MESSENGER: Software Interface Specification For The Mercury Laser Altimeter Calibrated, Reduced and Gridded Data Records Revision 6.01 NOTE: This is a plain text version of the document. It does not contain all images and formatting. It is highly recommended that you use the PDF version of this document (MLA_RDRSIS.PDF). Prepared by: Gregory Neumann Code 698 NASA Goddard Space Flight Center Greenbelt, MD 20771 March 16, 2017 Document Review * * This document and the archive it describes have been through PDS Peer Review and have been accepted into the PDS archive. * Gregory Neumann, MESSENGER MLA Scientist, has reviewed and approved this document. * Susan Slavney, PDS Geosciences Node Representative, has reviewed and approved this document. * Susan Ensor, MESSENGER Science Operations Center Lead, has reviewed and approved this document. CHANGE LOG DATE SECTIONS CHANGED REASON FOR CHANGE REVISION 03/01/09 Various Peer Review 4.00 11/10/09 5.4.3 Cartographic Coordinate Systems section added 5.10 12/18/09 06/06/08 1. Added Document Change History table. 2. Removed duplicate table of contents. 3. Appendices: moved "PDS_VERSION_ID" down one line. 4. DOCUMENT directory section: changed "documents are stored in PDF and HTML format" to indicate TXT format. 5. CATALOG directory: "INSTRUMENT_HOST.CAT" changed to "INSTHOST.CAT"; "INSTRUMENT.CAT" changed to "MLAINST.CAT; added PERSON.CAT 6. INDEX directory: Added MD5.TAB; removed non-existent columns from INDEX Table Contents section 1. 5.20 04/11/11 Various Revision, RDR and GDR sample labels added 5.13 06/17/11 Signature page Change Log table 1. Replace signature page with document review information. 2. Resized columns in this table, moved revision 4 entry to proper place in table. 5.14 11/11/11 All Fixed formatting. (M. Reid, JHU/APL) 5.15 04/04/12 Appendices Mission Phase name, HDEM product names, data quality flag in RDR label 5.16 06/01/12 Appendices, 6.2, 6.7 Radiometry Product Description 5.17 06/03/12 2, 7 1. Change app. doc. 2 name from "Data Management and Science Analysis Plan" to "Data Management and Archiving Plan" and update references to it. 2. 2. Replace PDS release schedule with reference to schedule in Data Management and Archiving Plan. 5.18 06/06/12 Fixed diagram Fig. 1 Formatting 5.19 06/13/12 All Added page numbers, section numbers, fixed table of contents, added missing spacecraft diagrams. 5.20 06/14/12 5.2 6.4 Fixed GDR DATA_SET_ID 5.21 06/14/12 8.4 8.5 8.6 8.10 Updated RDR altimetric data label. Updated RADR label. Added GDR label. Updated MLASCIRDR.FMT. 5.22 10/08/12 6.5 Updated section to accommodate PDS liens 10/15/12 8 Appendix Replaced labels and fmt files with revised versions 5.24 10/18/12 6.6 Added an EXTRAS and BROWSE image directories and browse images. 5.25 01/15/13 6.5, 8 Appendix Fixed formatting, editing for clarification; updated labels and format files. 5.26 01/18/13 5.1 kj: Edited to clarify orbit; mr: deleted TBD Items table. General edits. 5.27 02/08/13 6.6 Listed items in the DOCUMENT directory. 5.28 12/12/13 2, 5.2.3 Updated list of "Applicable Documents" and proper references to calibration materials 5.29 12/23/13 2, 5.1, 5.2 Formatting and corrected error relating to spacecraft orbital inclination. Ref. to calibration document. 5.30 12/01/14 8.4, 8.11 Added STARTPLS_WIDTH field to MLASCIRDR products in sample label and format files. 5.40 04/07/16 Various Updated for coordinate system, final product generation, end game, RDR and RADR format. 5.50 04/21/16 Various Updates to reflect the end of the mission and general edits. Revised labels and FMT files. 5.57 04/26/16 8.12 Restored MLASCIRDR.FMT file to indicate that the SAT_ALTITUDE is referenced to the 2440 km planetary radius. Changed reference for a document. 5.57 03/16/17 6.6, Various Added a section (6.6) about the reprocessed RDR & GDR products, the creation of a new version of the data sets, and the GSFC/MLA SPK. Multiple small edits in other sections. 6.01 Table of Contents 1 Purpose and Scope of Document 9 1.1 Purpose 9 1.2 Scope 9 2 Applicable Documents 9 3 Relationships with Other Interfaces 10 4 Roles and Responsibilities 10 5 Data Product Characteristics and Environment 10 5.1 Overview 10 5.2 Data Product Overview 12 5.2.1 Science CDR 12 5.2.2 Science RDR 12 5.2.3 Radiometric Active Data Record (RADR) 13 5.2.4 Status (STATUS) CDR 13 5.2.5 Hardware Diagnostic Lite (HAD) CDR 13 5.2.6 Topographic (TOPO) GDR 13 5.3 Data Processing 14 5.3.1 Data Processing Level 14 5.3.2 Data Product Generation 14 5.3.3 Data Flow 14 5.4 Standards Used in Generating Data Products 17 5.4.1 PDS Standards 17 5.4.2 Time Standards 17 5.4.3 Data Storage Conventions 17 5.5 Data Validation 18 6 Detailed Data Product Specifications 18 6.1 Data Product Structure and Organization 18 6.2 Data Format Description 18 6.2.1 Science CDR Table 18 6.2.2 MLA Status CDR Table 19 6.2.3 MLA Hardware Diagnostic Lite CDR Table 19 6.2.4 MLA Science RDR Table 19 6.2.5 MLA GDR Image 19 6.2.6 Radiometric Active Data Record (RADR) 19 6.3 Formats of Other Files in the MLA CDR/RDR/GDR Archive 19 6.3.1 Label and Header Descriptions 20 6.4 File Naming Conventions 22 6.5 Directory Structure and Contents for MLA CDR/RDR/GDR Data Archive Volume 23 6.6 Data Volumes 26 7 Archive Release Schedule to PDS 26 8 Appendices 27 8.1 Appendix - MLA Science CDR PDS Label 27 8.2 Appendix - MLA Status CDR PDS Label 27 8.3 Appendix - MLA Hardware Diagnostic Lite CDR PDS Label 28 8.4 Appendix - MLA Science RDR PDS Label 28 8.5 Appendix - MLA Radiometric Active Data Record (RADR) PDS Label 29 8.6 Appendix - MLA Gridded Data Record PDS Label 30 8.7 Appendix - MLA Gridded Data Record JPEG 2000 PDS Label 32 8.8 Appendix - MLA Polar DEM PDS Label 33 8.9 Appendix - Contents of MLASCICDR.FMT 35 8.10 Appendix - Contents of MLASTACDR.FMT 44 8.11 Appendix - Contents of MLAHADCDR.FMT 61 8.12 Appendix - Contents of MLASCIRDR.FMT 73 8.13 Appendix - Contents of MLARADR.FMT 77 8.14 Appendix - SPICE Kernel Files Used in MESSENGER Data Products 80 8.15 Appendix - Data Archive Terms 81 8.16 Appendix - CODMAC and NASA Data Levels 82 8.17 Appendix - Acronyms 83 8.18 Appendix - MLA Instrument Overview 84 1 Purpose and Scope of Document 1.1 Purpose This document describes the higher level data products generated from the MLA instrument telemetry. These products are formatted and organized to facilitate access to the instrument data by scientists and the public. The Committee on Data Management and Computation (CODMAC) has defined levels of data products as described in Appendix 8.13. The MLA Experiment Data Records (EDR) are the CODMAC Level 2 products, while the Calibrated Data Records (CDR), Reduced Data Records (RDR) and Radiometric Active Data Records (RADR) are higher level (calibrated, edited) products. The MLA Hardware EDR, Status EDR, and raw Science EDR are the source input to producing the Hardware and Status CDRs. The Science CDR, combined with the SPICE-format geometry and timing information derived from the spacecraft telemetry and radio tracking, is the source for the generation of the Science RDR and Gridded Data Record (GDR) products. The CDR, RDR, and GDR products are calibrated to scientific and engineering units. They provide altimetric profiles, laser pulse measurements, and instrument housekeeping for scientific and engineering purposes. Time-of-flight data are merged with the Spacecraft, Planet, Instrument, C-matrix Events (SPICE) archives. These provide instrument orientation, spacecraft orbit position and pointing, timing, planetary orientation and ephemerides to locate the Mercury Laser Altimeter (MLA) ranges in a planet-fixed, center-of-mass coordinate system. The merged data are aggregated into the CODMAC Level 4 RDR. The RDR is the primary altimeter science data product, from which resampled topographic models may be obtained. These models, and representations of these models by means of spherical harmonic expansions and other basis functions, constitute the Level 5 GDR data products. Active measurements of surface albedo and roughness may be derived from the RDR, as well as more precise models of spacecraft trajectory, planetary gravity, and libration. This document serves to provide users of the MESSENGER MLA CDR, RDR, RADR, and GDR data products with a detailed description of MLA product generation, validation, and storage. The MLA data products are deliverables to the Planetary Data System (PDS) and the scientific community that it supports. All data formats are based on the PDS standard. This document is a Data Product Software Interface Specification, or SIS. The description of the MLA archive volume is contained in section 6.5 of this document rather than in a separate Archive Volume SIS. 1.2 Scope The CDR/RDR/RADR/GDR Software Interface Specification (SIS) document is intended for general use by data analysts outside of the MESSENGER project and is intended to enable the typical science user to access the products routinely. The CDRs, RDRs, and RADRs are accessible as ASCII tables so as to be readable without regard to computer system and require no additional software for decoding. GDRs are stored as binary image arrays readable with standard image processing software. 2 Applicable Documents The MESSENGER MLA SIS is consistent with the following Documents: 1. Planetary Data System Standards Reference, February 27, 2009, Version 3.8. JPL D-7669, Part-2 2. MESSENGER Data Management and Archiving Plan, The Johns Hopkins University, APL, http://pds-geosciences.wustl.edu/missions/messenger/ 3. MESSENGER Mercury: Surface, Space Environment, Geochemistry, Ranging; A mission to Orbit and Explore the Planet Mercury, Concept Study, March 1999. Document ID number FG632/99-0479 4. Sun, X., and G. A. Neumann, Calibration of the Mercury Laser Altimeter on the MESSENGER Spacecraft, IEEE Transactions on Geoscience and Remote Sensing, Vol. 53, Issue 5, pp. 2860-2874, doi:10.1109/TGRS.2014.2366080, 2015. [SUN&NEUMANN2014] 5. MESSENGER mission overview, Sean C. Solomon, Ralph L. McNutt, Jr., Robert E. Gold, Deborah L. Domingue, Space Science Reviews, 131, 3-39, 2007 6. The Mercury Laser Altimeter Instrument for the MESSENGER Mission, John F. Cavanaugh, James C. Smith, Xiaoli Sun, Arlin E. Bartels, Luis Ramos-Izquierdo, Danny J. Krebs, Anne Marie Novo-Gradac, Jan F. McGarry, Raymond Trunzo, Anne Marie Novo-Gradac, Jamie L. Britt, Jerry Karsh, Richard B. Katz, Alan Lukemire, Richard Szymkiewicz, Daniel L. Berry, Joseph P. Swinski, Gregory A. Neumann, David E. Smith, Maria T. Zuber, and David E. Smith, Space Sciences Reviews, 131, 1-4, 10.1007/s11214-007-9273-4, 451-479, 2007. 7. Bright and dark polar deposits on Mercury: Evidence for surface volatiles, G. A. Neumann, J. F. Cavanaugh, X. Sun, E. Mazarico, D. E. Smith, M. T. Zuber, D. Mao, D. A. Paige, S. C. Solomon, C. M. Ernst, and O. S. Barnouin, Science, 339, 296-300, 2013 8. [PLR] Appendix 7 to the Discovery Program Plan; Program Level Requirement for the MESSENGER Discovery Project; June 20, 2001. 9. MESSENGER: Software Interface Specification For The Mercury Laser Altimeter Experiment Data Record, July 2015. 3 Relationships with Other Interfaces The MLA data products are stored at the MESSENGER Science Operations Center at the Johns Hopkins University Applied Physics Laboratory (JHU/APL) for rapid access during mission operations. The data products are electronically transferred to the PDS Geosciences Node according to the delivery schedule in the MESSENGER Data Management and Archiving Plan (Applicable Document 2). 4 Roles and Responsibilities The roles and responsibilities of the MLA instrument team, Applied Physics Lab (APL), Applied Coherent Technology (ACT), and the Planetary Data System (PDS), are defined in the MESSENGER Data Management and Archiving Plan (Applicable Document 2). 5 Data Product Characteristics and Environment 5.1 Overview MESSENGER stands for MErcury Surface, Space ENvironment, Geochemistry, and Ranging. It is a scientific spacecraft designed to aid in the study of the planet Mercury. It is the first mission to go to Mercury since Mariner 10 in 1975. MESSENGER's orbit about Mercury was highly elliptical, passing 200 km above the surface at its lowest point (periherm) and more than 15,000 km at its highest point (apoherm). Periherm altitude varied from 200 km to 505 km in the orbital portion of the primary mission (March 18, 2011 - March 17, 2012) and somewhat less in the extended mission (XM, March 18, 2012 - March 17, 2013) (230 to 412). During the mission endgame, spacecraft periherm altitude descended below 15 km and was raised to avoid impact by a series of propulsive Orbit Correction Maneuvers (OCM-10 to OCM-19) over the space of seven months until all propellant was exhausted and the spacecraft impacted the surface of Mercury as expected on April 30, 2015, concluding the second extended mission (XM2). The range to the southern hemisphere usually exceeded the 1800-km maximum range of the MLA instrument. The working range varied with laser energy, surface characteristics, and incidence/emission angle and was usually limited to 800 to 1200 km, depending on geometry and instrument status. See SOLOMONETAL2007 for a description of orbital ellipticity and mission design. The plane of the MESSENGER spacecraft orbit was inclined 83 degrees to Mercury's equatorial plane and the low point in the orbit was reached initially at latitude 60N. Orbit inclination varied from 82.85N to 83.96N in the primary mission and 84.04 N latitude in XM with minor oscillations driven by perturbations. Owing to solar gravitational perturbations the periherm latitude precessed over the north pole and reached latitude 60 deg. N again on the descending track during the final weeks of the mission. MESSENGER's first 12 months in orbit covered 2 Mercurian solar days. Because Mercury's rotation period (~58 Earth days) is two thirds of its revolution period around the Sun (~88 Earth days), the solar day, from sunrise to sunrise, is equal to ~176 Earth days. The first solar day of orbital operations was focused on obtaining global map products from the different instruments, and the second focused mainly on targeted science investigations. The first extended mission provided an additional two Mercurian solar days of operations focused mainly on targeted science investigations. At different times during Mercury's solar orbit, the Sun, Mercury, and MESSENGER were in different configurations, necessitating different observing strategies. The second extended mission provided an additional four Mercurian solar days of operations. MESSENGER's primary mission had a 12-hour orbit of which approximately 25-50 minutes were dedicated to MLA science, depending on Sunshade Keep-In (SKI) constraints. On April 17th and 20th , 2012, propulsive maneuvers reduced the orbital period to 8 hours. During a nominal orbit, the planet was within range for 35-50 minutes, although restrictions on pointing the spacecraft toward the Sun could limit the period of collection to less than 20 minutes. Approximately 15 minutes prior to taking science data, the MLA instrument was put into standby mode. The laser electronics and range measurement unit were powered on at the start of this mode and time was provided to allow the electronics and laser bench to warm up. Standby mode used less power than science mode because the laser was generally not firing. Hardware Diagnostic packets could be generated in Standby mode. When the planet was within 1800 km range, the MLA was put into Science mode, and the laser commenced firing within the minute. The science algorithms configured the electronics and generated Science raw telemetry packets. Hardware packets were not generated in Science mode, while Status packets continued to be output at more frequent intervals. The length of the Science mode varied during the course of Mercury's orbit about the Sun and the temperature of the instrument rose as it crossed the sunlit face of Mercury, in some cases approaching its highest working limits. For the remaining hours of the orbit MLA was in Keep Alive mode, during which time the instrument radiated heat into space and cooled down. This was a low power mode in which the analog and laser electronics were powered off and only Status packets were generated. During the extended mission phases, the orbital period was 8 hours and operations were similar with more orbits devoted to targeted observations. MLA operated nominally on each orbit where attitude permitted, subject to SKI and other operational constraints. More information on the mission phases is provided in Appendix 8 and the MISSION.CAT. The MLA was used to calculate the range between the spacecraft and Mercury's surface. The transmitter generated a brief laser pulse and the instrument measured the time required for the light to reach the surface and return. The time-of-flight measurements were used to make accurate determinations of Mercury's shape and determine its rotational dynamics. These shape and kinematics measurements, when combined with analyses of the very precisely tracked spacecraft orbit around Mercury, yield information on its internal density structure. More information on the MLA instrument is provided in the Appendix - MLA Instrument Overview. 5.2 Data Product Overview The MLA Level 3 and 4 products are grouped together into one data set, MESS-E/V/H-MLA-3/4-CDR/RDR-DATA-V1.0. Within that data set there are three CDR data products (Science CDR, Status CDR, and Hardware Diagnostic Lite CDR), a Science RDR data product, and a Radiometric Active Data Record (RADR) product. The Level 5 Gridded Data Records (GDR) are grouped into a separate data set, MESS-E/V/H-MLA-4-GDR-V1.0. See Sun and Neumann, 2013 for a description of calibration. Each MLA data product consists of two files. One contains the data itself, and is arranged in a PDS compliant table or image file. The other is a PDS label file that describes the content of the data file. GDR JPEG 2000 products have a third accompanying XML file that contains image metadata. The label file defines the start and end times of the observation, product creation time, etc. The label file may also contains a pointer to a format file that describes the different fields within the data table. During the Mercury Orbit mission phases a single CDR, RDR, or RADR data file contains the observations obtained in one orbit of the spacecraft around Mercury. Prior to the Mercury Orbit mission phases a single CDR, RDR, or RADR data file aggregates the observations such that all data within the file are taken on the same year, month, day, and hour. The CDR, RDR, RADR, and GDR data products are described as follows: 5.2.1 Science CDR The Calibrated Data Record 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. Up to 10 triggers on one of three filter channels may be associated with a given laser fire, as well as one trigger on channel 1 at a higher trigger threshold. Some or all of these triggers may be noise from sources other than the laser pulse itself. For each of the triggers, a channel identifier, leading edge time, and pulse width at the detection threshold are recorded. 5.2.2 Science RDR The time-of-flight data are 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 Mercury Laser Altimeter (MLA) ranges in a planet-fixed (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 orbit position is a joint product of the Laser Altimeter and Radio Science investigations, based primarily on radio tracking of the MESSENGER spacecraft. To facilitate analysis of the planetary rotational dynamics, extraneous (noise) returns collected within the range of a laser shot, if any, are flagged, and where appropriate, derived quantities regarding the laser pulse returns are provided. 5.2.3 Radiometric Active Data Record (RADR) The active radiometric measurement 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 radiometry is available for a subset of ground detections where sufficient link provides detections on multiple thresholds and enables a differential analysis of return signal strength. Such measurements are of particular interest in the persistently or permanently shadowed polar craters, where the very low surface and near-surface temperatures act as cold traps for volatiles. References to relevant papers in peer-reviewed journals are provided in REF.CAT, in particular the Supporting Online Information in NEUMANNETAL2013. 5.2.4 Status (STATUS) CDR The Status CDR contains the instrument status information, such as voltages, temperatures, and timing parameters. Status records are customarily output at intervals of 16 to 60 seconds. The measurements and status flags are stored in the CDR as original telemetry counts. The Status CDR also contains engineering values in the appropriate units. 5.2.5 Hardware Diagnostic Lite (HAD) CDR The HAD CDR contains diagnostic information about the instrument and background brightness information from the detector at 8 Hz resolution. It is designated as "Lite" because the "full" version of the packet, which contains more diagnostic fields, cannot be utilized during the course of the mission due to bandwidth limitations. The CDR product contains the original telemetry counts as well as the engineering values in the appropriate units. 5.2.6 Topographic (TOPO) GDR The GDR contains the binned, interpolated planetary shape (or elevation with respect to a reference spherical datum) at the appropriate sampling intervals. Coverage of the northern hemisphere reaches a density of approximately 64 pixels per degree in latitude and somewhat less in longitude, corresponding to 0.66 km at the equator, with sparse coverage obtained for several hundred kilometers south of the equator. These data are augmented with planetary occultations to produce a global Digital Elevation Model (DEM) in cylindrical equidistant coordinates that is transformed to spherical harmonic coefficients and archived at the PDS in the Radio Science volume as the SHADR product (PDS data set MESS-H-RSS/MLA-5-SDP-V1.0). A planetocentric, east-positive (right-handed) coordinate system is employed, in contrast to older planetographic coordinates using west-positive longitudes. Where the polar coverage reaches sufficient density, stereographic projections are used to interpolate data at higher resolution. The values are scaled from meters to integers and represented in a PDS compatible binary image format. 5.3 Data Processing 5.3.1 Data Processing Level The CDR/RDR/RADR/GDR Data Archive for the MLA instrument contain Level 3 and higher data products. Each product has a unique file name and conforms to the file naming convention in section 6.5. All CDR/RDR/RADR/GDR products are stored at the Applied Physics Laboratory/Science Operations Center (APL/SOC) during mission operations. Volumes are electronically transferred to the PDS Geosciences Node following the procedure in section 5.3.3. 5.3.2 Data Product Generation The MLA CDR/RDR/RADR/GDR files are produced by the MLA Science Team at the NASA Goddard Space Flight Center (GSFC). Inputs to the CDR/RDR/RADR/GDR consist of Experiment Data Records. Level 2 CODMAC data are extracted from the spacecraft telemetry and stored online at the SOC facility. Software ingests the Level 2 CODMAC data in the PDS format defined in the EDR SIS, applies calibrations, and outputs Level 2 and 3 tables (section 6.2). The CDR data products are made available to the MESSENGER Science Team for initial evaluation and validation. At the end of the evaluation and validation period, the data are organized and stored in the directory structure described in section 6.6 for transmittal to the Geosciences Node. The transmittal process is described in section 5.3.3, Data Flow. 5.3.3 Data Flow The MESSENGER SOC operates under the auspices of the MESSENGER Project Scientist to plan data acquisition, and to generate and validate data archives. The SOC supports and works with the MOC, the Science Team, instrument scientists, and the PDS. The SOC is located at the Johns Hopkins University/Applied Physics Lab (JHU/APL). The Data flow diagram in Figure 1 shows the general flow of data within the MESSENGER project as well as data flow to the PDS. The MOC handles raw data flow to and from the MESSENGER spacecraft and the SOC converts the raw telemetry into EDRs. The Science Team generates the derived products, transmitting them to the SOC for eventual delivery to the PDS Geosciences Node. SPICE kernels are delivered to the PDS Navigation and Ancillary Information (NAIF) node. Low altitude SPICE kernels that were generated by the MLA team to aid spacecraft positioning towards the end of the mission have been archived at the Geosciences node at the PDS (Volume MESSMLA_2101: DOCUMENT/NAVASSMT/SPK) as they have limited general use. The MESSENGER SOC delivers data for the MLA derived data volume to the PDS Geosciences Node in standard product packages. Each package comprises data and files organized into directory structures consistent with the volume design described in section 6.6. The electronic transfer process used to release data to PDS is described in the EDR SIS. No changes are anticipated to the delivery process, but should any arise, they are noted in an update to the SIS document and include the specific dates from which the changes take effect. The delivery of products to the PDS data archive follows the schedule in the MESSENGER Data Management and Archiving Plan (Applicable Document 2). Figure 1. MESSENGER data flow There is a PDS label file for every MLA data product. Example label files are shown in Appendices 8.1, 8.2, 8.3, and 8.4 for the Calibrated, Status, and Hardware Diagnostic Lite CDR products, as well as the Science Reduced Data Record. A sample GDR label is included in the appendices. The specific table structure for each data file is detailed in section 6.2. 5.4 Standards Used in Generating Data Products 5.4.1 PDS Standards The MLA data products are constructed according to the data object concepts developed by the PDS. By adopting the PDS format, the MLA data products are consistent in content and organization with other planetary data collections. In the PDS standard, the data file is grouped into objects with PDS labels describing the objects. The CDR and RDR data products contain 1. A table object (the primary data) contained in a fixed-length record ASCII data file. The fields in the MLASCIRDR*.TAB files are separated by commas. The fields in the MLARADR*.TAB files are separated by spaces. All tables have carriage-return+line-feed () end of line terminators. 2. A detached PDS label file. This contains a pointer to the data file as well as meta-data information and a pointer to a detailed description of the table structure. 3. A format file contained in the LABEL directory. All labels and format (.FMT) files also contain the required end-of-line terminators. MLA GDR products contain 1. An image object contained in data files in standard IMG and JPEG2000 formats. 2. A detached PDS label file, with a pointer to the data file as well as meta-data information. 3. Browse images in JPEG format are provided for some GDR products in the EXTRAS/BROWSE directory. 5.4.2 Time Standards The MET field in the MLA CDR table matches the spacecraft time in integer seconds that is transmitted to MESSENGER subsystems by the Integrated Electronics Module (IEM). This is referred to by the MESSENGER project as Mission Elapsed Time (MET). MET = 0 is August 3, 2004, at 05:59:16 UTC, which is 1000 seconds prior to the MESSENGER launch. Relativistic effects and circumstances occurring during the mission would result in MET not being a true account of seconds since launch. Following a planned spacecraft clock reset on January 8, 2013, partition numbers (1/, or 2/) were added to product labels to disambiguate MET seconds after the spacecraft clock reset (if partition number is not present, SPICE defaults to partition 1/). MET values that correspond to times prior to the clock reset fall into partition 1. Those after, into partition 2. For this reason the MESSENGER spacecraft clock coefficients file is archived at the PDS Navigation and Ancillary Information Facility (NAIF) Node (PDS data set MESS-E/V/H-SPICE-6-V1.0). This file is used in conjunction with the leap seconds kernel file to calculate the conversion between MET and UTC. 5.4.3 Data Storage Conventions The data are organized following PDS standards and stored on hard disk and in an SQL (Structured Query Language) database for rapid access during mission operations. The MESSENGER SOC transfers data to the PDS via electronic transfer and delivery methods detailed in section 5.3.3. After verification of the data transfer the PDS will provide public access to MESSENGER science data products through its online data distribution system. 5.5 Data Validation MLA data products are validated by the MLA Instrument scientist for science content and for compliance with PDS archive standards as described in the MESSENGER Data Management and Archiving Plan (Applicable Document 2). 6 Detailed Data Product Specifications 6.1 Data Product Structure and Organization The MESSENGER MLA derived data sets are archived at the PDS Geosciences Node as a data archive volume. The MLA CDR products in the data archive volume are calibrated products. The RDR and RADR products are a reduced product and were revised one or more times. The production and release of CDRs followed the release schedule in the MESSENGER Data Management and Archiving Plan (Applicable Document 2). When revisions occurred, the RDR and RADR data were replaced with updated RDRs and RADRs on the next scheduled delivery date. The GDR products were also revised one or more times. There are two MLA derived products archive volumes using PDS volume identifiers MESSMLA_2001 and MESSMLA_2101. 6.2 Data Format Description Calibrated and reduced data are stored in table format. The structure of the table is defined by an external format (.FMT) file. The MLA Science CDR or RDR is an ASCII table with all of the packet telemetry points needed to analyze the instrument data, and is only produced when the instrument is in Science Mode. It is a Level 3 product, in that units are not resampled or converted. The range data consist of multiple coarse and fine timing counts for transmitted and received pulses that must be combined with instrument configuration data. The MLA Hardware Diagnostic Lite (MLAHAD) CDR is derived from an engineering-mode packet used for calibration experiments and contains all of the background noise counter data but only a sample of the range measurement data. These packets are generated only in Standby Mode. The MLA Status CDR is a low-rate packet that contains instrument environmental parameters needed to interpret the science data, and may be generated in all modes. Gridded data consist of a map or DEM derived from the RDR products, stored as a binary image array. The dimensions, data type, and map projection information for the image are given in its detached PDS label. The files in the CATALOG directory of the data archive may provide additional useful information. 6.2.1 Science CDR Table The table consists of fixed-length records with 55 individual columns, each delimited by a comma (ASCII 44). The records are delimited with carriage-return (ASCII 13), line-feed (ASCII 10) pairs at the end of each line. The column position, length, data type, and descriptions are given in a pointer to a data structure, MLASCICDR.FMT, provided in the LABEL directory and given in the Appendix (8.6). 6.2.2 MLA Status CDR Table The table consists of fixed-length records with 116 individual columns, each delimited by a comma (ASCII 44). The column position, length, data type, and descriptions are given in a pointer to a data structure, "MLASTACDR.FMT", provided in the LABEL directory and given in the Appendix (8.7). 6.2.3 MLA Hardware Diagnostic Lite CDR Table The table consists of fixed-length records with 90 individual columns, each delimited by a comma (ASCII 44). The column position, length, data type, and descriptions are given in a pointer to a data structure, "MLAHADCDR.FMT", provided in the LABEL directory and given in the Appendix (8.8). 6.2.4 MLA Science RDR Table The table consists of fixed-length records, one or more per laser shot, having 24 individual columns. The column position, length, data type, and descriptions are given in a pointer to a data structure, "MLASCIRDR.FMT", provided in the LABEL directory and given in the Appendix ( 8.12 ). Data quality indicators applied are by manual edits, as noted in a comment appended to the detached label. 6.2.5 MLA GDR Image Geolocated, binned altimetry data are accumulated from all mission phases to create a digital elevation model of Mercury, with interpolation as necessary between individual profiles. Each DEM is a raster image composed of a set of pixels that represent finite areas, and not discrete points. Missing data (beyond a distance of 4 km from the nearest data point) are flagged with a special value. The models are provided at resolutions of 2^ n pixels per degree in cylindrical equidistant projection, and in north polar stereographic projection. The polar stereographic maps are provided as well at spacings of 250, 500, and 1000 meters where sufficient data coverage permits. The models are PDS IMG and JPEG2000 files with detached labels. 6.2.6 Radiometric Active Data Record (RADR) The table consists of fixed-length records, one per energy measurement, having 17 individual columns. The column position, length, data type and descriptions are given in a pointer to the data structure, "MLARADR.FMT", provided in the label directory and given in the Appendix. 6.3 Formats of Other Files in the MLA CDR/RDR/GDR Archive Aside from data products, the archive includes documentation, catalog and index files. Documents are provided in either ASCII or HTML, and an Adobe PDF version is also often provided. Each file is accompanied by either an internal (attached) or detached PDS label. Index files are given as ASCII tables with detached PDS labels. (See Section 6.7.2 for contents of index files.) Catalog files contain important descriptive information about the data products, MLA instrument, MESSENGER spacecraft and mission, and are provided in a keyword=value format similar to a PDS label, to be both human and software-readable. Viewable, reduced-size browse images are provided for the GDR images in the EXTRAS/BROWSE directory. 6.3.1 Label and Header Descriptions The following are the keyword definitions for the detached PDS label files accompanying the ASCII table data file. The detached PDS label file has the same name as the data file it describes, except for the extension .LBL. PDS_VERSION_ID Represents the version number of the PDS standards documents that is valid when a data product label is created. PDS3 is used for the MESSENGER data products. FILE_RECORDS Indicates the number of physical file records, including both label records and data records. RECORD_TYPE Indicates the record format of a file. RECORD_BYTES Indicates the number of bytes in a physical file record, including record terminators and separators. PRODUCT_ID Represents a permanent, unique identifier assigned to a data product by its producer. The product file name is used for a unique PRODUCT_ID. PRODUCT_VERSION_ID Identifies the version of the product, represented initially by "V1". The version number is incremented if the product needs to be regenerated as a result of a correction of the data or as a result of a change in the method used to create the product. PRODUCT_CREATION_TIME Defines the UTC system format time when a product was created. PRODUCT_TYPE Identifies whether the CDR contains science data ("DATA") or ancillary engineering data ("ANCILLARY"). STANDARD_DATA_PRODUCT_ID The MLA CDR files are identified as belonging to the same standard data product via this ID. SOFTWARE_NAME Identifies the data processing software used to convert from spacecraft telemetry into CDR products. SOFTWARE_VERSION_ID Indicates the version (development level) of the program defined in SOFTWARE_NAME. It is incremented if the program is modified during the course of the mission. INSTRUMENT_HOST_NAME The full name of the host on which an instrument is based. For MESSENGER this is the "MERCURY SURFACE, SPACE ENVIRONMENT, GEOCHEMISTRY, AND RANGING" satellite. However, since the project commonly uses the acronym for the satellite, it is simply MESSENGER. INSTRUMENT_NAME The "MERCURY LASER ALTIMETER". INSTRUMENT_ID Provides an abbreviated name or acronym that identifies an instrument. In this case "MLA". DATA_SET_ID The data_set_id for the MLA data products. There is only 1 data set id for the entire MLA CDR/RDR archive, MESS-E/V/H-MLA-3/4-CDR/RDR-DATA-V1.0. The gridded data product id is MESS-E/V/H-MLA-4-GDR-V1.0. DATA_SET_NAME The full PDS name of the data set. MISSION_PHASE_NAME Identifies the project designation of the mission phase associated with the data product. COORDINATE_SYSTEM_NAME The name of the coordinate system to which state vectors are referenced. TARGET_NAME Identifies a target. The targets for the MLA are Earth, Venus, Mercury, and Calibration. PRODUCER_ID The identifier of the organization that produced the data set. PRODUCER_FULL_NAME The full name of the person or organization that produced the data set. PRODUCER_INSTITUTION_NAME The name of the institution with which the data producers are affiliated. PRODUCT_RELEASE_DATE The data that the PDS publicly released the data set. ORBIT_NUMBER The number of the orbit during which the spacecraft acquired the source data. START_TIME Provides the UTC date and time corresponding to the MET of the first record in the table. STOP_TIME Provides the UTC date and time corresponding to the MET of the last record in the table. SPACECRAFT_CLOCK_START_COUNT The value of the spacecraft clock corresponding to the MET of the first record in the table. This value has the form "

/ where

is the clock partition number 1 or 2 and is the integer clock count (e.g., "2/67509886"). SPACECRAFT_CLOCK_STOP_COUNT The value of the spacecraft clock corresponding to the MET of the last record in the table. This value has the form "

/ where

is the clock partition number 1 or 2 and is the integer clock count (e.g., "2/67511852"). INSTRUMENT_MODE_ID The mode that the instrument was in at the time of data acquisition. ^TABLE This is a pointer to the external data file containing the table. The TABLE object is a uniform collection of rows containing ASCII values stored in columns. 6.4 File Naming Conventions The file names developed for PDS data volumes are restricted to a maximum 36 character file name and a 3 character extension name with a period separating the file and extension names. Given this restriction the general form of the MLA CDR, RDR, and RADR data product files is "MLAZZZZZZYYMMDDHHNN". All ASCII table data files will end in ".TAB" and PDS label files will end in ".LBL". The components of the base filename are described below. Note that references to time units in the filename refer to UTC time. The UTC time used in the filename corresponds to the first record in the table. Recall that the data files group observations in two different methods, depending on whether the data is gathered during the Mercury Orbit phases or prior to Mercury orbit (section 5.2). MLA : Instrument name - Mercury Laser Altimeter ZZZZZZ: Data record type: SCICDR - Science calibrated range and ancillary data SCIRDR - Science reduced data STACDR - Status calibrated data HADCDR - Hardware Diagnostic Lite calibrated data. RADR - Radiometric active data YY : The last two digits of the year in which the first data record was acquired. MM : The two digit month in which the first data record was acquired. DD : The two digit day in which the first data record was acquired. HH : The two digit hour corresponding to the first record in the data. NN : The two digit minute corresponding to the first record in the data. Each PDS label file contains a ^STRUCTURE pointer to an external file. This external file will contain the definition of the table object. Due to the large number of columns in the table, and since the structure of the table does not change, the structure is defined once in an external file in the LABEL directory and a pointer to it is in every PDS detached label file. GDR image data products are named according to resolution in pixels per degree or in kilometers per pixel. They have the form: H_ Where H : Target planet Mercury PPP : Product type: DEM - Digital Elevation Model DEC - Digital Counts RR : Resolution in pixels per degree LBL - PDS label For example, the topographic projection HDEM_16 is named as follows: H represents Mercury, DEM stands for Digital Elevation Model, and 16 would be the resolution in pixels per degree. The corresponding "counts" file, HDEC_16, has values for the number of ground returns corresponding to a particular topographic value. Image file names end in ".IMG" and are accompanied by detached PDS labels with the same name but with the extension ".LBL". Geospatially referenced JPEG-2000 files will have the extension ".JP2". The GDR data set also contains a north polar stereographic map DEM product produced from MLA data. This product has the form MSGR_DEM_MLA_NP.IMG with accompanying JP2, XML, and label files. It is named in accordance with the naming convention of corresponding DEM products produced by the USGS with MDIS data available at the PDS in the MESS-H-MDIS-5-DEM-ELEVATION-V1.0 data set. "NP" refers to "north polar." This product is accompanied by a supporting "counts" product that contains a graphical depiction of the number of observations for each pixel that were used to produce the primary product. This product nam is MSGR_DEM_MLA_NP_COUNT_V01. The product files have file extensions of: .IMG - Binary image .TAB - ASCII format table .JP2 - JPEG 2000 image product .XML - XML format metadata file associated with the JP2 product .JPG - JPEG format image browse product (found in EXTRAS/BROWSE) 6.5 Directory Structure and Contents for MLA CDR/RDR/GDR Data Archive Volume The following illustration shows the directory structure overview for the MLA CDR/RDR/GDR Data Archive Volume. This volume contains the MLA data products, supporting documentation, and any additional files required for the volume to be compliant with PDS standards. The content of the volume is expected to be updated with periodic releases according to the schedule in the MESSENGER Data Management and Archiving Plan (Applicable Document 2). Revised RDRs and GDRs (if needed) are delivered according to the same schedule. Revised RDRs and GDRs have an incremented version number in the PDS label. Directory Structure Overview | | _______________________________|______________________________________ | | | | | | | | | | | | | | | |