Radio wave propagation in the arctic

Abstract

The report is divided into six main sections. The first five deal in turn with the five main Tasks specified in the contract; the sixth describes three other phases of work also concerned with radio wave propagation in the Territory. The progress in these various fields is summarized very briefly below. Task No. 1 Sweep-frequency Ionospheric Back-Scatter No progress was made on this task, owing to lack of equipment. Task No. 2 Auroral Radar Echoes An SCR-270 radar was modified for auroral radar research, and two main investigations were carried out with this equipment. The first one was to determine the mode of propagation of V.H.F. auroral echoes; the results showed conclusively that a strong aspect sensitivity exists, due to the auroral ionization being aligned along the lines of force of the earth's magnetic field. The second investigation was to determine the relationship between the radar echoes and the occurrence of visual aurora; these observations showed that the radar echoes are usually closely associated in range and azimuth with visual aurora, but that the visual brightness of the aurora is not the factor controlling the strengths of the echoes. No echoes were obtained at frequencies greater than 106 mc, owing to lack of suitable equipment. Task No. 3 Investigation of Microwave Link The experimental, observations carried out on this link showed the absence of significant tropospheric refraction effects, and the work has now been terminated. Task No. k Prediction of Auroral and Ionospheric Storms The prediction of aurora and ionospheric storms presumes a thorough understanding of the phenomena. A brief review is given of the source of the disturbances, a stream of ionized particles from the sun, and the several influences which are observed during £nd subsequent to the bombardment of the atmosphere by these particles. Research in several phases of the problem which are in progress at the Institute are mentioned as well as that which is being done on this contract. The principle effort during the past year on this contract was development of some techniques for a better understanding of the aurora. These are the all-sky camera which is being used to study the development of an auroral display and the photoelectric photometer which appears to be useful in supplying data for an index of auroral activity. Some preliminary results from both of these equipments are presented. Task No. 5 Whistlers Observations have shown the fairly frequent occurrence of whistlers at College during the early part of July 1955» Tape recordings of some of these whistlers are now being analysed to determine their frequency dispersion. Additional Work Three main phases of additional work, dealing respectively with the tropospheric propagation of V.H.F. radio waves, the diffraction and scattering of V.H.F. radio waves by mountains, and the absorption of H.F. radio waves of the ionosphere were carried out at the Geophysical Institute. Numbers one and three of these were conducted at the request of the Alaskan Command, U.S. Air Force; the second problem was investigated in view of its possible importance in point-to-point communication in the Territory.