Aiming at the problems of low accuracy and poor real-time performance of Noctiluca scintillans red tide extraction in the field of satellite remote sensing, a Noctiluca scintillans red tide extraction method from Unmanned Aerial Vehicle (UAV) images based on deep learning was proposed. Firstly, the high-resolution RGB (Red-Green-Blue) videos collected by UAV were used as the monitoring data, the backbone network was modified to VGG-16 (Visual Geometry Group-16) and the spatial dropout strategy was introduced on the basis of the original UNet++ network to enhance the feature extraction ability and prevent the overfitting respectively. Then, the VGG-16 network pre-trained by using ImageNet dataset was applied to perform transfer learning to increase the network convergence speed. Finally, in order to evaluate the performance of the proposed method, experiments were conducted on the self-built red tide dataset Redtide-DB. The Overall Accuracy (OA), F1 score, and Kappa of the Noctiluca scintillans red tide extraction of the proposed method are up to 94.63%, 0.955 2, 0.949 6 respectively, which are better than those of three traditional machine learning methods — K-Nearest Neighbors (KNN), Support Vector Machine (SVM) and Random Forest (RF) as well as three typical semantic segmentation networks (PSPNet (Pyramid Scene Parsing Network), SegNet and U-Net). Meanwhile, the red tide images of different shooting equipment and shooting environments were used to test the generalization ability of the proposed method, and the corresponding OA, F1 score and Kappa are 97.41%, 0.965 9 and 0.938 2, respectively, proving that the proposed method has a certain generalization ability. Experimental results show that the proposed method can realize the automatic accurate Noctiluca scintillans red tide extraction in complex environments, and provides a reference for Noctiluca scintillans red tide monitoring and research work.
Focusing on the content distribution acceleration problem in Mobile Edge Computing (MEC), with the consideration of the influence of MEC server storage space limitation on content cache, with the object obtaining delays of the mobile users as optimization goal, an Interest-based Content Distribution Acceleration Strategy (ICDAS) was proposed. Considering the MEC server storage space, the interests of the mobile user groups on different objects and the file sizes of the objects, the objects were selectively cached on MEC servers, and the objects cached on MEC servers were timely updated in order to meet the content requirements of mobile user groups as more as possible. The experimental results show that the proposed strategy has good convergence performance, which cache hit ratio is relatively stable and significantly better than that of the existing strategies. When the system runs stably, compared with the existing strategies, this strategy can reduce the object data obtaining delay for users by 20%.
Considering the problems of low-enthusiasm workers and task expiration in the mobile crowd sensing system, a task assignment algorithm based on initial cost and soft time window was proposed. As the corresponding task assignment problem belongs to the category of NP-hard problems and the computationally efficient optimal algorithm cannot be found, thus, an algorithm was developed based on Discrete Cuckoo Search Algorithm (DCSA). Firstly, the corresponding global search process and local search process were designed respectively according to the problem characteristics. Secondly, to derive the better solution, the priorities of tasks with respect to the distance between tasks and workers' starting positions as well as the size of time windows were analyzed. Finally, feasible operations were executed to guarantee that the related constraints were satisfied by each task assignment. Compared with genetic algorithm and greedy algorithm, the simulation results show that DCSA-based task assignment algorithm can improve the enthusiasm of workers to participate, solve the problem of task expiration, and ultimately reduce the total system cost.
Focused on the issues that circular domain extraction is not accurate and effective correction field angle can not reach 180 degrees in the vertical direction, Variable Angle Line Scan (VALS) method and Longitudinal Compression Cylindrical Projection (LCCP) method were proposed respectively. By changing the inclination angle of the scan line, the VALS method got coordinates of those cut points, then it filtered out invalid cut points coordinates and further got the parameters of the circular domain by using the Kasa circle fitting method. As for the LCCP method, it artificially bended the optical path of traditional cylindrical projection so that the light projected onto the infinity point could be projected back on the cylindrical surface, thus preserved the image information effectively. The comparison with two known methods named longitude-latitude mapping and Mercator mapping proves the effectiveness of the proposed algorithm in weakening the blurring effect due to stretching caused by the edge of image correction. The result looks more nature.