Circular Scanning Synthetic Aperture Radar Research Articles

Processing of Circular-Scanning SAR Data Using Deramping-Based Imaging Approach

With the circular-scanning mode, we can obtain real-time synthetic aperture radar (SAR) images of wide areas including both sides of the nadir line, which considerably benefits the terrain matching procedure. However, due to the continuous rotation of the antenna beam, the azimuth Doppler bandwidth of the circular-scanning SAR data will increase noticeably, which in turn will lead to the azimuth spectrum aliasing phenomenon. Existing approaches for the azimuth processing of the circular-scanning SAR data are based on the subaperture technique. However, when the pulse repetition frequency (PRF) is limited, these approaches result in the loss of azimuth resolution. In this letter, a new circular-scanning approach based on the deramping operation is proposed. The deramping operation could solve the problem of spectrum aliasing and the loss of azimuth resolution can be avoided. The performance of the proposed imaging approach is demonstrated by point targets simulation and real circular-scanning SAR data processing results.

Experimental analysis of sea clutter using airborne circular scanning SAR in medium grazing angle

The theoretical statistical model of sea clutter is a key issue for maritime surveillance. In recent years, the statistical model of sea clutter has attracted much attention to design the detector well. Meanwhile, the circular scanning synthetic aperture radar (SAR) has been applied to wide surveillance of the sea surface. Therefore, the paper analyzes the validity of available sea clutter models for range Doppler images from different scan angles for moderate sea state in the medium grazing angle. The parameter estimation method for different distribution models employs the method of logarithmic cumulant (MoLC) based on Mellin transform uniformly. By the analysis of the fitting performance between the histogram of real data and the amplitude probability density function (PDF) of empirical distribution models and the goodness-of-fit (GoF) test for real data from different scan angles, it is indicated the generalized K (GK) distribution with generalized Gamma texture distribution can fit the sea clutter well for different scan angles in the medium grazing angle.

Ship detection using online update of clutter map based on fuzzy statistics and spatial property

The ship detection is the key importance for the maritime surveillance. If the sea clutter is contaminated by the ship targets or interferences, that is the outliers, the detection performance will deteriorate. Aiming at this question, the study develops the detection method of the extended ship targets using the online update of the clutter map in circular scanning synthetic aperture radar (SAR) mode. The algorithm first removes the outliers using the prior clutter map, and then further obtains the pure clutter distribution based on the iterative censoring algorithm which rejects the outliers using the fuzzy statistical theory, the spatial property of the ship target and goodness-of-fitness test. After censoring the outliers, the constant false alarm rate detection is used. As the intensity of a ship target is fluctuant, the detected ship may be split into several parts, and thus the target clustering is an imperative procedure. Meanwhile, the false targets are rejected by the prior size of the ship. Finally, the effectiveness of the proposed detection method is verified by the real data from airborne circular scanning SAR. Compared with other conventional methods, the experimental results indicate that the proposed method has a good performance and strong availability.

Sea Surface Current Estimation Using Airborne Circular Scanning SAR with a Medium Grazing Angle

Circular scanning synthetic aperture radar (SAR) is a novel imaging mode wherein the radar antenna rotates from 0 degrees to 360 degrees along the platform flight direction, providing us with a potentially effective technique to estimate the sea surface current velocity. In this paper, we propose a novel method to estimate the sea surface current velocity utilizing the Doppler centroid shifts of different scan angles over 360 degrees after the airborne platform motion compensation. In this method, the Doppler centroid shifts of the sea clutter at different scan angles are first extracted, and the corresponding compensation errors caused by the azimuth pointing and the incidence angle of the radar beam are considered. Finally, the least squares (LS) technique is applied to estimate the along-track velocity component and the cross-track velocity component of the sea surface current. The effectiveness of the proposed method is verified by the real data recorded by an airborne circular scanning SAR system.

The Geometric-Distortion Correction Algorithm for Circular-Scanning SAR Imaging

The image formation scheme for circular-scanning synthetic aperture radar includes generating a set of focused subimages and the followed mosaiking processing. However, due to the particular acquisition geometry and irregular motion of the radar platform, the inevitable geometric distortions in the subimages are necessary to be corrected. In this letter, a 2-D geometric-distortion correction algorithm based on projection transformation between the scatterers and the images is presented, in condition of focusing the subimages using a linear range-Doppler algorithm. The point target simulation and real circular-scanning data implementation results are provided to demonstrate the validity of the proposed method.