range-Doppler Imaging Algorithm Research Articles

Fast SAR Image Simulation Based on Echo Matrix Cell Algorithm Including Multiple Scattering

We present a novel fast synthetic aperture radar (SAR) image simulation method based on the echo matrix cell algorithm including multiple scattering. To improve the efficiency of SAR image simulation while ensuring the fidelity of the simulated results, we first discretized the target facets set in the SAR beams footprint into lattice targets using the range-Doppler (RD) imaging geometry model and provided the basis for simulating electromagnetic wave transmission. Based on the simulation of electromagnetic waves transmission, we used the ray tracing algorithm to calculate the multiple backscattering field including multi-polarimetric information and various material properties. Then, based on the echo matrix cell algorithm, we set the echo matrix cell as the subfield of the target backscattering field and designed the CUDA kernel function to implement a computation parallelization for SAR echo generation. All the echo matrix cells are traversed in parallel to obtain the total backscattering field of the target, reproducing the time-varying characteristic of the backscatter coefficient for each lattice target within the synthetic aperture time. The echo signal is processed using the RD imaging algorithm to obtain the simulated SAR image. Finally, we select some targets including aircraft carrier and airplane models for simulation tests. The computation efficiency is improved over 170-fold by comparing the computations of the proposed method and CPU single-thread. We also performed some qualitative and quantitative evaluations on the fidelity of the simulated SAR images. The experimental results verify the effectiveness of the proposed method.

An Improved Range-Doppler Imaging Algorithm Based on High-Order Range Model for Near-Field Panoramic Millimeter-Wave ArcSAR

An Improved Range-Doppler Imaging Algorithm Based on High-Order Range Model for Near-Field Panoramic Millimeter-Wave ArcSAR

SAR Image Simulation Based on Effective View and Ray Tracing

We present a novel echo-based synthetic aperture radar (SAR) image simulation method that comprehensively utilizes both SAR effective view and ray tracing algorithms. To improve the fidelity of simulated SAR images, we first design an SAR effective view algorithm to process the selected facet target model, with the purpose of discretizing the facets in the SAR effective view into lattice targets and ensuring that the interval of lattice targets is set strictly following the Nyquist sampling law. Then, we combine the ray tracing algorithm and SAR echo time-domain simulation and perform SAR echo time-domain simulation of lattice targets based on ray tracing. Various kinds of backscatter coefficient for each point target can be recorded, corresponding to the number of transmitted pulses within the synthetic aperture time. The echo matrixes of lattice targets are superimposed to generate the raw echo signal. Finally, the raw echo signal is processed by using the range-Doppler (RD) imaging algorithm to obtain the simulated SAR image. We conducted SAR image simulation tests on several facet target models, including car body, assault boat, and airplane, with different material properties. The simulated SAR images obtained by the proposed method were qualitatively and quantitatively evaluated. The experimental results verify the effectiveness of the proposed method.

Moon Imaging Technique and Experiments Based on Sanya Incoherent Scatter Radar

This article introduces the experiment design for Moon imaging based on Sanya incoherent scatter radar (SYISR) and algorithm research in data processing. The peak power of SYISR is 2 MW. The transmitted frequency used for Moon imaging experiments is 430 MHz. We conducted Moon imaging experiments using two types of waveforms, 13-bit Barker code, and linear frequency modulation (LFM) chirp. Considering both resolution and signal-to-noise ratio (SNR), the use of an LFM chirp with a bandwidth of 0.3 MHz and a pulsewidth of 2 ms can give higher SNR and resolution for Moon imaging using SYISR. Several key techniques were applied in the experiment design and data processing: 1) for the reliability of the imaging algorithm, the range-Doppler imaging algorithm commonly used in synthetic aperture imaging was applied; 2) to avoid the sidelobe effect of the 13-bit Barker code matched filter, a sidelobe-free filter was used; and 3) to mitigate the problem of “north–south ambiguity,” mosaic imaging of the Doppler northern and southern hemispheres of the nearside of the Moon was adopted. Two types of imaging results are obtained: mosaic images of the northern and southern hemispheres of the Moon and local regional images. The results demonstrate the feasibility and reliability of Moon imaging based on SYISR, which enables potential further lunar geology investigations in the future.

An Efficient Multichannel SAR Channel Phase Error Calibration Method Based on Fine-Focused HRWS SAR Image Entropy

Azimuth multichannel synthetic aperture radar (SAR) is a useful approach to solving minimum antenna area constraint and realizing high resolution and wide swath (HRWS) imaging by multichannel signal reconstruction. However, channel phase error will significantly degrade the reconstruction performance and leads to azimuth ghost. This article presents an efficient minimum entropy channel error estimation method based on fine-focused SAR image. The multichannel SAR images are obtained by using Range-Doppler imaging algorithm applied for preprocessed data of each channel. Then, the reconstruction and the residual range cell migration and residual second range compression compensation are performed to achieve multichannel fine-focused SAR images. After overlapping these multichannel fine-focused SAR images and iteratively calibrating the channel phase error, fine-focused HRWS SAR image can be achieved. Therefore, the SAR image used in the channel error estimation process can directly obtain the fine focused HRWS SAR image after minimum entropy iteration without additional imaging operations. Compared with the minimum entropy method by using the coarse-focused SAR image based on azimuth deramp, redundant reconstruction, and imaging operations are avoided. Thus, error estimation and imaging processing procedures are optimized. Processing efficiency improvement are analyzed, and simulation and acquired data processing verify the effectiveness of the proposed method.

High-Squint SAR Imaging of Maritime Ship Targets

High-squint synthetic aperture radar (HS-SAR) imaging technology greatly enhances the flexibility of SAR. However, the existing HS-SAR imaging algorithms are generally based on the assumption that the illuminated target is static during the synthetic aperture formation. As a consequence, the state-of-the-art algorithms are unable to focus on moving targets well, thus leading to displaced and blurred images of the targets. A maritime ship is a typical kind of moving target with complex noncooperative motion, which has received much attention. Thus, it is a difficult but valuable issue to study HS-SAR imaging of ship targets. In this work, the influence of ship translation and fluctuation is theoretically analyzed. On the basis of these analyses, the new conception of ``third range compression (TRC)'' caused by ship translation is proposed, and the squint minimization (SM) operation is implemented for the compensation of TRC. Moreover, considering that the target Doppler parameters induced by ship fluctuation are related to its position, a novel method called WASH-CLEAN (watershed and CLEAN) is proposed to automatically focus ship scattering points with different swings. Finally, we propose an integrated modified range-Doppler (RD) imaging algorithm by combining the advantages of HS-SAR and inverse synthetic aperture radar (ISAR). The simulation results show the validity and effectiveness of the presented method.

Accelerating range Doppler imaging algorithm for multiple-receiver synthetic aperture sonar on multi-core-based architectures

Synthetic aperture sonar (SAS) is an underwater high-resolution imaging method. But with the increase in resolution and mapping width, the amount of raw data used for imaging increases dramatically. To solve the problem of low imaging efficiency of SAS, an acceleration method of SAS imaging in shared memory environment is proposed. By analyzing the calculation characteristics of each step from the original data received to the synthetic aperture imaging result, the range compression, equivalent conversion from multi-receiver signal to single-receiver signal and azimuth compression are designed in parallel with OpenMP instructions, and the multi-core computing resources are fully utilized to accelerate the imaging process. Simulation experiment verifies the correctness of the parallel imaging algorithm. The experimental result of real data shows that the parallel imaging algorithm has high efficiency and can realize super real-time imaging. The efficiency of the proposed method can be changed with the number of computational kernels. The relationship between the acceleration ratio and the computational kernels is approximately linear, which improves the adaptability of the algorithm. Efficient synthetic aperture sonar imaging algorithm provides conditions for post-processing of image, such as image enhancement, image target detection and recognition.

An Indirect Range-Doppler Algorithm for Multireceiver Synthetic Aperture Sonar Based on Lagrange Inversion Theorem

This paper presents a novel imaging algorithm which has the capacity of processing multireceiver synthetic aperture sonar (SAS) data based on Vu’s spectrum. There are two important issues when developing the fast Fourier-based imaging algorithms. One is the point target reference spectrum (PTRS) with analytical expression in the 2-D frequency domain; the other is the space variance of the PTRS. Vu has solved the first issue based on the Lagrange inversion theorem. However, the second issue has not been solved yet. Our approach in this paper is to apply Vu’s spectral result in an indirect range-Doppler (R-D) imaging algorithm. For each transmitter/receiver pair, the close-form azimuth modulation is derived first, and then, range/azimuth coupling can be obtained via the difference between the PTRS and the azimuth modulation. Unlike traditional R-D algorithm, which utilizes the interpolation operation to eliminate the range cell migration (RCM), the RCM correction (RCMC) in this paper is carried out through two steps, i.e., bulk RCMC and differential RCMC. Bulk RCMC accounts for the RCMC in one reference range. Differential RCMC accomplished with a range-dependent subblock postprocessing method is used to compensate for the space variant deviation phase error. Via the proposed method, the echoed signal corresponding to each transmitter/receiver pair is processed first. Following which, a high-resolution SAS complex image is obtained by coherent superposition of all the coarse subimages. Numerical simulations and real data processing results show that the proposed method has the similar focusing capabilities with the accurate back projection algorithm across the whole swath. Although the presented method has the disadvantage of latency, it is very easy to make a complete phase center approximation correction, allowing for the tandem nature of the collected data. Besides, the proposed algorithm can handle general case with explicit point of stationary phase (PSP) no matter how complicated the PSP is, and it is also suitable for the imagery of tandem synthetic aperture radar.

A novel range-Doppler imaging algorithm with OFDM radar

Traditional pulse Doppler radar estimates the Doppler frequency by taking advantage of Doppler modulation over different pulses and usually it requires a few pulses to estimate the Doppler frequency. In this paper, a novel range-Doppler imaging algorithm based on single pulse with orthogonal frequency division multiplexing (OFDM) radar is proposed, where the OFDM pulse is composed of phase coded symbols. The Doppler frequency is estimated using one single pulse by utilizing Doppler modulation over different symbols, which remarkably increases the data update rate. Besides, it is shown that the range and Doppler estimations are completely independent and the well-known range-Doppler coupling effect does not exist. The effects of target movement on the performances of the proposed algorithm are also discussed and the results show that the algorithm is not sensitive to velocity. Performances of the proposed algorithm as well as comparisons with other range-Doppler algorithms are demonstrated via simulation experiments.

Real-time Implementation of Azimuth Compression for Airborne SAR Using C67 High-speed DSP

Airborne SAR could gain high-quality image during aircraft flight. Due to its theoretical advantages, SAR imaging has been widely applied in both military and civilian areas. Range and azimuth processing are the two crucial steps of SAR imaging. The major challenges of real-time implementation with digital signal processing techniques lie in the algorithm complexity and high data rate of radar systems. This paper describes a high-speed DSP system based on C67 to realize real-time azimuth compression of Range-Doppler imaging algorithm. Through optimized board structure and software programming, processing system's data throughput is greatly enhanced. Both experimental simulation and field flight have shown that this system is successful.

Error Effects on SAR Image Resolution using Range Doppler Imaging Algorithm

Synthetic Aperture Radar (SAR) is an imaging radar form by taking full advantage of the relative movement of the antenna with respect to the target. Through the simultaneous processing of the radar reflections over the movement of the antenna via the Range Doppler Algorithm (RDA), the superior resolution of a theoretical wider antenna, termed synthetic aperture, is obtained. Therefore, SAR can achieve high resolution two dimensional imagery of the ground surface. In addition, two filtering steps in range and azimuth direction provide accurate enough result. This paper develops a simulation in which realistic SAR images can be generated. Also, the effect of velocity errors in the resulting image has also been investigated. Taking some velocity errors into account, the simulation results on the image resolution would be presented. Most of the times, algorithms need to be adjusted for particular datasets, or particular applications. Keywords—Synthetic Aperture Radar (SAR); Range Doppler Algorithm (RDA); Image Resolution

Study of SAR imaging with COMPASS signal

A concept of space-surface bistatic synthetic aperture radar (SS-BSAR) passive imaging system is proposed, which is parasitic on the signal of COMPASS Navigation Satellite System (CNSS). The feasibility is demonstrated by analyzing the signal ambiguity function and the range resolution as well as the system topology. Due to the multiple peaks of signal in the auto-correlation function, a new correlation is used to remove the side-peaks. A double-channel receiver is employed to receive the direct satellite signal and the ground reflected signal. The direct signal is a reference signal in range compression, and may also be used for transmitter-receiver signal synchronization. The reflected signal is raw data collected for imaging. Then, a modified range-Doppler imaging algorithm is derived based on the system geometric models and BSAR imaging principle. The proposed algorithm is verified via signal simulation. The work in this paper is of great value to the further use of COMPASS signal, as well as other global navigation satellite signals in passive imaging.