Wenge Chang

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.

Fourier-Based 2-D Imaging Algorithm for Circular Synthetic Aperture Radar: Analysis and Application

Circular synthetic aperture radar (CSAR) has become a research hotspot in the SAR community. Since the Fourier-based imaging methods of CSAR are underdeveloped, further developments have to be investigated. In this paper, the exact expression and property analysis of the spectrum of CSAR are presented first. It turns out that the challenges of the Fourier-based 2-D imaging processing of CSAR lie in the projection of spectrum from the slant plane into the ground plane. Correspondingly, a spectrum-projection method by matched filtering as well as the practical subaperture-based imaging flow of CSAR are proposed, during which the trajectory deviation has been taken into account. Simulation and experimental tests are carried out to measure the efficiency and accuracy of the proposed method. The corresponding results verify that the proposed signal model is correct and the presented imaging flow is a good candidate to produce well-focused CSAR imagery with much less time consumption.

An improved method for the real-time pulse compression based on FPGA

Pulse compression is an important signal processing technique in radar system. Based on field programmable gate array (FPGA), an improved method for implementing pulse compression is proposed to reduce the resource usage. As the FFT and IFFT transform are the main calculations of the pulse compression and take up many resources, single FFT IP core is used to realize two operations in the improved method. To clarify the practical feasibility of this method, the judgment is carried out in detail based on the resource usage, time, and data accuracy which are the key parameters for the implementation of the pulse compression. At last, the effectiveness of the method is verified in the signal processor. The result indicates that many resources are saved and no data accuracy is lost at expense of increasing a little of time.

The formation of high-resolution FMCW SAR video

In this paper, the formation of high-resolution FMCW SAR video is introduced in detail. With the application of rational design and compact devices, a miniaturized FMCW SAR prototype is successfully realized. Based on this high-performance FMCW SAR system, the continuous real-time video is achieved after the preprocessing of raw data, the parallel realization of extended FSA and the reprocessing of imaged data. Moreover, the time consuming of each procedure is accurately tested on the processing board of FMCW SAR system. In the end, several airborne experiments have been performed, and beneficial FMCW SAR video results have been obtained.

A compact high-speed storage system for an airborne SAR

The technology of the miniature high-speed mass data storage for an airborne FMCW SAR is investigated in this study. The compact flash (CF) card with the light weight, high read/write speed, and large capacity is used as the storage medium in the data storage system. The major problem of high speed data storage is the irregular response time due to the internal overhead of the CF card and frequently cluster switching involving retrieving and updating of the FAT and FDT in the file system. Two techniques are presented to overcome these problems. The experimental results indicate that the miniature requirement of the data storage system is satisfied, the capability of high-speed storage is achieved.

An efficient geometric distortion correction method for SAR video formation

In this paper, an efficient method to correct the geometric distortion for onboard processing SAR video is proposed. Based on the EDMA data transmission of the compact multi-core DSP, the geometric distortion is corrected much more efficient compared to the traditional measures. With the application of the proposed correction method, the continuous real-time images are obtained. Moreover, the extra time consuming introduced by correction processing is greatly reduced, which will be very beneficial to achieve real-time processing. The proposed efficient correction method has been applied to a compact FMCW SAR system, and many continuous real-time images with high resolution have been achieved.

Study on an onboard data storage system for frequency-modulated continuous-wave synthetic aperture radar

Abstract. The airborne frequency-modulated continuous-wave synthetic aperture radar presents an enormous technical challenge on the design of data storage system due to its characteristics of high-data rate, small size, light weight, and low-power consumption. There are two main problems for the high-speed storage under the miniature requirement. One is the unpredictable response time of the flash translation layer in the CompactFlash card. The other is the relatively long response time of the file system. This paper designs a data storage system in a real-time signal processor. Two techniques called configurable buffer structure and FPFQA (FAT pre- and FDT quasiallocation) are presented to overcome these two problems. The evaluated performance indicates that the size, power consumption, and weight meet the miniature requirement, while the function of the high-speed data storage with approximately 121u2009u2009MB/s storage speed and real-time file management are realized.

Influence of flight angle error on the geometric correction

The geometric correction method based on SAR image simulation, with advantages of no requirement of ground control points (GCP) and all the processing can be done automatically, has attracted broad attention and application. However, the imprecise input parameters of SAR image simulation, especially the flight angle, will deform the texture of the simulated SAR image, and degrade the matching probability and matching precision of GCPs extracted from it and the real SAR image, and then lose the geometric accuracy. The influence of flight angle error on the image texture, matching probability and matching precision was analyzed in this paper, and a quantificational analysis using the real data was also completed. Results show that GCPs can get a high matching probability and precision when the flight angle error is less than 6°.

Multiple moving targets real-time detection in single-channel SAR using median filter

With the development of hardware, the detection of ground moving targets with single-channel synthetic aperture radar (SAR) can be achieved by a relatively higher pulse repetition frequency (PRF). This high PRF can bring adequate amount of information, but it also expands the non-clutter spectrum which affects the precision of the real-time detection by the Doppler spectrum shifting methods. In order to make sure that the single-channel SAR can achieve real-time imaging and detection of moving targets, a new method based on former Doppler shifting methods is presented in this paper. First, we calculate the azimuth spectrum by Fourier transform in segments. Then, the median filter is introduced to eliminate the high-energy, narrow-spread spikes in the real data, which makes the whole procedure to be realistic and improves the location precision of moving targets significantly. In the end, we confirm the estimated Doppler centroids for the latter imaging and detection of moving targets. The corresponding flow of the whole system is also given in this paper. The effectiveness of this method is illustrated with the simulation results based on the real data.