Reception of the NKL (Jim Creek) Transmitter Onboard GEOS-1

Abstract

At the beginning of the GEOS lifetime, some attempts have been made for taking advantage of the passes over Alaska. GEOS was then commanded in a fixed mode and the corresponding telemetry data were recorded at the NASA stations. For two passes over Jim Creek (48°2’N– 121°9’W) where a powerful VLF transmitter (f ₀ = 18.6 kHz) is located, GEOS was put in a specific mode in order to study the magnetospheric electromagnetic field in the vicinity of f ₀. The results of one pass (June 11, from 0755 UT) are presented here.

During this pass, a strong enhancement of all the e.m. components at f0 has been observed for a specific period of time, when GEOS was very near to the exact conjugacy with NKL. The distance, as measured on the ground, over which the signal was above - 6 dB from the maximum is of the order of 800 km. During the corresponding period of time (0740-0750 UT), the satellite altitude varied between 8000 and 6000 km. The magnetospheric region where the signal is strong appears to be structured, as if there were many ducts.

Preliminary results concerning the polarization characteristics of the signal are presented. In the absence of precise measurements of these characteristics, the comparison between the electric and magnetic components of the received signal is not easy to interpret. An examination of the onboard computed correlograms (in the frequency range from f ₀ - 0.6 kHz to f ₀ + 3.3 kHz) shows that, for this pass, no VLF emissions were triggered by NKL, at the altitude of the satellite.