Due to the limitations of clock synchronization technology and non-ideal clocks of the sensors, it is not feasible to achieve precise clock synchronization for distributed multiple-input multiple-output (MIMO) radar systems. In this paper, a closed-form solution for locating moving target in distributed MIMO radar systems with clock synchronization errors by using the time delay and Doppler shift measurements is proposed. Specifically, a transmitter is utilized as the reference and the clock synchronization errors are introduced to establish estimation formulations about the target position and velocity, and the formulations are solved by best linear unbiased estimator firstly. Then, the estimates of the target position and velocity are refined based on the relation between the reference parameters and unknowns. The proposed solution is demonstrated to be approximately unbiased and able to reach the Cramer-Rao lower bound under weak noise conditions through the theoretical derivation and numerical simulations. Furthermore, the simulations show that the proposed solution enjoys better target localization accuracy than the state-of-the-art algorithms.
Focused on small celestial body deflection missions using a kinetic impactor spacecraft, we propose a method for estimating the center of small objects with unknown shape and small size, which relaxes the requirement for prior information of the object shape model and lowers the risk of missing the target. The impact center is inferred using the visible part of the object in a single image. In the first step, the illuminated part of the object’s true contour is segmented from the whole contour extracted from the image based on the prior information of the illumination direction. In the second step, the concave–convex characteristic of the illuminated contour is identified. In the third step, one of two modes, moment estimation or skeleton center estimation, is chosen based on the concave–convex characteristic to calculate the impact center. The proposed algorithm was verified by a simulation study under various conditions. Due to the problems of the unknown model shapes of small objects and complex illumination conditions in kinetic impact missions, the proposed centroiding algorithm will play an important role.
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