Interplanetary plasma concentration measurements by use of dual frequencies from separated sites
Article first published online: 7 DEC 2012
Copyright 1982 by the American Geophysical Union.
Volume 17, Issue 4, pages 773–785, July-August 1982
How to Cite
1982), Interplanetary plasma concentration measurements by use of dual frequencies from separated sites, Radio Sci., 17(4), 773–785, doi:10.1029/RS017i004p00773., and (
- Issue published online: 7 DEC 2012
- Article first published online: 7 DEC 2012
- Manuscript Accepted: 18 JAN 1982
- Manuscript Received: 3 SEP 1981
Since 1965 the dual-frequency method has been used for measuring densities of plasmas near planets and in interplanetary space. Signals at two frequencies are sent from an antenna on the earth to a spacecraft, or vice versa. The speed of the higher-frequency signal is less affected by plasma than that of the lower-frequency signal. The difference of delays provides a measure of the integrated effect of plasma along the radio path. In essence, the higher-frequency signal serves as a benchmark against which the lower-frequency effect is measured. Two markedly different sets of equipment have thus far been used to perform dual-frequency observations; their strengths and weaknesses are reviewed, and it shown that many of the weaknesses could be overcome by using separate sites on the earth from which to transmit the low and high frequencies. A survey of the expected error in measurements using separated sites suggests that the critical element is time synchronization between them. The best available device for performing this function is the cesium beam clock; six such clocks were tested under conditions that accurately simulate an operational system. The test results are related to errors that would arise in plasma densities derived by this method. While the feasibility of site separation is dependent upon the specific mission to be accomplished, it appears practicable at the present state of the art for many planetary, solar wind, and comet applications.