Although Cramér-Rao Bounds (CRB) for angle-of-arrival (AOA) based position estimation have been extensively studied for decades, the existing works mainly focused on target direction finding errors, neglecting the deviations of mutual measurements in collaborative environment of surface ships. The deviations of mutual direction-finding and ranging between cooperative ships should be taken into account for source localization using mutual measurements in collaborative environment of surface ships. In this paper, we derive quantitative expressions of the CRB on the positioning accuracy while considering the deviations of mutual measurements, and calculate the lower bound on the circular error probability (CEP) of the cooperative localization system. The derived bounds are simple to evaluate and provide a good prediction of the actual AOA based cooperative localization system performance in collaborative environment of surface ships. Numerical examples illustrate our theoretical results.

Azimuth periodically gapped sampling occurs in satellite Synthetic Aperture Radar (SAR) due to new radar mission or sensor geometries. For resolving this issue, a novel strategy is presented in this paper for obtaining high-resolution satellite SAR image via processing azimuth periodically gapped echo data by segmented recovery. To avoid azimuth frequency aliasing, the proposed method splits echo data into several sub-blocks in azimuth direction. Then, sub-blocks are compensated with curved orbit phase compensation function and recovered with iterative adaptive approach. Afterwards, sub-blocks are combined as the whole echo data in time domain. Subsequently, the recovered data is processed by curved orbit deramping-based approach and modified range migration algorithm. The proposed strategy is validated with simulation and actual SAR data experiment.

Existence of periodical interruption in Synthetic Aperture Radar (SAR), which is caused by various avenues, leads to challenges on SAR data imaging. To resolve this issue, a novel approach is developed in this paper. The proposed approach deal with periodically interrupted raw SAR data by complex deconvolution. Complex Fast Iterative Shrinkage-Thresholding Algorithm (FISTA) is operated to perform complex deconvolution and restore the azimuth spectrum from periodically interrupted SAR echo. Then, conventional SAR focusing method is able to attain imaging result from interrupted echo data. The proposed method processes interrupted echo with lower fake targets and operates more quickly than approach on basis of Iterative Shrinkage-Thresholding Algorithm (ISTA). Experiments on simulation data and actual SAR echo illustrate the effectiveness of the proposed approach.

A novel algorithm is proposed in this paper to focus the azimuth periodically gapped Synthetic Aperture Radar (SAR) raw data with suppressed artificial targets. The proposed method mainly consists of phase compensation in range frequency domain, subsequent sparse recovery via complex Fast Iterative Shrinkage-Thresholding Algorithm (FISTA) and focusing recovered SAR data with traditional SAR imaging algorithm. With phase compensation, the gapped data becomes sparser in range Doppler domain and complex FISTA is utilized to restore complete data from gapped data in range Doppler domain. Afterwards, the conventional SAR focusing algorithms are capable of coping with the recovered data. The proposed method focuses azimuth gapped data with lower artificial targets and performs faster than method based on complex Iterative Shrinkage- Thresholding Algorithm (ISTA). In experiments, point target simulation and real SAR data processing are utilized to demonstrate the validity of the proposed method.

Algorithms for high resolution spotlight Synthetic Aperture Radar (SAR) focusing typically face challenges of curved orbit and azimuth aliasing. To conquer these difficulties, a novel algorithm, which is named as Modified Generalized Omega-K (MGOK) algorithm, is proposed in this paper for focusing low-orbit high resolution spotlight spaceborne Synthetic Aperture Radar (SAR). The proposed method modifies the Generalized Omega-K algorithm with orbital state vectors and deramping-based approach in order to accommodate the scenario of Low Earth Orbit (LEO) high resolution spaceborne SAR. Experiments are performed on point target simulation for assessing the effectiveness of the proposed method. In simulation, the range and azimuth resolution can both obtain 0.5m with scene size of 4km by 4km.