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In order to study the performance of different elimination methods on the distance estimation forward error caused by the non-line-of-sight (NLOS) propagation of radio signals, this paper is based on the mean value, root mean square delay spread, skewness, kurtosis and peak-to-average ratio extracted from the channel state information (CSI), and combine it with the logarithmic estimated distance based on the time of arrival (TOA) as the feature input vector, through the establishment of Gaussian process regression (GPR), least square support vector machine regression (LS-SVMR) and BP neural network training model for experimental performance comparison. Through the actual measurement of the 2.4 to 5.4 GHz wireless propagation channel in the typical indoor environment, the error elimination experiment is carried out to compare the NLOS error elimination performance under different input characteristics, different bandwidths and different frequency bands. The experimental results show that the GPR model has the best NLOS error elimination performance, and the extracted CSI multi-features as the input of the GPR model can reduce the average absolute error and root mean square error by 71.12% and 81.36%, respectively. As the bandwidth continues to increase, the error elimination performance is gradually optimized. By increasing the bandwidth, the NLOS positioning error when the input features are less can be effectively improved. The positioning error of the low frequency band is smaller than that of the high frequency band under the multi-features, so the combination of all available frequency bands can eliminate the NLOS positioning error better than a single frequency band. 为了研究不同消除方法对无线电信号由非视距(NLOS)传播而产生的距离估计正偏误差的消除性能, 基于信道状态信息(CSI)提取出均值、均方根延迟扩展、偏度、峰度、峰均比特征, 并将其与基于到达时间(TOA)的对数估计距离相结合作为特征输入向量, 通过建立高斯过程回归(GPR)、最小二乘支持向量机回归(LS-SVMR)与BP神经网络训练模型进行实验性能比较。对实际测量的典型室内环境中2.4~5.4 GHz的无线传播信道进行误差消除实验, 比较不同输入特征、不同带宽和不同频带下的NLOS误差消除性能。实验结果表明：GPR模型表现出最好的NLOS误差消除性能, 且所提取的CSI多特征作为输入向量可以将平均绝对误差(MAE)和均方根误差(RMSE)分别减小71.12%和81.36%;随着带宽不断增加, 误差消除性能逐渐优化, 即可通过增大带宽有效地改善输入特征较少时的NLOS定位误差; 在多特征输入下, 低频带的NLOS测距误差与高频带不同, 因此将所有可用的频带结合可以比单频带更好地消除NLOS定位误差。

In order to investigate the environment and acoustic filed change induced by typhoon in shallow sea, we conducted two ex- periments just before and after the passage of typhoon Damrey, which is the strongest to affect the area north of the Yangtze River since 1949, in the Yellow sea in 2012. The data show that the temperature of the whole water column increases dramati- cally except the sea surface layer after the passage of Damrey while the salinity decreases obviously. The thermocline deepens and weakens, which leads to a change of internal wave activity. The transmission losses （TL） of the two experiments show that the environment change induced by typhoon can increase the TL as large as 8 dB at a distance of 9.2 km and depth of 15 m. The scintillation index （SI） of the sound intensity is simulated to estimate the change of the effect of internal wave activity on acoustic field showing that the SI decreases to a half after the typhoon＇s passage. The normal mode structures of the two experiments are also significanOy different due to the thermocline changes. In addition, the signal arrives earlier after the ty- phoon＇s passage due to the water temperature increase.

Here we report characteristics of more than 100 cases of Narrow Bipolar Events （NBEs） occurred during two thunderstorms on the basis of our analysis of the dataset collected by a GPS based three-station time of arrival （TOA） lightning location system deployed in Northeast China during the summer of 2010. All of the NBEs were of positive polarity and the amplitude of VLF/LF initial pulse of NBE was comparable to that of return strokes. The waveform characteristics of 166 NBEs that oc- curred within 150 km were consistent with the results of other reports. The average value of initial peak width of the bipolar pulse is 7.8±1.5 μs, full width at half maximum is 4.6±1.0 μs, and the ratio of initial peak amplitude to overshoot peak is 2.1±0.6. The inferred source height of NBEs occurred in two thunderstorms averaged 9.6 and 7.4 km above mean sea level, whereas the corresponding virtual ionosphere heights at two different times were 89 and 78 km, respectively. In NBE- producing thunderstorms, NBEs tended to burst during the active stage of normal lightning; nevertheless, no determinate quan- titative relations could be established between them. In Storm 0711, NBEs were inclined to cluster at the proximity of particu- lar convective cores with high radar reflectivity, and NBEs tended to move consistently at the front area of those NBE-producing convective cores during the evolution of thunderstorm.

In order to improve the efficiency of 3D near-surface velocity model building, we develop a layer-stripping method using seismic first-arrival times. The velocity model within a Common Mid-Point （CMP） gather is assumed to be stratified into thin layers, and the velocity of each layer var- ies linearly with depth. The thickness and velocity of the top layer are estimated using minimum-offset first-arrival data in a CMP gather. Then the top layer is stripped and the second layer becomes a new top layer. After removing the effect of the top layer from the former first-arrival data, the new first-arrival data are obtained and then used to estimate the parameters of the second layer. In this manner, the velocity model, being regarded as that at a CMP location, is built layer-by-layer from the top to the bottom. A 3D near-surface velocity model is then formed using the velocity models at all CMP locations. The tests on synthetic and observed seismic data show that the layer-stripping method can be used to build good near-surface velocity models for static correction, and its computation speed is approximately hundred times faster than that of grid tomography.

X-ray pulsars offer stable, periodic X-ray pulse sequences that can be used in spacecraft positioning systems. A method using X-ray pulsars to determine the initial orbit of a satellite is presented in this paper. This method suggests only one detector to be equipped on the satellite and assumes that the detector observes three pulsars in turn. To improve the performance, the use of incremental phase in one observation duration is proposed, and the incremental phase is combined with the time difference of arrival（TDOA）. Then, a weighted least squares（WLS） algorithm is formulated to calculate the initial orbit. Numerical simulations are performed to assess the proposed orbit determination method.

Later earthquake-sourced PmP phases have the potential to significantly improve ray coverage and resolution of crustal tomography methods, as their trajectories are quite different from those of shallower P phases. This paper analyzes the characteristics of later PmP arrival times from earthquakes with different focal depths. The results show that PmP arrival time differences from earthquakes at a range of focal depths are gradually lowered with increasing offset. We found that where the first recorded P-wave phase was the intra-crustal refraction phase （Pg）, the differences in arrival time between Pg and PmP phases decreased with increasing focal depth at an offset of less than 120 km. Where the first P-wave phase is the upper mantle refraction phase （Pn）, the difference in arrival times between Pn and PmP phases became larger with an increase in focal depth at an offset of more than 150 km. A total of 394 PmP phases and 3356 first P phases were picked from seismograms in the active volcanic area of northeastern Japan, according to the characteristics of calculated arrival times, amplitudes and particle motions. These were used to investigate the role of PmP phases in crustal tomography beneath an active volcanic region. Results of the detailed resolution analysis show that the addition of PmP data can improve significantly the resolution of the lower crustal structure in tomographic images. After the PmP data were included in the tomographic inversion, the path of upwelling magma, along which a series of low-frequency microearthquakes is clearly distributed, was better imaged. These results suggest that the PmP phase has an important role in detailed crustal tomography.

The lunar probe often has some remaining fuel on completing the predefined Moon exploration mission and may carry out some additional tasks from the Moon orbit using the fuel. The possibility for the lunar probe to escape from the Moon and the Earth is analyzed. Design and optimization of the trajectory from the Moon orbit to the Near Earth Asteroids （NEAs） using the spacecraft＇s residual fuel is studied. At first, the semi-major axis, inclinations and the phase relations with the Earth of all the numbered NEAs are investigated to preliminarily select the possible targets. Based on the Sun-centered two-body problem, the launch window and the asteroid candidates are determined by calculating the minimum delta-v for two-impulse rendezvous mission and one-impulse flyby mission, respectively. For a precise designed trajectory, a full ephemeris dynamical model, which includes gravities of the Sun, the planets and the Moon, is adopted by reading the JPL ephemeris. The departure time, arrival time, burning time duration and thrust angles are set as variables to be designed and optimized. The optimization problem is solved via the Particle Swarm Optimization （PSO） algorithm. Moreover, two feasible NEA flyby missions are presented.

The main aim of this work is to understand the distribution of minerals by obtaining a shallow velocity structure around the Karatungk（喀拉通克） region.Data were acquired in 2009 by a denser array in deploying a transportable seismometer with 4.5 Hz vertical geophone.All the P-wave arrival times are picked automatically with Akaike information criterion,and then checked man-machine interactively by short-receiver geometry.The database for local active-source tomographic in-version involves 4 241 P-wave arrival time readings from 96 shots and three quarry blasts.Checker-board tests aimed at checking the reliability of the obtained velocity models are presented.The result-ing Vp distribution slices show a complicated 3-D structure beneath this area and offer a better under-standing of three well-defined mineral deposits.Near the surface we observe a series of zones with slightly high-velocity which probably reflect potential deposits.Based on features of metallic ores we attempt to delimit their distributions and stretched directions.

Accurate measurement of transit time for acoustic wave between two sensors installed on two sides of a furnace is a key to implementing the temperature field measurement technique based on acoustical method. A new method for measuring transit time of acoustic wave based on active acoustic source signal is proposed in this paper, which includes the followings: the time when the acoustic source signal arrives at the two sensors is measured first; then, the difference of two arriving time arguments is computed, thereby we get the transit time of the acoustic wave between two sensors installed on the two sides of the furnace. Avoiding the restriction on acoustic source signal and background noise, the new method can get the transit time of acoustic wave with higher precision and stronger ability of resisting noise interference.