期刊
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION
卷 69, 期 7, 页码 4033-4048出版社
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TAP.2020.3044654
关键词
Reflection; Ionosphere; Ionization; Antenna measurements; Clouds; Refractive index; Plasmas; Brewster angle; ionosphere; polarization; radio noise; radio wave propagation; sporadic-E (Es); very high frequency (VHF)
资金
- U.K. Natural Environment Research Council for Cathryn N. Mitchell's KE Fellowship [NE/P006450/1]
This study investigates the enhanced ionization phenomenon in sporadic-E clouds in the E-region of the ionosphere, focusing on the reflection of radio waves. An experimental system has been developed to accurately measure and analyze the oblique reflection of 50 MHz radio waves. The results show evidence of magneto-ionic double refraction and the importance of environmental noise reduction for optimizing system sensitivity.
In the E-region of the ionosphere, at heights between 90 and 130 km, thin patches of enhanced ionization occur intermittently. The electron density in these sporadic-E (Es) clouds can sometimes be so high that radio waves with frequencies up to 150 MHz are obliquely reflected. While this phenomenon is well known, the reflection mechanism itself is not well understood. To investigate this question, an experimental system has been developed for accurate polarimetric and fading measurements of 50 MHz radio waves obliquely reflected by mid-latitude Es layers. The overall sensitivity of the system is optimized by reducing environmental electromagnetic noise, giving the ability to observe weak, short-lived 50 MHz Es propagation events. The effect of the ground reflection on observed polarization is analyzed and the induced amplitude and phase biases are compensated. It is found that accurate measurements are only possible below the pseudo-Brewster angle. To demonstrate the effectiveness of the system, initial empirical results are presented which provide clear evidence of magneto-ionic double refraction.
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