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The imagery of highly squinted synthetic aperture radar mounted on maneuvering platforms with nonlinear trajectory is a challenging task due to the existence of acceleration and the cross-range-dependent range migration and Doppler parameters. In order to accommodate these issues, a frequency-domain imaging algorithm based on tandem two-step nonlinear chirp scaling (TNCS) with small aperture is proposed. For the cross-range-dependent range cell migration (RCM) caused by the linear range walk correction and acceleration, the first-step NCS is introduced to suppress this dependence and realize the unified RCM correction. Based on the differences between full-aperture and small-aperture data in the cross-range processing, the second-step NCS is introduced in frequency domain to equalize the cross-range-dependent Doppler parameters, for cross-range processing is more sensitive to the cross-range dependence than range processing. Furthermore, a novel geometric correction method based on inverse projection is utilized to eliminate the negative effects caused by the imaging processing. Simulation results and real data processing are presented to validate the proposed approach. [ABSTRACT FROM AUTHOR]

An efficient and accurate inverse extended omega-K algorithm (IEOKA) is proposed to simulate synthetic aperture radar (SAR) raw data with trajectory deviations. Different from the traditional inverse omega-K algorithm that assumes an ideal flight trajectory, the IEOKA not only recovers the range cell migration accurately but also considers the motion errors including both range and phase errors due to the use of inverse extended Stolt interpolation. Furthermore, the azimuth dependence of the motion errors is discussed. A beam division method based on frequency division technique is presented to generate the azimuth-dependent phase error more accurately. The accuracy and effectiveness of the proposed algorithm have been verified using the generated SAR raw data consisting of the azimuth-dependent motion error. [ABSTRACT FROM PUBLISHER]

For high-squint synthetic aperture radar (SAR) with curved trajectory, the traditional hyperbolic range model (HRM) is inaccurate, and the variation of velocity caused by constant acceleration in azimuth dimension cannot be ignored. Thus, the traditional omega-K imaging algorithms based on HRM are no longer available. For this problem, this letter proposes an improved range model, which can precisely take account for the curved trajectory. Then, a modified omega-K algorithm based on this new range model is proposed for high-squint SAR imaging. Simulation results validate the effectiveness of the improved range model and imaging algorithm. [ABSTRACT FROM PUBLISHER]

This letter proposes a new motion compensation approach for high-squint and high-resolution airborne spotlight synthetic aperture radar (SAR) integrated with polar format algorithm (PFA). The motion error is coarsely compensated by means of measuring systems. In PFA, the expressions of the line-of-sight polar interpolation are first explicitly revealed, and the nonsystematic range cell migration (NsRCM) induced by residual motion error is also corrected, which paves the way for autofocus application. After the NsRCM correction, the enhanced total least square estimator-based phase adjustment by contrast enhancement (PACE) algorithm is considered to account for the residual phase errors extended to the range-dependent case. The processing results of airborne SAR real data are presented to demonstrate the validity of the proposed algorithm. [ABSTRACT FROM PUBLISHER]

The squinted imaging mode has been successfully applied to synthetic aperture radar (SAR) mounted on moving platforms of high speed. The developed focusing algorithms for squint SAR data usually perform the linear range walk correction (LRWC) in the azimuth time domain as the first step, to mitigate the bulk range-azimuth coupling. Unfortunately, when applied on high-speed platforms with large squint angle and large azimuth scene length, these algorithms for airborne SAR considering only the first-order azimuth dependence of the Doppler frequency-modulation (FM) rate will introduce a large residual phase error, and therefore degrade the final radar image quality. Meanwhile, those algorithms, originally designed for full-aperture data, cannot be applied directly to the small-aperture data. Due to these problems, a high-order phase correction approach (HPCA) combined with SPECAN operation for focusing high-squint SAR (HS-SAR) small-aperture data is developed in this paper to deal with the above issues. In this approach, both the first- and the second-order azimuth dependence of the Doppler FM rate are compensated for, and the same to the cubic phase term, by introducing a correction phase term in the azimuth frequency domain. The presented approach has been successfully used to focus the real airborne radar data recently. [ABSTRACT FROM PUBLISHER]