Discrete Echoes in Ionospherically Propagated Ground Backscatter
Technical rept. no. 5, May 1968-Dec 1970
STANFORD RESEARCH INST MENLO PARK CA
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Ionospherically propagated ground-backscatter signals in the 10-to- 30-MHz frequency band have been used for decades as a means for studying the earths ionosphere. Long pulse lengths and wide antenna beamwidths have resulted in backscatter echoes that were spatially averaged enough to give ambiguous information about the ionosphere. The purpose of this research is to explore experimentally how a backscatter sounder having high resolution in time delay 3 microsec and in azimuth 12 deg could be used to better measure ionospheric effects in backscatter signals. A pulse-compression waveform commonly referred to as sweep-frequency, continuous-wave SFCW modulation was used to achieve very short effective pulse lengths while allowing the transmitter to use a unity duty cycle. This waveform is very resistant to the effects of interference. A receiving-antenna azimuthal beamwidth of 12 deg was obtained through the use of an existing 2.5-km filled-aperture array of vertical monopoles. It is found that with a backscatter sounder having these characteristics, the spatial variations in ground-scatter coefficient are remarkably prominent in backscatter data.
- Atmospheric Physics
- Radiofrequency Wave Propagation