Revista Mexicana de Astronomía y Astrofísica ISSN: 0185-1101 [email protected] Instituto de Astronomía México

Arias, E. F. ATOMIC SCALES FOR THE 21ST Revista Mexicana de Astronomía y Astrofísica, vol. 43, -, 2014, pp. 29-34 Instituto de Astronomía Distrito Federal, México

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Orellana eMxA(ei eConferencias) de (Serie RevMexAA ieDprmn,Pvlo eBeei,930S`evres, Franc 92310 Breteuil, ([email protected]). de Pavillon Department, Time inlraiain fteaoi iesaebecome scale time na- atomic 2006), the Mesures of realizations et Bu- Poids tional (SI, des Units International of System reau International measure- the chemical to and ments physical of traceability objective the ultimate is the where metrology, for their dination for procedure the of announces application synchronization. and of dates atomic the and of be- rotational relationship irregularities tween the determines the rotation, Earth’s studies the which In- (IERS), the Systems Reference Service and and of time; Rotation syn- Earth’s dissemination rotation its ternational for Earth’s the procedure to for the chronization establishing rules for the and UTC fixing respon- for (ITU), sible Union Inter- Telecommunication the national (UTC); time Time reference Universal Coordinated international of scale the charge of in (BIPM), computation Measures the and Weights Bu- International of joint the reau the organizations: from three of arises actions coordination in- time structures, ternational well-established countries. of different advantage the Taking between interactions facilitat- the for time. ing necessary national is astro- coordination the International cases maintain national some observatories the in nomical of although or responsibility institute, “legal”, the metrology within under as time country to providing a for (referred maintained times are “official”) National tions. elaboration the Words: in Key state-of-the-art ( the Time describes Universal article inter This with Coordinated coordination disseminates purposes. different in and Measures, maintains and institutes, Weights tional of Bureau International The Existen est (UTC). el art´ıculo presenta tiempo. Coordinado Este de Universal inter aplicaciones. escalas distintas organizaciones Tiempo satisfacer coordinaci´on con el para en disemina tiempo Medidas, y y mantiene Pesas nacionales, de Internacional Bureau El 1 napoesebde nteitrainlcoor- international the in embedded process a In applica- different for developed are scales Time nentoa ueuo egt n esrs(BIPM), Measures and Weights of Bureau International tnad time — standards .INTRODUCTION 1. TMCTM CLSFRTE2S CENTURY 21ST THE FOR SCALES TIME ATOMIC , 43 93 (2013) 29–34 , ABSTRACT .F Arias F. E. RESUMEN e n10 in in(rapoiain oUC dnie ihthe with identified UTC( UTC, acronym to approximation) (or tion entoa oprsna h IM laboratory A BIPM. the “ in- at relevant comparison the in ternational participating by UTC to traceable ne ihottnigfeunysaiiy( parts refer- (3 international 10 stability the frequency in provides outstanding with UTC ence, needs. lar com- financial, etc. scientific, exchanges: in mercial, international measurements of in kinds for na- confidence all between frontiers, assuring and thus the activities, tions, within societal the levels: mea- supporting two in at confidence the the SI surements follow guarantee and the that territories the to mechanisms respective disseminate traceability their These within giving institutes. SI top national the to units at is BIPM h ed fcvltmkeig h oa realiza- local The timekeeping. covering civil UTC( those tions of to needs demanding, most the the from tions, lztoso T ihost iie otolerance to system. each limited for offsets specified with values UTC re- of to from synchronized alizations computed are and are readings They individual producing solutions. and the navigation system for the the scales synchronizing time of internal purpose define satellite (GNSS) navigation systems for Global maintained and applications. developed particular ns. are 20 scales and time 5 Other are between and uncertainties microseconds, by to characterized up nanoseconds few a from k 1 ufiln hscniinmitisalclrealiza- local a maintains condition this fulfilling ” iesae r osrce ofllparticu- fulfil to constructed are scales Time the where pyramid metrological a is system The 16 16 ;i scneunl utdfralapplica- all for suited consequently is it ); ,adhg rqec cuay(e parts (few accuracy frequency high and ), k prxmt T ihost ranging offsets with UTC approximate ) k d cule aeaoaio eestas elaboraci´on de la en actual ado ). T) te ieclseitfor exist timescales Other UTC). ainlognztosadna- and organizations national fteetm scales. time these of ab´ norseclsde escalas tambi´en otras ainlseinstitutos e nacionales 29 © 2014: Instituto de Astronomía, UNAM - Astronomía Dinámica en Latino América (ADeLA-2012) Ed. C. Allen, F. Arias, & R. Orellana h nebe(oeta 0)aesra world-wide. spread in are 400) the than where (more lo- ensemble case the extreme geographical the different is in a UTC or within cations. either laboratory clocks, a the in of room location differences ensemble. the clock the on the evaluating depend in for is clocks used scale devices the time The between a such difference infor- of basic the establishment The the scale. for time mation clocks, the of of the quality ensemble on requested depend an characteristics of whose algorithms basis obey the on constructed geswt h Iscn yafwprsi 10 in parts few interval a by unitary whose SI the scale with time agrees uniform and ous spread observatories clocks and atomic institutes industrial world-wide. 420 national about 72 BIPM of the in at basis monthly to the calculated close is on be It to second. constrained SI not the is interval unitary Its 10 in algorithm stability parts 3 frequency an (about mid- average by for weighted treated designed the clocks especially is contributing it the UTC; of of calculation the corrections. pri- applying, (rate) of by frequency that and necessary, with if (PFS), scale standards time frequency the mary the of comparing (rate) by improved fre- frequency be algorithm the can an stability, accuracy of frequency quency basis required the the on scale conferring time cal- a the of After culation counterpart. theoretical to interval its scale reproduce unitary scale its theoretical time of aptitude a its the of represents accuracy and frequency interval The be- scale ratio counterpart. scale unitary fixed time a its maintain a tween to of capacity underlying stability its the represents frequency of The accuracy the frequency. and stability the by 30 o oeln h oin fatfiiladnatural exploration the and in artificial applications dynamics, with of in bodies, motions celestial used the scales modelling time basis the for of of is realizations any TAI of the computation. It that of its than for only. used better clocks frequency EAL, the of for stability broad- reference the not a is has it provides clocks, it by represented rotation cast; not Earth’s is the to It ac- tie time. no provides has needed. EAL” TAI TAI. of is to curacy “steering frequency called the may process, to it This correction laboratories, a of frequency that number primary result small by a realized dura- in second the standards SI to the EAL of of interval tion unit the of comparison h opst iecls hti,toeta are that those is, that timescales, composite The nentoa tmcTm TI sacontinu- a is (TAI) Time Atomic International in step first the is (EAL) Scale Atomic Free The characterized is scale time a metrology, time In .SM AI CONCEPTS BASIC SOME 2. 16 vritraso 0t 0days). 40 to 20 of intervals over 16 By . ARIAS iesadrsfo hc ea ie nmn coun- defined. many are in national times tries to legal which UTC from to standards and time second SI the to traceability ec 0n o nairtdeupet( equipment can uncalibrated for which ns and 20 reach component, statistical present the the surpasses In that uncertainty an contribute considered. calibrations sys- be situation, cal- the also the comparisons, should from coming time ibration, B), of (Type case the uncertainty tematic the affects In uncertainty denom- (statistical) valid process. the A strictly only is Type where assertion inated This comparisons, frequency days. for few com- a a integration of allow over standards to times atomic sufficient best nanosecond priori the a of a parison and links, best nanoseconds the of for tens few a tween links. the time international on of BIPM Based network the a establishes comparisons, defined. non-redundant well of be designed principle to the needs with consistent algorithm for comparison, strategy clock a therefore the planet; the over major spread a tories scale. often time were a of they construction past, the the in in limitation stability clocks; frequency the the time of contaminate of methods not the do that is distanttransfer requisite of prime comparison laboratories A of different clocks. methods of in use the located requires clocks of readings etclbain r nipnal o lc com- clock for indispensable parison. are calibrations ment T Circular htpoie tfiedyitras h aus[UTC- values the UTC( intervals, five- s. at 0.9 provides of be- that value maximum offset a the to limits UTC and procedure UT1 This tween of insertion for . procedure leap the Union including Telecommunication 2002), International (ITU recommenda- the a in of reference defined world tion is It the as coordination. mainte- time adopted for its been in has to clocks and data by nance, contribute represented that is laboratories It of rate the Earth. irregular the the of for rotation compensate of to insertion second of leap a the at one- discontinuities presents second the but TAI, has of as It moment qualities 2014). metrological the January same 1 at until num- (35 accumulated computation the seconds its TAI leap to of applying by ber BIPM the at monthly geo- geodesy, theories, etc. of studies, tests environmental system, physics, solar the of h netit fcokcmaiosrne be- ranges comparisons clock of uncertainty The labora- 72 of contribution the with built is UTC the of basis the on scale time a of calculation The IMCrua T Circular BIPM calculated is (UTC) Time Universal Coordinated k ]frec otiuiglaboratory contributing each for )] .I a eifre htrpae equip- repeated that inferred be can It ). .COKCOMPARISONS CLOCK 3. stemnhypublication monthly the is § of 6 k tgives It . BIPM © 2014: Instituto de Astronomía, UNAM - Astronomía Dinámica en Latino América (ADeLA-2012) Ed. C. Allen, F. Arias, & R. Orellana rnfrdt ntefr facmaio ftheir of comparison a of form time the UTC( provide in laboratories data compar- participating transfer these The organize to isons. BIPM the by established T ti sacs ftowyobservations). two-way of of case realization a local is another (this to UTC or scale) time GNSS a h rcso ihwihTIi eotd Code- reported. is TAI which with precision code the GPS uses link of kind only. This measurements better. allow or and uncer- tainty, statistical al. nanosecond data with et comparisons ionosphere-free clock (Defraigne provide P3 2001a,b), GPS denominated receivers, 2008). Jiang & (Petit ones particularly long links, very adding time the of the the of benefit improving uncertainty elevations method the high statistical AV with at the satellites CV from use and GPS data to orbits the possible satellite of been instead from has coming im- it the error clocks, minimizes the this Since of Time. pact GPS than the better of magnitude that of 10 relative orders two whose order time, (IGST), of averaging IGS is the instability of frequency scale referred time products the clock to satellite GPS precision high satellites. observed suitable having for length baseline the the of of that independent becoming ob- 2008) thus simultaneous Jiang servations, having & of constraint (Petit (AV) the eliminates View technique, in another All of named introduction param- the clock allowed and eters orbits advances calcula- satellite Then, the precise 2006. obtaining for until in BIPM used the at been UTC had of tion CV clocks GPS satellite orbits. the observing and from two originated the elimi- mostly to to common stations, necessary sources use error is in the it still nate when is It comparisons clock signal. several emitted for by same reception the the of on receivers relies (1980) Weiss & lan transfer. specifically time been used for have be to receivers commercialized GPS and developed purpose, lab- this a For satellite in a installed oratory. equipment by specific emitted by received being and signal one- a the con- is method, It which way information. satellites, positioning and GPS timing by using tains of broadcast consists signal It construction the scales. time the of in dissemination improvement and major a troduced ewr fitrainltm ik a been has links time international of network A otrmiigerrsucsaeudr01ns, 0.1 under are sources error remaining Most dual-frequency using obtained links GPS The provides (IGS) Service GNSS International The Al- by proposed method (CV) common-view The in- comparisons time in satellites GPS of use The k ihrsett nte iesae(currently scale time another to respect with ) 3.1 s fGS o ietransfer time for GNSS of Use . TMCTM CLSFRTE2S ETR 31 CENTURY 21ST THE FOR SCALES TIME ATOMIC 15 o n day one a for cal sdfretbihn i ik o T (Jiang UTC 2012). for combination Lewandowski links of- & six link is establishing for GLONASS a used and ficially developed GPS of has combination strategy; BIPM the fer, com- to used are IGS corrections. the pute Analysis by provided iono- Information maps and Federation spheric the Russian the by from (IAC) Centre Pre- provided since 2012). orbits UTC Lewandowski suc- cise of & been (Jiang calculation have 2009 the November links stud- in CV of included GLONASS series cessively a tests, After and flying ies now constellation. is complete GLONASS the satellites, of number small ephemerides. using satellite positions precise satellite post-processed for IGS corrected All IGS. are the links by produced GPS mak- maps by ionospheric delays of use ionospheric ing for corrected are calcu- lations UTC regular in with used observations receivers GPS single-frequency increasing transfer. time thus of accuracy ionosphere, the the the by of introduced removal delay the permit long over laboratories many participating compared in installed clocks receivers Dual-frequency of baselines. case in comparisons, the today. time in GPS ns the particular in of 1 errors one below significant introduce delay most is uncertainty ionospheric GPS of the effects via The modeling, comparison clock and of treatment data in ns. 0.3 present uncertainty at statistical on comparison, tech- clock smallest used this of the By being obtain is 2009. we September and nique compu- since UTC basis the for routine in time links a use reference time for a of implemented to tation been station a has in scale GPS clock via reference comparing for the and used phase are frequency measurements posi- dual code Kouba precise which 2008; in The Jiang H´eroux 2001) & & sources. Petit (PPP, error technique two tioning these ef- of the on fects minimizes depending receivers measure- variations geodetic-type phase from of slow ments addition with The bias ns, conditions. and 0.1 weather noise few present short-term a still introducing of is data, delay the Tropospheric either AV. in transfer or time CV code-only representing with to long-term, limit the ultimate ba- in term the values short higher a on and ns sis 1 reach can effects multipaths ehiu tlzsagottoaytelecommunication geostationary a utilizes technique 3.2 safis tptwrsmlisse ietrans- time multi-system towards step first a As a with operations limited of many After improvements to and hardware new to Thanks h WTT(asn18;Krhe 1991) Kirchner 1989; (Hanson TWSTFT The w-a aelt ieadfeunytransfer frequency and time satellite Two-way . (TWSTFT) © 2014: Instituto de Astronomía, UNAM - Astronomía Dinámica en Latino América (ADeLA-2012) Ed. C. Allen, F. Arias, & R. Orellana sdfrteeauto faot1 ik nUTC. in links 10 about of regularly & evaluation is the (Jiang for combination PPP used This GPS of 2012). stability Lewandowski term short the and ytmmr eibe o h ik hr GNSS where links the For reliable. the a more making techniques, for system independent results using has comparing link observations of time GLONASS TWSTFT opportunity the the the allowed of of is and introduction situation technique present the The different; methods. quite other with to performance respect its TAI, of in test any comparisons impossible clock rendering for tool unique a provided 2009). 2005, al. et with (Piester BIPM equipment the TWSTFT of orga- support the laboratories the of the calibrations different; nize is to links Tis- UTC TWSTFT & in (Lewandoswki en/TimeCalibrations.jsp used and once 2010a,b,c least about equipment serand at in GNSS calibrated result the be 2001, of since their 65% conducted which comparing equipment, been by in- BIPM have traveling for laboratories with compensate in equipment to BIPM delays deter- the ternal equipment for by time organized Campaigns UTC GNSS are of of delays dissemination. stability differential mining its the for for and fundamental is transfer ikcaatrzdb h cuayo W( TW of accuracy the by characterized link a ns. below two- 1 (statistical) at uncertainty day an every with intervals made are TAI in TWSTFT observations the link of laboratories, all installation in the stations With automated region. Asia-Pacific Europe the America, North and allow- between number and equipment, A within two-way links ing stations. operate ground laboratories positions the of the and in satellite tropo- uncertainty the and the of ionospheric and as delays such spheric one- sources error, some the systematic reducing The of over or eliminating advantage baseline. of method the the way simultane- of has are ends method clocks both two-way at their compared that ously so pairs laboratories between of scheduled system. independent the are to observations is redundancy Two-way adding technique thus This GNSS, from receiving- two in stations. located emitting clocks compare to satellite 32 3.3 o w eae,GSCAcd observations C/A-code GPS , two For time for equipment the of delays the Measuring h obnto fT n P P eut in results PPP GPS and TW of combination The hrceiaino h eaiedly ftime of delays relative the of Characterization . 3.4 ielnscomparison links Time . rnfrequipment transfer http://www.bipm.org/jsp/ .Testainfrthe for situation The ). ∼ ns) 1 ARIAS eaiewih fclock of weight relative uayo TAI ac- of and stability curacy frequency the guarantee to designed scale. time the of tinuity edn fclock of reading clock h eut ftm ikcmaiosaeaalbeat available and are links comparisons link time ftp://tai.bipm.org/TimeLink/LkC. backup time cal- The as of the results kept 2012). the in other(s) Lewandowski used the & is and (Jiang UTC, best of the com- culation are compared; links and all available, puted are techniques TW and l 94 unt&Toa 98 n ie the gives and clocks 1988) participant each Thomas as: and et & EAL (Thomas between Guinot 1970s difference the 1994; in BIH al. the at a developed was in connected comparisons. and time world precise allows the located that of types, network parts different different of clocks in atomic possible of largest the number on relies frequency therefore ) extreme UTC a stability. is (about requirement long-term the and reliability UTC, international as an such for scale; reference the on requirements the on where n h nevlo aclto oemonth), (one calculation of interval the ing .TEAGRTMO ACLTO OF CALCULATION OF ALGORITHM THE 4. x • • j LO sbsclycmoe ftrealgorithms three of composed basically is ALGOS h rgnlagrtmAGSfrdfiigEAL defining for ALGOS algorithm original The depending considered be can algorithms Different ( h rdcinagrtmue nAGSto different to ALGOS due jumps in frequency and used time avoid algorithm prediction The predominant a having clocks avoid to role. weight to relative maximum fixed A clock, data. is of the one of over EAL, frequencies recipro- the computed the variance from classical is individual the the clock 1996; of each computation, cal Azoubib to EAL attributed the & weight In Thomas term 2001). 1988; Azoubib long (Guinot elements Thomas the contributing in & the stable of any more than is weighted a that obtain sta- to average long-term is its objective weight the reflects the since bility, clock TAI; a of to stability attributed long-term guaran- the to tee optimized algorithm weighting The t = ) H N i ttime at EAL stenme fpriiaigcok dur- clocks participating of number the is ( t H ) t − and , i EAL/TAI/UTC htsre ogaatetecon- the guarantee to serves that h j ( t h = ) H i ′ ( i t , stepeito fthe of prediction the is ) X i =1 N h i ( w t steraigof reading the is ) i [ h i ′ ( t . ) − x i,j w ( t i )] the (1) , © 2014: Instituto de Astronomía, UNAM - Astronomía Dinámica en Latino América (ADeLA-2012) Ed. C. Allen, F. Arias, & R. Orellana ext org/TFG/TT(BIPM)/TTBIPM.12 vlain ftefeunyo A ytePFS. the by TAI January each the of computed of frequency is average TT(BIPM) weighted the a of on 2003, evaluations based (Petit is TT(BIPM) which time 2009), deferred therefore BIPM in almost The computes in realization. computed optimal not does an is it provide constraints, it operational as has and but, real-time one TT In- provides of the TAI realization by Union. defined Astronomical system ternational reference geocentric the netaoaino h aetraiaini published month is realization each latest the of extrapolation an tmcsae A,UCadT(IM.Cokand Clock TT(BIPM). and UTC TAI, scales atomic BIPM the to 1992. submitted since measurements PFS all uses .T(IM,BP’ ETRAIAINOF REALIZATION BEST BIPM’S TT(BIPM), 5. • 2 3 . ersra ie(T sacodnt iein time coordinate a is (TT) Time Terrestrial h IMcluae naruiebssthe basis routine a on calculates BIPM The h aetT(IM2 saalbeat available is TT(BIPM12) latest The e e.g. See n hs hne r none nadvance in announced the are in changes these TAI, of and stability ) (several degrading long-term without are the accuracy correction def- ensure steering to its the expected to to conforms Changes TAI of inition. ensure frequency to the all EAL to that using applied is (frequency PFS correction) shift of steering frequency a that and of with data, available frequency compared a The by is maintained EAL PFS laboratories. of metrology number few small accuracy a its in and from kept laboratories, clocks sta- a contributing atomic its in the industrial gets time the TAI from coordinate bility a system. TT, reference of geocentric realization TAI a Time Atomic is ac- International the TAI. improve of to curacy used algorithm month steering a The on constant as taken frequency is period. the describe clocks to and the used behavior of is clocks’ 2012) atomic the al. et quadratic (Panfilo a cal- 2011 model August consecutive since in periods; used culation being ensembles clock rneu 97 ra ei 2005). Petit & Arias (Azoubib TAI 1977; of Granveaud unit & scale the of duration estimate the to of combined are BIPM. PFS the several to from regularly Data less or more reported which are measurements, PFS on depends therefore ftp://tai.bipm.org/TFG/TT(BIPM)/TTBIPM.12. IMCrua T Circular BIPM 3 t optto trsi 93and 1993 in starts computation Its . ERSRA TIME TERRESTRIAL .CONCLUSION 6. . TMCTM CLSFRTE2S ETR 33 CENTURY 21ST THE FOR SCALES TIME ATOMIC h cuayo TAI of accuracy The . ftp://tai.bipm. 2 ic 2009, Since . in,Z,Ais .F,Lwnosi . ei,G. Petit, & W., Lewandowski, F., E. Arias, Frequency Z., on Jiang, Symp. Annual 43rd the 1989, of W. Report D. Annual Hanson, 1988, C. Thomas, & B., Proc. Guinot, 2001b, C. Bruyninx, & G., Petit, P., Defraigne, Senior, & J., Ray, J., Clarke, C., Bruyninx, P., Defraigne, zui,J 01 5hMeigo h CF Docu- CCTF, the of Meeting 15th 2001, J. Azoubib, Metrolo- 1977, FCS B. IEEE Guinot, & Joint M., Proc. Graveaud, J., 2005, Azoubib, G. Petit, Annual & 34th F., Proc. E. 1980, Arias, M. A. Weiss, & W., D. Allan, Recom- 2002, Union Telecommunication International IM21,BP iclrT305, T Circular BIPM 2013, BIPM (8th (SI) Units of System International The 2006, BIPM long- the improves TAI. calculation of stability of refinementterm algorithm the and the TAI; of of accuracy is the laboratories to in essential the oper- standards and frequency improve developing primary ating to comparison; clock equipment allows of transfer techniques methods calculation. time processing its new to and of serving development elements the The all of ment messages. navigation their in broad- approximations cast via reinforce UTC GNSS of ITU; dissemination the the by established follow- rules UTC(k) the local disseminate ing partici- its calculation institutes; the to to national second pants SI in the UTC(k) and realizations gives UTC T to Circular BIPM traceability monthly and means; levels dis- different different Broad at by achieved is scales. 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