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Swept-Frequency Sounder

NSSDCA ID: 1971-024A-01

Mission Name: ISIS 2
Principal Investigators:Dr. J. H. Whitteker
Principal Investigators:Mr. Donald B. Muldrew


The purpose of this experiment was to measure the ionospheric electron density in the altitude range 300 to 1400 km. Another important function of the sounder was to provide correlative data for the other ISIS 2 experiments, particularly those measuring ionospheric parameters. The ISIS 2 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 14 or 21 s, and one of six selected frequencies was also used for sounding for a few seconds during each 14- or 21-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. Virtual range at a given frequency was primarily a function of distance traversed by the signal, electron density along the propagation path, and mode of propagation. The standard data format was an ionogram (graph) showing virtual range as a function of radio frequency.

Alternate Names

  • ISIS2/Swept-FrequencySounder
  • Sweep Frequency Sounder

Funding Agencies

  • Communications Research Centre, Canada (Canada)
  • NASA-Office of Space Science (United States)


  • Space Physics: Ionospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Dr. Dieter K. Bilitza



NameRoleOriginal AffiliationE-mail
Dr. Yoshiharu OgataOther InvestigatorRadio Research Laboratory
Mr. John E. JacksonOther InvestigatorNASA Goddard Space Flight Center
Dr. K. Roland ChanOther InvestigatorNASA Ames Research Center
Dr. R. B. NortonOther InvestigatorNOAA Environmental Research Laboratories
Dr. Ravipati RaghavaraoOther InvestigatorPhysical Research
Mr. J. F. TurnerOther InvestigatorIonospheric Prediction Service
Dr. Olav HoltOther InvestigatorAuroral Observatory
Dr. Michel SylvainOther InvestigatorCNRS, Laboratoire de Geophysique Externe
Dr. R. S. UnwinOther InvestigatorDepartment of Scientific and Industrial Research
Dr. J. H. WhittekerPrincipal InvestigatorDepartment of Communications/Communications Research Centre
Mr. Donald B. MuldrewPrincipal InvestigatorDepartment of Communications/Communications Research
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