Table of contents:
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
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
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,
Reports of CDDIS SLR tracking data holdings:
Related SLR data and information links: