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Typical measurements of the electron density in the various regions of the ionosphere are reviewed and the current availability of predictions based on these measurements is discussed. A method is suggested to combine regular ionospheric predictions such as /oF2 and foE with estimates of electron density in the lower ionosphere "imd w-ith empirical expressions for the electron density in the upper ionosphere to obtain a first approximation to the electron density versus height profile for the quiet ionosphere. Sample profile predictions based on regular ionospheric predictions are shown for iono· spheric heights of most importance in the design and operation of high-frequency communication systems. E region, (2) the E region, extending from about 90 km to about 170 km, (3) the F region, extending from about 170 km to about 500 km, and (4) the upper ionosphere, extending above the F region.We will review the systematic, long-term ionospheric measurements that have been made and give an outline of ionospheric predictions now available.

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The functions of the National Bureau of Standards include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and struc¬ tures; advisory services to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications, including assistance to industry, business and con¬ sumers in the development and acceptance of commercial standards and simplified trade practice recommendations. The work includes basic and applied research, development,engineering, instru¬ mentation, testing, evaluation, calibration services, and various consultation and information serv¬ ices. Research projects are also performed for other government agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau's unique competence is re¬ quired. Hie scope of activities is suggested by the listingof divisionsand sections on the inside of the back cover. Publications