High-resolution Wide-swath Research Articles

A High Resolution Wide Swath SAR method based on intra-pulse null steering and MIMO

High Resolution Wide Swath (HRWS) Synthetic Aperture Radar (SAR) often suffers from low Signal-to-Noise Ratio (SNR) due to small transmitting antenna, especially in phased array antenna systems. Digital Beam Forming (DBF) based on Single Input and Multiple Output (SIMO) achieves receiving array gain at the cost of increasing data rate. This letter proposes a new HRWS SAR method, which employs intra-pulse null steering to get receiving gain in elevation and decrease the data rate, and Multiple Input and Multiple Output (MIMO) using Space-Time Block Coding (STBC) in azimuth to get transmitting gain and receiving array gain simultaneously. The feasibility is verified by deduction and simulations.

Processing of Bistatic SAR Data From Quasi-Stationary Configurations

Standard synthetic aperture radar (SAR) processing algorithms use analytically derived transfer functions in the 2D frequency and range/Doppler domains. These rely on the assumption of hyperbolic range histories of monostatic SARs with straight flight paths. For bistatic SARs, the range histories are no longer hyperbolic, and simple analytic transforms do not exist. This paper offers two solutions for bistatic SAR data processing under the restriction of quasi-stationarity, i.e., sufficiently equal vectors of transmitter and receiver. 1) Moderately bistatic configurations can be handled satisfactorily by using hyperbolic range functions with a modified parameter, which is a solution already well known for the accommodation of curved orbits in the monostatic case. This velocity approach is shown to be of surprising range of validity even for pronounced bistatic situations. It is not to be confused with the monostatic flight path approximation, which is shown to be inapplicable for any practical case. 2) With increasing separation of transmitter and receiver, the equivalent approximation deteriorates. To cope with extreme bistatic configurations, a general approach named NuSAR is proposed, where the involved transfer functions are replaced by numerically computed ones. This paper describes how the transfer functions are computed from the given orbits and the shape of the Earth surface. In any of these two cases, the bistatic SAR data can be processed by standard SAR processors; only the conventional transfer functions need to be replaced. Neither are there time-domain prefocusing or post focusing steps required nor complicated mathematical expansions involved. The presented algorithms are also applicable to very high resolution wide-swath (or squinted) SARs on curved orbits.

Side scan sonar using phased arrays for high resolution imaging and wide swath bathymetry

Abstract: The design of a new bathymetric sidescan sonar dedicated to the survey of the continental shelf is described. It uses linear phased arrays in order to perform dynamically the control of the resolution through the focusing of the beams, and beam steering to compensate for yaw and pitch. The 4m long array, working at ll2kHz, yields high resolution imaging. In addition, an interferometric doublet, with a i!h spacing, provides a wide swath bai hymetric capability. Both functions take advantage of a fast digital pulse compression process. Results of sea trials with the hull mounted system (high resolution images and topographic maps) are discussed. -- I Introduction Remote acoustic sensing of the sea floor aims at two complementary goals: imaging for target localisation, bottom classification or small relief Characterisation and sounding in order to draw charts. Two techniques are now widely used for these purposes. Multibeam echosounders are hull mounted systems that are mainly devoted to bathymetric surveys. Most implementations are based on cross shaped phased arrays with a preformed beams technique. The floor is investigated across-track of the surveying ship. The perturbative motions of the ship (i.e. roll and pitch) are compensated dynamically. The soundings are derived from the backscattered echoes by considering either the amplitude or the phase when an interferometric process is performed. Such systems can build images by taking into account the energy backscattered within each beam. Side scan sonar is a much longer established lech- nique. It was originally devoted to imaging only. Antennas point to each side of the ship track and scan, with a single beam, a long and narrow strip of the sea floor. The backscattered strength provides the informa- tion needed to build images with a much higher resolu-