With the broad attention of countries in the areas of sea transportation and trade safety, the requirements of efficiency and accuracy of moving ship tracking are becoming higher. Therefore, a systematic design of moving ship tracking onboard based on FPGA is proposed, which uses the Adaptive Inter Frame Difference (AIFD) method to track a ship with different speed. For the Frame Difference method (FD) is simple but the amount of computation is very large, it is suitable for the use of FPGA to implement in parallel. But Frame Intervals (FIs) of the traditional FD method are fixed, and in remote sensing images, a ship looks very small (depicted by only dozens of pixels) and moves slowly. By applying invariant FIs, the accuracy of FD for moving ship tracking is not satisfactory and the calculation is highly redundant. So we use the adaptation of FD based on adaptive extraction of key frames for moving ship tracking. A FPGA development board of Xilinx Kintex-7 series is used for simulation. The experiments show that compared with the traditional FD method, the proposed one can achieve higher accuracy of moving ship tracking, and can meet the requirement of real-time tracking in high image resolution.
Mean shift is a traditional moving target tracking algorithm, which has some deficiencies such as: A tracking window of a target needs to be initialed manually in the first frame; the window size cannot be adaptively changed according to a moving object in the process of tracking; if a target is obscured, it might be lost in the tracking window. In order to solve these problems, a method combining Kalman filter and Scale and Orientation Adaptive Mean Shift Tracking (SOAMST) is proposed. Firstly we use Kalman filter to locate a moving target at the beginning. Then the ratio of the first order moment to the zero order moment is used to estimate its center, and the second order center moment is used to estimate its size and orientation. Meanwhile, whether the target is obscured is determined by the Bhattacharyya coefficient based on the target model and a candidate one. A candidate model is more similar to the target and the estimation result of the target is more reliable when the Bhattacharyya coefficient is closer to 1. On the contrary, if the Bhattacharyya coefficient decreases to 0, the target will be lost for being totally obscured. If the target is partially obscured or not obscured, SOAMST is used directly to track the target; if totally obscured, Kalman filter is imposed to estimate the location of the target in the next frame before SOAMST. The experiments show that the proposed algorithm can track a moving target automatically at the initial frame without prior knowledge. It can also track a completely obscured target accurately by Kalman filtering based location estimation.