CRD Format Overview

Version V1.01

Due to recent technology changes, the existing International Laser Ranging Service (ILRS) formats for exchange of laser fullrate, sampled engineering and normal point data are in need of revision. The main technology drivers are the increased use of kilohertz firing rate lasers which make the fullrate data format cumbersome, and anticipated transponder missions, especially the Lunar Reconnaissance Orbiter (LRO), for which various field sizes are either too small or nonexistent. Rather than patching the existing format, a new flexible format encompassing the 3 data types and anticipated target types has been created.

The purpose of the Consolidated Laser Ranging Data Format (CRD) is to provide a flexible, extensible format for the ILRS fullrate, sampled engineering, and normal point data. The primary motivations for creating a new format at this time is to allow for transponder data, and to handle highrepetitionrate laser data without unnecessary redundancy. This format is based on the same features found in the ILRS Consolidated Prediction Format (CPF), including separate header and data record types assembled in a building block fashion as required for a particular target. There are 3 separate sections to the data format: 1) the header section which contains data on the such topics as station, target, and start time; 2) the configuration section containing an expanded version of data previously described by the SCI and SCH fields; and 3) the data section containing laser transmit and receive times, and other highly dynamic information. The data headers are fixed format and similar in content to those of the CPF files. The configuration and data records are free format with spaces between entries. Records can be added as needed for the specific data types and at frequencies commensurate with the data rate. For example, at a 2 kHz ranging rate, meteorological data and pointing angles are commonly read far less frequently than the ranges. Note that 1 way outbound, 1 way inbound, and 2 way ranges could all appear within one file. Also note that multiple colors could appear in one file.

Advantages of this format over the current ILRS formats are as follows:

  • Flexibility. The data files can be simple and compact for kiloHertz ranging or comprehensive for more complex data structures, as appropriate.
  • The building block structure with multiple record type allows for including and omitting certain
    records types as needed by a station or target.
  • Configuration descriptions are addressed in a more explicit, logical and extensible manner than the
    current format.
  • A single integrated format can be used for current and future data and target types.
  • Multiple color data, multiple ranging modes (transponder one and twoway ranges) and multiple configurations can be included naturally within a single data file.
  • The format can be expanded in the future as needs expand without abandoning the entire format.
  • All data types (full rate, sampled engineering, and normal point) can be managed in a single file if desired, e.g., for archival and reference purposes.
  • Extensibility to XML is provided for in the design.
  • Fields in the Configuration sections are compatible with the SLR Engineering Data File (EDF)
    format.

Data from a subset of the ILRS network sites (e.g., MLRS, created by Randy Ricklefs) are available from selected stations and accessible at the CDDIS:

ftp://cddis.gsfc.nasa.gov/pub/slr/data/npt_crd
ftp://cddis.gsfc.nasa.gov/pub/slr/data/fr_crd

and the EDC:

ftp://edc.dgfi.tum.de/pub/slr/data/npt_crd/
ftp://edc.dgfi.tum.de/pub/slr/data/fr_crd/

CRD sample code (also created by Randy Ricklefs) is available. An errata page (last updated 30-Oct-2009) has been created to annotate changes to/problems in the documentation and source code. The current status of station comversion to the CRD status is also available.

Personnel at EDC have developed a procedure to test CRD files. This capability will help SLR station staff in
checking their generated CRD files for format and content. It provides a rigorous check of the format and the content of CRD files. The software is available at:: http://129.187.165.2/typo3_crd. Users must register; EDC will then create and activate the account.

Related information: