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This paper presents a new approach for high-resolution airborne SAR real-time imaging, which uses a subaperture nonlinear chirp scaling algorithm (NCSA) to accommodate the correction of the motion errors along track and cross track. The proposed algorithm is computationally efficient and can reduce the memory requirement by half with a great shorten of lag time before block processing. Simulation...
According to the characteristic that the bandwidth of spaceborne SAR is generally quite wide, a new method called "sub-band double carrier frequency conjugated processing" is presented in this paper. The approach can decrease the equivalent central frequency of the synthetic signal and remove the Doppler ambiguity. Consequently, Keystone transform can be used to correct the linear range...
Superresolution array processing methods have been applied to inverse synthetic aperture radar (ISAR) imaging in order to enhance the resolution for many years. Nevertheless, because the excellent performances of the methods are based on the accurate knowledge of the data model, the performance of superresolution methods is degraded extremely, when the signal-to-noise-ratio is not very high, and the...
Based on wave-front reconstruction theory, this paper analyzes the principle of improving azimuth resolution in spotlight mode by multiple SAR surveys, and the approach to implement it. Meanwhile, topographic effect on the approach is investigated. And the way to eliminate topographic effect is presented. The numerical simulation examples are given in the end to illustrate the results
Bistatic radar, especially illuminating of opportunity, has recently been one of interesting research hotspot due to its military stealth and economic advantages. In this paper, we consider non-cooperative bistatic SAR using aircraft as receiver and spaceborne radar as illuminating of opportunity. Firstly, we qualitatively descript the relationship between geometry and resolution of bistatic SAR....
Passive millimeter wave imaging radar systems provide advantages over the optical and infra-red (IR) systems, especially under the poor weather with fog, clouds and light drizzle which are effectively transparent at millimeter wavelength. Due to the higher diffraction in millimeter wave range, the images are often acquired with poor resolution. In order to enhance these images and recover the spatial...
In this paper, the processing algorithm of high resolution range profile of chirp-stepped signal is studied in the view of system, and the process of chirp-stepped signal SAR imaging on helicopter platform is analyzed. Furthermore, technology difficulties of helicopter-borne SAR imaging are showed, and imaging results are presented by experimental data
This paper presented circular scanning synthetic aperture radar (SAR) based on circular scanning antenna. The work principle of this scanning radar was described. The variations of synthetic, aperture time, azimuth resolution and time-bandwidth product were analyzed. Also a focused imaging algorithm instead of DBS was used to form high resolution image. This algorithm based on extended chirp scaling...
Synthetic aperture radar (SAR) image despeckling is an important problem in the SAR applications. A novel despeckling approach using a local contextual hidden Markov model (LCHMM) in the contourlet domain is presented in this paper. The proposed method can not only use the multiresolution and multidirection characteristics of the contourlet transform, but also exploit the local statistics and capture...
Reconstructing three-dimensional scattering centers of radar targets without knowledge of viewing angles or relative radar-target motion is investigated. The performance bounds are deduced in which the parameter constraints and rotatory ambiguities are specially treated. We propose a novel method based on the signal subspace invariance in multiple one-dimensional projection sequences, which greatly...
For tissue characterization in medical ultrasound imagery or terrain characterization in synthetic aperture radar imagery, it is necessary to preprocess imagery to reduce granular, texture-alike noise called speckle. This preprocessing is difficult when it is needed to preserve delicate image details that are buried in speckle. Speckle reducing anisotropic diffusion (SAR) is a partial differential...
Based on the multi-scale direction characteristics of overcomplete brushlet transform, a feature extraction method called multiresolution grey level co-occurrence probabilities (GLCP) in overcomplete brushlet domain is presented, which makes full use of the direction information in different subbands. The segmentation results of Brodatz mosaics and synthetic aperture radar (SAR) image show that the...
In order to improve radiometric resolution of space-borne synthetic aperture radar (SAR) image without changing geometric resolution, the system parameters must be chosen optimally. ScanSAR mode has special signal characteristics and different data formats from conventional SAR, so it needs to be analyzed specially. This paper analyzes the relationship between radiometric resolution and relative system...
A new mode of curvilinear SAR called "composite mode curvilinear SAR (CCLSAR)" is proposed in this paper. In CCLSAR, the SAR operates in strip mode in azimuth and range dimension but spotlight mode in the height dimension. CCLSAR can synthesize a very large aperture in the direction of height, which cause very high resolution in the height dimension. Compared with the conventional curvilinear...
Although techniques for resolution enhancement in single-aspect radar imaging have made rapid progress in recent years, it does not necessarily imply that such enhanced images will improve target identification or recognition. However, when multiple looks of the same target from different aspects are obtained, the available knowledge base increases allowing more useful target information to be extracted...
An improved two-look processing is presented to despeckle synthetic aperture radar (SAR) images. The azimuth spectrum is halved after a constant phase is removed. Each half is extrapolated conjugate symmetrically to form a full-band azimuth spectrum, and the full-band azimuth spectrum is used to generate a look. Then, the two looks are averaged incoherently to obtain a two-look image. In this algorithm,...
In this paper, we describe how an active radar/sonar imaging problem may be formulated as a virtual passive sensor array processing problem. We consider an active sensing problem where it is desired to form a range-Doppler image at a slow- time rate, even though the radar/sonar can transmit pulses at a fast time rate. By transmitting pulses at the fast time rate we can estimate the second-order statistics...
A novel method based on de-chirping technique for compressing stepped-frequency chirp signal (SFCS) was firstly introduced, and then applied to imaging simulation for a spacecraft by a ground based ISAR using SFCS. The echo signal model for an orbiting spacecraft (the Chinese Shenzhou Spacecraft) was analyzed by deriving the equivalent translational and rotational movement. Result showed that the...
This paper concerns initial simulation study of an imaging radar system employing frequency division multiplexing as means of generating radar pulses. General architecture of OFDM communication system with realistic parameters was adopted and then modified to be used for synthetic aperture radar modeling. Arbitrary target function consisting of several point scatterers was used to test system's ability...
In this paper, an automatic aircraft target recognition (ATR) framework is presented, which is based on the high resolution range profiles (HRRP) of aircraft targets. This work is divided into two major parts. First, we consider the generation of the HRRP, which includes the modeling and simulation of radar cross section (RCS), the design of step frequency waveform (SFW), and IFFT processing for HRRP...
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