CDDIS Bulletin - July 2001
Volume 16 No. 4

In this issue:

• Articles:
  • CDDIS Site and Data "Locator"
  • High-Rate SolarMax IGS/GPS Campaign "HIRAC/SolarMax"
  • New RAID Disks Installed
• Data Bits and Bytes:
  • Permanent GPS and GLONASS Network Update
  • Frequency Error at Cagliari SLR Station
  • New Calendar Web Page

CDDIS Site and Data "Locator"

The CDDIS archives and distributes GPS, GLONASS, SLR, VLBI, and DORIS data in support of the various IAG-sponsored services, the IGS, ILRS, IVS and IDS. The CDDIS has provided access to maps of the global networks supporting these services. New maps have recently been created that present these networks on a regional level, each map showing observing sites for all data types.

A web page has been designed to provide an easy interface to all these maps as well as queries to the CDDIS data base. This site and data "locator" can be viewed at URL http://cddisa.gsfc.nasa.gov/mappage.html, A clickable image map of the world is presented which links to GIF images of regional maps. Each regional map displays all GPS, GLONASS, SLR, VLBI, and DORIS sites participating in the IAG-sponsored services. Alternatively, users can download PDF versions of these maps. Global maps by data type can be viewed and downloaded through this map page as well.

The site and data locator page also provides access to forms that query the CDDIS metadata data base. For example, users can enter a four-character monument ID into the GPS query form; once submitted, the system will return general information about the site as well as a list of data available for this monument for each year since 1992.

The maps available through this facility have also been used to generate a "random map" image on the CDDIS Home Page. Comments, suggestions, corrections, etc. to this web page are of course welcome and should be directed to the CDDIS Manager.

High-Rate SolarMax IGS/GPS Campaign "HIRAC/SolarMax" – Update

The 2001 HIRAC/SolarMax campaign was discussed in the April 2001 issue of the CDDIS Bulletin. Since that time, additional data have been submitted to the CDDIS and archived. The data are available through anonymous ftp to host cddisa.gsfc.nasa.gov in the filesystem /gps/01solarmax/yyddd/yyt, where yy is the two-digit year, ddd is the three-digit day of year, and t is the file type (d, g, m, n, o, s). A list of the stations (PS or PDF) and map (GIF or PDF) whose data have been archived is available. Thus far, 15K hourly files, totaling over 12 Gbytes in size, from 104 stations have been received. These sites are located in thirty countries and sponsored by over twenty agencies.

Questions about the campaign can be directed to Dr. Joachim Feltens and/or Dr. Norbert Jakowski; questions about data access can be directed to the CDDIS Manager, Carey Noll.

New RAID Disks

A new RAID disk array was recently installed on the CDDIS computer host cddisa.gsfc.nasa.gov. This disk array increases the on-line magnetic archive by nearly 470 Gbytes. To date, nearly all of the on-line archive of the CDDIS has been migrated to this new disk array. Plans are to increase the amount of on-line data available, particularly with older GPS data sets.

DATA BITS AND BYTES

This section is designed to give brief notices of special events, new data sets, or problems encountered in recent months. The CDDIS staff believes the user community should be informed of these problems in order to ensure that the best results possible are produced from data issued by the archive.

Permanent GPS and GLONASS Network Update

Since the April 2001 issue of the CDDIS Bulletin, the CDDIS has archived daily and hourly 30-second GPS data (Table 1), hourly high-rate data (Table 2), and daily GLONASS data (Table 3) from the following new tracking sites:

Table1. New GPS Daily and Hourly Tracking Sites

Note: ¹ Daily sites previously archived at the CDDIS that have just recently started to provide hourly data.
² Daily sites previously archived at the CDDIS that have just recently started to provide meteorological data.
³ OBER was renamed to OBE2 when the antenna was relocated.

Table 2. GPS Stations Supplying High-Rate Data to the CDDIS

Note: ¹ Hourly meteorological data also available.
² Data from OBER available through day 01172; OBEM data started on day 01206.

Table 3. New GLONASS Tracking Sites

Notes: An * in the above table denotes daily sites previously archived at the CDDIS that have just recently started to provide hourly and/or meteorological data.

Frequency Error at Cagliari SLR Station

The Cagliari station, station 7548, has resumed ranging operations after approximately one year. During this period, the telescope was refurbished and a frequency error was corrected. As of mid-July, the system has obtained SLR data from several satellites.

In addition, all data from this site (7548) prior to July 1, 2001 contains a frequency error of unknown magnitude due to the station time interval unit (HP5370) operating on internal frequency. The nature of the error will induce a range dependent error that will drift over time (i.e., pass-to-pass, day-to-day, month-to-month, etc.). Solving for a range and time bias will not properly model a frequency error. Therefore, analysts should be wary of historical Cagliari data. Peter Dunn (Raytheon) has shown that a bias problem at one site can be absorbed into the orbit and thereby affecting the apparent data quality of systems in close proximity.

New Calendar Web Page

A new web page listing upcoming meetings and events of interest to the space geodesy community has been created. The web page also includes meetings pertinent to the IGS, ILRS, IVS, and IDS communities. This calendar page is accessible through the What's New page of the CDDIS web site.