Measures for Progress: A History of the National Bureau of Standards

RADIO AND RADIO-WEATHER PREDICTING 405
An aircraft disaster in the European theater, attributed to failure ckf
communications resulting from a magnetic storm, led the British and,
after, the Australians to establish their propagation services in 1941, in order
to furnish radio weather predictions to their Armed Forces.109 A similar
program had its inception in this country when NDRC asked the Bureau to
prepare a textbook for the services on basic principles of radio skywave
propagation. Assembled by a group under Newbern Smith in Dellinger's
radio section, the Radio Transmission Handbook—Frequencies 1000 to
30,000 kc, appeared a year later, in January 1942. In addition to the prin-
ciples, it gave such computational procedures as were then available, offered
preliminary versions of prediction charts, and provided radio predictions for
that winter. A supplement in June gave the summer predictions.
So valuable was the information in these handbooks to service radio
communication systems that NDRC asked the Bureau to continue the work,
and in the summer of 1942, by order of the U.S. Joint Chiefs of Staff, the
Interservice Radio Propagation Laboratory (IRPL) was established at the
Bureau. It was directed to centralize radio propagation data and furnish
the resulting information to the services.'10
The data were compounded of a number of variables of which little
was known. First of all, 'long-range radio communication depends upon the
ionosphere, which acts as an infinite series of tiny radio mirrors to reflect
signals back to earth. Communication is imperiled, no matter how good the
transmitting or receiving equipment, unless radio waves are propagated with
sufficient strength to be receivable. That strength depends upon knowledge
of the ever-changing characteristics of the ionosphere, which vary with lati-
tude and longitude, geomagnetic latitude, layer height, ionization density,
energy absorption, and radio noise. The latter, radio noise, is both geo-
physical, caused principally by thunderstorms, and extraterrestrial (stellar
and solar), resulting from meteor activity and solar storms.'11
To predict useful frequencies over skywave paths anywhere in the
world, the Bureau had first to obtain adequate ionospheric data on a world-
wide basis. With the data, it had to establish methods for calculating maxi-
mum usable frequencies over long paths, methods for calculating skywave
Unavoidable because it results from the event, yet similar as a phenomenon, is the
total blackout of radio communications experienced by the astronauts in their space flights
while reentering the atmosphere. The heat of the falling capsule during reentry ionizes
the air around it, sealing off both incoming and outgoing radio signals and stopping regis-
tration of the instruments tracking the capsules.
Suits, Harrison, and Jordan, Applied Physics, Electronics, Optics, Metallurgy, pp.
148—9. For the wartime financing of IRPL, first by the Bureau, NDRC, Army, and Navy,
and after 1943 wholly by the Army and Navy, see memo, Deputy Secretary, Joint Com-
munications Board, JCS, for Director, NBS, May 24, 1945 (NBS Blue Folder Box 24).
Dellinger, "The ionosphere," Sci. Mo. 65, 115 (1947).