IGY Bulletin, Number 7, January 1958 - Ionospheric studies using Earth satellites

This is a summary the last article from the January 1958 issue of the IGY Bulletin.

By the end of January, 1958, three satellites had been successfully launched: Sputnik 1 (launched Oct. 4, 1957), Sputnik 2 (Nov. 3, 1957), and Explorer 1 (Jan. 31, 1958).

The article starts by stating that a conference on the study of the ionosphere by using radio observations of satellites was help on Nov. 5, 1957 (just after the launch of Sputnik 2), at the Central Radio Propagation Laboratory of the National Bureau of Standards (now the National Institute of Standard and Technology), under the direction of Alan H. Shapley.

Twelve projects that had utilized radio observations of Sputnik 1 are tabulated in the article.

The article is fairly dry, but a good summary of how Sputnik 1 could be used to infer ionospheric properties is given in: Sputnik 1 and the First Satellite Ionospheric Experiment, a poster co-authored by V. D. Kuznetsov (Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation) as a contribution to the 40th COSPAR Scientific Assembly, August, 2014. His explanation is as follows:

Any luminous body such as an artificial satellite, moving along a closed orbit around the earth, becomes optically visible at an observation point on the earth’s surface when it rises above the horizon at that point. The rays of visible light propagate in the atmosphere and space on a nearly perfectly straight path. The moving body optically disappears, at the same observation point, when the body falls below a straight line to the opposite horizon. ... The propagation paths of the radio waves emitted by satellite, however, are curved [refracted] in the ionosphere, that is, in the ionized part of the atmosphere where free electrons and ions are produced. ... The curvature of the radio waves' paths becomes appreciable at altitudes of 60-70 km above the surface of the earth; it is greatest at about 250-350 km, and disappears at about 1000-1500 km, where the paths of the waves ... are approximately straight. Therefore, the radio appearance of a satellite precedes its optical visibility. Similarly, in disappearing from view, the radio disappearance of the satellite is late with respect to the disappearing optical view. This effect depends upon the ionization level of the ionosphere and, in particular, on the altitude distribution of the density of free electrons and ions, which are produced in the atmosphere by ultraviolet solar radiation [emphasis mine]. Therefore, to determine the times of the rise and set of the radio signal, it is necessary to know the altitude dependence of the electron density in the ionosphere. On the other hand, if you know these times and the position of the body, and if you also have some initial data, that is, some characteristics of the ionosphere at that time, you can find the average, smoothed altitude dependence of electron concentration [emphasis mine].

From Kuznetsov (2014). The position labeled O on the Earth's surface is the observation point. Note that the optical set points are on the horizon, while the radio set points are below the horizon.

This is similar to the phenomenon of the Fata Morgana discussed in a previous post.

In my collection, I have a 1959 issue of the Proceedings of the Institute of Radio Engineers, the cover of which is shown below.

Articles in this issue related to IGY studies of the ionosphere 

Article authors include IGY luminaries Lloyd Berkner, Sydney Chapman, and Marcel Nicolet.

In the preface, guest editor Millett G. Morgan describes the issue as follows: 

The issue opens with a guest editorial by L. V. berkner. The first papers describe the undisturbed ionosphere, and the succeeding ones, the severe disturbances which are produced by solar flares. Following these are

papers describing rocket and satellite measurements in both the undisturbed and the disturbed ionosphere. As an addendum, papers have been added describing some of the special purpose radio equipment used in making ionospheric measurements, and the global system of warning and communication developed for the IGY.