Subject: [IGSMAIL-259] Time
From: Ruth Neilan
Date: 24 MAY 1993 09:45:15

IGS Electronic Mail       24-MAY-1993 09:45:15       Message Number 259
***********************************************************************

From: Ruth Neilan 
Subj IGS Newsletter, 93-1
-------------------------

                       Subject:                               Time:1:19 PM
  OFFICE MEMO          IGS Newsletter, 93-1                   Date:5/23/93

IGS NEWSLETTER 93-1 MAY 1993               

Prof. Gerhard Beutler	
Chair, IGS Oversight Committee	
Astronomical Institute, University of Bern	
Sidlerstrasse 5	
CH-3012 Bern  Switzerland	
FAX: +41-31-65 38 69	
Tel.:  +41-31-65 85 91	
[email-masked]	

Ruth E. Neilan
Director, Central Bureau of the IGS
JPL / Caltech MS 238-540
4800 Oak Grove Drive
Pasadena, CA 91109  USA
FAX: +1-818-393-6686
Tel.:  +1-818-354-8330
[email-masked]  

The 1993 Bern IGS Workshop and the 
4th IGS Oversight Committee Meeting
              24 - 27 March, 1993 in Bern, Switzerland
----------------------------------------------------------------------

About 90 participants attended the 1993 IGS workshop in Bern.  The
workshop was very interesting and stimulating.  The 1992 IGS Test
Campaign, Epoch'92, and first results stemming from the IGS Pilot
Service were reviewed and discussed.  The high quality standard
reached by the IGS processing centers during the 1992 IGS Test
Campaign and the steady improvements made since are impressive.  I
found it most encouraging that the IGS products (orbits and earth
rotation parameters) proved their usefulness for the processing of
Epoch'92 campaigns.  The conclusion is simple :  The 1992 IGS Test
Campaign in conjunction with Epoch'92 may be considered as the proof
of concept for the routine IGS.

Very fruitful were the discussions between the IERS Directing Board
and the IGS Oversight Committee.  It was stated that the relationships
between the two organizations were excellent from the very beginning
of the IGS operations in June 1992; the regular analyses made by the
IERS Rapid Service (Dennis McCarthy) and by the IERS Central Bureau
(Martine Feissel) were and are stimulating for all IGS participants.
According to plans the IGS will be responsible for all GPS
observations in future, the IERS will establish direct contacts with
the IGS processing centers in order to continue the fruitful
collaboration that already exists.  The IGS will adopt (as a matter of
fact already has adopted) the IERS standards and will help developing
them if necessary.  The IERS will also be responsible for the
terrestrial reference frame used by the IGS.

The IGS Campaign Oversight Committee decided to start writing the IGS
proposal to IAG (International Association of Geodesy) without further
delay.  According to our plans the routine IGS should start on January
1st, 1994.  It seems that IGS will indeed be established in a very
efficient way.  (Remember :  IGS was mentioned for the first time in
1989 at the IAG Meeting in Edinburgh)!

In its experimental phase the International GPS Geodynamics Service
was a great and a truly International experiment.  It was successful
to an extent nobody has expected.  These should also be the
characteristics for the future Service.

Let me thank all of you who attended the IGS meetings in Bern and/or
contributed to the proceedings of the workshop. It was a pleasure to
host this meeting and I already look forward to the next workshop,
probably a combined IERS/IGS workshop hosted by Martine Feissel and
Claude Boucher in Paris.
                                       Au revoir

Bern, 4 April 1993                        Gerhard Beutler
                                           Chairman
                                           IGS Oversight Committee

_______________________________________________________________

NETWORK OPERATIONS GROUP REPORT

Ruth Neilan

The Network Operations working group met in Bern and discussed 
three key issues that are critical to the improved operations of the IGS: 
          - Network implementation, 
          - Network operation, 
          - Network information: site catalog and information
          - Remote location communications

In order to achieve greater cooperation within the Network Working 
group, a sub-set of people from key agencies implementing more than 
two core stations was established as cognizant and responsible points 
of contact for the coordinated operations of the global network.  
These people include:
      Loic Boloh, CNES
      John Dow, ESOC
      Bjorn Engen, Statens Kartverk
      Pierre Herroux, EMR
      Gerry Mader, NOAA
      Ruth Neilan, NASA/JPL
      Chris Reigber, GFZ
It is also recognized that there are other responsible points of 
contact for additional stations who will be included in the network 
communications correspondence.  

Network Implementation 
-------------------------------------------
It was recognized by all that the weak areas of the network are the 
Southern Hemisphere, Russia and China.  A partial projected inter-
agency implementation plan is listed below and it was agreed that it is 
necessary to accelerate the implementation in the areas of poor 
coverage.  

Network Operation 
-------------------------------------------
One of the areas that needs attention is the coordinated operation of the 
network, and it is hoped that the establishment of this group can 
facilitate communication and jointly develop and agree to procedures 
for monitoring and reporting station health, notification of change and 
configuration control, problem reporting.  This will be important over 
the next few years as we learn to deal with the AS environment and 
work towards integrating into the system the replacement or upgrade 
of existing station hardware, as well as new stations.   

Station Information and Documentation
-------------------------------------------
It is evident that there is a lack of a reliable station information for the 
different user groups and the analysis centers.  This is a problem that 
must be dealt with immediately by this group.  At the Bern meeting, it 
was decided that an electronic form would be generated for detailing 
the basic information about the site.  This was developed by Zuheir 
Altamini, Yehuda Bock, Werner Gurtner, Ulf Lindqwister, and Ruth 
Neilan.  This form is attached to this newsletter.  All station 
information should be sent to the Central Bureau and the electronic 
forms will be available via the Data Centers.  The Central Bureau will 
compile the catalog of information, which includes horizon mask, site 
map and photographs of the site and this will be distributed to 
interested users.  An additional set of critical information will be the 
list of station coordinates from the IERS, Zuheir Altamini and Claude 
Boucher.  

Remote Communication
------------------------------------------
One of the reasons for the slower implementation in the Southern 
Hemisphere is the lack of adequate communications for timely 
retrieval of data in the absence of the Internet.  This is also a problem 
for station locations projected for Russia and China.  One of the next 
tasks for the group is to investigate various possibilities and 
telecommunication options that may be available through the different 
agencies  to see if we can arrive at a solution for the remote locations.  

The Network group hopes to convene a splinter meeting at the Beijing 
review status and progress in these areas. 

List of Current Continuously Operating Precision GPS Stations, 
June 1993:
		             		
	SITE	AGENCY	COUNTRY	
1	Alberthead	EMR/GSC	B.C., Canada	
*2	Algonquin	EMR/CGS	Ont., Canada	
*3	Fairbanks	NASA/JPL	Alaska, USA	
4	Fortaleza	NOAA	Brazil	
*5	Goldstone	NASA/JPL	California, USA	
6	Graz	ISR	Austria	
7	Greenbelt	NASA/JPL-GSFC	Maryland, USA	
*8	Hartebeesthoeck	CNES	South Africa	
*9	Herstmonceux	RGO	East Sussex, U.K.	
10	Hobart	NOAA	Tasmania	
11	JPL Mesa	NASA/JPL	Pasadena, California	
*12	Kokee	NASA/JPL-GSFC	Kuai, Hawaii, USA	
*13	Kootwijck	DUT	Delft, Netherlands	
14	Kourou	ESA/ESOC	French Guiana	
*15	Madrid	NASA/JPL	Spain	
16	Maspalomas	ESA/ESOC	Canary Islands	
*17	Matera	ISA	Italy	
*18	McMurdo	NASA/JPL	Antarctica	
*19	Metsahovi	FGI	Finnland	
20	North Liberty	NASA/JPL	Iowa, USA	
*21	Ny Alesund	SK	Spitzbergen Island, Norway	
*22	Onsala	OSO	Sweden	
*23	Penticton	EMR/GSC	British Colombia, Canada	
24	Pie Town	NASA/JPL	New Mexico, USA	
*25	Pinon	SIO/JPL	California, USA 	
26	Quincy	NASA/JPL	California, USA	
*27	Richmond	NOAA	Florida, USA	
*28	Santiago	NASA/JPL	Chile	
29	Scripps	SIO	California, USA	
*30	St. John's	EMR	New Foundland	
*31	Tahiti	CNES	French Polynesia	
*32	Taipei	AS-IES	Taiwan	
*33	Tidbinbilla	NASA/JPL	Australia	
*34	Tromso	SK	Norway	
*35	Usuda	ISAS	Japan	
36	Vandenberg	SIO/JPL	California, USA	
37	Westford	NOAA	Massachussets, USA	
*38	Wettzell	IfAG	Germany	
*39	Yarragadee	NASA/JPL	Australia	
*40	Yellowknife	EMR	Canada	
41	Zimmerwald	BfL	Bern, Switzerland	
*IGS Core, oringinal
				
	PLANNED SITE	AGENCY	COUNTRY	DATE
				
	Arequipa	NASA/JPL-GSFC	Peru	1/94
	Bangalore	GFZ	India	
	Bar-Giora	Survey of Israel	Israel	
x	Bermuda	NOAA	British	
	Bogota	NASA/JPL	Columbia	1/94
	Darmstadt	ESA/ESOC	Germany	
	Darwin	AUSLIG	Antarctica	12/93
x	Easter Island	NASA/JPL-GSFC	Chile	4/93
	Galapagos Island	NASA/JPL	Ecuador	
	Guam/Kwadjalien	NASA/JPL	U.S Territory	1/94
	Kerguelen Island	CNES	French Territory	10/93
	Kiruna	ESA/ESOC	Sweden	
x	Kitab	GFZ	Uzbekistan	7/92
	La Platta,	GFZ	Argentina	
	Libreville,	CNES	Gabon, Africa	12/93
	McDonald	NASA/JPL	Texas, USA	6/93
	Malindi	ESA/ESOC	Kenya, Africa	12/93
	Novosibirsk	GFZ	Russia	
	Perth	ESA/ESOC	Australia	
	Petropalovosk	GFZ	Russia	
	Seychelles	NASA/JPL	Island	'94
	Tiksil	ESA/ESOC	Russia	
	Tsukuba	GSI	Japan	12/93
	Villafrance	ESA/ESOC	Spain	
x Station installed, resolving communications problems.

________________________________________________________________

DATA FORMATS

Werner Gurtner

The following topics have been identified and discussed:

RINEX under AS
----------------------------------------
RINEX version 2 does not distinguish between data collected under "normal"
conditions and data collected under Anti-spoofing. Between October 1992
and March 1993 discussions between JPL/NGS/AIUB have been going on in which
way this missing information could be incorporated into the RINEX format:

- One proposal was to define new observation types according to the actual
way different receivers are handling the AS problem (e.g. a "cross-correlation
code delay" type, a "cross-correlation phase" type, a squared L2 phase type, 
etc.)

- The second proposal wants to keep the five basic observation types defined
in RINEX (CA,P1,P2,L1,L2), synthesize if necessary these
observation types from the actual observations (e.g. P2=C1+(Y2-Y1))
and flag them using a new flag (bit number 2 in the Loss-of-
Lock Indicators)

It was decided to follow the second proposal. Gurtner will draft a message
to be reviewed by the interested parties and then distribute it through IGSMAIL
and other appropriate channels.

RINEX Header Contents
----------------------------------------
There are still fields in the IGS data RINEX headers that contain non-standar-
dized information, such as:

- Receiver type
- Receiver (firmware) version (Rogues!)
- Antenna type
- Antenna heights

Receiver/Antenna types:

Between October 1992 and March 1993 Ulf Lindqwister compiled a list of
receiver type and antenna type names which has been reviewed several times
by interested parties such as Miranda Chin, Jeff Freymueller, Werner Gurtner.

This list still needs to be further refined  --> U. Lindqwister

Receiver firmware version (Rogues):

Ulf Lindqwister promised to define what version numbers should be put
into the corresponding version field

Antenna heights:

Many RINEX files either don't contain an antenna height at all (although
their should be one!) or a height that does not refer to the Antenna Reference
Point.

Actions to be done:

-  List of the actual antenna heights according to the specs
-  List of the actual antenna types used at the sites
-  Operational centers will have to make sure that the correct info
   is put into the files
-  Generation of character graphics tables for each antenna type
   with antenna dimensions

Some of these actions have to be coordinated with similar actions to
create a site description table (site catalogue) suitable for wide 
distribution!

Overall responsibility for the proper execution of these actions should
be at the Central Bureau.

Quality Control
----------------------------------------

Operational centers should do some minimum tests such as the size of
the RINEX files prior to transmission in order to prevent empty or nearly
empty files to be sent to the data centers.

___________________________________________________________

COMMUNICATIONS
Werner Gurtner / (Peter Morgan)

Peter Morgan expressed concerns about the IGS-generated data volume, both
mails and file transfers.

On some international nodes up to 5 percent of the Internet traffic may be 
IGS data.

Actions:

- IGSREPORTs will be mailed to processing and data centers only (and to
those parties explicitly requesting them)

- IGSREPORTs will be available for public ftp access on several centers,
such as CODE, CDDIS, IfAG, IGN

- The IGSMAIL distribution list will be frequently scanned

- The IGS data flow has to be streamlined to avoid redundant transmission
and to minimize transatlantic or transpacific data traffic. An IGS data flow 
chart will be prepared (CDDIS) and distributed. All other traffic generated
by additional bilateral agreements will not be part of IGS.

Actions in Europe have already been initiated to streamline the European
data traffic.

- The hierarchical data structure has to be improved. Not all permanent
stations have to appear on the global data centers.

- Processing centers should download data that is actually processed only

- Concatenation of the daily navigation files into one non-redundant file
on each level. The file called "BRDC" is the only navigation file necessary
on top level.

________________________________________________________________

IGS GLOBAL DATA CENTER REPORT
Carey Noll

    The IGS is supported by three global, or network, data centers.  These
data centers maintain an on-line archive of GPS tracking data and products.  
They serve as the main interface between the data and the analysis centers and
product users.

    The three global data centers supporting the IGS are:  the Crustal Dynamics
Data Information System (CDDIS) at NASA/GSFC in Greenbelt, Maryland; the
Scripps
Institution of Oceanography (SIO) in La Jolla, California; and the Institut 
Geographic National (IGN) in Paris, France.  Operational and regional data 
centers interface to the GPS receiver, download, RINEX, and compress the data,
and forward these data to a global data center.  The three global centers then
equalize their data holdings by accessing and retrieving required data sets
from
each other. All data transmission is near real time; typically, the data
arrives at a global data center within 72 hours of the end of the observation. 
The global data centers submit weekly status reports detailing data and 
products holdings.

    During the 1992 IGS Test Campaign, over 30 global sites participated as
IGS core sites; additional "non-core" sites also submitted data for analysis.
The CDDIS, for example, archived data from over 5400 observations at 60 
distinct sites/receivers for a total of 2.6 Gbytes.  One day's worth of GPS
data in compressed RINEX format totaled approximately 16 Mbytes.  The table
below illustrates the timeliness of the data delivered to the CDDIS during
the 1992 IGS Test Campaign (June 14 through October 31, 1992):

                                                     All        Prime
                                      All  Sites  Core Sites  Core Sites
                                      ----------  ----------  ----------
         Arriving within:  One day:       46%         49%         48%
                           Two days:      67%         71%         72%
                           Three days:    79%         84%         85%
                           Four days:     85%         90%         91%
                           One week:      91%         95%         96%
     Additional (later than one week):     9%          5%          4%
                      Number of Sites:    60          44          27

Analysis centers would like to see data arrive at the global data center level
even sooner; thus far, the IGS Pilot Service has delivered 75% of the core data
within 48 hours of the observation. 

    The global data centers also serve as an archive for products, such as
precise satellite ephemerides, Earth rotation parameters, etc., generated from
IGS data by the analysis centers.

    In conclusion, the proposed concepts of the IGS, in particular the
real-time availability of a global set of GPS tracking data, were realized
during the 1992 IGS Test Campaign.  The three global data centers successfully
provided the main interface between the IGS data and the user community.  The
CDDIS, in particular, learned a great deal from the test campaign.  New
archiving procedures, such as automation of data transfers, were developed for
the IGS and are now utilized in other CDDIS activities.  The success of the
1992 IGS Test Campaign lives on in the current IGS Pilot Service and will
continue through the operational service. 

GLOBAL DATA CENTER CONTACTS:   

CDDIS:  Carey E. Noll                        Phone:  301-286-9283
        Code 902.2                           Fax:  301-286-4943
        NASA/GSFC                            E-mail:  [email-masked]
        Greenbelt, MD 20771  
        USA

SIO:    Yehuda Bock                          Phone:  619-534-5292
        Scripps Institution of Oceanography  Fax:  619-534-5332
        IGPP 0225                            E-mail:  [email-masked]
        9500 Gilman Drive
        La Jolla, CA
        USA
  
IGN:    Loic Daniel                          Phone:  33-1-4398-8338
        Institut Geographic National         Fax:  33-1-4398-8488
        2, Avenue Pasteur                    E-mail:  [email-masked]
        F-94160 Saint-Mande
        FRANCE

__________________________________________________________________

ANALYSIS CENTER COORDINATOR REPORT
Clyde Goad

    On Wednesday, March 24, the Analysis Center Coordinator presented his
    summary of the orbital comparisons for a 36-week period starting from
    GPS week 650 along with an example of early plot-based comparisons that
    were useful in spotting a few startup problems.  A typical three-week
    orbit comparison was shown.  Maximum  and minimum deviations in an rms 
    sense were given for the extended period.  The findings of the study are 
    given below:

                   Maximum and Maximum RMS Differences 
                For a 36-Week Period During and After the
                              IGS Campaign

Begin Day  Week    Minimum RMS  Day Centers   Maximum RMS  Day Centers
  M-D-Y                (m)                        (m)       

02-21-93   685         0.35      4  COD-EMR       1.37      6  ESA-EMR
02-14-93   684         0.23      4  EMR-JPL       1.99      7  EMR-JPL
02-07-93   683         0.23      6  EMR-JPL       0.82      4  ESA-SIO
01-31-93   682         0.21      2  EMR-JPL       1.03      5  COD-ESA
01-24-93   681         0.20      4  EMR-JPL       0.75      6  ESA-SIO
01-17-93   680         0.19      7  EMR-JPL       1.41      1  COD-JPL
01-10-93   679         0.26      5  COD-EMR       1.07      7  COD-ESA
01-03-93   678         0.26      1  EMR-JPL       1.38      3  ESA-JPL
12-27-92   677         0.21      5  EMR-JPL       1.14      3  COD-ESA
12-20-92   676         0.18      7  EMR-JPL       1.01      5  COD-ESA
12-13-92   675         0.24      7  EMR-JPL       1.35      1  ESA-JPL
12-06-92   674         0.27      5  EMR-JPL       1.73      2  COD-ESA
11-29-92   673         0.31      4  EMR-JPL       3.15      5  COD-ESA
11-22-92   672         0.20      3  EMR-JPL       1.48      7  COD-ESA
11-15-92   671         0.19      2  EMR-JPL       1.14      7  COD-ESA
11-08-92   670         0.18      4  EMR-JPL       1.58      2  COD-SIO
11-01-92   669         0.18      7  EMR-JPL       1.34      2  ESA-JPL
10-25-92   668         0.20      5  EMR-JPL       1.57      2  ESA-JPL
10-18-92   667         0.23      3  EMR-JPL       2.95      1  ESA-SIO
10-11-92   666         0.21      3  EMR-JPL       6.37      6  SIO-JPL
10-04-92   665         0.31      5  EMR-JPL       2.47      1  ESA-SIO
09-27-92   664         0.34      4  EMR-JPL       2.31      2  SIO-JPL
09-20-92   663         0.32      4  EMR-JPL       2.71      2  SIO-JPL
09-13-92   662         0.38      5  EMR-JPL       5.83      1  ESA-SIO
09-06-92   661         0.32      2  EMR-JPL       1.72      3  ESA-GFZ
08-30-92   660         0.29      6  UTX-JPL       0.71      7  ESA-JPL
08-23-92   659         0.28      7  EMR-JPL       3.25      2  COD-GFZ
08-16-92   658         0.35      4  GFZ-JPL       4.38      7  COD-SIO
08-09-92   657         0.31      4  COD-JPL       4.76      1  COD-SIO
08-02-92   656         0.34      4  UTX-JPL       4.67      1  UTX-SIO
07-26-92   655         0.32      2  GFZ-JPL       3.32      7  UTX-SIO
07-19-92   654         0.36      1  UTX-JPL       1.69      1  COD-UTX
07-12-92   653         0.37      1  COD-SIO       2.13      3  SIO-GFZ
07-05-92   652         0.39      3  COD-UTX       2.63      6  ESA-GFZ
06-28-92   651         0.45      6  COD-JPL       1.35      1  ESA-GFZ
06-21-92   650         0.68      3  COD-SIO       2.70      1  ESA-UTX

Another item discussed during this presentation was the desire on the
coordinator's part to investigate the possibility of providing precise
satellite clock information in the future.  His view was that this was the
one last piece of information left to provide users with a full complement
of products.  Currently, to some degree, orbits, station coordinates, and
Earth rotation parameters are available.  Discussion from the floor led to
the recommendation that if such information was provided it should not be
included with the current orbital product.

At a subsequent meeting of analysis center representatives, it was decided that
a two-week period of orbits should be redetermined for comparison using a 
common set of station coordinates.  These coordinates should then be held
fixed among the several centers' determinations if any of these stations's 
data were used in the orbit determinations.  The chosen  stations were as 
follows:

      ALGONQUIN
      FAIRBANKS
      GOLDSTONE
      HARTEBEESTHOEK
      KOKEE PARK
      MADRID               
      SANTIAGO
      TIDBINBILLA         
      TROMSO               
      WETZELL              
      YARAGADEE        
      YELLOWKNIFE     

Altamimi and Boucher agreed to provide the set of coordinates for the above 
stations.  Orbital results were to be deposited into the computer system at 
the University of Bern so as not to cause any confusion with the standard 
distribution of orbits.  The two-week period for the study starts with
GPS week 680 (Jan. 17, 1993)

The above information was presented to the meeting attendees at the Friday
afternoon session (March 26, 1993)