Measurements of Siple transmitter signals on the DE 1 satellite: Wave normal direction and antenna effective length

Abstract

A new experimental technique is developed to simultaneously measure the wave propagation direction and the effective length of a small (L ≪ λ) electric dipole antenna on a spin stabilized satellite in the magnetosphere. The technique relies on the near simultaneous measurement of single components of the electric and magnetic fields of a coherent VLF signal injected into the medium from a ground‐based source. The spin fading characteristics of the signal received by the electric dipole and the magnetic loop antenna permit the measurement of the wave normal direction assuming whistler‐mode propagation. In situ and remote measurements of the local cold plasma density are used to determine the refractive index. The wave electric field is then inferred from the wave magnetic field as measured on the loop antenna, the refractive index and the direction of propagation. Comparing this electric field with the measured voltage across the dipole antenna leads to the determination of the effective length of the receiving electric dipole. The technique is applied to data from the Dynamics Explorer 1 satellite observations of whistler mode signals injected into the magnetosphere from the Siple, Antarctica, VLF transmitter. In one case, with the measured background cold plasma density being 15 el cm−3, the effective length of the 200 m long electric dipole antenna is found to be 222±56 m, i.e., about twice the conventional value.