2.2.0 spase://SMWG/Instrument/ISIS1/SFS ISIS1 Swept-Frequency Sounder Topside Sounder 2019-05-05T12:34:56Z The ISIS 1 (International Satellites for Ionospheric Studies) Swept-Frequency Sounder measured the ionospheric electron density in the altitude range 300 to 3500 km, and provided correlative data for the other ISIS 1 experiments, particularly those measuring ionospheric parameters. The ionosonde was a radio transmitter that recorded the time delay between a transmitted and returned radio-frequency pulse. A continuum of frequencies between 0.1 and 20 MHz was sampled every 19 or 29 s, and one of six selected frequencies was also used for sounding for a few seconds during each 19- or 29-s period. In addition to the sweep- and fixed-frequency modes of operation, a mixed mode was available in which the transmitter frequency was fixed at one of six possible frequencies while the receiver swept. Several virtual-range (delay-time) traces resulting from ground reflections, plasma resonances, birefringence of the ionosphere, nonvertical propagation, etc., were normally observed. spase://SMWG/Person/James.H.Whitteker PrincipalInvestigator NSSDC's Master Catalog https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1969-009A-01 Information about the Sweep-Frequency Sounder on ISIS 1 Sounder Swept-Frequency Sounder on ISIS 1 spase://SMWG/Observatory/ISIS1