Atomic Standards Group

The Atomic Standards group maintains the primary frequency standard, the time scale, and the transfer operations for the U.S. contribution to the International Bureau of Weights and Measures. The primary frequency standard for the U.S. is currently our cesium fountain standard, NIST F1, with the next generation, NIST F2, under development. The time scale is a weighted average of, primarily, six hydrogen masers, whose frequencies linear frequency drifts are regularly measured against NIST F1. Two-way satellite time and frequency transfer is the method for comparing our clocks with standards around the world for our participation in the generation of international atomic time (TAI and UTC). GPS common-view time transfer is the back-up method for participating in TAI, as well as a method for disseminating UTC(NIST) at state-of-the-art accuracies.