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Time synchronization in wireless sensor networks,aiming to provide a common sense of timing among distributed sensor nodes, is a key enabling technology for many applications, such as collaborative condition monitoring, time-of-flight localization and underwater navigation and tactical surveillance. In order to solve the challenges of the manufacturing tolerance and working condition variations in any real-world environments, a novel state-space model for pulse-coupled non-identical oscillators is proposed to model a realistic clock oscillator with nonidentical and time-varying frequency. A state feedback correction, referred to as hybrid coupling mechanism, is also proposed to ensure the system move into steady state, thus achieving time synchronization in wireless sensor networks. Furthermore, the intensive simulations of single-hop wireless sensor networks have been carried out to evaluate the performance of proposed pulsecoupled non-identical oscillators. It is shown that a partially connected wireless network consisting of 50 non-identical pulsecoupled oscillators can achieve the synchronization with the precision of $40us.$

Terrain geometry and radiation characteristics of radar images have strong influence. The correction of these effects becomes indispensable when quantitative image analysis is performed with respect to the derivation of geo- and biophysical parameters. Based on RD geo-location model and digital elevation model, an ortho-rectification and TRC implementation flow was introduced. The correctness and effectiveness of the method were qualitatively and quantitatively evaluated through several experimentations. By comparing two kinds of effective TRC methods, we found the project-angle based method is more effective than the local incidence-angle based method. The rationality of computing effective TRC factor using initial SAR geo-location model was also demonstrated.

Digital elevation model (DEM), as an important product of digital photogrammetry and digital surveying and mapping, it plays an increasingly important role in the field of surveying and mapping and geographic information system. In this paper, it introduces the current generation methods of DEM by contour, and analyzes those interpolation methods that commonly are used to build DEM, and then describes the advantages and disadvantages of different building DEM methods systematically. Focusing on the DEM that represented by Grid and TIN, it compares the optimization methods of interpolation contour data systematically, and makes the contour interpolating DEM reflect the surface condition of the real nature more effectively.

Network coordinates (NC) system is an efficient mechanism for Internet distance prediction with scalable measurements. The intrinsical cause for the unsatisfactory accuracy of the simulation-based NC algorithms has been identified. Then Pharos, a fully decentralised and hierarchical scheme, is proposed to solve this problem. Pharos leverages multiple coordinate sets at different distance scales, with the right scale being chosen for prediction each time. We evaluate the performance of Pharos system with the King data set and latency data from PlanetLab, and compare it with the representative NC system, Vivaldi. The experimental results show that Pharos greatly outperforms Vivaldi in Internet distance prediction without adding any significant overhead. Our extensive evaluation results also demonstrate that Pharos can significantly improve the performance in distributed Internet applications, such as overlay multicast and server selection.