A re-evaluation of the relativistic redshift on frequency standards at NIST, Boulder, Colorado, USAContribution of US government, not subject to Copyright

• Published in: Metrologia 2017-07, Vol.54 (4), p.535-548
• Main Authors: Pavlis, Nikolaos K, Weiss, Marc A
• Format: Article
• Language: English
• Subjects: frequency standard; general relativity; gravity potential; relativistic frequency redshift
• ISSN: 0026-1394; 1681-7575
• DOI: 10.1088/1681-7575/aa765c

We re-evaluated the relativistic redshift correction applicable to the frequency standards at the National Institute of Standards and Technology (NIST) in Boulder, Colorado, USA, based on a precise GPS survey of three benchmarks on the roof of the building where these standards had been previously housed, and on global and regional geoid models supported by data from the GRACE and GOCE missions, including EGM2008, USGG2009, and USGG2012. We also evaluated the redshift offset based on the published NAVD88 geopotential number of the leveling benchmark Q407 located on the side of Building 1 at NIST, Boulder, Colorado, USA, after estimating the bias of the NAVD88 datum at our specific location. Based on these results, our current best estimate of the relativistic redshift correction, if frequency standards were located at the height of the leveling benchmark Q407 outside the second floor of Building 1, with respect to the EGM2008 geoid whose potential has been estimated to be W0=62 636 855.69 m2 s−2, is equal to (−1798.50  ±  0.06)  ×  10−16. The corresponding value, with respect to an equipotential surface defined by the International Astronomical Union's (IAU) adopted value of W0=62 636 856.0 m2 s−2, is (−1798.53  ±  0.06)  ×  10−16. These values are comparable to the value of (−1798.70  ±  0.30)  ×  10−16, estimated by Pavlis and Weiss in 2003, with respect to an equipotential surface defined by W0=62 636 856.88 m2 s−2. The minus sign implies that clocks run faster in the laboratory in Boulder than a corresponding clock located on the geoid.