PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "2018-10-16 GEO:SHS Added pointer to README.TXT for the PDS4 archive" RECORD_TYPE = STREAM OBJECT = TEXT PUBLICATION_DATE = 2017-05-12 NOTE = "AAREADME.TXT describes this volume." END_OBJECT = TEXT END PLEASE NOTE: This archive has been migrated from PDS3 to PDS4. The contents and directory structure of the PDS3 archive have not changed, but PDS4 metadata in the form of XML files have been added. The file README.TXT in the root directory has more information. The file you are now reading, AAREADME.TXT, was written for the original PDS3 archive and does not have information about the PDS4 additions. ---- Original contents of AAREADME.TXT are below this line. ---- MESSENGER Mercury Laser Altimeter Calibrated (CDR), Reduced (RDR), and Gridded (GDR) Data Archive Prepared for the Geosciences Discipline Node of the Planetary Data System ======================================================================== Introduction ======================================================================== This volume contains Calibrated Data Records (CDR), Reduced Data Records (RDR), Radiometric Active Data Records (RADR), Gridded Data Records (GDR), and associated ancillary files and documentation from the MESSENGER Mercury Laser Altimeter (MLA) instrument. The Calibrated Data Record (CDR) contains the ranging time-of-flight and ancillary information as collected by the instrument in "Science" mode, as a set of eight time-ordered records per 1-s telemetry packet, for a nominal rate of 8 Hz. The values have been calibrated or converted into physical and engineering units. The Reduced Data Record (RDR) contains the time-of-flight altimetric data merged with the Spacecraft, Planet, Instrument, C-matrix and Events (SPICE) archives of instrument orientation, spacecraft orbit position and pointing, timing, planetary orientation and ephemerides to locate the MLA ranges in a planetocentric center-of-mass coordinate system as well as inertial coordinates tied to a celestial frame. One or more records are generated for each laser shot due to noise concerns. The Radiometric Active Data Record (RADR) consists of time-ordered, geolocated, 1064-nm geometric albedo at zero phase and ancillary data, derived from energy measurements inferred from pairs of laser returns via the lidar link equation. The Gridded Data Record (GDR) contains the binned, interpolated planetary shape and planetopotential topography at appropriate sampling intervals. These products are also sometimes referred to as the MLA Digital Elevation Model (DEM) products or "MLA DEMs," but they are not to be confused with the MESSENGER MDIS DEMs provided in another volume). The CDR products are generated from the EDRs, the RDRs from the CDRs, and the RADRs and GDRs from the RDRs. A complete description of these products and the design of this volume is given in the MLA CDR/RDR/GDR Software Interface Specification, "MESSENGER Software Interface Specification for the Mercury Laser Altimeter Calibrated, Reduced and Gridded Data Records." An electronic copy of this document is located on this volume in DOCUMENT/MLA_RDRSIS.PDF. A description of the processing that produced these products and how they relate to each other is given in this volume in the document "MESSENGER MLA EDR-to-CDR-to-RDR/GDR Processing" in DOCUMENT/MLA_EDR_TO_CDR_TO_RDR-GDR.PDF. This volume is intended for the use of scientists and students in the study of the geography and geochemistry of the planet Mercury. The data may be used for research and publication. ======================================================================== Volume Format ======================================================================== All science data are located in the CDR, RDR_RADR, and GDR directories. The INDEX directory contains a listing of all of the data products included on the volume. The CATALOG directory contains PDS documentation describing the mission, spacecraft, instrument, and data set. These include: MISSION.CAT MESSENGER mission description INSTHOST.CAT MESSENGER spacecraft description MLAINST.CAT MLA instrument description CDR_RDR_DS.CAT MLA calibrated and reduced data set description GDR_DS.CAT MLA gridded data set description REF.CAT MESSENGER mission reference information, including MLA references PERSON.CAT MLA personnel contact information Additional information on volume organization is given in the CDR/RDR/GDR SIS (described above), and in section the "Volume Contents" below. ======================================================================== File Formats ======================================================================== The CDR, RDR, and RADR data files on this volume are provided in ASCII table format (extension .TAB). The GDR data files are provided in binary image format (extension .IMG). Each data file is also accompanied by a detached PDS label file (extension .LBL), which is an ASCII file containing information describing the data file and data record format. Catalog files (extension .CAT) are provided in ASCII format. Document files describing the volume and the data are given in ASCII and PDF formats. Text files and detached label files contain ASCII records, with a carriage-return character (ASCII 13) and a line-feed character (ASCII 10) at the end of the record. This format allows the files to be read on all major contemporary operating systems. Note that while both label and catalog files are ASCII, some operating systems will not recognize the .LBL and .CAT extensions as ASCII types. It may be necessary to either remap these extensions as ASCII in the system or text browser, or else to open the files from within the text browser. ======================================================================== Volume Contents ======================================================================== Directory Structure and Contents for MLA CDR/RDR/RADR/GDR Data Archive Volume The following illustration shows the directory structure overview for the MLA CDR/RDR/RADR/GDR Data Archive Volume, which bears the PDS-assigned volume ID MESSMLA_2001. This volume contains the MLA CDR/RDR/RADR/GDR data products, supporting documentation, and any additional files required for the volume to be compliant with PDS standards. Directory Structure Overview | | _______________________________|______________________________________ | | | | | | | | | | | | | | | | | |