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

406 WORLD WAR I! RESEARCH (1941-45)
field intensity, determine minimum required field intensities, and methods for
forecasting ionospheric storms.
At the time, ionospheric observations were available to IRPL only
from the Bureau laboratory in Maryland, two observatories in Australia, and
one in New Zealand.h12 Before the end of the war, through the cooperation
of the Carnegie Institution of Washington, the U.S. Army and Navy, the
Canadian Navy and Air Force, the new British and Australian propagation
services, the British Admiralty, the National Physical Laboratory, the British
Broadcasting Corp., and the U.S.S.R., 44 stations were regularly reporting
ionospheric observations by cable and radio, in cipher, to IRPL.
As a first step, the Bureau evolved a technique for predicting iono-
sphere characteristics on a worldwide basis, using standard statistical methods
and recording the data on comprehensive charts published for the services
each month. Next, a simple rapid method was devised for obtaining the
maximum usable frequency (m.u.f.) over sky paths in any part of the world
for distances up to 2,500 miles.. The method made possible preparation of
world charts giving predictions of mu.f. 3 months in advance. The prepa-
ration and distribution of these charts, which began in April 1942, was
the most important achievement of the Bureau in the field of skywave
propagation.113
The urgent need to know distance ranges and lowest useful high fre-
quency (l.u.h.f.) necessitated many more calculations of skywave field inten-
sities than were currently available. The Bureau's intensity-recording pro.
gram, begun early in the previous decade, was expanded by installing re-
corders at new ionospheric stations set up in the services and elsewhere on
the North American continent. Commercial radio companies supplemented
these records with their observed worldwide radio traffic log sheets. With
the data on skywave field intensity, knowledge of the minimum field den-
sities necessary to overcome atmospheric radio noise was also required. A
study began of thunderstorms, the common source of this noise, whose prin-
cipal generating centers are in the East Indies, Central and South America,
and Africa, with secondary centers in the tropical oceans.
A final major problem of IRPL was forecasting ionospheric storms,
the great magnetic storms, invisible but of vast energy, triggered by solar
flares and eruptions that often blanket the earth and for periods of
The Bureau's ionosphere recording equipment and field intensity recorders were located
at its field station at Md., until 1942 when the Air Force took over the site for
Andrews Air Base. The Bureau found another meadowland, an area of 450 acres, at
Sterling, Va., near Chantilly, 23 miles northwest of the Bureau. That too was lost when
in 1954 it became the site of the Dulles International Airport. By then other field sta-
tions of the Bureau, including those at Boulder, Cob., were providing adequate coverage.
"3NBS War Research, p. 36.