Time signals emitted from Transit satellites and received by the NAVICODE type receiver at Mizusawa, Japan are presented. The International Latitude Observatory of Mizusawa and the U. S. Naval Observatory were compared using the time signals. Propagation delays, a receiver delay, effects of relative motion of satellites, and effects of the ionosphere are discussed

Hara, J.

Sato, K. H.

English

NASA Technical Reports Server

TIME SYNCHRONIZATION VIA THE TRANSIT SATELLITE 
AT MIZUSAWA 
T, Hara and K.-H. Sato 
International Latitude Observatory of Mizusawa 
Nizusawa-shi, Iwate-ken, 023 Japan 
ABSTRACT 
Time signals emitted from Transit satellites 
have been received by the NACODE type receiver 
sinc? 1974 at Mizusawa, Japan (station 0 2 7 ) .  
By using these time sfpnals, we can make a time 
comparison between the International Latitude 
Observatory of Mizusawa (ILOM) and USNO. To 
complete tine comparison by this method, many 
c~rrections are, however, necessary such as 
propagation delays, a rece,iver delay, effects 
of relative motion of satellites, effects of the 
ionosphere and so on. Propagation delays are 
calculated from the precise ephemeris of the 
satellite (30190) supplied by the Topographic 
Center of DMA. The receiver delay is rfieasured 
by supplying a simulated sigral to the spa;: 
near the receiving antenna. Effects af the 
ionosphere *Jn the propagation delays may be the 
order of one microsecond. Standard deviations of 
each pass are estimated to be 215.5 micro- 
seconds for the data UTC(IL0M)-UTS(USN0) obtained 
in December 1976. 
Time comparisons by the Loran-C system between 
ILOM and USNO are referred for a check of the 
Transit satellite timing method. 
Timing experiments via satellites have been carried 
out many times since 1962 (Blair 1974). In Japan also, 
experiments of time synchronizations between the Radio 
Research Labolatories (RRL) and the U.S.Nava1 Observatory 
(USNO) were carried out i r ,  1965 and 1975 with accuracies 
of cne micrcsecond and 10 nanosecond's order respectively 
(Frequency Standard Section and Kashima Branch 1965; 
Yamamoto et al. 1976). These experiments were made in the 
two way method and attained to the very high accuracy. 
https://ntrs.nasa.gov/search.jsp?R=19790016581 2020-03-20T18:49:33+00:00Z
This method is, however, much expensive and is not conven- 
ient for "he frequent measurements. 
Although the measurements via the Transit satellite (Navy 
Navigation Satellite) have relatively low accuracies as 
compared with the two way method, this method has the 
advantage that time comparison can usually be made twice 
a day 2; moderate expence. The Navy Navigation Satellites 
hzve been tracked by the TRANET I type receiving shstem 
since late 1974, and time information data in punched paper 
tape are available s;nce 1976. In this repcrt, timing 
analysis and variaus corrections whlch are necessary to 
derive time differences 5etween UTC(1LOM) and UTC(USN0) are 
presented by using the data obtained in 1976. Time synchro- 
nizat-ion via Loran-C system w..l be referred to examine the 
consistency of these two methods. 
OUTLINE OF COMPARISON SYSTEM 
Satellite trackings by measdring doppler shifts have '-een 
mzde with the rubidium oscillator as a frequency stanaard 
at the station 027 .  Time alld frequency comparisons have 
been mad? between the rubTdium atomic clock and UTC(IL0M) 
which is maintained by a cesium atomic clock. At the same 
time, satellite timi~g pulses are monitored by UTC(USNO! 
and the results are published regularly. Then, time dii'feAa- 
ences between UTC(IL0M) and UTC(USN0) can be derived by 
using these data. 
S a t e l l i t e  
TRANET I 
Station Clock 
Rubidium Clock 
Jl I UTC ( ILOM)~ 
Flg. -- Z,irnplified block diagram cf the 
tim? comparison system. 
On the other hand, Loran-C signals of the Northweet Facific 
chain are received at ILOM regularly with standard devia- 
tions oi' ~ e s s  than 0.1 microseconds. This chain (SS3) is 
monitored by flying clock from USMO. Thus we have :inother 
method of time co~y~risons bztween UTC(IL0M) and UTC(USN0). 
An outline of ol,r tine comparisor. system is shown in Fig. 1. 
The TRANET I -:stem receiver amplifies and demodulates 
signals from satellites, and demod~lated signals are fed to 
the tiine burst detectcr which discriminates the satellite 
time marks. Time interval between this fiducial time mark 
and the station clock is measurea to ore micraaecond. 
CORRECTIONS FOR PROPAGATION DETJAY, RECEIVER DELAY, AND 
RELATIVE NOTION OF SATELLITE 
As the orbital elements of satellites are not decoded by 
the TRAdET I system receiver, propagaJ;lon delays from satel- 
lites to the receiving antenna are calculated by using the 
data of Cartesian cocrdinates of the satellite 30190 which 
are supplied by t5.e Topographi-c Center of DMA. Fig. 2 shows 
an example of prcipagation delays in vqcuum spadr- which were 
calculated by the preci~e ephereris or' the satellite 30190. 
Receiver delays are me~sured by transmitting a simulated 
signal i~lto a space near t.he receiving antenna -t few days 
interval. During the period before NovembeL1 28, 1976, the 
AF type of tracking reoeiver was used  a d  adjustments of IF 
circuit were made s *  as to give a constant delay in the 
receiver. Thereafter tk.0 IF phase-lock track: ng re: .I ver 
was used and only measurements of receiver delsy v, .*e made 
without frequent adjustme~ts. Delay time of the TF phase- 
icck tracking receiver is shown in F2g. 3. 
Delays of time signals emitted from satellites cen be cal- 
culated according to the Lorentz trar.-for ma ti or^. Eut clas- 
sical treatment, is suffiz!ent, I'. -, r : i ~  radial velocity ot' 
satellites (v) relative to the station fixed on the Earth 
is very small against the light ve1ocit.y (c). Then time 
< 
3elay sallsed by the motion of satellite relative to the 
t:.acking stat,ion is estimated as 
(v/c) (propagat*on time) 5 O.r US 
Time delay of this kind is corrected, althr>ugh this i, 
small. 
0340 0050 UTC 
January 2, 1978 
F i g .  2-An e x a a p l e  o f  p r o p a g a t i o n  d e l a y s  i n  
vacuum s p a c e  which were c a l c u l a t e d  from t h e  
p r e c i s e  ephemer i s  o f  t h e  s a t e l l i t e  30190. 
1 5 10 15 2 0 2 5 30 
December, 1976  date 
F i g .  3 - R ~ r e i v e r  d e l a y s  o f  t h e  TRANET I 
IF phase- lock  t r a c k i n g  r c z e i v e r .  
RESULTS 
Time differences between the satellite 30190 and the station 
clock are shown in Fig. 4, where the corrections for propa- 
gation delay, receivela delay, and motion of satellite men- 
tioned above are made. 
h 
0 
L 
l-i lJ s 
m 
L, O loo 1 
E: 
0 
rl 
U 
rd 
C 
(A I----- Jan. . June , . . , , , Dec . 
month 
Fig. 4-Emission time of the satellite 30190 
observed by the station clock (rabidium 
atomic clock). 
In this calculation, receiver delays are corrected by three 
constant values in the three periods, respectively, as fol- 
lows ; 
775702 us befoi-e 23 January 1976, 
775'763 us until 28 November 1976, 
775966 us after 28 November 1976, 
where system delay of 775434 microseconds and 4 0 6  Hz cir- 
cuit delay are included. 
The raw data included some extremely  deviate^ values, and 
these data were rejected by a fixed range filter to pass 
~ n l y  the data which were in the range from 0 to 350 micro- 
seconds. The refined data were proved to have the standard 
deviations of k19 microseconds. The above measurements ~Gere 
made with the station clock of which deviations were about 
k1.5 microseconds. 
In order to estimate the intrinsic error of the clock 
comparison via satellite, we tried to remove all the 
errors qf the station clock and satellite-borne clock (see 
Fig. 5;  and receiver delay only for the period after 
November 28, 1976, 
n 
o 
z 
5 
U 
. 
Jan.  
1976 
June Dec . 
month 
Fig. 5-Time differences between sateliite- I 
borne clock (30190) and UTC(USNO). This 
graph was plotted from the data in Transit 
Satellite Repo~>t, Series 17 which was published 
5y the U.S.Neval Observatory. 
The final form of clock comparison was reduced to UTC(IL0M) 
-UTC(USNO) (see Fig. 6). These twc time scales are main- 
tained by the cesium clocks and fluctuations in UTC(IL0M)- 
UTC(USN0) can be ascribed to tlming error aroused by tne 
satellite timing system. Results are summarized below with 
standard deviations in microseconds; 
Station Clock - ~at.(30190) tlg 
Sat.(30190) - UTC(USNO) 212 
UTC(IL0M) - Station Clock +- 7 . 5  
Receiver Delay ti4 
UTC(IL0M) - UTC(USN3) k15.5 
Standard deviations were reduced froirl tlgusto -+15.51.1s, 
showing that only slight improvements were attained. This 
may due to instability of the receiver delay and/or to 
inap~roprlate correction of satellite clock. 
Q .  I w w w v . m 
1 5 10 15 20 25 30 
December, 1976 date 
7ig. 6-UTC(ILOM) - UTC(USN0) via Transit 
satellite 30190. 
TIME SYNCHRONIZATION VIA LORAN-C SIGNAL 
The Northwest P&:ific Lopan-C chain is available in the 
vicinity of Japan. Most institutes in Jzpan have bezn 
receiving the master statio:~ Iwo-jima with the standard 
dpviation of less than +O.lus. Receiver delay can be aeas- 
ured with sufficient accuracies, but propagation time seems 
to be hard to estimate with high accuracies. Propagation 
time fron Iwo-jima to the manitorlng station of the chain 
(Fuchu) was once determined by USNO as 4070.0l.1~ from a 
calculation combined with a t~ansportation experiment with 
an atomic clock. RRL when it was in Nidori-cho, Koganei- 
shi, japan had calculated t h e  propagation time based on 
above value as 4122.5~s. On the other hand, time synchro- 
nizzition between RRL and ILOM has been made with the aid of 
a portable ?lock as well as Loran-C receptions. The differ- 
ence of propagation times bstween these t!vo stations and 
the Iwo-jima station was determined as 1192.4+0.24~s by 
five clock transportation experiments. Then, propagation 
time from Iwo-jima to ILOM was obtained as 5314.9~s. 
Thus, the quantity of UTC(IL0M) - lJTC(USN0) is derived from 
the Loran-C receptions and the data "Daily Phase Values, 
S e r i e s  4'' which i s  p u b l i s h e d  by USNO ( s e e  F ig .  7 ) .  By com- 
p a r i n g  t h e s e  v a l u e s  w i t h  t h e  one o b t a i n e d  by s a t e l l i t e  t i m -  
i n g  s i g n a l s ,  i t  was found t h a t  t h e r e  i s  a d l s c r e 3 a n c y  of  
about  35:ls .  
Jan. 
1976 
Dec . 
month 
F i g .  7-UTC(ILOI4) - UTC(USN0) v i a  Loran-C. 
DISCUSSION 
The i o n o s p h e r i c  e f f e c t  c n  r a d i o  w a v e  p ropaga t ion  was n o t  
c o r r e c t e d  i n  t h e  above r e s u l t z .  The o r d e r  of  t h e  e f f e c t s  
on p ropaga t ion  d e l a y  w i l l  be e s t i m a t e d  h e r e .  A s  t h e  r e c e i v -  
i n g  f requency i s  400MHz, geomagnetic f i e l d  and c o l l i s i o n  
of  e l e c ~ r o n s  w i t h  n e u t r a l  g a s  can  w z l l  be n e g l e c t e d .  Then 
t h e  3 p t i c a l  l e n g t h  ( r )  i s  c a l c u l a t e d  a c c o r d i n g  t o  t h e  
formula r  = Jnds ,  where t h e  i n t e g r a t i o n  must b e  done a l o n g  
t h e  p ropaga t ion  p a t h  and n i s  t h e  r e f r a c t i v e  index  which i s  
i n  r e l a t i o n  w i t h  t h e  plasma f requency ( f p )  and t h e  o p e r a t -  
i n s  f requency ( f )  as n 2  = l - ( f p / f ) 2 .  The plasma f requency 
i s  r e l a t e d  w i t h  e l e c t r o n  d e n s i t y  ( N )  a s  f p 2  = 8 0 . 6 ~  i n  MKS 
u n i t  system. Then t h e  o p t i c a l  l e n g t h  can  be e s t i m a t e d  from 
t h e  e q u a t i o n  r  = / ( 1 - 8 0 . 6 ~ / f ~ / 2 ) d s  D Y  u s i n g  a model iono-  
sphe re  (Tsuchiya  1976) f o r  t h e  N(h) p r o f i l e .  A numer ica l  
c a l c u l a t i o n  was made f o r  t h e  s a t e l l i t e  which i s  on observ-  
e r ' s  z e n i t h ,  y i e l d i n g  0 . 1 ~ ~  a r d  0 . 0 5 ~ s  i n  daxt ime and 
n i g h t t i m e  r e s p e c t i v e l y .  The d i s t a n c e  t o  t h e  s a t e l l i t e  which 
i s  on t h e  h o r i z o n  w i l l  be f o u r  times a s  l a r g e  as t h e  one 
when a  s a t e l l i t e  i s  on t h e  z e n i t h .  So,  maximum propaga t ion  
d e l a y  may amount t o  0 . 4 ~ s  and 0 . 2 ~ ~ ~  r e s p e c t i v e l y .  
On t h e  o t h e r  hand, t h e  mean v a l u e  of  s t a t i o n  c l o c k  - s a t e l -  
l i t e  was o b t a i n e d  as 48.95 t 1 . 3 9 ~ ~  and 48.70 + 1 . 7 7 ~ s  f o r  
t h e  dayt ime and n i g h t t i m e  p e r i o d ,  r e s p e c t i v e l y .  That  i s ,  
r e c e p t i o n  e r r o r  i s  above t h e  i o n o s p h e r i c  e f f e c t ,  s o  we can  
f i n d  no s i g n i f i c a n t  d i f f e r e n c e s  i n  i o n o s p h e r i c  e f f e c t  be- 
tween dayt ime p ropaga t ion  and n i g h t t i m e  one from t h e  above 
r e s u l t s .  Never the le s s  we may s u f e l y  say  t h a t  t h e  i o n o s p h e r i c  
e f f e c t  produces no e r r o r s  l a r g e r  t h a n  one microsecond when 
t h e  s o l a r  a c t i v i t y  i s  moderate .  
A t  TRANET s t a t i o n s  on ly  t h e  d a t a  which a r e  o b t a i n e d  when t h e  
s a t e l l i t e  i s  n e a r  t o  t h e  c l o s e s t  approach ( C . A . )  a r e  used 
f o r  t ime s y n c h r o n i z a t i o n  purpose .  A l l  t h e  d a t a  t h a t  f a l l  i n  
t h e  r ange  from O p s  t o  3 5 0 ~ s  were used ,  i n  o u r  c a s e .  Depend- 
ency of d e l a y  t ime o f  t i m i n g  s i g n a l s  upon t h e  d o p p l e r  s h i f t  
o f  s a t e l l i t e  were examined f o r  each  datum p o i n t  i n  whole 
p a s s e s  o b t a i n e d  i n  1976 ( s e e  F i g .  8 ) .  
7 
V) I 
Doppler S i f t s  i l i  uni t s  of 10 -6 
F i g .  8 - s t a t i o n  c l o c k  - S a t e l l i t e  30190 
which was obsery,red eve ry  two minu tes .  
The a b s c i s s a  i s  t aken  a s  Doppler s h i f t  
in u n i t s  of  10'~. Average v a l u e  i s  shown 
by l a r g e  , i r c l e s .  
S c a t t e r i n g  of  d a t a  a r e  r e l a t i v e l y  sma l l  n e a r  C . A . ,  and 
fu r the rmore  t h e r e  i s  a tendency t h a t  r e c e i v e d  s i g n a l s  ad- 
vance by about  l o p ;  f o r  pre-C.A. p e r i o d  and v i c e  v e r s a  f o r  
pcst-C.A. p e r i o d .  This tendency does n o t  d i f f e r  d i s t i n c t l y  
whether t h e  r e c e p t i o n  was made d u r i n g  dayt ime o r  n i g h t t i m e  
periods. The physical explanation of this tendency is left 
unsolved even if we take into consideration the tropospheric 
refraction effects, since these are the order of one micro- 
second at most. 
CONCLUDING REMARKS 
A timing experiment via the Navy Navigation Satellite for 
the year of 1976 was shown. Our time comparison has shown 
that fluctuations of the obtained data have the standard 
deviation of216 u s .  This is almost the same order as the 
reparted values by Hunt and Cashion (1978) and Cashion et 
al. (1975). But there is a discrepancy of 3 5 p s  as compared 
with the data obtained by the Loran-C receptior. There might 
be some probl2ms in delay time measurement. Furthermore, 
fluctuations in timing pulses may be pretty large, since-the 
band width of the receiver is narrow. 
ACKNOWLEDGEMENTS 
- 
Our tha~ks are due to Mr.M.Aihara and Dr.I.Oka1coto for 
their disciission and assistance i.n improving expressions. 
I 'EREMCES 
1-11 BLAIR,B.E., Time and frequency dissemination: An 
overview of principles and techniques, NBS 
Monograph 140, 233-313, 1974. 
2 1 CASHION, R.E., G.A. HUNT, and J.D. LAVANCEAU, 
Precise time recovery from Transit satellites, 
paper presented at Symposium on Tlme and Frequency 
XIXth General Assembly of URSI, 1978. 
FREQUENCY STANDARD SECTION and KASHIMA BRANCH, 
Report on clock pulse synchr-mization experiment 
via Relay I1 satellite, J.Radio Res. Labs., - 12, 63, 
311-316, 1965. 
HUNT, G.A. and R.E. CASHION, A Transit satellite 
timing receiver, Proc. Ninth Annual P~ecise Time 
and Time Interval Planning Meeting, 153-166, 1978. 
TSUCHIYA, A., Geodetic applicatioil feasibility of 
new technics in position astronomy, J. Geod. Soc. 
Japsn, 22, 4, 264-274, 1976. 
U.S.NAVA-OBSERVATORY, Daily phase values and time 
differences, series 4 and Transit satellite report, 
Series 17. 
YAMAMOTO, M., K .  HARADA, and Y. SABURI, A t.ime 
comparison experiment perfo~med by SSPA via ATS-1, 
J. Radio Res. Labs., 3, 10, 85-103, 1976. 
QUESTIONS AND ANSWERS 
MR. LAUREN RUEGER, Johns Hopkins Un ivers i ty ,  Appl ied Physics iab: 
Before I open t h i s  paper f o r  comments from the audience, I would 
l i k e  t o  make a couple o f  comments myself. The f i r s t  i s  t h a t  the  
small s h i f t  he saw i n  t h i s  l a s t  curve i s  c h a r a c t e r i s t i c  o f  what we 
observed i n  the  t rack ing  loop cha rac te r i s t i cs  o f  t he  VCO. He was 
us ing a f a i r l y  e a r l y  scdel Nikode-type rece iver  t h a t  has a f a i r l y  
simple t r a n s f e r  f unc t i on  f o r  the t rack ing  loop. The lags i n  t h a t  
would g ive  him the  10 microseconds I t h i n k  he i s  observing. 
The second comment i s  t h a t  dur ing  1977, f o l l o w i n g  t h i s  data, 
we d i d  an experiment i n  making t ime t rans fe rs  between the U.S. Naval 
Observatory and the  Nat ional  Bureau o f  Standard, i n  which we had 
very c a r e f u l l y  c a l i b r a t e d  the rece iver  delay, t o  a reso lu t i on  o f  
10 nanoseconds. And i n  us ing tha t ,  we discovered, bu r i ed  i n  
the  data t h a t  we now prov ide through B u l l e t i n  ;7, a possi -  
b i l i t y  o f  a 50 microsecond b ias  because o f  the  uncer ta in ty  o f  the  
rece iver  delay. 
I f  you take the  50 microseconds from t h i s  source and the  35 
microsecond discrepancy t h i s  man found, they are i n  the  same d i r -  
ec t i on  and compensating. His  data i s  r e a l l y  w i t h i n  h i s  e x p e r i ~ e ~ t a l  
e r ro r .  We should t e l l  him someday. 


Time synchronization via the transit satellite at Mizusawa

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