A Chinese Antarctic Magnetometer （CAM） chain from Zhongshan Station （ZHS） to Dome-A （DMA） has been established since February 2009. A regular magnetometer is operated at ZHS, and four low power magnetometers are...A Chinese Antarctic Magnetometer （CAM） chain from Zhongshan Station （ZHS） to Dome-A （DMA） has been established since February 2009. A regular magnetometer is operated at ZHS, and four low power magnetometers are operated along the interior route from ZHS to DMA in the cusp latitude, extending over a distance of 1260 km. These stations fill an important void in the Antarctic magnetometer network. Furthermore, the CAM chain is magnetically conjugated with the Arctic region reaching from the Svalbard archipelago to Daneborg, on the east coast of Greenland. Conjugate measurements using the Arctic and Antarctic magnetometers provide excellent opportunities to investigate phenomena related to the coupling of the solar wind to the magnetosphere and ionosphere, such as magnetic impulse events, flux transfer events, traveling convection vortices and ultra-low frequency waves.展开更多
A new method for reconstructing electrical conductivity distribution from electromagnetic (EM) data by using traveltime tomography is presented in this paper. Diffusive EM fields can be mathematically transformed to w...A new method for reconstructing electrical conductivity distribution from electromagnetic (EM) data by using traveltime tomography is presented in this paper. Diffusive EM fields can be mathematically transformed to wavefields defined in a time like variable. The transform uniquely relates a field satisfying a diffusion equation in time, or in frequency, to an integral of the corresponding wavefield. This paper first transforms numerically calculated transient magnetic fields to wavefields. Traveltime data from a source to the receivers are estimated from the transformed wavefields. Then an iterative reconstruction algorithm is used to obtain the slowness distribution of a medium. This algorithm is an improved ART algorithm taking account of bending ray paths. The slowness distribution is transformed to electrical conductivity distribution according to their relation. The simulation result is presented in this paper.展开更多
Traveltime tomography is a technique to reconstruct acoustic, seismic, or electromagnetic wave-speed distributions from first arrival traveltime data. The ray paths that should be used for tomographic techniques stro...Traveltime tomography is a technique to reconstruct acoustic, seismic, or electromagnetic wave-speed distributions from first arrival traveltime data. The ray paths that should be used for tomographic techniques strongly depend on the wave-speed distribution. In this paper, a new method is proposed for finding out the ray paths from Fermat's principle, that means the traveltime of the ray path should be a minimum value. The problem of finding out the ray path is actually an optimum problem. Our new method uses the idea to find out the shortest path in a weighted directed graph to solve the problem. The ray paths found out by this method are used in the iterative reconstruction algorithm. Computer simulation result produced by this reconstruction algorithm is better than that by the conventional ones. It also shows that the new algorithm is effective with good convergency and stability.展开更多
TH network has been applied successfully to linear optimum and some quadratic optimum problems.This paper discusses how to determine the gain function of the net amplifiers and choose appropriate parameters to solve w...TH network has been applied successfully to linear optimum and some quadratic optimum problems.This paper discusses how to determine the gain function of the net amplifiers and choose appropriate parameters to solve weighted least-squares problems.To test the performance of the net,it is used for seismic traveltime tomography in computer simulation. Two media of different contrast are taken in simulation.The experimental results show that if the parameters are determined appropriately, the performance of the network is good and the results are close to the ideal ones.展开更多
in the study of electrical conductivity tomography using low frequency electromagnetic waves,the equation that describes the EM field is a diffusion equation. In this paper,a stable finite difference method called Pea...in the study of electrical conductivity tomography using low frequency electromagnetic waves,the equation that describes the EM field is a diffusion equation. In this paper,a stable finite difference method called Peaceman-Rachford scheme is used to solve the diffusion equation. The solution is derived in detail and a computer simulation is given. The calculated EM data are shown in waveforms. The simulation result shows that this method is simple and accurate.The EM data in time domain can be transformed to a wave field in time-like domain by an integral transformation and the traveltime data can be calculated. Compared with the theoretical value, the first travel time data obtained through transformation have a normalized mean square error or 5 percent, which proves the method to be accurate.展开更多
基金supported by the CNSF project(Grant nos.41574164,41431072)the International Cooperation Project(Grant no.IC201509)of the Chinese Arctic and Antarctic Administration,State Oceanic Administration
文摘A Chinese Antarctic Magnetometer （CAM） chain from Zhongshan Station （ZHS） to Dome-A （DMA） has been established since February 2009. A regular magnetometer is operated at ZHS, and four low power magnetometers are operated along the interior route from ZHS to DMA in the cusp latitude, extending over a distance of 1260 km. These stations fill an important void in the Antarctic magnetometer network. Furthermore, the CAM chain is magnetically conjugated with the Arctic region reaching from the Svalbard archipelago to Daneborg, on the east coast of Greenland. Conjugate measurements using the Arctic and Antarctic magnetometers provide excellent opportunities to investigate phenomena related to the coupling of the solar wind to the magnetosphere and ionosphere, such as magnetic impulse events, flux transfer events, traveling convection vortices and ultra-low frequency waves.
文摘A new method for reconstructing electrical conductivity distribution from electromagnetic (EM) data by using traveltime tomography is presented in this paper. Diffusive EM fields can be mathematically transformed to wavefields defined in a time like variable. The transform uniquely relates a field satisfying a diffusion equation in time, or in frequency, to an integral of the corresponding wavefield. This paper first transforms numerically calculated transient magnetic fields to wavefields. Traveltime data from a source to the receivers are estimated from the transformed wavefields. Then an iterative reconstruction algorithm is used to obtain the slowness distribution of a medium. This algorithm is an improved ART algorithm taking account of bending ray paths. The slowness distribution is transformed to electrical conductivity distribution according to their relation. The simulation result is presented in this paper.
文摘Traveltime tomography is a technique to reconstruct acoustic, seismic, or electromagnetic wave-speed distributions from first arrival traveltime data. The ray paths that should be used for tomographic techniques strongly depend on the wave-speed distribution. In this paper, a new method is proposed for finding out the ray paths from Fermat's principle, that means the traveltime of the ray path should be a minimum value. The problem of finding out the ray path is actually an optimum problem. Our new method uses the idea to find out the shortest path in a weighted directed graph to solve the problem. The ray paths found out by this method are used in the iterative reconstruction algorithm. Computer simulation result produced by this reconstruction algorithm is better than that by the conventional ones. It also shows that the new algorithm is effective with good convergency and stability.
文摘TH network has been applied successfully to linear optimum and some quadratic optimum problems.This paper discusses how to determine the gain function of the net amplifiers and choose appropriate parameters to solve weighted least-squares problems.To test the performance of the net,it is used for seismic traveltime tomography in computer simulation. Two media of different contrast are taken in simulation.The experimental results show that if the parameters are determined appropriately, the performance of the network is good and the results are close to the ideal ones.
文摘in the study of electrical conductivity tomography using low frequency electromagnetic waves,the equation that describes the EM field is a diffusion equation. In this paper,a stable finite difference method called Peaceman-Rachford scheme is used to solve the diffusion equation. The solution is derived in detail and a computer simulation is given. The calculated EM data are shown in waveforms. The simulation result shows that this method is simple and accurate.The EM data in time domain can be transformed to a wave field in time-like domain by an integral transformation and the traveltime data can be calculated. Compared with the theoretical value, the first travel time data obtained through transformation have a normalized mean square error or 5 percent, which proves the method to be accurate.
