186 Alaskan Science Conference 



a D.T.M. Model #3 Multifrequency Ionospheric Recorder, 

 was on loan from the Department of Terrestrial Magnetism, 

 Carnegie Institute of Washington, and was manually operated. 

 This was later modified for automatic operation. Every 15 

 minutes a survey is made of radio wave energy reflected from 

 the ionosphere throughout a frequency range of 0.52 to 16.00 

 megacycles per second. The resulting photographic records 

 are reduced to tabulations of numbers giving for each hour 

 the penetration frequency of the F 2 , ¥ 1 and E-layers, minimum 

 virtual height of the F 2 , F t and E-layers, minimum frequency 

 of returning echos at normal incidence, maximum frequency 

 of boundary E-layer reflections, F 2 -layer, F r layer maximum 

 usuable frequencies for 1500 and 3000 km distance, height of 

 maximum electron density for the F 2 , F x and E-layers, and notes 

 as to intensity of fadeouts. At present the D.T.M. machine is 

 being replaced by a National Bureau of Standards C-3 Iono- 

 spheric Recorder with increased output power, variable pulse 

 repetition rate and direct recording on motion picture film. 



Summary data are transmitted daily to the Central Radio 

 Propagation Laboratory at the National Bureau of Standards, 

 Washington, D. C. Complete tabulations are mailed to the 

 Central Radio Propagation Laboratory at the end of each month 

 together with a report giving logs of operation, comparison of 

 current with previous results, notations of propagation mode, 

 and fade-out summaries. Original records and reproductions of 

 the tabulations are retained at the Geophysical Institute. 



These basic data are extremely useful for determining iono- 

 spheric structure, variations of this structure with time, mech- 

 anism of ionization agents involved, state of the upper atmos- 

 phere, and the influence of both terrestrial and extra-terrestrial 

 phenomena. The data are also extremely useful in the pre- 

 diction of radio wave propagation conditions in the Arctic. The 

 series of observations, unbroken since June 1941, constitute one 

 of the most powerful tools for research in this field particularly 

 because many of the basic phenomena must be investigated by 



