Table of contents:

• About the CDDIS SLR data archive
• About the CDDIS SLR product archive
• Obtaining access to the CDDIS SLR data archive
• CDDIS SLR data holdings summary
• CDDIS SLR data holdings reports
• Related SLR data and information links

About the CDDIS SLR archive:

The SLR data in the CDDIS are in the form of on-site normal point and full-rate data. Until recently, scientists typically required full-rate SLR data; these data included all valid points or returns from the satellite. Since 1988, SLR normal points have been produced from the global full-rate data set. Normal point data are compressed data using sampling over time based upon the presence of some minimum number of data points in the sampling interval. The monthly data volume is considerably reduced. Since the early 1990's, normal point and engineering data (sometimes referred to as "quick-look" data) are generated on-site by laser ranging systems and transmitted daily (and sometimes hourly) to a regional processing center via electronic means.

On-site normal point data, and occasionally quick-look SLR data, sampled at a rate of typically fifty points per pass, are transmitted electronically when possible back to the NASA and European SLR processing headquarters. These groups then forward the on-site data to the CDDIS for on-line access to the SLR user community. The data from each satellite are stored in separate files and directories, by satellite. Each file contains all data received during the last 24-hour period. Additionally, a single file containing all data received during the last 24 hours is available.

The full-rate data are sorted by satellite and time and are available in daily and monthly increments. The initial, or A, release of a monthly data set is available from the CDDIS sixty days after the end of the observation month; follow-up releases contain additional and/or corrected data and are available six months or more after the end of the observation month. Recently-delivered full-rate SLR data are accessible on-line; older data are stored in the CDDIS off-line tape archive. Normal point data, generated from SLR full-rate data from 1988 through 1994, are also available for on-line retrieval. Summaries of SLR data from the recently supported satellites are stored on-line in the data base.

SLR product files. Products derived from SLR data are under development by the ILRS Analysis Working Group. These products include station positions and Earth orientation parameters (EOP) and are located on the CDDIS in subdirectories by data type at ftp://cddis.gsfc.nasa.gov/slr/products.

A description of the structure of the CDDIS SLR data and product ftp archive is available.

Obtaining access to the CDDIS SLR data archive:

The archive of SLR and LLR data are accessible through anonymous ftp and the WWW at URL ftp://cddis.gsfc.nasa.gov/slr; contact the CDDIS manager regarding questions about obtaining SLR data and products or consult the on-line ftp archive description.

Summary of CDDIS SLR tracking data holdings:

• SLR spatial coverage information
• List of SLR sites
• Map of SLR sites
• SLR temporal coverage information
• Data Volume:
• On-site SLR data (normal points/sampled): ~1 Mbyte/day
• Full-rate SLR data: ~250 Mbytes/month
• Normal point SLR data (generated from full-rate): ~10 Mbytes/month
• Data Formats:
  • On-site SLR data (normal points/sampled): ILRS Normal Point Data Format (formerly known as the CSTG format) and CRD Format
  • Full-rate SLR data: ILRS Full-Rate Data Format (formerly known as the MERIT-II format) and CRD Format
• Data Availability:
  • On-site SLR data (normal points/sampled): since 1991, on-line
  • Full-rate SLR data: 1976-present data sets on-line
  • Normal point SLR data (generated from full-rate): 1988-1994, on-line

Reports of CDDIS SLR tracking data holdings:

• Weekly and monthly reports (since mid-1995)

Related SLR data and information links:

• International Laser Ranging Service (ILRS)
• SLR occupation, coordinate, and eccentricity information
• SLR system configuration information (ILRS site logs)
• SLR satellite information
• University of Texas, Center for Space Research (CSR)
• EUROLAS Data Center (EDC)