418 research outputs found
Ultra-Wide Swath SAR Imaging With Continuous PRF Variation
Innovative multi-channel synthetic aperture radar (SAR) concepts enable high-resolution wide-swath imaging, but the antenna length typically restricts the achievable swath width. This limitation can be overcome by a novel technique which is based on a single azimuth channel but operates the system with a continuously varied pulse repetition frequency (PRF) by this allowing in principle for arbitrary wide swaths. This paper introduces the basic principles and discusses design constraints for such a PRF variation. Further, a systematic performance analysis of an L-band reflector antenna system is carried out with focus on the sensitivity versus different input parameters
Advanced Concepts for Ultra-Wide-Swath SAR Imaging
This paper reviews advanced multi-channel SAR system
concepts for the imaging of ultra-wide swaths with high azimuth
resolution. Novel system architectures and operational
modes are introduced and compared to each other with regard
to their performance
Advanced Synthetic Aperture Radar Based on Digital Beamforming and Waveform Diversity
This paper introduces innovative SAR system
concepts for the acquisition of high resolution radar images with
wide swath coverage from spaceborne platforms. The new concepts
rely on the combination of advanced multi-channel SAR front-end
architectures with novel operational modes. The architectures
differ regarding their implementation complexity and it is shown
that even a low number of channels is already well suited to
significantly improve the imaging performance and to overcome
fundamental limitations inherent to classical SAR systems. The
more advanced concepts employ a multidimensional encoding of
the transmitted waveforms to further improve the performance
and to enable a new class of hybrid SAR imaging modes that are
well suited to satisfy hitherto incompatible user requirements for
frequent monitoring and detailed mapping. Implementation
specific issues will be discussed and examples demonstrate the
potential of the new techniques for different remote sensing
applications
An Efficient Polyphase Filter Based Resampling Method for Unifying the PRFs in SAR Data
Variable and higher pulse repetition frequencies (PRFs) are increasingly
being used to meet the stricter requirements and complexities of current
airborne and spaceborne synthetic aperture radar (SAR) systems associated with
higher resolution and wider area products. POLYPHASE, the proposed resampling
scheme, downsamples and unifies variable PRFs within a single look complex
(SLC) SAR acquisition and across a repeat pass sequence of acquisitions down to
an effective lower PRF. A sparsity condition of the received SAR data ensures
that the uniformly resampled data approximates the spectral properties of a
decimated densely sampled version of the received SAR data. While experiments
conducted with both synthetically generated and real airborne SAR data show
that POLYPHASE retains comparable performance to the state-of-the-art BLUI
scheme in image quality, a polyphase filter-based implementation of POLYPHASE
offers significant computational savings for arbitrary (not necessarily
periodic) input PRF variations, thus allowing fully on-board, in-place, and
real-time implementation
Spaceborne synthetic-aperture imaging radars: Applications, techniques, and technology
In the last four years, the first two Earth-orbiting, space-borne, synthetic-aperture imaging radars (SAR) were successfully developed and operated. This was a major achievement in the development of spaceborne radar sensors and ground processors. The data acquired with these sensors extended the capability of Earth resources and ocean-surface observation into a new region of the electromagnetic spectrum. This paper is a review of the different aspects of spaceborne imaging radars. It includes a review of: 1) the unique characteristics of space-borne SAR systems; 2) the state of the art in spaceborne SAR hardware and SAR optical and digital processors; 3) the different data-handling techniques; and 4) the different applications of spaceborne SAR data
Innovative Adaptive Techniques for Multi Channel Spaceborne SAR Systems
Synthetic Aperture Radar (SAR) is a well-known technology which allows to coherently combine
multiple returns from (typically) ground-based targets from a moving radar mounted either on an airborne
or on a space-borne vehicle. The relative motion between the targets on ground and the platform
causes a Doppler effect, which is exploited to discriminate along-track positions of targets themselves.
In addition, as most of conventional radar, a pulsed wide-band waveform is transmitted periodically,
thus allowing even a radar discrimination capability in the range direction (i.e. in distance).
For side-looking acquisition geometries, the along-track and the range directions are almost
orthogonal, so that the two dimensional target discrimination capabiliy results in the possibility to
produce images of the illuminated area on ground. A side-looking geometry consists in the radar
antenna to be, either mechanically or electronically, oriented perpendicular to the observed area.
Nowadays technology allows discrimination capability (also referred to as resolution) in both alongtrack
and range directions in the order of few tenths of centimeters.
Since the SAR is a microwave active sensor, this technology assure the possibility to produce images
of the terrain independently of the sunlight illumination and/or weather conditions. This makes the SAR
a very useful instrument for monitoring and mapping both the natural and the artificial activities over
the Earth’s surface. Among all the limitations of a single-channel SAR system, this work focuses over some of them
which are briefly listed below:
a) the performance achievable in terms of resolution are usually paid in terms of system
complexity, dimension, mass and cost;
b) since the SAR is a coherent active sensor, it is vulnerable to both intentionally and unintentionally
radio-frequency interferences which might limit normal system operability;
c) since the Doppler effect it is used to discriminate targets (assumed to be stationary) on the
ground, this causes an intrinsic ambiguity in the interpretation of backscattered returns from
moving targets.
These drawbacks can be easily overcome by resorting to a Multi-cannel SAR (M-SAR) system
Innovative Adaptive Techniques for Multi Channel Spaceborne SAR Systems
Synthetic Aperture Radar (SAR) is a well-known technology which allows to coherently combine
multiple returns from (typically) ground-based targets from a moving radar mounted either on an airborne
or on a space-borne vehicle. The relative motion between the targets on ground and the platform
causes a Doppler effect, which is exploited to discriminate along-track positions of targets themselves.
In addition, as most of conventional radar, a pulsed wide-band waveform is transmitted periodically,
thus allowing even a radar discrimination capability in the range direction (i.e. in distance).
For side-looking acquisition geometries, the along-track and the range directions are almost
orthogonal, so that the two dimensional target discrimination capabiliy results in the possibility to
produce images of the illuminated area on ground. A side-looking geometry consists in the radar
antenna to be, either mechanically or electronically, oriented perpendicular to the observed area.
Nowadays technology allows discrimination capability (also referred to as resolution) in both alongtrack
and range directions in the order of few tenths of centimeters.
Since the SAR is a microwave active sensor, this technology assure the possibility to produce images
of the terrain independently of the sunlight illumination and/or weather conditions. This makes the SAR
a very useful instrument for monitoring and mapping both the natural and the artificial activities over
the Earth’s surface. Among all the limitations of a single-channel SAR system, this work focuses over some of them
which are briefly listed below:
a) the performance achievable in terms of resolution are usually paid in terms of system
complexity, dimension, mass and cost;
b) since the SAR is a coherent active sensor, it is vulnerable to both intentionally and unintentionally
radio-frequency interferences which might limit normal system operability;
c) since the Doppler effect it is used to discriminate targets (assumed to be stationary) on the
ground, this causes an intrinsic ambiguity in the interpretation of backscattered returns from
moving targets.
These drawbacks can be easily overcome by resorting to a Multi-cannel SAR (M-SAR) system
High-Temporal-Resolution High-Spatial-Resolution Spaceborne SAR Based on Continuously Varying PRF
Synthetic Aperture Radar (SAR) is a well-established and powerful imaging technique for acquiring high-spatial-resolution images of the Earth's surface. With the development of beam steering techniques, sliding spotlight and staring spotlight modes have been employed to support high-spatial-resolution applications. In addition to this strengthened high-spatial-resolution and wide-swath capability, high-temporal-resolution (short repeat-observation interval) represents a key capability for numerous applications. However, conventional SAR systems are limited in that the same patch can only be illuminated for several seconds within a single pass. This paper considers a novel high-squint-angle system intended to acquire high-spatial-resolution spaceborne SAR images with repeat-observation intervals varying from tens of seconds to several minutes within a single pass. However, an exponentially increased range cell migration would arise and lead to a conflict between the receive window and 'blind ranges'. An efficient data acquisition technique for high-temporal-resolution, high-spatial-resolution and high-squint-angle spaceborne SAR, in which the pulse repetition frequency (PRF) is continuously varied according to the changing slant range, is presented in this paper. This technique allows echo data to remain in the receive window instead of conflicting with the transmitted pulse or nadir echo. Considering the precision of hardware, a compromise and practical strategy is also proposed. Furthermore, a detailed performance analysis of range ambiguities is provided with respect to parameters of TerraSAR-X. For strong point-like targets, the range ambiguity of this technique would be better than that of uniform PRF technique. For this innovative technique, a resampling strategy and modified imaging algorithm have been developed to handle the non-uniformly sampled echo data. Simulations are performed to validate the efficiency of the proposed technique and the associated imaging algorithm
An introduction to the interim digital SAR processor and the characteristics of the associated Seasat SAR imagery
Basic engineering data regarding the Interim Digital SAR Processor (IDP) and the digitally correlated Seasat synthetic aperature radar (SAR) imagery are presented. The correlation function and IDP hardware/software configuration are described, and a preliminary performance assessment presented. The geometric and radiometric characteristics, with special emphasis on those peculiar to the IDP produced imagery, are described
Moving Target Azimuth Velocity Estimation for the MASA Mode Based on Sequential SAR Images
A novel azimuth velocity estimation method is proposed based on the multiple azimuth squint angles (MASA) imaging mode, acquiring sequential synthetic aperture radar images with different squint angles and time lags. The MASA mode acquisition geometry is given first, and the effect of target motion on azimuth offset and slant range offset is discussed in detail. Then, the azimuth velocity estimation accuracy is analyzed, considering the errors caused by registration, defocusing, and range velocity. Moreover, the interaction between target azimuth velocity and range velocity is studied for a better understanding of the azimuth velocity estimation error caused by the range velocity. With the proposed error compensation step, the new method can achieve a very high accuracy in azimuth velocity estimation, as verified by experimental results based on both simulated data and the TerraSAR-X data
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