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Swept-Frequency Sounder

NSSDCA ID: 1969-009A-01

Mission Name: ISIS 1
Principal Investigators:Mr. Donald B. Muldrew
Principal Investigators:Dr. George Leroy Nelms


The purpose of this experiment was to investigate the ionospheric electron density in the altitude range 300 to 3500 km for a full solar cycle (by combining the ISIS 1 measurements with the Alouette 2 data). Another important function of the sounder was to provide correlative data for the other ISIS 1 experiments, particularly those measuring ionospheric parameters. The ISIS 1 ionosonde was basically a radio transmitter/receiver that recorded the time delay between a transmitted and a returned radio frequency pulse. A continuum of frequencies between 0.1 and 20 MHz was sampled once every 19 or 29 s, and one of six selected frequencies was also used for a period of 3 to 5 s during this 19- or 29-s period. In addition to the sweep- and fixed-frequency modes of operation, a mixed mode was possible where the transmitter frequency was fixed at 0.82 MHz while the receiver swept. Several virtual-height (delay-time) traces were normally observed due to ground reflections, plasma resonances, birefringence of the ionosphere, nonvertical propagation, etc. Virtual height 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 showing virtual height as a function of frequency.

Alternate Names

  • ISIS1/Swept-FrequencySounder
  • Sweep Frequency Sounder

Funding Agencies

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


  • 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. J. H. WhittekerOther InvestigatorDepartment of Communications/Communications Research Centre
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. George Leroy NelmsPrincipal InvestigatorDepartment of Communications/Communications Research Centre
Mr. Donald B. MuldrewPrincipal InvestigatorDepartment of Communications/Communications Research
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