Low-frequency (ULF/ELF/VLF) radio polarimetry and some a

摘要

Abstract: Polarimetry covers the entire electromagnetic spectrum and 'Low Frequency Polarimetry' applies to the polarimetric vector field nature of the magnetic and electric fields within the Ultra-Low Frequency (ULF: below 3 Hz), the Extremely Low Frequency (ELF: 3 Hz to 3 kHz) and the Very-Low Frequency (VLF: 3 kHz to 30 kHz) spectral regions. The acoustic complementary spectral regions are identified as Infrasonic (.01 - to 20 Hz) and Audiosonic (20 Hz - to - 20 kHz). These low frequency waves play an important role in coupled lithospheric-ionospheric wave interaction especially in the upper ULF (above .01 Hz) to lower VLF (below 10 kHz) for which the radiowaves display pronounced polarimetric effects, i.e., strong field component dependence. In this paper, an introduction to this exciting re-emerging field is presented, paying major emphasis on recent findings regarding the observation of elevated electromagnetic low frequency noise, strongly peaking in the 0.1 to 5 Hz spectral region before an earthquake seismic distress event. Also, polarimetric signatures resulting from the interaction of large space vehicles with the ionosphere will be discussed.!8