FMCW SAR

To meet the miniature requirement, a frequency modulated continuous wave synthetic aperture radar (FMCW SAR) puts tight constraint on the compactness, which causes the interference of narrow band noise. The aim of this study is to suppress the strong noise for an FMCW SAR. First, the quantitative analysis of the noise is performed. It is found that a strong spurious noise of the analog-to-digital converter (ADC) is introduced from interferences and significantly affects the image quality; the other noise components are sufficiently small, thus having ignorable influences. Then, a Fast Fourier Transform (FFT) based method of noise suppression is proposed to eliminate the ADC strong spurious noise, adopting an ADC and a field programmable gate array (FPGA). Finally, using the real Ku-band FMCW SAR data, the level of the noise components is measured and the effectiveness of the proposed noise suppression method is validated. The results show that the measured noise level coincides with the theoretical noise level, and the proposed noise suppression method effectively eliminates the ADC strong spurious noise.

Simplified Real‐Time Imaging Flow for High‐Resolution FMCW SAR

This letter considers the feasibility of a simplified real-time imaging flow theoretically for frequency-modulated continuous-wave synthetic aperture radar (FMCW SAR). The simplified imaging flow is based on the range-Doppler algorithm, whereas the simplifications contain absolving the residual-video-phase correction and performing the second-order motion compensation ahead of the range cell migration correction (RCMC). During the analysis, the platform movement within the transmission of a sweep is considered. Moreover, the hardware technique, i.e., the enhanced direct memory access, is used to improve the efficiency of the bulk RCMC. Eventually, the simplified imaging flow is evaluated in terms of quality and efficiency by using real Ku-band FMCW SAR data. The results indicate that the simplified method could produce SAR imagery of high resolution (0.25 m × 0.25 m) in real time, with a speed-up factor of 2.77 comparing with the frequency scaling algorithm.

Eksperymentalna weryfikacja algorytmu RDA w systemie SAR pracuj�cym z fal� ci�g��

The article presents a description of the Range-Doppler Algorithm tailored to the specific character of the FMCW sensor as well as a description of the results of the experimental tests. The tested sensor has been developed for a radar terrain imaging system operating from miniature unmanned aerial vehicle. (Experimental verification of the Range-Doppler Algorithm in a continuous wave SAR system). Slowa kluczowe: FMCW SAR, algorytm RDA, BSL.

Study on the improvements for the high‐resolution frequency modulated continuous wave synthetic aperture radar imaging

This study develops two aspects of improvement, performing the range-dependent secondary range compression (SRC) and correcting the motion errors within the sweep of the transmitted signal, for the high-resolution frequency modulated continuous wave synthetic aperture radar (FMCW SAR). In cases of more complex imaging scenarios such as higher squint angle and larger range swath, the range dependence of SRC should be considered to avoid severe degradation. Moreover, when the trajectory deviations are severe, the motion error within the sweep causes new noticeable residual range cell migration, which should be considered for the motion compensation of FMCW SAR. Experimental results on the simulated and actual Ku-band SAR data proved that, for full swath and high squint mode FMCW SAR, the proposed approaches are valid and greatly helpful to improve the imaging quality.

Imaging analysis of frequency modulation continuous wave synthetic aperture radar in near range mode

Frequency-Modulation Continuous-Wave Synthetic Aperture Radar (FMCW SAR) has shown great potential in the applications of civil and military fields because of its easy deployment and low cost. However, most of these work and analysis are concentrated on airborne FMCW SAR, where the characteristics of the imaging geometry and signal are much similar to that of traditional pulsed-SAR. As a result, a series of test campaigns of automobile-based FMCW SAR were sponsored by Institute of Electronics, Chinese Academy of Sciences (IECAS) in the autumn of 2012. In this paper, we analyze the imaging issues of FMCW SAR in automobile mode (named as near range mode), where a vehicle is used as moving platform and a large looking angle is configured. The imaging geometry and signal properties are analyzed in detail. We emphasize the difference of the near range mode from the traditional airborne SAR mode. Based on the analysis, a focusing approach is proposed in the paper to handle the data focusing in the case. Simulation experiment and real data of automobile FMCW SAR are used to validate the analysis.

High-resolution automobile FMCW SAR and signal processing

The paper presents a high-resolution automobile Frequency Modulation Continuous Wave Synthetic Aperture Radar (FMCW SAR) named MiniSAR and the procedure of its signal processing. The imaging geometry of automobile SAR is very different from that of airborne SAR, leading to a different data processing method for automobile SAR. Therefore, in the paper, we propose an image formation approach that can well handle the focusing issues of automobile SAR. The effects of the strong reflected signal and the spatial-variant synthetic aperture length are analyzed. The processed results with automobile FMCW SAR read data validate the presented method.

Nonlinearity Correction of FMCW SAR Based on Homomorphic Deconvolution

In this letter, a novel algorithm based on homomorphic deconvolution is proposed to give a theoretically unbiased estimation of transmitted nonlinearity in the beat signal in frequency-modulated continuous-wave synthetic aperture radar. Transmitted and received nonlinearities in the beat signal are separated in the Cepstrum domain by using a controllable delay line, and the transmitted nonlinearity can be extracted by comb notch filter. Moreover, an integrated nonlinearity correction strategy with residual-video-phase removal is presented by combining with the proposed estimation algorithm. Extensive simulations are performed to validate the generality and the robustness of the proposed algorithm.

AN EXTENDED INVERSE CHIRP-Z TRANSFORM ALGORITHM TO PROCESS HIGH SQUINT SAR DATA

This paper proposes an Extended Inverse Chirp-Z Transform (EICZT) algorithm to handle the high squint FMCW SAR data, where the conventional Inverse Chirp-Z Transform (ICZT) cannot work due to the failure in dealing with the range-variance of second- and higher-order range-azimuth coupling terms. A pre- processing operation is implemented in the azimuth-Doppler and range-time (Doppler-time) domain, where a perturbation function consisting of second-order and third-order range time variables is implemented to compensate the range variance of the second order range terms. Moreover, a new scaling factor is formulated to represent the Range Cell Migration (RCM), and further corrected by the presented EICZT approach. The proposed approach is analyzed and compared with the conventional ICZT. The simulated high squint SAR scene with nine targets is well focused by the proposed approach and the quality is greatly improved with respect the conventional ICZT. The proposed algorithm is also validated by the X-band high-resolution real SAR data.

An Improved FS Algorithm for Range Anti-aliasing of FMCW SAR

原始的频率变标算法(Frequency Scaling, FS)用于调频连续波SAR 成像处理时，会导致严重的距离频谱混叠。该文从频率变标算法原理出发，结合傅立叶变换的尺度变换性质从距离时域和距离频域的角度进行分析，通过引入归一化因子，提出了一种消除距离频谱混叠的改进FS 算法。该算法保留了原RVP 项，并且不改变原始FS算法的处理步骤和处理效率。最后利用该算法对点目标进行聚焦成像，验证了该算法的有效性。

The Analysis of FMCW SAR Signal and Image Study

The Analysis of FMCW SAR Signal and Image Study