359 research outputs found
Investigations on OFDM Signal for Range Ambiguity Suppression in SAR Configuration
International audienceThis paper presents an opportunity to cancel range ambiguities in synthetic aperture radar (SAR) configuration. One of the limitations of SAR systems is the range ambiguity phenomenon that appears with long delayed echoes. The reflected signal corresponding to one pulse is detected when the radar has already transmitted the next pulse. Thus, this signal is considered as an echo from the next pulse. This paper investigates the opportunity of coding the transmitted pulses using an orthogonal frequency-division multiplexing pulse. The results show that coded-OFDM signals outperform conventional chirp signal and make it possible to relax constraints placed upon the pulse repetition frequency
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
Radar systems for the water resources mission, volume 2
The application of synthetic aperture radar (SAR) in monitoring and managing earth resources was examined. The function of spaceborne radar is to provide maps and map imagery to be used for earth resource and oceanographic applications. Spaceborne radar has the capability of mapping the entire United States regardless of inclement weather; however, the imagery must have a high degree of resolution to be meaningful. Attaining this resolution is possible with the SAR system. Imagery of the required quality must first meet mission parameters in the following areas: antenna patterns, azimuth and range ambiguities, coverage, and angle of incidence
Radar systems for the water resources mission. Volume 4: Appendices E-I
The use of a scanning antenna beam for a synthetic aperture system was examined. When the resolution required was modest, the radar did not use all the time the beam was passing a given point on the ground to build a synthetic aperture, so time was available to scan the beam to other positions and build several images at different ranges. The scanning synthetic-aperture radar (SCANSAR) could achieve swathwidths of well over 100 km with modest antenna size. Design considerations for a SCANSAR for hydrologic parameter observation are presented. Because of the high sensitivity to soil moisture at angles of incidence near vertical, a 7 to 22 deg swath was considered for that application. For snow and ice monitoring, a 22 to 37 deg scan was used. Frequencies from X-band to L-band were used in the design studies, but the proposed system operated in C-band at 4.75 GHz. It achieved an azimuth resolution of about 50 meters at all angles, with a range resolution varying from 150 meters at 7 deg to 31 meters at 37 deg. The antenna required an aperture of 3 x 4.16 meters, and the average transmitter power was under 2 watts
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
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