Standard Time and Frequency:Its Generation, Control, and Dissemination by the National Bureau of Standards

摘要

The Time and Frequency Division of the National Bureau of Standards maintains primary frequency standards, which provide a realization of the internationally-defined second, and two atomic time scales, AT(NBS) and UTC(NBS). AT(NBS) is dependent upon the primary frequency standards, an ensemble of commercial cesium clocks, and a computer algorithm to process the data. The UTC(NBS) scale is derived from AT(NBS) by the addition of small annual frequency adjustments and leap second adjustments to keep its time nominally synchronous with the inter-national time scale UTC. The UTC(NBS) time scale is used to calibrate the clocks and secondary standards necessary for the operation of the NBS radio stations, WWV, WWVH, WWVB, and WWVL. These stations transmit various standard frequency and time signals throughout the world, and, in addition, provide certain official announcements such as geoalert warnings, marine weather advisories, and radio propagation forecasts.