Search for Terrestrial Exo-Planets - 致密天体与弥漫介质 ....ppt

Outline Time Standard TAI and UTC Pulsar Time Scale algorithm simulation real data Potential Application of PT(FAST) Problem and future improvements Discussion Ensemble Atomic Time Scale TAI calculation is done each month BIPM firstly computes a free atomic scale: EAL, from around 400 clocks all over the world, to get the optimal high 1-month stability. --AlGOS: weighted average algorithm. --An average of N identical clocks may be more stable than individual one clock -- Time comparison to same laboratory (PTB) of different laboratories (time transfer GPS CV) -- EAL is stable but may have some values shift to SI second. Every month, primary frequency standard (PFS) are used to estimate the TAI from the frequency correction of EAL in order to be more closer to SI second. Time Links and Comparation TAI and UTC: leap second Coordinated Universal Time (UTC), maintained by the BIPM, is the time scale that forms the basis for the coordinated dissemination of standard frequencies and time signals. The UTC scale is adjusted by the insertion of leap seconds to ensure approximate agreement with the time derived from the rotation of the Earth. Physical realizations of UTC – named UTC (k) – are maintained in national metrology institutes or observatories contributing with their clock data to the BIPM. The dates of leap seconds of UTC are decided and announced by the International Earth Rotation and Reference Systems Service (IERS), which is responsible for the determination of Earth rotation parameters and the maintenance of the related celestial and terrestrial reference systems. TT(BIPM) TAI is computed in real time and will not be updated even an error is discovered, so it is not optimal. Therefore the BIPM computes a post-processed time scale TT(BIPM) Each new version TT(BIPMxx) updates and replaces the previous one. – Post-processed using all available PFS data. – Complete re-processing starting 1993 (change of algorithm). –