Forward simulation of coal fire model by transient electromagnetic method with electrical source

Uncontrolled coal fires are natural disasters that may cause mineral loss and environmental damage.The traditional loop source transient electromagnetic method can effectively detect the low-resistivity region of coal fires,but its detection efficiency is not so good for high-resistivity regions.In view of this limitation,a technique based on electrical source transient electromagnetics is proposed in this paper to detect high-resistivity regions in the spontaneous combustion process of coal.Considering the complex geometry of the coal fire area,an unstructured tetrahedral grid is used in this study to realize the spatial discretization of the model,and solve the electromagnetic field based on a vector finite element algorithm.Numerical analysis is used to investigate methods for detecting coal fires and the characteristics of effective anomalies are further examined to provide guidance for practical detection.

Analysis of the Initial Stage Intracloud Lightning Using the Pulse Location Technique Based on the Fast Electric Field Change

Academy of Sciences,Beijing 100029 2 Lanzhou University,Lanzhou 730000 3 Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences,Lanzhou 730000 4 Nanjing University of Information Science＆Technology,Nanjing 210044 Using both fast and slow electric field change sensors and field mill,multi-station observations on lightning flashes over China inland plateau areas were conducted during the summer of 2004.All of the stations were synchronized by GPS with a time-resolution of±50 ns.Using the different time of arrival（DTOA）and based on the fast electric field change sensor,a lightning radiation location technique was developed.Radiation pulses in the initial stages of five intracloud（IC）lightning discharges which occurred on 20 August were analyzed.The results indicate that the technique developed could effectively locate the lightning radiation sources.Furthermore,the lightning discharges were compared with the Doppler radar data.The results show that the radiation sources were well associated with the storm development.When the storm was at the mature stage with an echo top of about 10.9 km,the radiation sources ranged from 5.2 to 8.3 km above mean sea level;when the storm gradually became weaker,with echo top of about 7.9 km,the radiation sources ranged from 3.0 to 5.9 km.In particular,one of the IC lightning discharges ranged from 3.0 to 4.9 km during the dissipation stage of the storm.The results also indicate that the radiation sources were closely associated with the high reflectivity region（25–50 dBZ）of the storm,which,to some extent,demonstrates the reliability of the location results,thereby showing that multi-station observations of fast electric field change sensors could be a useful tool for monitoring the storm development.Location errors from radiation sources were also compared with the radar data and the results of a simple simulation.It was found that the errors were getting smaller when the radiation sources approached the center of the detection network, and vice versa.Compared with the limited experimental observations,the simulation results were found capable of effectively reflecting the location errors.