]966020453 https://ntrs.nasa.gov/search.jsp?R=19660020453 2020-03-16T20:56:40+00:00Z i ( ,, i Reports of the Department of G _odefic Science Reporl No. 70 THE DETERMINATIONAND D!"""-• --m,Lmm,'"'----m,_-'..4•""_-m-y.-.'*'.-,. OF PRECISETIME GPO PRICE CFSTI PRICE(S} $ by Ha_s D. Preuls Hard copy (HC) / tf P-,SJJuly 65 Prepared leo _ NATIONAL AERONAUTICS and SPACE ADMINMISTRATIONicrofiche (ME)_ ./ •_,9.:_,4 _ WASHINGTON, D.C. 1 _"qi J_ ..Eo.,o_r._u,,,v_.s,. I I RESEARCHFOUNDATION r,_ .. ColumbuS,Ohio 43212 I. ' "_ " log _JNOd _ll'll_lyJ 1966020453-002 REPORTS OF T}JE DEPART_._.NTOF GEODETIC SCI_'CE Report No. 70 _qTY.F.DEs._RMINAYION AND DISTRIBUTION OF PRECISE TL_E by Hans D. Preuss Contract No. NSS"36-OO8-O_3 OSURF Project No. 1997 Prepared for Natio-al Aeronautics and Space Administration _ash_ ngton , D.C. The Ohio State University Research Fo Andation Columbus, Ohio Apr_l, 1966 g 1966020453-003 , Precise time, distributed by means of radio broadcasts, is re- quired for two similar _eodetic tasks: astrcnomlc oos_tion determlna- tionj and obse_Tations of artificial satellites for geodetic purposes. The aim of this report is to assimi!ate under one cover the various phases of the determination and distributio:, of precise time. The determination of time has become a specialized f_eld of astronomy and is presented in Chao_er If. Ti::_eep_n_ and the basis of constant frequency _.sd_scussed _n Chepter !_I. Chapter l-v deals w_th_ variations in the time systems which are conmected to the rotation of the Earth, and w_th _he corrections that have to be applied to observed Q time. The diotr_bution of precise time throu_h radio broadcasts is pre- , sented in Chapter V. Finall_,, the manner in which the geodesist o_:ht to use distributed time and _he corrections thab have to be applied to received radio time s_pnals are discussed in Chaoter V!. Althou_h the disc::ssion lea:_s _.-tcnon-_eodetic fields and theo- retica! found__t_cns have %0 he ned!erred for want ef space, it _s hoped that th_s stu_v of bhe present state of the art w_ll pro_-i,_esome under- - stard_.._,of the bas_s of precise ti_,_a-d its distribution. The report was prepared under the b;_Oervision of Pro_. Ivan I. M_eller. The execution of th'a research is un4er the technical dlrect_on of the Director, Physics a:/ Astrunomy Programs, and of the Project _na_er of the National C_odetlc Satellite Program, both at EASA Head- " quartsrs, _ash_ng%on, D.C. The contract is administered by the office of Grants and .Research Contracts, Office of Space Science and Applications, I/''"- =_ ] 966020453-004 ! _ AC1_.. ,.C_LEI' _ >.,'._,._%, T8" The writer _ratefully acknowledges the help, _u_dance and encouragement received from Professor Ivan I. Mueller, not only wh_,ie prepar_n_ %h's _auer but durin_ his entire period of study at th_s -- university. Further, _ratitude is extended to Dr. W_lliam F_r_owitT, Director, U. S. Naval Observatory Time Service, for a stimulating discussion on tbe subject of this paper _n September 1965. Several other _nd%'iduais have contr_.buted _reatly. Special than_s _,oto Mr. Jch_ Badekas for his valuable tran,!ativ,,s of French outlic_tiors, and to Mrs. Jan ,eller for _ _p_ nF %h"_ report. / 1966020453-005 • TABLE OF CONTENTS , PAGE PREFACE ii ACANCkLEDGE_NTS iii TABLE OF CO_!TBRTS iv LIST OF ILLUSTRATIO_!S ix LIST OF TABLES • xi h_,_T_TION Ih_EX x iii i. DEFIniTION OF TI_ SYSTEF_ I i.i Introduction i i.2 Ator_c Tim_ 1.21 The atomic ti:_eepoch 5 1.22 The atomic time interval 6 II. OBSERVATORY DETERF_NATION OF THE EPOCH OF TI_ 8 2oi Introduction 8 2.2 The Determination of %he Universal Time Epoch 8 2.21 Meridian observations with the FZT_ 9 2.211 Errors in the PZT observations 16 2.22 Extra-meridian observations with the Danjon impersonal prismatic astrolabe 17 2.221 Accuracy c_nsiderations 2-5 2.23 The calculation of univ_.rsaltime from observed local sidereal time _ 26 2.2_ The accuracy of universal time determination 28 iv 1966020453-006 k ! x TABLE OF CONTINTS (cont'd.) :_ PAGE 2.3 The Determination of the Ephemeris Time Epoch 30 _i 2.31 The dual-rate Moon camera 31 _ 2.32 The dete_nation of the eQuatori_l coordinates of the I'_on 3h 5_ 2.33 The interpolation of _T 37 _._ III. FREQUENCY STA_._A_LT_AND TI_._KE_,_ING 39 4 3.i Introduction 39 3.2 Primary Frequency Standards hl 3.21 The caesium atomic beam standard h3 • 3.22 The hydro_:enMaser standard h5 3.3 Secondary Frequency Standards h6 3.31 Principle of quartz vibrators h7 3.32 Quartz standards 50 3.33 The rubidium vapor standard 51 3.h Clocks and Chrcncmeters 52 3.hl _chanical clocks 53 3.h2 Quartz crystal clocks " 5h 3.421 Portable quartz crystal chronometers 55 3.h3 Atomic cloc_(s f_ 60 3.h31 Portable atomio clocks 62 IV. VARIATIONS IN ROTATIONAL TII_ A2D RELATED TOPICS 63 h.l Introduction 63 1966020453-007 . TABLE OF CONTENTS (eont'd.) PAGE | h.2 Polar Motion 63 h.2! Principles of observation and reduction methods 65 2.22 The effect of i _!ar motion on latitude and longitude 67 _.23 The total motion of the pole and the IP_ 72 h.24 The Rapid Latitude Service 77 h.25 Comparison between IPF_ and RLS coordinates 80 4.3 Variation in the Earth,s Rotation Speed 82 2.31 The seasonal variation 8h 2.32 Lunar tidal variations 87 . _ h.h The Non-Uniformity Of U_ 87 V. D_STR!BUTIOI_ OF PRECISE TI!_ A_D FREQUENCY 89 5.1 Introduction 89 5.2 International Agreements Concerning Tii,leSignal Broadcasts 90 5.21 Frequency offsets and 3teo adjustments in phase 90 5.22 Definition of a coordinated station 92 5.23 Internationally accepted types of radio time signal 93 5.3 Standard Ti:_,eand Frequency Broadcasts 95 5.31 Broadcasts of the U. S. _!stional Bureau of Standards 95 5.311 Transmissions from NBS stations v_WV and _WVH 98 5.312 Transmissions from N_b stations WwVB and wWVL 103 5.32 Broadcasts controlled by the U. S. Naval Observatory 105 5.321 Transmissions from U. S. Naval radio stations _06 " 5.322 Transmissions from Loran-C statiors 108 vi 1966020453-008 I ,° TABLE OF CONTENTS (cont'd.) PAGE 5.33 Agreement in the epoch of time signals transmitted iii by U. S. Government stations 5.32 Standard time broadcasts from international stations iii 5.2 Time Synchronization 112 5.21 Propagation characteristics of radio waves 122 _i 5.211 Propagation characteristics of HF radio signals 122 5.212 Propagation characteristics of LF/VLF radio signals 126 5.&13 Propagation characteristics of Loran-C 127 5.22 International time coordination 128 5.421 Time s_nchronization through monitorlng _ : 126_ 5._22 Time synchronizationwith portable atomic clocks 129 5._23 Time synchronizationvia artificial satellites 130 Vl. GECDZTIC USES OF _IST_IBUT._DPRECISE TI_ 132 6.i Introduction 132 6.2 Time Comparison Methods of Highest Accuracy 133 6.21 Ti_e comparisons using HF transmissions 133 6.21] Tick phasing adjustment method 133 6.212 Time comparison with stroboscopic devices 136 6.213 Time comparison using delay counters 138 6.22 Time co_r.parisonsusing VLF transmissions 139 6.23 Specific methods of time synchronization I_O 6.231 Ti_e comparison method used at USC & GS satellite i_O observing stations 1966020453-009 TABLE OF CONTENTS (cont'd.) t PA_ 6'232 A unique system of time s_chronization 1)41 6.3 Time Comparison Methods of Medium Accuracy i_5, 6.h Tir,eComparison i_thods of Low Accuracy lh7 6_5 Corrections to Radio Time Signals I_8 6.51 Explanation and use of the U. S. Naval Observatory 1249 time correction publications 6.511 Remarks about Tim_ Signal Bulletins issued for periods 160 .4 prior to January i 1962 - ":_::...... _ :"_ 6.52 Explanaticn and use of the Bulletin?H_ai_e '_ _:_162,_ 6.521 The formation of the mean o_'ser¢,_O_:...... !i_2: -- : ' _-"i_'5 ? : 6.522 The use of the Bulletin Roraxre proper : - ,, VII. S_'iP/ARY . °'178 '- % : - : b_.bEC_NDBIBLIOG_}_ - " ,J viii 1966020453-010 I LIST OF ILJJU_TRATIO_ISTC_ Titl_____e _p_ i.i Rotational and ephemeris time systems 3 2.1 The photographic zenith tube, PZT i0 2.2 Appearance of star image_ on the FZT plate 12 2.3 Frinciole of the prismatic astrolabe 18 2.2 Image formation using a double symmetrical Wollaston prism 19 2.5 The Danjon imperscnal prismatic astrolab_ 20 2.6 The i_mrkowitzMoon camera 32 3.] Schematic of a caesium atomic beam device L_ 3.2 Schematic of a quartz frequency standard 50 3.3 The master clock room of the U. S. ,;avalObservatory 62 LI.] The effect of polar motion on latitude and longitude 68 _,2 RLS coordinates of the instantaneous pole 78 2.3 Polar mction 1960 - 196h 81 _._ Monthly means of UT2-A.I 8_ _._ BIH values for the seasonal variation for 1966 86 5.1 The international ONOGO system 92 5.2 The evolution of the USFS 96 o 5.3 Time code transmission from W_V 102 5.4 Hourly time broadcast schedule of NBS stations 102 5.5 Location of standard time and frequency station_ 123 6.1 The Newtek Chronofax lh3 6.2 _hronofax ti_e record i_ 6.3 Preliminary Emission T_mes s_ecimen 153 6.2 T_me Signals Bulletin specime_ 15_ 6.5 Values UTI - UTO of the Bulletin Horaire 170 ix 1966020453-011 LIST OF ILLUSTRATI_S (cont'd.) Figure Title PA___ 6.6 Values UT2 - UTI of +he Bulletin Horaire 171 6.7 Observatorie3 Dar%icip@ting in the formation of the mean observatory 172 6.@ Values UT2 - A3 of the Bulletin Horaire 173 6.9 Values UT2 - UTC and UT2 - Signal of the Bulletin Horaire 1?2 6,10 Values UT2 - Signal of the Bulletin Horaire 175 7.1 Interdependence of various phases of time deter_dnation 179 and dJstribution t x Ig66020453-012 LIoT OF TABLF,5 Table Title PA____ 2.1 Probable errors of PZT observations at ;_ash_ngton 17 2.2 Quarterly deviations at i of UT2 29 2.3 Standard error of UT2 for 0.i year intervals 30 3.1 Com_ercially available _uartz crystal chronometers 56 4.1 International latitude observatories of the I£_'_ 73 4.2 Secular motion of +he mean pole from ILS observations 75 4.3 Coordinates of the mean Dole of the eocch from 1903 76 to 1957 _._ Comparison of published IP_'_and _ coordinates of 82 the instantaneous ,Dole _.5 Coefficients for seasonal variation adopted by the BiH 85 since 1956 5,1 U.