Search

We develop a method of synthetic frequency generation to construct an atomic clock with blackbody radiation (BBR) shift uncertainties below 10 ^−19 at environmental conditions with a very low level of temperature control. The proposed method can be implemented for atoms and ions, which have two different clock transitions with frequencies ν _1 and ν _2 allowing to form a synthetic reference frequency ν _syn = ( ν _1 − ɛν _2 )/(1 − ɛ ), which is absent in the spectrum of the involved atoms or ions. Calibration coefficient ɛ can be chosen such that the temperature dependence of the BBR shift for the synthetic frequency ν _syn has a local extremum at an arbitrary operating temperature T _0 . This leads to a weak sensitivity of BBR shift with respect to the temperature variations near operating temperature T _0 . As a specific example, the Yb ^+ ion is studied in detail, where the utilized optical clock transitions are of electric quadrupole ( S → D ) and octupole ( S → F ) type. In this case, temperature variations of ±7 K lead to BBR shift uncertainties of less than 10 ^−19 , showing the possibility to construct ultra-precise combined atomic clocks (including portable ones) without the use of cryogenic techniques.

The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor is currently being operated on both Terra and Aqua spacecrafts. MODIS uses 36 bands arranged in four focal plane assemblies (FPAs)-visible, near infrared, short- and middle-wavelength infrared, and long-wavelength infrared. Misregistrations between spectral bands and FPAs and changes of spatial characterization on-orbit could impact the quality of science data products generated with multiple bands located on different FPAs. In this paper, an approach is presented to compute the MODIS band-to-band registration (BBR) using ground measurements. A special ground scene with unique features is selected to calculate the spatial registration along-scan and along-track. The monthly and yearly spatial deviations are calculated for the bands of both Terra and Aqua MODIS except for some ocean bands, cloud bands, and the Aqua MODIS band 6. The comparison with results derived from the spectroradiometric calibration assembly, a device operated on-orbit to track the BBR shift between any two of the spectral bands, generally shows good agreement. The measured differences between these two approaches are typically less than 100 m in the scan direction and 200 m in the track direction. This approach can provide more frequent characterization of the MODIS BBR and is extremely useful for other sensors that do not have an onboard spatial characterization device. [ABSTRACT FROM AUTHOR]