An FDTD Study of Errors in Magnetic Direction Finding of Lightning Due to the Presence of Conducting Structure Near the Field Measuring Station

Yosuke Suzuki,Vladimir Rakov,Yoshihiro Baba,Shohei Araki,Toshihiro Tsuboi,Shigemitsu Okabe

doi:10.3390/atmos7070092

Abstract

Lightning electromagnetic fields in the presence of conducting (grounded) structure having a height of 60 m and a square cross-section of 40 m × 40 m within about 100 m of the observation point are analyzed using the 3D finite-difference time-domain (FDTD) method. Influence of the conducting structure on the two orthogonal components of magnetic field is analyzed, and resultant errors in the estimated lightning azimuth are evaluated. Influences of ground conductivity and lightning current waveshape parameters are also examined. When the azimuth vector passes through the center of conducting structure diagonally (e.g., azimuth angle is 45°) or parallel to its walls (e.g., azimuth angle is 0°), the presence of conducting structure equally influences Hx and Hy, so that Hx/Hy is the same as in the absence of structure. Therefore, no azimuth error occurs in those configurations. When the conducting structure is not located on the azimuth vector, the structure influences Hx and Hy differently, with the resultant direction finding error being greater when the structure is located closer to the observation point.

Highlights

Two vertical and orthogonal loops, each measuring the magnetic field from a given vertical radiator, can be used to obtain the direction to the source; that is, as a magnetic field direction finder (DF) [1]
In order investigate the validity of our finite-difference time-domain (FDTD) simulation, magnetic field due to a lightning
Hy at an observation point (7080 m, 7080 field is strike to a flat ground without conducting structure computed, and the FDTD-computed m) for a lightning strike to a flat perfectly-conducting ground

Summary

Introduction

Two vertical and orthogonal loops, each measuring the magnetic field from a given vertical radiator, can be used to obtain the direction to the source; that is, as a magnetic field direction finder (DF) [1]. This is the case because the output voltage of a given loop is proportional to the cosine of the angle between the magnetic field vector and the normal vector to the plane of the loop. The ratio of the two signals from the loops is proportional to the tangent of the angle between the normal vector to the plane of one of the loops and direction to the source. The direction-finding technique involves an implicit assumption that the radiated electric field is oriented vertically and the associated magnetic field is oriented horizontally and perpendicular to the propagation path.

Methods

Results

Conclusion