An Improved Generalized Chirp Scaling Algorithm Based on Lagrange Inversion Theorem for High-Resolution Low Frequency Synthetic Aperture Radar Imaging

Abstract

The high-resolution low frequency synthetic aperture radar (SAR) has serious range-azimuth phase coupling due to the large bandwidth and long integration time. High-resolution SAR processing methods are necessary for focusing the raw data of such radar. The generalized chirp scaling algorithm (GCSA) is generally accepted as an attractive solution to focus SAR systems with low frequency, large bandwidth and wide beam bandwidth. However, as the bandwidth and/or beamwidth increase, the serious phase coupling limits the performance of the current GCSA and degrades the imaging quality. The degradation is mainly caused by two reasons: the residual high-order coupling phase and the non-negligible error introduced by the linear approximation of stationary phase point using the principle of stationary phase (POSP). According to the characteristics of a high-resolution low frequency SAR signal, this paper firstly presents a principle to determine the required order of range frequency. After compensating for the range-independent coupling phase above 3rd order, an improved GCSA based on Lagrange inversion theorem is analytically derived. The Lagrange inversion enables the high-order range-dependent coupling phase to be accurately compensated. Imaging results of Pand L-band SAR data demonstrate the excellent performance of the proposed algorithm compared to the existing GCSA. The image quality and focusing depth in range dimension are greatly improved. The improved method provides the possibility to efficiently process high-resolution low frequency SAR data with wide swath.

Comparative Analysis of Single-View and Multi-View Airborne SAR Positioning Error and Course Planning for Multi-View Airborne SAR Optimal Positioning

“…Simulated flight experiment: Add single motion error (position or velocity) to the aircraft in the imaging coordinate system, and then obtain the position and velocity of the radar antenna phase center through the simulation experiment, and complete the error locating of the target according to Equation (1). Based on the known real position of the target, we can obtain the actual target positioning error d caused by the aircraft motion error according to Equation (5).…”

“…It can be seen from Table 4 that, under the influence of seven error sources, the actual target positioning error d through the simulation flight experiment is basically consistent with the target positioning error estimation d1 which is calculated through the error transfer model, and the root mean square error of d and d1 is 0.07 m, showing that the positioning error analysis accuracy of the multi-view airborne SAR positioning error transfer model on target can reach a high level. Compared with using signal simulation experiments which need the iterative solution of the positioning system (1) to analyze the positioning error, the error transfer model is simple and efficient, and it is an useful tool for analyzing the influence of multi-view airborne SAR platform motion error on the target positioning accuracy.…”

“…The relatively The position of the target can be determined by the position and velocity of the radar antenna phase center and the slant distance between target and antenna. The relatively strict distance condition and Doppler frequency condition (1) are satisfied between target Q and the radar antenna phase center on the routes under Earth Center Fixed (ECF) coordinate system. Solving the Equation (1) can realize target location.…”

“…Synthetic aperture radar (SAR) has the advantages of all-sky and all-weather imaging, and is an important tool for high-resolution earth observation [1][2][3]. Accurate target location is one of the important uses of SAR [4,5], and SAR image positioning is an effective means to obtain three-dimensional position information of the target, which has important application value in digital elevation model (DEM) generation of imaging area, topographic map drawing and accurate interpretation of military targets.…”

Radar and Sonar Imaging and Processing

“…Another interesting approach to SAR data processing is presented by Chen et al [4]. As a result of the method developed by the authors, image quality and depth of field have been significantly improved.…”