Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere
نویسندگان
چکیده
[1] ELF/VLF radio waves (300 Hz–30 kHz) are difficult to generate with practical antennae, because of their extraordinarily long (10–1000 km) wavelengths, and the lossy nature of the Earth’s surface at these frequencies. ELF/VLF waves have been successfully generated via amplitude modulated (AM) HF (2–10 MHz) heating of the lower ionosphere. Through the temperature-dependent conductivity of the lower ionospheric plasma, a patch of the ionospheric current becomes a large radiating ‘antenna’. We implement a new method of ELF/VLF wave generation, herein named ‘geometric modulation’, involving scanning the HF heating beam in a geometric pattern without modulating its power. Utilizing results from the upgraded 3.6 MW radiated HAARP HF antenna array, we show that geometric modulation can enhance ELF/ VLF wave generation by up to 11 dB over the conventional AM method. Geometric modulation also allows directional launching of the signal into the Earth-ionosphere waveguide, forming an unprecedented steerable large-element ELF/VLF ionospheric phased array. Citation: Cohen, M. B., U. S. Inan, and M. A. Golowski (2008), Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere, Geophys. Res. Lett., 35, L12101, doi:10.1029/2008GL034061.
منابع مشابه
Geometric modulation: A new, more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere
ELF/VLF waves can be generated via amplitude modulated HF heating of the auroral electrojet, which turns a patch of ionospheric currents into a radiating antenna. A new, more powerful technique, termed `geometric modulation', involves scanning the HF beam in geometric patterns with no power modulation. Utilizing results obtained from the HAARP facility, we show that geometric modulation enhance...
متن کاملComment on ‘‘Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere’’ by
[1] Cohen et al. [2008] overlook observations presented by Barr et al. [1988], which have a direct and possibly significant impact on two of their primary conclusions. The two conclusions of interest are: 1) that ‘geometric modulation’ in the form of circle-sweeping is significantly more efficient than amplitude modulation at generating ELF/VLF waves, and 2) that the ELF/VLF beam generated usin...
متن کاملOn the generation of ELF/VLF waves for long‐distance propagation via steerable HF heating of the lower ionosphere
[1] ELF/VLF radio waves (300 Hz to 30 kHz) have been successfully generated via modulated HF (3–10 MHz) heating of the lower ionosphere in the presence of natural currents, most recently with the HAARP facility in Alaska. Generation is possible via amplitude modulation or via two techniques involving motion of the HF beam during the ELF/VLF cycle, known as beam painting and geometric modulation...
متن کاملReply to comment by R. C. Moore and M. T. Rietveld on ‘‘Geometric modulation: A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere’’
[1] We thank Moore and Rietveld [2009] (hereafter referred to as MR09) for their comments to Cohen et al. [2008] (hereafter referred to as CA08). MR09 consider the two following conclusions of CA08 concerning the generation of ELF/VLF (0.3–30 kHz) waves with typical amplitude modulation (AM) and geometric modulation of ionospheric High-Frequency (HF) heating: 1) ‘‘Geometric modulation can enhan...
متن کاملELF/VLF wave generation via ionospheric HF heating: Experimental comparison of amplitude modulation, beam painting, and geometric modulation
[1] Generation of ELF/VLF radio waves (300 Hz to 10 kHz) is achievable via modulation of natural currents in the lower ionosphere with high‐power HF (2–10 MHz) heating. Recently, Cohen et al. (2008b) put forth an alternative to conventional amplitude HF power modulation, therein referred to as geometric modulation, in which the HF ionospheric heating beam is geometrically steered at the desired...
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