**Current Status of and Backup Plans for**

**Flow of IGS Data and Products**

Carey Noll

*NASA GSFC, Greenbelt MD, USA*

> **ABSTRACT --** *The IGS has been operational for nearly seven years.
> Recent changes in the data and products archived at the data centers
> prompts the review of the current IGS data flow and archiving
> methodologies. This presentation will outline the current structure at
> the IGS data centers, including the flow of both the daily and hourly
> data products, and will detail ideas for improvements to the data flow
> to ensure timely and consistent availability of IGS data and
> products.*

**1 Introduction**

The International GPS Service (IGS) has been an operational service
within the IAG since 1994. During the planning phases for the IGS, it
was realized that a distributed data flow and archive scheme would be
vital to the success of the IGS. Thus, the IGS has established a
hierarchy of data centers to distribute data from the network of
tracking stations: operational, regional, and global data centers. This
scheme provides an efficient access and storage of GPS data, thus
reducing traffic on the Internet, as well as a level of redundancy
allowing for security of the data holdings.

**2 Background**

Operational or local data centers (OCs or LDCs) are responsible for the
direct interface to the GPS receiver, reliably and regularly connecting
to the remote site, hourly or daily, and downloading and archiving the
raw receiver data. The quality of these data is validated and the data
are then translated from raw receiver format to a common format (RINEX),
decimated if necessary, and compressed. Both the daily observation and
navigation files (and meteorological data, if available) are then
transmitted to a regional or global data center ideally within an hour
following the end of the observation day. For hourly data, files are
transmitted from the operational data center within a few minutes of the
end of the hour.

Regional data centers (RDCs) gather data from various operational data
centers before transmitting them to the global data centers, thus
reducing traffic over electronic networks. RDCs maintain an archive for
users interested in stations of a particular region. Typically, data not
used for global analyses are archived and available for on-line access
at the RDC level.

The IGS global data centers (GDCs) are typically the principle GPS data
source for the IGS analysis centers and the user community in general.
The GPS data available through the global data centers consists of
observation, navigation, and meteorological files, all in RINEX format.
The GDCs provide an on-line archive of daily and sometimes hourly data
files as well as the products derived from these data, generated by the
IGS analysis centers, associate analysis centers, and analysis
coordinators. These data centers equalize holdings of global sites and
derived products on a daily basis (at minimum). The three GDCs currently
supporting the service provide the IGS with a level of redundancy, thus
preventing a single point of failure should a data center become
unavailable. Furthermore, three centers reduce the network traffic that
could occur to a single geographical location.

**3 Current flow of data and system status**

Table 1 lists the major data centers currently supporting the IGS. Table
2 lists the types of data archived by the IGS data centers and the
products created by the IGS analysis centers; Table 3 shows the types of
data and products supported at the global data center archives.

Figure 1 depicts the current flow of thirty-second daily data files from
the OCs to the GDCs; the table in Appendix A lists these sites by
monument name. Only sites with complete site logs at the IGS Central
Bureau are reflected in this figure and the corresponding table found in
the appendix. Both the CDDIS and SIO archive data from sites outside the
IGS "umbrella"; these sites are not listed in the figure or table.
Figure 2 shows the data flow for hourly data files; at this time, hourly
data are archived and distributed by the GDCs at CDDIS and IGN and the
RDC at BKG.

To aid in further understanding the flow of daily and hourly data files
within the IGS, it is important to study the timeliness of the data
products. Table 4 presents the data latency statistics for daily data
archived at the CDDIS. Over fifty percent of the data are archived
within two hours of the end of the observation day. Table 5 presents the
current data latency statistics for hourly data at the CDDIS. As can be
seen from this table, over fifty percent of the hourly data are
available for download from the CDDIS within fifteen minutes. These
statistics were derived by programs developed by the IGS Central Bureau
and executed on a regular basis at many of the IGS data centers; the
results for the CDDIS are updated frequently during the day and can be
viewed at
*ftp://cddisa.gsfc.nasa.gov/pub/reports/gpsdata/check_import.cddisa*
(daily data) and
*ftp://cddisa.gsfc.nasa.gov/pub/reports/gpsdata/check_hourly.cddisa*
(hourly data).

**4 Backup strategies**

The mission of the IGS has been broadened to include the flow and
analysis of hourly data sets, thus requiring a rapid turn-around of data
from the station to the user. Furthermore, this access must be reliable,
24 hours per day, seven days per week. The IGS infrastructure must
establish backup data flow paths to ensure that not only daily but also
hourly data sets are accessible to users on an uninterrupted basis even
if a key data center is unavailable. This scheme must be extended to
include hourly high-rate data sets at those data centers supporting the
efforts of future LEO missions.

During the past year, the CDDIS global data center experienced two major
computer failures. Unfortunately, the extended outage of the facility
had dramatic effects on the IGS analysis centers and the user community
in general since some sites only deposited their data at CDDIS.
Furthermore, most IGS ACs and AACs send their data products to the CDDIS
where they are made available to the other IGS data centers, the IGS ACs
and AACs, and the user community. Not only were some data and products
not immediately available, the CDDIS user community may have been
unfamiliar with accessing the other data centers. Some redundant data
flow paths already existed, but other sites had no data center to
transmit their data to when the CDDIS was down. To prevent the
unavailability of key IGS sites in the future, a strategy for the backup
of the IGS data flow infrastructure must be developed and tested. This
plan, once operational, can then be utilized in the case of planned
system downtimes (e.g., for scheduled computer upgrades or network
outages) or when unexpected failures occur.

The first step in the development of a backup plan for data (and
product) flow is to identify the current network topology; this data
flow is shown in Figure 1. This figure illustrates the fact that many
operational and regional data centers deposit data to the CDDIS;
fortunately, SIO also has access to many of these data centers and
routinely downloads data from them as well for their archive. IGN mainly
handles the flow of data in Europe with BKG and retrieves the remaining
IGS global sites from either CDDIS or SIO.

The second step in the development of a backup plan is to identify
possible alternate data flow paths should any of the three GDCs be
inaccessible; the plan can then be extended to include other major IGS
data centers (e.g., RDCs). It should be noted at this time that UNAVCO
serves as a backup OC for JPL. During the past few months several
successful tests have been conducted between UNAVCO, JPL, and the CDDIS
where UNAVCO downloads data from selected JPL stations and forwards
these data to the CDDIS. The CDDIS has installed procedures to peruse
the UNAVCO data delivery area and archive any data not previously found
in the JPL data delivery area. This process is now in place for both
daily and hourly data. Each OC is designated a secondary data flow path
to another data center. The proposed alternate data routes for the
distribution of daily data files through the GDCs are illustrated in
Figure 3; this process could be extended to the hourly data flow. For
products, the current and proposed alternate data flow paths are shown
in Figure 4.

In order to make the transition to another data center easier for OCs
and RDCs, arrangements need to be made with each data center to minimize
special instructions for depositing or retrieving data. The majority of
the data handled by the CDDIS are delivered to password-protected
accounts established on the computer facility for each data source. The
CDDIS also retrieves data from a few data centers (e.g., AUSLIG, BKG,
RDAAC, and SIO). SIO and IGN primarily retrieve data from all GPS data
sources.

To ensure that data can be delivered and processed quickly in a backup
situation, it is recommended that each GDC (and participating RDC)
establish a general ftp area that OCs and RDCs can utilize when they are
required to post data to alternate data centers because their "prime"
data center is inaccessible. For example, the directory
*/ftp/incoming/igsdaily* has been created at the CDDIS (host
*cddisa.gsfc.nasa.gov*) to allow data centers to deposit daily GPS data
via anonymous ftp. Similarly, procedures need to be established for IGS
analysis centers to deposit weekly product files to alternate GDCs when
their primary contact is unavailable. Automated programs could then be
created at the data centers to peruse these anonymous ftp put-areas on a
routine basis and process any data or products found there. These ftp
areas should be secured so that files placed there can not be deleted or
modified by anyone other than authorized data center personnel. A more
secure method may be to allow anonymous ftp deposits through a "trusted"
mode where only users from a list of pre-approved hosts could deposit
files to the data center's incoming area. Setting the protections on
directories and subdirectories to prevent browsing and downloading could
further enhance security with these anonymous ftp put areas by anonymous
ftp users. The use of anonymous ftp to deposit data precludes the need
for the data centers to establish and administer accounts for each data
source and allows for easy monitoring for incoming data or product
files; alternatively, a single username for depositing data could be
utilized at all data centers. This method, however, would require the
coordination and distribution of username and password information to a
list of data center representatives but may be more secure than
anonymous ftp.

These backup procedures should not only include data center instructions
but user notification instructions. Furthermore, the IGS needs to
determine how long the analysis community can tolerate a data center's
outage and subsequent delay in the availability of either daily or
hourly data products. For example, when a data center outage occurs for
more than one day (for centers involved in distribution of daily data
only) or more than two hours (for centers involved in distribution of
hourly data), the affected data center should send an advisory email to
all data center contacts. If computer problems at the affected data
center preclude a direct email, the data center contact should make
arrangements with an alternate data center to post these alerts. This
advisory message should include a description of the problem and an
estimated time to recovery. At this time, the backup data flow
procedures should begin. The data centers tasked to act in a backup
capacity should notify the affected data center they are ready to
proceed with alternate data flow procedures. Once all participants are
notified and prepared, data should be transmitted to these alternate
data centers. The data center or an alternate, advising the general user
community of the outage and other sources for IGS data and products
should send an email to IGSMail. Should the outage continue for several
days, messages should be issued periodically to let the IGS community
know the affected system's current status and when users can expect
operations may return to normal. Once the data center has resumed
operation a follow-up email to data center contacts and IGSMail should
be issued stating that "normal" operations can resume.

A future enhancement to this backup data flow plan would be to automate
the switchover to alternate paths. This automation could be achieved
when a specified data center is unreachable for a pre-determined amount
of time, dependent upon the type of data to be transmitted.

Although the IGS Central Bureau Information System (CBIS) was not
discussed previously in this paper, its importance in the daily
operations of the IGS should not be overlooked. The CBIS provides
information to both the IGS and the general user community about the
service and the use of IGS orbits and data. The CBIS also maintains the
various email exploders utilized to notify users and the members of the
IGS infrastructure of general announcements, station, data center, and
analysis center alerts, and routine reports. The IGS ftp site is
mirrored at IGN, but a full web site mirror does not exist. Furthermore,
no alternate email system is currently available for use in the event
that the IGS ftp/web server computer or its network is inaccessible. The
IGS Central Bureau should identify alternate servers for these important
activities.

5 Recommendations

The following recommendations have been made to aid in the
implementation of a viable plan for the distribution of data and
products, both operationally and in a backup situation, through the IGS
infrastructure.

-   Ensure that data center information available through IGS Central
    Bureau (*ftp://igscb.jpl.nasa.gov/igscb/center/data/*) is complete
    and current for all IGS participants. Add backup data flow paths to
    this data center information.

-   Establish and maintain email distribution lists for key data center
    contacts at the IGS Central Bureau. The use of distribution lists
    could be extended for all components of the IGS as has successfully
    been implemented within the ILRS
    (*http://ilrs.gsfc.nasa.gov/pointsof.html*).

-   Complete a backup data flow plan for daily and hourly IGS data and
    IGS products. Ensure all data center (and analysis center) contacts
    have reviewed the plan and will implement its procedures.

-   Data centers should create and monitor ftp put areas (anonymous or
    username/password) to facilitate flow of data and products in a
    backup situation.

-   Schedule tests of the backup data flow paths on a regular basis to
    ensure their operational readiness.

-   Identify backup facilities for the IGS Central Bureau Information
    System (CBIS) ftp and web sites. Create a backup system for the
    various mail exploders maintained by the CBIS, in particular
    IGSMail.

-   Ensure the viability and commitment of all IGS data centers to the
    routine and backup operations of the service.

**Table 1.** Data Centers Supporting the IGS in 2000

  --------------------- -------- ----- --------------------------------------------------------
  **Operational/Local                  
  Data Centers**                       

                        ASI      \*    Italian Space Agency

                        AUSLIG         Australian Surveying and Land Information Group

                        AWI            Alfred Wegener Institute for Polar and Marine Research,
                                       Germany

                        CASM           Chinese Academy of Surveying and Mapping

                        CNES           Centre National d'Etudes Spatiales, France

                        DGFI           Deutsches Geodätisches ForschungsInstitut, Germany

                        DUT            Delft University of Technology, The Netherlands

                        ESOC     \*    European Space Agency (ESA) Space Operations Center,
                                       Germany

                        GFZ      \*†   GeoForschungsZentrum, Germany

                        GSI            Geographical Survey Institute, Japan

                        ISR      \*    Institute for Space Research, Austria

                        JPL      \*†   Jet Propulsion Laboratory, USA

                        KAO            Korean Astronomical Observatory

                        NGI            National Geography Institute, Korea

                        NIMA           National Imagery and Mapping Agency, USA

                        NMA      \*    Norwegian Mapping Authority

                        NOAA     \*    National Oceanic and Atmospheric Administration, USA

                        NRCan    \*    Natural Resources of Canada

                        PGC      \*    Pacific Geoscience Center, Canada

                        RDAAC          Regional GPS Data Acquisition and Analysis Center on
                                       Northern Eurasia, Russia

                        SIO            Scripps Institution of Oceanography, USA

                        UNAVCO         University NAVSTAR Consortium, USA

                        USGS           United States Geological Survey

                        WTZR     \*    Bundesamt für Kartographie und Geodäsie (Wettzell),
                                       Germany

  **Regional Data                      
  Centers**                            

                        AUSLIG   †     Australian Surveying and Land Information Group

                        BKG      \*    Bundesamt für Kartographie und Geodäsie, Germany

                        JPL      \*†   Jet Propulsion Laboratory, USA

                        NOAA           National Oceanic and Atmospheric Administration, USA

                        NRCan          National Resources of Canada

                        RDAAC          Regional GPS Data Acquisition and Analysis Center on
                                       Northern Eurasia, Russia

  **Global Data                        
  Centers**                            

                        CDDIS    \*†   Crustal Dynamics Data Information System, NASA GSFC, USA

                        IGN      \*    Institut Géographique National, France

                        SIO            Scripps Institution of Oceanography, USA
  --------------------- -------- ----- --------------------------------------------------------

Notes: \* indicates data center currently transmitting and/or archiving
hourly, 30-second GPS data from selected sites.

† indicates data center proposing to transmit and/or archive hourly,
high-rate GPS data for LEO activities.

**Table 2.** Summary of IGS Data and Products

  ------------ ----------------- --------------- --------------------------------------
  **GPS DATA**                                   

               **Daily**         Sampling:       30 seconds

                                 Frequency:      Daily

                                 Number of       \~240 at IGS CBIS
                                 stations:       

                                 Average delay:  2 hours to GDC (average)

                                 Format/file     RINEX observation data (O)
                                 types:          

                                                 RINEX observation data, Hatanaka
                                                 compression (D)

                                                 RINEX meteorological data (M)

                                                 RINEX broadcast ephemeris data (N)

                                                 summary output from teqc (S)

               **Hourly**        Sampling:       30 seconds

                                 Frequency:      Hourly

                                 Number of       \~70 regularly submitting data
                                 stations:       

                                 Average delay:  5-15 minutes to GDC (average)

                                 Format/file     RINEX observation data, Hatanaka
                                 types:          compression (D)

                                                 RINEX meteorological data (M)

                                                 RINEX broadcast ephemeris data (N)

               **High Rate**     Sampling:       \~10 seconds (TBD)
               (future)                          

                                 Frequency:      Hourly

                                 Number of       \>30 planned
                                 stations:       

                                 Average delay:  TBD

                                 Format:         TBD

  **IGS                                          
  PRODUCTS**                                     

               **Orbit, clock,   Analysis        Seven
               ERP**             Centers:        

                                 Frequency:      Weekly submission of daily orbits,
                                                 clocks; weekly ERP

                                 Format:         SP3

                                 Combination:    Weekly precise (AIUB)

                                                 Daily predicted (AIUB)

                                                 Daily rapid (AIUB)

               **Positions**     Analysis        Three GNAACs, three RNAACs
                                 Centers:        

                                 Frequency:      Weekly solutions

                                 Format:         SINEX

                                 Combination:    Weekly (NRCan)

               **Ionosphere**    Analysis        Five AACs
                                 Centers:        

                                 Frequency:      Daily files

                                 Format:         IONEX

                                 Combination:    Not yet available

               **Troposphere**   Analysis        Seven AACs (AAC solutions not archived
                                 Centers:        at GDCs)

                                 Frequency:      Weekly files

                                 Format:         SINEX_TRO

                                 Combination:    Weekly (GFZ)
  ------------ ----------------- --------------- --------------------------------------

> **Table 3.** Global Data Center Holdings

+------------+---+---+-----------------------+--------+--------+--------+
|            | * |   |                       | **C    | *      | *      |
|            | * |   |                       | DDIS** | *IGN** | *SIO** |
|            | D |   |                       |        |        |        |
|            | a |   |                       |        |        |        |
|            | t |   |                       |        |        |        |
|            | a |   |                       |        |        |        |
|            | T |   |                       |        |        |        |
|            | y |   |                       |        |        |        |
|            | p |   |                       |        |        |        |
|            | e |   |                       |        |        |        |
|            | * |   |                       |        |        |        |
|            | * |   |                       |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            | # |   |                       |        |        |        |
|            | # |   |                       |        |        |        |
|            |   |   |                       |        |        |        |
|            | D |   |                       |        |        |        |
|            | a |   |                       |        |        |        |
|            | t |   |                       |        |        |        |
|            | a |   |                       |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   |   | Daily GPS (D format)  | X      | X      |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   |   | Daily GPS (O format)  | X      |        | X      |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   |   | Hourly GPS            | X      | X      |        |
|            |   |   | (30-second)           |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   |   | Hourly GPS            | Future |        |        |
|            |   |   | (high-rate)           |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   |   | Daily GLONASS (D      | X      | X      |        |
|            |   |   | format)               |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   |   | Daily GLONASS (O      | X      |        |        |
|            |   |   | format)               |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            | * |   |                       |        |        |        |
|            | * |   |                       |        |        |        |
|            | P |   |                       |        |        |        |
|            | r |   |                       |        |        |        |
|            | o |   |                       |        |        |        |
|            | d |   |                       |        |        |        |
|            | u |   |                       |        |        |        |
|            | c |   |                       |        |        |        |
|            | t |   |                       |        |        |        |
|            | s |   |                       |        |        |        |
|            | * |   |                       |        |        |        |
|            | * |   |                       |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   | O |                       | X      | X      | X      |
|            |   | r |                       |        |        |        |
|            |   | b |                       |        |        |        |
|            |   | i |                       |        |        |        |
|            |   | t |                       |        |        |        |
|            |   | s |                       |        |        |        |
|            |   | , |                       |        |        |        |
|            |   | e |                       |        |        |        |
|            |   | t |                       |        |        |        |
|            |   | c |                       |        |        |        |
|            |   | . |                       |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   | S |                       | X      | X      | X      |
|            |   | I |                       |        |        |        |
|            |   | N |                       |        |        |        |
|            |   | E |                       |        |        |        |
|            |   | X |                       |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   | T |                       | X      | X      | X      |
|            |   | r |                       |        |        |        |
|            |   | o |                       |        |        |        |
|            |   | p |                       |        |        |        |
|            |   | o |                       |        |        |        |
|            |   | s |                       |        |        |        |
|            |   | p |                       |        |        |        |
|            |   | h |                       |        |        |        |
|            |   | e |                       |        |        |        |
|            |   | r |                       |        |        |        |
|            |   | e |                       |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+
|            |   | I |                       | X      | X      |        |
|            |   | O |                       |        |        |        |
|            |   | N |                       |        |        |        |
|            |   | E |                       |        |        |        |
|            |   | X |                       |        |        |        |
+------------+---+---+-----------------------+--------+--------+--------+

> **Table 4.** Latency of Daily Data at the CDDIS
>
> (01-Feb-2000 through 30-Jun-2000)

+-----------------------------+-----------+----------------+-----------+
|                             | **Delay** | **No. of**     | **        |
|                             |           |                | Percent** |
|                             | **        | **Station      |           |
|                             | (hours)** | Days**         |           |
+-----------------------------+-----------+----------------+-----------+
|                             | 1         | 10,488         | 43.36%    |
+-----------------------------+-----------+----------------+-----------+
|                             | 2         | 3,137          | 12.97%    |
+-----------------------------+-----------+----------------+-----------+
|                             | 3         | 1,911          | 7.90%     |
+-----------------------------+-----------+----------------+-----------+
|                             | 4         | 1,225          | 5.06%     |
+-----------------------------+-----------+----------------+-----------+
|                             | 6         | 1,191          | 4.92%     |
+-----------------------------+-----------+----------------+-----------+
|                             | 8         | 635            | 2.63%     |
+-----------------------------+-----------+----------------+-----------+
|                             | 9 or more | 5,601          | 23.16%    |
+-----------------------------+-----------+----------------+-----------+

> Total number of station days: 24,188
>
> Total number of sites 182
>
> **Table 5.** Latency of Hourly Data at the CDDIS
>
> (24-Apr-2000 through 30-Jun-2000)

+----------------------------+------------+----------------+-----------+
|                            | **Delay**  | **No. of**     | **        |
|                            |            |                | Percent** |
|                            | **(        | **Station      |           |
|                            | minutes)** | Days**         |           |
+----------------------------+------------+----------------+-----------+
|                            | 5          | 10,714         | 13.34%    |
+----------------------------+------------+----------------+-----------+
|                            | 10         | 16,715         | 20.82%    |
+----------------------------+------------+----------------+-----------+
|                            | 15         | 14,907         | 18.57%    |
+----------------------------+------------+----------------+-----------+
|                            | 20         | 12,890         | 16.05%    |
+----------------------------+------------+----------------+-----------+
|                            | 25         | 7,971          | 9.93%     |
+----------------------------+------------+----------------+-----------+
|                            | 30         | 2,766          | 3.44%     |
+----------------------------+------------+----------------+-----------+
|                            | 35         | 2,295          | 2.86%     |
+----------------------------+------------+----------------+-----------+
|                            | 40         | 2,582          | 3.22%     |
+----------------------------+------------+----------------+-----------+
|                            | 45 or more | 9,451          | 11.77%    |
+----------------------------+------------+----------------+-----------+

> Total number of station hours: 80,291
>
> Total number of sites 64
>
> ![](media/image1.pct)
>
> **Figure 1.** Flow of daily IGS data files (by data center)

![](media/image2.pct)

**Figure 2.** Flow of hourly IGS data files (by data center)

![](media/image3.pct)

Figure 3. Backup flow of daily IGS data files

![](media/image4.pct)

Figure 4. Backup Flow of IGS Product Files

**Appendix A.** IGS Sites by Site Acronym

  ---------- --------------------- --------------- ----------- ------------ ------------- ----- ------------- ----------- --
  **Site**   **Location**          **Country**                 **OC/LDC**   **Global?**         **Hourly?**   **Met.?**   

  ALBH       Victoria              Canada                      PGC          Y                   Y             Y           

  ALGO       Algonquin Park        Canada                      NRCan        Y                   Y             Y           

  ALIC       Alice Springs         Australia                   AUSLIG                                                     

  AMC2       Colorado Springs      USA                         NOAA                                                       

  AMMN       Amman                 Jordan                      RJGC/SIO                                                   

  ANKR       Ankara                Turkey                      WTZR         Y                                             

  AOA1       Westlake, CA          USA                         JPL                              Y                         

  AOML       Key Biscayne, FL      USA                         NOAA         Y                                 Y           

  AREQ       Arequipa              Peru                        JPL          Y                                             

  ARTU       Arti                  Russian                     RDAAC        Y                                             
                                   Federation                                                                             

  ASC1       Ascension Island      Ascension                   JPL          Y                                             
                                   Island                                                                                 

  AUCK       Whangaparaoa          New Zealand                 JPL          Y                   Y             Y           
             Peninsula                                                                                                    

  AZU1       Azusa, CA             USA                         USGS (CA)                                                  

  BAHR       Manama                Bahrain                     NIMA         Y                                 Y           

  BAKO       Cibinong              Indonesia       NCASM/SIO                              Y                               

  BARB       Bridgetown            Barbados                    NOAA         Y                                             

  BARH       Bar Harbor, ME        USA                         NOAA                                                       

  BILI       Bilibino              Russian                     RDAAC                                                      
                                   Federation                                                                             

  BILL       Temecula, CA          USA                         SIO                                                        

  BJFS       Beijing               China                       CASM                                           Y           

  BLYT       Blythe, CA            USA                         SIO                                                        

  BOGT       Bogota                Colombia                    JPL          Y                                             

  BOR1       Borowiec              Poland                      ISR                              Y                         

  BRAN       Burbank, CA           USA                         SIO                                                        

  BRAZ       Brasilia              Brazil                      DGFI                                                       

  BRMU       Bermuda               UK Territory                NOAA         Y                                             

  BRUS       Brussels              Belgium                     ROB/BKG                          Y             Y           

  BUCU       Bucuresti             Romania                     WTZR                                                       

  BZRG       Bolzano               Italy                       ASI                                                        

  CAGL       Cagliari              Italy                       ASI                                                        

  CARR       Parkfield, CA         USA                         USGS (CA)                                                  

  CAS1       Casey                 Antarctica                  AUSLIG                                                     

  CASA       Mammoth Lakes, CA     USA                         JPL                                                        

  CAT1       Catalina, CA          USA                         USGS (CA)                                                  

  CEDU       Ceduna                Australia                   AUSLIG                                                     

  CHAT       Waitangi              New Zealand                 JPL          Y                                 Y           

  CHIL       San Gabriel           USA                         SIO                                                        
             Mountains, CA                                                                                                

  CHUR       Churchill             Canada                      NRCan        Y                   Y                         

  CHWK       Chilliwack            Canada                      PGC                                                        

  CIC1       Ensenada              Mexico                      JPL                              Y                         

  CIT1       Pasadena, CA          USA                         USGS (CA)                                                  

  CLAR       Claremont, CA         USA                         USGS (CA)                                                  

  CMPG       Sylmar, CA            USA                         USGS (CA)                                                  

  COCO       Cocos Island          Australia                   AUSLIG       Y                                             

  CORD       Cordoba               Argentina                   JPL                                                        

  COSO       Coso Junction, CA     USA                         SIO                                                        

  CRFP       Yucaipa, CA           USA                         SIO                                                        

  CRO1       Christiansted, St.    US Virgin                   JPL          Y                   Y                         
             Croix                 Islands                                                                                

  CSN1       Northridge, CA        USA                         USGS (CA)                                                  

  DAEJ       Taejon                Korea                       KAO                                                        

  DARW       Darwin                Australia                   AUSLIG       Y                                             

  DAV1       Davis                 Antarctica                  AUSLIG       Y                                             
  ---------- --------------------- --------------- ----------- ------------ ------------- ----- ------------- ----------- --

**Appendix A.** IGS Sites by Site Acronym (continued)

  ------------- --------------------- ---------------- ------------ ------------- ----- ------------- ----------- --
  **Site**      **Location**          **Country**      **OC/LDC**   **Global?**         **Hourly?**   **Met.?**   

  DGAR          Diego Garcia Island   UK Territory     JPL          Y                                             

  DHLG          Durmid Hill, CA       USA              SIO                                                        

  DRAG          Metzoki Dragot        Israel           TAU/SIO                                                    

  DRAO          Penticton             Canada           PGC          Y                   Y             Y           

  DUBO          Lac Du Bonnet         Canada           PGC                                                        

  EBRE          Roquetes              Spain            ICC/BKG                                                    

  EISL          Easter Island         Chile            JPL          Y                   Y                         

  EPRT          Eastport, ME          USA              NOAA                                                       

  ESTI          Esteli                Nicaragua        NOAA                                                       

  FAIR          Fairbanks, AK         USA              JPL          Y                   Y             Y           

  FLIN          Flin Flon             Canada           PGC                                                        

  FORT          Eusebio, Fortaleza    Brazil           NOAA         Y                                             

  GALA          Galapagos Island      Ecuador          JPL                              Y                         

  GENO          Genova                Italy            ASI                                                        

  GLSV          Kiev                  Ukraine          MAO/BKG                                                    

  GODE          Greenbelt, MD         USA              JPL          Y                   Y                         

  GOL2          Goldstone, CA         USA              JPL          Y                   Y                         

  GOLD          Goldstone, CA         USA              JPL                                                        

  GOPE          Ondrejov              Czech Republic   ISR                                                        

  GOUG          Gough Island          UK Territory     AWI          Y                                             

  GRAS          Caussols              France           CNES                                                       

  GRAZ          Graz                  Austria          ISR                                            Y           

  GUAM          Dededo                Guam             JPL          Y                   Y                         

  HARK          Pretoria              South Africa     CNES         Y                                             

  HARV          Harvest Platform, CA  USA              JPL                                                        

  HERS          Hailsham              England          NERC/BKG                         Y             Y           

  HFLK          Innsbruck             Austria          ISR                                                        

  HNPT          Cambridge, MD         USA              NOAA                                                       

  HOB2          Hobart                Australia        AUSLIG       Y                                             

  HOFN          Hoefn                 Iceland          WTZR                             Y                         

  HOLB          Holberg               Canada           PGC                                                        

  HOLC          Pearblossom, CA       USA              SIO                                                        

  HOLP          Hollydale, CA         USA              USGS (CA)                                                  

  HRAO          Krugersdorp           South Africa     JPL          Y                   Y                         

  IAVH          Rabat                 Morocco          JPL                                                        

  IGM0**^1^**   Buenos Aires          Argentina        DGFI                             Y                         

  IISC          Bangalore             India            JPL          Y                                             

  INEG          Aguascalientes        Mexico           INEGI/SIO                                                  

  IRKT          Irkutsk               Russian          DUT          Y                                             
                                      Federation                                                                  

  ISTA          Istanbul              Turkey           WTZR                                                       

  JAB1          Jabiru                Australia        AUSLIG                                                     

  JAMA          Kingston              Jamaica          NOAA                                                       

  JOZE          Jozefoslaw            Poland           ISR                                                        

  JPLM          Pasadena, CA          USA              JPL          Y                   Y             Y           

  KARR          Karratha              Australia        AUSLIG                                                     

  KELY          Kangerlussuaq         Greenland        NOAA         Y                                             

  KERG          Port Aux Francais     Kerguelen        CNES         Y                                             
                                      Islands                                                                     

  KIRU          Kiruna                Sweden           ESOC                             Y                         

  KIT3          Kitab                 Uzbekistan       GFZ                                                        

  KODK          Kodiak, AK            USA              SIO                                                        

  KOKB          Kokee Park, HI        USA              JPL          Y                   Y             Y           

  KOSG          Kootwijk              The Netherlands  DUT          Y                                             
  ------------- --------------------- ---------------- ------------ ------------- ----- ------------- ----------- --

**Appendix A.** IGS Sites by Site Acronym (continued)

  ---------- ------------------------- ---------------- ------------ ------------- ------------- ----------- --
  **Site**   **Location**              **Country**      **OC/LDC**   **Global?**   **Hourly?**   **Met.?**   

  KOUR       Kourou                    French Guyana    ESOC         Y             Y                         

  KSTU       Krasnoyarsk               Russian          GFZ                        Y                         
                                       Federation                                                            

  KUNM       Kunming                   China            JPL                                                  

  KWJ1       Kwajalein Atoll           Marshall Islands JPL                                                  

  LAMA       Olsztyn                   Poland           ISR                                                  

  LBCH       Long Beach, CA            USA              USGS (CA)                                            

  LEEP       Hollywood, CA             USA              USGS (CA)                                            

  LHAS       Lhasa                     China            WTZR         Y                                       

  LONG       Irwindale, CA             USA              SIO                                                  

  LPGS       La Plata                  Argentina        GFZ          Y             Y                         

  MAC1       Macquarie Island          Antarctica       AUSLIG       Y                                       

  MAD2       Robledo                   Spain            JPL          Y             Y                         

  MADR       Robledo                   Spain            JPL                                                  

  MAG0       Magadan                   Russian          RDAAC        Y                                       
                                       Federation                                                            

  MALI       Malindi                   Kenya            ESOC         Y                                       

  MANA       Managua                   Nicaragua        NOAA                                                 

  MAS1       Maspalomas                Spain            ESOC         Y                                       

  MATE       Matera                    Italy            ASI          Y             Y             Y           

  MATH       Lake Mathews, CA          USA              SIO                                                  

  MAW1       Mawson                    Antarctica       AUSLIG       Y                                       

  MCM4       Ross Island               Antarctica       JPL          Y             Y                         

  MDO1       Fort Davis, TX            USA              JPL          Y             Y             Y           

  MDVO       Mendeleevo                Russia           DUT                                                  

  MEDI       Medicina                  Italy            ASI                                                  

  METS       Kirkkonummi               Finland          NMA          Y                           Y           

  MKEA       Mauna Kea, HI             USA              JPL          Y             Y                         

  MOIN       Moin                      Costa Rica       JPL                                                  

  MONP       Laguna Mountains, CA      USA              SIO                                                  

  NANO       Nanoose Bay               Canada           PGC                                                  

  NICO       Nicosia                   Cyprus           WTZR                                                 

  NKLG       Libreville                Gabon            CNES                                                 

  NLIB       North Liberty, IA         USA              JPL          Y             Y                         

  NOTO       Noto                      Italy            ASI                                                  

  NOUM       Noumea                    France           CNES         Y                                       

  NRC1       Ottawa                    Canada           NRCan        Y             Y             Y           

  NRC2       Ottawa                    Canada           NRCan                      Y                         

  NSSP       Yerevan                   Republic of      JPL                                                  
                                       Armenia                                                               

  NTUS       Singapore                 Republic of      DUT          Y                                       
                                       Singapore                                                             

  NYA1       Ny-Alesund                Norway           NMA          Y                                       

  NYAL       Ny-Alesund                Norway           NMA          Y                                       

  OAT2       Santa Susana Mountains,   USA              USGS (CA)                                            
             CA                                                                                              

  OBER       Oberpfaffenhofen          Germany          GFZ                        Y                         

  OHIG       O\'Higgins                Antarctica       WTZR                       Y                         

  ONSA       Onsala                    Sweden           NMA          Y             Y                         

  PENC       Penc                      Hungary          ISR                                                  

  PERT       Perth                     Australia        ESOC         Y             Y                         

  PETP       Petropavlovsk-kamchatka   Russian          RDAAC        Y                                       
                                       Federation                                                            

  PIE1       Pie Town, NM              USA              JPL          Y             Y                         

  PIMO       Quezon City               Phillipines      JPL          Y             Y                         

  PIN1       Pinyon Flat, CA           USA              SIO                                                  

  POL2       Bishkek                   Kyrghyzstan      UNAVCO       Y                                       

  POTS       Potsdam                   Germany          GFZ          Y             Y             Y           
  ---------- ------------------------- ---------------- ------------ ------------- ------------- ----------- --

**Appendix A.** IGS Sites by Site Acronym (continued)

  ------------- --------------------- -------------- ------------- ------------ ------------- ---- ------------- ----------- --
  **Site**      **Location**          **Country**                  **OC/LDC**   **Global?**        **Hourly?**   **Met.?**   

  PRDS          Calgary               Canada                       NRCan                           Y             Y           

  PVEP          Palos Verdes, CA      USA                          SIO                                                       

  QUIN          Quincy, CA            USA                          JPL                             Y                         

  RAMO          Mitzpe Ramon          Israel                       TAU/SIO                                                   

  REYK          Reykjavik             Iceland                      WTZR         Y                  Y                         

  RIOG          Rio Grande            Argentina                    GFZ          Y                                            

  RIOP          Riobamba              Ecuador                      JPL                                                       

  ROCH          Pinemeadow, CA        USA                          SIO                                                       

  ROCK          Simi Valley, CA       USA                          USGS (CA)                                                 

  SANT          Santiago              Chile                        JPL          Y                  Y                         

  SCH2          Schefferville         Canada                       NRCan                           Y             Y           

  SCIP          San Clemente Island,  USA                          SIO                                                       
                CA                                                                                                           

  SELE          Almaty                Kazakstan                    JPL          Y                                            

  SEY1          La Misere             Seychelles                   JPL                                                       

  SFDM          Piru, CA              USA                          USGS (CA)                                                 

  SFER          San Fernando          Spain                        ROA/BKG                                                   

  SHAO          Sheshan               China                        JPL                                                       

  SIO3          La Jolla, CA          USA                          SIO                                                       

  SNI1          San Nicholas Island,  USA                          USGS (CA)                                                 
                CA                                                                                                           

  SOFI          Sofia                 Bulgaria                     WTZR                                                      

  SOL1          Solomons Island, MD   USA                          NOAA                                          Y           

  SPK1          Saddle Peak, CA       USA                          USGS (CA)                                                 

  STJO          St. John\'s           Canada                       NRCan        Y                  Y             Y           

  STR1          Canberra              Australia                    AUSLIG                                                    

  SUTH          Sutherland            South Africa                 JPL          Y                  Y                         

  SUWN          Suwon-shi             Korea                        NGI                                                       

  SYOG          East Ongle Island     Antarctica                   GSI                                                       

  TABL          Wrightwood, CA        USA                          USGS (CA)                                                 

  TAIW**^2^**   Taipei                Taiwan                       GSI                                                       

  TEGU          Tegucigalpa           Honduras                     NOAA                                                      

  THTI          Papeete               Tahiti, French               CNES         Y                                            
                                      Polynesia                                                                              

  THU1          Thule                 Greenland                    JPL          Y                                            

  TID1          Tidbinbilla           Australia                    AUSLIG                                                    

  TID2          Tidbinbilla           Australia                    JPL          Y                  Y                         

  TIDB          Tidbinbilla           Australia                    JPL                                                       

  TIXI          Tixi                  Russian                      RDAAC        Y                                            
                                      Federation                                                                             

  TORP          Torrance, CA          USA                          USGS (CA)                                                 

  TOUL          Toulouse              France                       CNES                                                      

  TOW2          Cape Ferguson         Australia                    AUSLIG       Y                                            

  TRAB          Trabzon               Turkey                       WTZR                                                      

  TRAK          Irvine, CA            USA                          SIO                                                       

  TRO1          Tromsoe               Norway                       NMA          Y                                            

  TROM          Tromsoe               Norway                       NMA                                                       

  TSKB          Tsukuba               Japan                        GSI          Y                                            

  TUBI          Gebze                 Turkey         TUBITAK/BKG                                                             

  UCLP          Los Angeles, CA       USA                          USGS (CA)                                                 

  UCLU          Ucluelet              Canada                       PGC                                                       

  UNSA          Salta                 Argentina                    GFZ                             Y                         

  UPAD          Padova                Italy                        ASI                                                       

  URUM          Urumqi                China                        GFZ                                                       

  USC1          Los Angeles, CA       USA                          USGS (CA)                                                 

  USNA          Annapolis, MD         USA                          NOAA                                                      
  ------------- --------------------- -------------- ------------- ------------ ------------- ---- ------------- ----------- --

**Appendix A.** IGS Sites by Site Acronym (continued)

  ------------- --------------------- --------------- --------- ------------ ------------- ------------- ----------- --
  **vSite**     **Location**          **Country**               **OC/LDC**   **Global?**   **Hourly?**   **Met.?**   

  USNO          Washington, D.C.      USA                       NOAA         Y                           Y           

  USUD          Usuda                 Japan                     JPL          Y             Y                         

  UZHL          Uzhgorod              Ukraine                   MAO/BKG                                              

  VENE          Venezia               Italy                     ASI                                                  

  VESL          Sanae IV              Antarctica                AWI          Y                                       

  VILL          Villafranca           Spain                     ESOC         Y             Y                         

  VNDP          Vandenberg Air Force  USA                       SIO                                                  
                Base, CA                                                                                             

  WES2          Westford, MA          USA                       NOAA         Y                           Y           

  WHC1          Whittier, CA          USA                       USGS (CA)                                            

  WHIT          Whitehorse            Canada                    PGC          Y                                       

  WIDC          Sky Valley, CA        USA                       SIO                                                  

  WILL          Williams Lake         Canada                    PGC          Y                                       

  WLSN          Mt. Wilson, CA        USA                       USGS (CA)                                            

  WSLR          Whistler              Canada                    NRCan                                                

  WSRT          Westerbork            The Netherlands           DUT          Y                                       

  WTZR          Koetzting             Germany                   WTZR         Y             Y                         

  WTZT          Koetzting             Germany                   WTZR                                                 

  WUHN          Wuhan City            China                     NOAA         Y                                       

  XIAN          Lintong               China                     JPL                                                  

  YAKZ          Yakutsk               Russian                   RDAAC        Y                                       
                                      Federation                                                                     

  YAR1          Mingenew              Australia                 JPL          Y                                       

  YAR2          Dongara               Australia                 AUSLIG                                               

  YELL          Yellowknife           Canada                    NRCan        Y             Y             Y           

  YKRO          Yamoussoukro          Cote D\'ivorie            JPL          Y                                       

  YSSK          Yuzhno-sakhalinsk     Russian                   RDAAC                                                
                                      Federation                                                                     

  ZECK          Zelenchukskaya        Russian                   WTZR                                                 
                                      Federation                                                                     

  ZIMM          Zimmerwald            Switzerland               FOT/BKG                    Y             Y           

  ZWEN          Zwenigorod            Russian                   GFZ          Y             Y             Y           
                                      Federation                                                                     

  **Totals:**   236 stations                          24                     93            56            28          
                                                      OC/LDCs                                                        
  ------------- --------------------- --------------- --------- ------------ ------------- ------------- ----------- --

Notes: **^1^** Data not public

**^2^** No data since 1997