Laser ranging normal points constitute the primary International Laser Ranging Service (ILRS) data product, and they are generated following the conclusion of the laser pass and typically transmitted to NASA’s Crustal Dynamics Data Information System (CDDIS) within hours of the observation.
SLR normal point (NPT) data are transmitted in hourly and daily files where each file contains all data collected by the ILRS operations center in the previous hour or daily time period. Therefore, these daily files may contain data spanning several operating days. These daily and hourly files containing data from all satellites are available from the "allsat" subdirectory within the normal point archive area. Each day, CDDIS updates monthly satellite-specific files containing all normal point data received to date for the month. The monthly files contain all normal point data for each satellite during the month.
As of April 25, 2017, CDDIS changed its directory structure for quarantined normal point data. CDDIS implemented changes to our incoming SLR data processing and archiving procedures. These changes required that we now archive quarantined normal point data in subdirectories by station number, rather than subdirectories by site name; these directories are located at https://cddis.nasa.gov/archive/slr/data/npt_crd/quarantine/.
Older data will be transitioned to this new structure in the near future. The EUROLAS Data Center (EDC) has used this directory convention for its quarantined normal point data files. Please email the CDDIS Manager.
if you have any questions or problems with the new CDDIS archive structure.
Daily and monthly normal point data are available from the CDDIS in subdirectories by satellite and year.
Files in current CRD format
The starting directory varies based on the Consolidated Laser Ranging Data (CRD) format version available.
Learn more about the differences between the CRD versions.
Append the following directory and file names to the starting directory:
| Directory/File Name | DOI |
|---|---|
| allsat/YYYY/allsat_YYYYMMDDHHMI.npt (hourly file) | 10.5067/SLR/SLR_DATA_HOURLY_NPT_001 |
| SATNAME/YYYY/SATNAME_YYYYMMDD.npt (daily file) | 10.5067/SLR/SLR_DATA_DAILY_NPT_001 |
| SATNAME/YYYY/SATNAME_YYYYMM.npt (monthly file) | 10.5067/SLR/SLR_DATA_MONTHLY_NPT_001 |
| SATNAME/YYYY/sum/SATNAME_YYYYMM.sum (monthly summary file) | 10.5067/SLR/SLR_DATA_MONTHLYSUM_NPT_001 |
as described in the table below:
| Code | Meaning |
|---|---|
| SATNAME | Satellite name |
| YYYY | 4-digit year |
| MM | 2-digit month |
| DD | 2-digit day |
| HH | 2-digit hour |
| MI | 2-digit minute |
Files in the former ILRS format
For files in the CSTG (Commission on International Coordination of Space Techniques for Geodesy and Geodynamics) format, the normal points were formed with the version of data by NASA contractors. Please note that some files were submitted without a version number (ex: starlette.9212.Z). If there is a file without a version number and one with, the one with the version number is the updated file that contains data from the initial submission (ex: starlette_b.9212.Z). Where the version of data is not a letter but “dgfi” or “dut”, the versions were created by Deutsches Geodätisches Forschungsinstitut (DGFI) and Durban University of Technology (DUT) respectively. Issues with the epochs have been detected in the DGFI and DUT files, please keep this in mind when using this data.
The file format is available under: https://ilrs.gsfc.nasa.gov/data_and_products/data/npt/npt_format.html.
The starting directory is: https://cddis.nasa.gov/archiveslr/data/npt/ (daily and monthly files)
Append the following directory and file names to the starting directory:
| Directory/File Name | DOI |
|---|---|
| allsat/YYYY/allsat_YYMMDD.Z (daily file) | 10.5067/SLR/SLR_DATA_DAILY_NPT_001 |
| SATNAME/YYYY/SATNAME.YYMMDD (daily file) | 10.5067/SLR/SLR_DATA_DAILY_NPT_001 |
| SATNAME/YYYY/SATNAME.YYMM (monthly file) | 10.5067/SLR/SLR_DATA_MONTHLY_NPT_001 |
| SATNAME/YYYY/sum/SATNAME_sum.YYMMDD (monthly summary file) | 10.5067/SLR/SLR_DATA_MONTHLYSUM_NPT_001 |
| SATNAME/YYYY/SATNAME.YYYY (yearly file) |
as described in the table below:
| Code | Meaning |
|---|---|
| SATNAME | Satellite name |
| V | version of data (a, b, c, etc.) |
| YYYY | 4-digit year |
| YY | 2-digit year |
| MM | 2-digit month |
| DD | 2-digit day |