315 research outputs found
New Approach for Unambiguous High-Resolution Wide-Swath SAR Imaging
The high-resolution wide-swath (HRWS) SAR system uses a small antenna for transmitting waveform and multiple antennas both in elevation and azimuth for receiving echoes. It has the potential to achieve wide spatial coverage and fine azimuth resolution, while it suffers from elevation pattern loss caused by the presence of topographic height and impaired azimuth resolution caused by nonuniform sampling. A new approach for HRWS SAR imaging based on compressed sensing (CS) is introduced. The data after range compression of multiple elevation apertures are used to estimate direction of arrival (DOA) of targets via CS, and the adaptive digital beamforming in elevation is achieved accordingly, which avoids the pattern loss of scan-on-receive (SCORE) algorithm when topographic height exists. The effective phase centers of the system are nonuniformly distributed when displaced phase center antenna (DPCA) technology is adopted, which causes Doppler ambiguities under traditional SAR imaging algorithms. Azimuth reconstruction based on CS can resolve this problem via precisely modeling the nonuniform sampling. Validation with simulations and experiment in an anechoic chamber are presented
Motion Estimation and Compensation in Automotive MIMO SAR
With the advent of self-driving vehicles, autonomous driving systems will
have to rely on a vast number of heterogeneous sensors to perform dynamic
perception of the surrounding environment. Synthetic Aperture Radar (SAR)
systems increase the resolution of conventional mass-market radars by
exploiting the vehicle's ego-motion, requiring a very accurate knowledge of the
trajectory, usually not compatible with automotive-grade navigation systems. In
this regard, this paper deals with the analysis, estimation and compensation of
trajectory estimation errors in automotive SAR systems, proposing a complete
residual motion estimation and compensation workflow. We start by defining the
geometry of the acquisition and the basic processing steps of Multiple-Input
Multiple-Output (MIMO) SAR systems. Then, we analytically derive the effects of
typical motion errors in automotive SAR imaging. Based on the derived models,
the procedure is detailed, outlining the guidelines for its practical
implementation. We show the effectiveness of the proposed technique by means of
experimental data gathered by a 77 GHz radar mounted in a forward looking
configuration.Comment: 14 page
Study of the effects of moving targets in SAR images for their detection.
Synthetic Aperture Radar’s (SAR) are systems designed in the early 50’s that are capable of obtaining images of the ground using electromagnetic signals. Thus, its activity is not interrupted by adverse meteorological conditions or during the night, as it occurs in optical systems.
The name of the system comes from the creation of a synthetic aperture, larger than the real one, by moving the platform that carries the radar (typically a plane or a satellite). It provides the same resolution as a static radar equipped with a larger antenna. As it moves, the radar keeps emitting pulses every 1/PRF seconds —the PRF is the pulse repetition frequency—, whose echoes are stored and processed to obtain the image of the ground.
To carry out this process, the algorithm needs to make the assumption that the targets in the illuminated scene are not moving. If that is the case, the algorithm is able to extract a focused image from the signal. However, if the targets are moving, they get unfocused and/or shifted from their position in the final image. There are applications in which it is especially useful to have information about moving targets (military, rescue tasks,studyoftheflowsofwater,surveillanceofmaritimeroutes...).Thisfeatureiscalled Ground Moving Target Indicator (GMTI). That is why the study and the development of techniques capable of detecting these targets and placing them correctly in the scene is convenient.
In this document, some of the principal GMTI algorithms used in SAR systems are detailed. A simulator has been created to test the features of each implemented algorithm on a general situation with moving targets. Finally Monte Carlo tests have been performed, allowing us to extract conclusions and statistics of each algorithm
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