MESSENGER Neutron Spectrometer Calibrated and Derived Data Record Software Interface Specification Version 3.9 February 9, 2016 Prepared by: David J. Lawrence Applied Physics Laboratory Jennifer G. Ward PDS Geosciences Node Washington University Document Review This document and the archive it describes have been through PDS Peer Review and have been accepted into the PDS archive. David Lawrence, MESSENGER NS Instrument 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 See PDF version of document for table. TBD Log DESCRIPTION The following changes to the data products/format files will be implemented before the first PDS delivery: 1. The reference frame for geometry keywords will be changed from Mercury-centric to target-centric. The target is defined using the TARGET_NAME keyword in the PDS label. In most cases, TARGET_NAME = MERCURY, however for data acquired during the Venus Flyby, TARGET_NAME = VENUS. In this case, the reference frame will be Venus-centric. For TARGET_NAME= CALIBRATION (Cruise Phase), the reference frame will be Mercury-centric with geometry values calculated using Mercury as the target, however these values are essentially meaningless for data interpretation purposes. This change was implemented with PDS release 5 (first release of NS CDRs). 2. A data quality flag will be added for each spectrum. In lieu of this, the NS team has added a table to CATALOG/DATASET.CAT that lists the times of the solar particle events. 3. All spectra will be corrected for deadtime, as appropriate. It has been determined that the deadtime correction for nominal solar quiet conditions is minimal and is therefore not being applied. Deadtime remains an important uncorrected effect for periods of intense solar activity. However, those periods of intense solar activity, which are listed in the data confidence note in CATALOG/DATASET.CAT, do not provide valid planetary data and are not used in the normal planetary data processing. The following changes to the data products/format files will be implemented at a future date: 4. An additional data product, Gamma Burst CDRs, will be added to the CDR dataset. Burst records will be in ASCII format with UTC time tags. These data products were added with PDS Release 7. 5. The 3-angle nadir-centric spacecraft attitude coordinates used in the GRNS SciBox and GRS CDR may be included in addition to or in place of the 9-element rotation matrix for the NS_CDR_SPECTRA CDRs. The NS Team has decided not to include this information. Table of Contents Document Review Change Log TBD Log Table of Contents 1 Purpose and Scope of Document 1.1 Purpose 1.2 Scope 2 Applicable Documents 3 Relationships with Other Interfaces 4 Roles and Responsibilities 5 Data Product Characteristics and Environment 5.1 Instrument Overview 5.2 Data Product Overview 5.3 Data Processing 5.3.1 Data Processing Level 5.3.2 Data Product Generation 5.3.3 Data Flow 5.3.4 Labeling and Identification 5.4 Standards Used in Generating Data Products 5.4.1 PDS Standards 5.4.2 Coordinate Systems 5.4.3 Data Storage Conventions 5.5 Data Validation 5.6 Software 6 Detailed Data Product Specifications 6.1 Common Elements of Calibrated and Derived Data 6.1.1 Handling Errors 6.1.2 Geometric Elements 6.1.3 PDS Label File Keywords 6.1.4 Format File Keywords 6.2 NS Spectra - NS_CDR_SPECTRA 6.2.1 Data Product Structure and Organization 6.2.2 Data Format Descriptions 6.2.3 File Naming Conventions 6.2.4 Label Description 6.3 NS Counts Data - NS_CDR_COUNTS 6.3.1 Data Product Structure and Organization 6.3.2 Data Format Descriptions 6.3.3 File Naming Conventions 6.3.4 Label Description 6.4 NS Galactic Cosmic Ray Spectra - NS_CDR_GCR_SPECTRA 6.4.1 Data Product Structure and Organization 6.4.2 Data Format Descriptions 6.4.3 File Naming Conventions 6.4.4 Label Description 6.5 NS Engineering Data - NS_CDR_ENG 6.5.1 Data Product Structure and Organization 6.5.2 Data Format Descriptions 6.5.3 File Naming Conventions 6.5.4 Label Description 6.6 NS Gamma Ray Burst - NS_CDR_GAB 6.6.1 Data Product Structure and Organization 6.6.2 Data Format Descriptions 6.6.3 File Naming Conventions 6.6.4 Label Description 6.7 NS Net Neutron Count Rates - NS_DDR_NCR 6.7.1 Data Product Structure and Organization 6.7.2 Data Format Descriptions 6.7.3 File Naming Conventions 6.7.4 Label Description 6.8 NS Neutron Composition Product - NS_DDR_NCP 6.8.1 Data Product Structure and Organization 6.8.2 Data Format Descriptions 6.8.3 File Naming Conventions 6.8.4 Label Description 6.9 Directory Structure and Contents for NS CDR/DDR Archive Volume 6.9.1 Directory Contents 6.9.2 Data Product Sizes 7 Appendices 7.1 Appendix A: SPICE Kernel Files Used in MESSENGER Data Products 7.2 Appendix B: CODMAC/NASA Definition of Processing Levels 7.3 Appendix C: NS Glossary and Acronym List 7.4 Appendix D: NS PDS Label Files 7.4.1 NS_CDR_SPECTRA 7.4.2 NS_CDR_COUNTS 7.4.3 NS_CDR_GCR_SPECTRA 7.4.4 NS_CDR_ENG 7.4.5 NS_CDR_GAB 7.4.6 NS_DDR_NCR 7.4.7 NS_DDR_NCP 7.5 Appendix E: NS PDS FMT Files 7.5.1 NS_CDR_SPECTRA.FMT 7.5.2 NS_CDR_COUNTS.FMT 7.5.3 NS_CDR_GCR_SPECTRA.FMT 7.5.4 NS_CDR_ENG.FMT 7.5.5 NS_CDR_GAB.FMT 7.5.6 NS_DDR_NCR.FMT 1 Purpose and Scope of Document 1.1 Purpose This document provides users of the MESSENGER Neutron Spectrometer (NS) data products with a detailed description of the NS and Calibrated and Derived Data Record (CDR/DDR) generation, validation, and storage. Please note that the Gamma Ray and Neutron Spectrometer instruments are generally referred to as the GRNS instrument. However, they are two separate sensors, each with its own Event Processing Unit (EPU), and the data products are described within the specific Software Interface Specification (SIS) of each sensor. 1.2 Scope The goal of this document is to provide thorough and complete information, so that Planetary Data System (PDS) users can read and understand the data product long after the completion of the MESSENGER mission. As such, this document provides a common reference for scientists, data analysts, software engineers, and researchers to access and understand the MESSENGER NS CDR and DDR PDS archived data. This document describes the calibrated and derived data products for the MESSENGER NS. These data products correspond to National Research Council Committee on Data Management and Computation (CODMAC) levels 3 and 4, respectively. These data levels are described more fully in Appendix B: CODMAC/NASA Definition of Processing Levels, Section 7.2. This document has been updated for version 2 of the CDR and DDR data sets (MESS-E/V/H-GRNS-3-NS-CDR-V2.0 and MESS-E/V/H-GRNS-4-NS-DDR-V2.0). 2 Applicable Documents The MESSENGER NS CDR/DDR SIS is responsive to the following documents: * Planetary Data System Archive Preparation Guide, NASA/JPL, August 29, 2006, Version 1.1, JPL D-31224. * Planetary Data System Standards Reference, February 27, 2009, Version 3.8. JPL D-7669, Part-2. * MESSENGER Instrument Neutron Spectrometer (NS) Flight Software Specification, JHU/APL 7386-9042, a, October 17, 2006. * MESSENGER EDR Software Interface Specification for the Neutron Spectrometer. * MESSENGER Data Management and Archiving Plan. The Johns Hopkins University, APL. Document ID number 7384-9019. * MESSENGER Project Archive Generation, Validation, and Distribution Plan. * MESSENGER MErcury: Surface, Space ENvironment, GEochemistry, and Ranging; A mission to Orbit and Explore the Planet Mercury, Concept Study, March 1999. Document ID number FG632/ 99-0479. * [PLR] Appendix 7 to the Discovery Program Plan; Program Level Requirement for the MESSENGER Discovery project, June 20, 2001. * The MESSENGER Gamma-Ray and Neutron Spectrometer, Space Science Reviews 131, 339-391, 2007. * Evidence for Water Ice Near Mercury's North Pole from MESSENGER Neutron Spectrometer Measurements, Science 339, 292-296, 2013. 3 Relationships with Other Interfaces The NS CDR and DDR data products are dependent on the NS Experiment Data Record (EDR) data products. Changes to the EDR product require revisions to the associated CDR/DDR products. The NS CDR/DDR data products are also dependent on valid Spacecraft, Planet, Instrument, C-matrix Events (SPICE) Kernel generation for timing and spatial information (see Appendix A, Section 7.1). Changes or revisions to the SPICE Kernel generally result in revisions to the NS CDR/DDR products. Changes to data processing programs that convert EDR data to CDR/DDR data may also result in revised CDR/DDR data products. 4 Roles and Responsibilities The roles and responsibilities of the instrument teams, Applied Physics Laboratory (APL), Applied Coherent Technology Corp. (ACT), and the PDS are defined in the MESSENGER Data Management and Archiving Plan. 5 Data Product Characteristics and Environment 5.1 Instrument Overview The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission launched in August 2004 and used flybys of Earth, Venus, and Mercury to achieve an orbit insertion around Mercury in March 2011. MESSENGER completed its Primary Mission in March 2012, operated for an additional year in its First Extended Mission which was completed in March 2013, followed by an additional two years of orbital operations in its Second Extended mission which completed as planned with the impact of the MESSENGER spacecraft on the surface of Mercury on April 30, 2015. Observations from orbit are designed to answer questions about the nature and composition of Mercury's crust, tectonic history, structure of the atmosphere/magnetosphere, and the nature of polar deposits. A year of data analysis and distribution followed the end of operations. (See the "MESSENGER Data Management and Archiving Plan" for further details.) The Neutron Spectrometer (NS) is one of the instruments onboard the MESSENGER spacecraft. It is designed to observe the neutrons emitted from Mercury's surface in the thermal, epithermal, and fast energy ranges, from ~ 0.01 eV to 7 MeV, that are produced by nuclear reactions by the cosmic ray background (CRB). The NS is designed to separately measure thermal and epithermal neutrons using the Doppler filter technique. With this technique, an enhancement of thermal neutrons is measured when the spacecraft velocity vector is in line with the sensor normal vector, while a relative decrease in thermal neutrons is measured when the spacecraft velocity vector is anti-parallel to the sensor normal. No Doppler effect occurs when the spacecraft velocity vector is perpendicular to the sensor normal vector. Elements that can be most readily identified by the NS include those that strongly moderate and absorb neutrons (hydrogen and rare earths). The approximate average element atomic mass can also be estimated. The MESSENGER NS consists of a sandwich of three scintillators that are optically decoupled from each other. The first and third scintillators are lithium (6Li)-glass scintillators (LiG), which respond to a combination of thermal and epithermal neutrons that span the range between 0 eV and about 1 keV. (Thermal neutrons correspond to 0 to ~ 0.025 eV and epithermal neutrons correspond to ~ 0.025 eV up to ~ several keV.) The middle scintillator is a borated plastic (BP) scintillator that responds only to epithermal and fast neutrons, since it is surrounded by thermal neutron absorbers (LiG on each end and wrapped with a sheet of gadolinium). When a neutron interacts with one of these scintillators, a charge is generated in its electronics. The charge is converted into one of 64 LiG channels or 64 BP channels, which are correlated to the energy deposited in the scintillators. Over a commanded integration time period the distribution of events (neutron interactions) as a function of equivalent-electron energy (channel number) is recorded. The result is a histogram of the number of events in each channel accumulated over the integration period, which is designated as a singles prompt neutron spectrum. Three such spectra are produced, one by each lithium-glass (LiG) scintillator and one by the borated plastic (BP) scintillator. These spectra are called singles spectra because only events are recorded in each spectrum that are not time-coincident with events in the other two scintillators, and they are called prompt because only events are recorded that occur instantaneously (within much less than a microsecond) after the first interaction of a neutron in the scintillator. Time-correlated events in the BP scintillator provide a measure of the neutron energies of the flux of fast neutrons (0.7 MeV < E < 7 MeV). These events are defined by a time-correlated pair of pulses in the BP scintillator. The first pulse corresponds to a neutron that loses all of its energy (above detection threshold and thermal neutron energies) in the BP scintillator, and the second pulse corresponds to the energy released by the 10B(n,a)7Li reaction after the neutron has slowed down to thermal energies and has been absorbed in the scintillator. The signature of the time-correlated events includes the pulse height (measure of energy) of the first event (called the prompt energy, Ep), the pulse height of the second event that corresponds to the Q-value of the 10B (n,a)7Li reaction (called the capture energy, Ec), and the time between first and second events (or Time To Second Pulse, TTSP). When a fast neutron interacts with the BP scintillator, a charge is generated corresponding to Ep. The charge is converted to channel number, which correlates to neutron energy. A similar signal is generated for the capture pulse, Ec. Over a commanded integration time period the distribution of Ep events as a function of energy (channel number) is recorded. The result is a histogram of the number of events in each channel accumulated over the integration period for TTSP values that fall between 0.3 microseconds and 5.4 microseconds and with Ec values that fall within a commanded range of values defined as the capture window. The resulting histogram is designated as the time-correlated early spectrum. A time-correlated late spectrum is also accumulated, for events whose second pulse occurs substantially later than expected, for TTSP values between 20 and 25 microseconds as a measure of spectrum background. The early and late prompt spectra each have 256 channels. 5.2 Data Product Overview There are five NS CDR standard data products: Spectra (NS_CDR_SPECTRA), Counts (NS_CDR_COUNTS), Galactic Cosmic Ray (NS_CDR_GCR_SPECTRA), Engineering (NS_CDR_ENG), and Gamma Ray Burst (NS_CDR_GAB). Each CDR contains all the data of a given type recorded for a given day of Earth year. The following operations are applied to the EDRs to arrive at calibrated spectra (CDRs): * Normalization of total counts to the accumulation time, so that the units are in counts per second. * Corrections (if needed) for gain variations in the spectra data. * Corrections (if needed) for GCR variations in the spectra and counting rates. * Corrections for deadtime (if needed) in the spectra and counting rates. All of these corrections are reversible such that the EDR and CDR datasets can be derived from each other. See messns_processing.pdf located in the CALIB directory for additional information. There is one NS DDR standard data product (Neutron Count Rate, NS_DDR_NCR) and one NS DDR special data product (Neutron Composition, NS_DDR_NCP). The NCR data products are derived data consisting of net (background subtracted) neutron count rates from each of the three NS sensors, namely the two lithium glass (LG) sensors and the epithermal neutron singles data from the borated plastic (BP) sensor. Net fast neutron data do not need to be provided in the NCR dataset as those values can be easily derived from the CDR data using time-corrected (TC) count rates and spectra. Each DDR NCR data file contains all the data of a given type recorded for a given day of Earth year. The NCP data product contains latitude-binned relative neutron count rates taken during the primary MESSENGER mission from 26 March 2011 to 25 February 2012. Specifically, these data are the exact data points given in Figure 2 and Figure 3A from Lawrence et al., Science, 339, 292-296, 2013. The delivered values include measured and simulated data for fast and epithermal neutron data within 2 degree wide latitude bins; the latitude values are the midpoint values within each bin and the data are the average values within each latitude bin. The simulated data include two cases: one case assumes there is no hydrogen in Mercury's north polar radar bright regions; the other case assumes that the north polar radar bright regions contain 100 wt. percent H2O. Details of how the DDR data are derived are given in the document messns_processing.pdf located in the CALIB directory. Table 5.1 is an overview of the CDR and DDR data products. Data Product Product Description NS_CDR_SPECTRA (section 6.2) * Detached PDS label file (*.lbl). * Binary table (*.dat) - LG1 singles, LG2 singles, BP singles, Time Correlated (TC) early, TC late (fast neutron spectra = TC early - TC late), along with associated timing, spatial, and engineering data. NS_CDR_COUNTS (section 6.3) * Detached PDS label file (*.lbl). * Binary table (*.dat) - NS counting rate data for 17 different monitored counting rates, along with associated timing, spatial, and engineering data. NS_CDR_GCR_SPECTRA (section 6.4) * Detached PDS label file (*.lbl). * Binary table (*.dat) - Spectra from LG1 and LG2 when a coincidence condition is detected in both LG sensors and the BP sensor, along with associated timing, spatial, and engineering data. NS_CDR_ENG (section 6.5) * Detached PDS label file (*.lbl). * ASCII table (*.tab) - NS instrumental engineering data. NS_CDR_GAB (section 6.6) * Detached PDS label file (*.lbl). * ASCII table (*.tab) - Contains the values from the NS Gamma Ray Burst EDR in ASCII format. Data is time sensitive, so rendering it in ASCII format helps real-time coordination with ground-based sensors. NS_DDR_NCR (section 6.7) * Detached PDS label file (*.lbl). * ASCII table (*.tab) - Net neutron count rates, along with associated timing, spatial, and engineering data. NS_DDR_NCP (section 6.8) * Detached PDS label file (ns_ddr_ncp.lbl). * ASCII table (ns_ddr_ncp.tab) - Fast and epithermal count rates and one-sigma uncertainties as a function of latitude, along with simulated count rates for the cases of no hydrogen and for a thick layer of 100 wt. percent water ice in all radar bright regions. Latitude values are the midpoint values for 2 degree wide latitude bins; the data are the average values within each latitude bin. Table 5.1. Data Product Overview With the exception of the DDR NCP, each CDR and DDR consists of three files. One file contains the data itself, arranged in binary (*.DAT) or ASCII (*.TAB) table format (e.g., NS_CDR_SPE2008003ZZZ.DAT, NS_CDR_ENG2008010ZZZ.TAB, etc.). Another file is a label that describes the content of the data file (e.g., NS_CDR_SPE2008003ZZZ.LBL, NS_CDR_ENG2008010ZZZ.LBL, etc.). The label file defines the start time and end time of the observation, product creation time, etc. It does not describe the structure of the table file itself. Instead, the PDS label file contains a reference pointer to a separate format file (e.g., NS_CDR_SPECTRA.FMT, NS_CDR_ENG.FMT, etc.). The format file describes the structure of the table and each of the different fields within the table. This format file resides in the top level of the archive volume LABEL directory, because it applies to the structure of all the associated table files. The DDR NCP does not contain an associated format file; instead, the table structure is described in the label file. 5.3 Data Processing 5.3.1 Data Processing Level The CDR and DDR use the Committee on Data Management and Computation (CODMAC) data level numbering system to describe the processing level of the NS data products. NS CDR products are considered a CODMAC "Level 3" (Calibrated) or NASA "Level 1A," which are edited data that are still in units produced by the instrument, but have been transformed (e.g. calibrated, rearranged) in a reversible manner and packaged with needed ancillary and auxiliary data (e.g. temperatures with calibration equations applied). NS DDR products are considered a CODMAC "Level 4" (Resampled) or NASA "Level 1B," which are irreversibly transformed (e.g. resampled, remapped, calibrated) values of the instrument measurements (e.g. radiances, magnetic field strength). For a more detailed description, see Appendix B: CODMAC/NASA Definition of Processing Levels, Section 7.2. 5.3.2 Data Product Generation The NS CDR/DDR files were produced by APL and provided to the MESSENGER Science Operations Center (SOC), operated jointly by APL and ACT. ACT was responsible for converting the data to the proper PDS labeled format. See messns_processing.pdf in the CALIB directory for information on how the EDRs are converted to CDRs and DDRs. The CDR/DDR data products were made available to the MESSENGER Science Team for initial evaluation and validation. At the end of the evaluation and validation period, the data were organized and stored on the best-determined media and made available to the PDS for distribution to the science community. These products are used for engineering support, direct science analysis, and construction of other science products. 5.3.3 Data Flow The MESSENGER SOC generated and validated data archives under the auspices of the MESSENGER Project Scientist. The SOC supported and worked with the Mission Operations Center (MOC), the Science Team, instrument scientists, and the PDS. A primary data server residing at the SOC, located at APL, served as the data storage facility for all MESSENGER instruments during the MESSENGER mission. Inputs to the SOC consisted of telemetry in the form of CCSDS packets. Files were received from the SOC and delivered to the SOC via ftp (See Figure 1). In the case of the NS CDR/DDR data products, APL read NS EDR data from the SOC, transformed the data into valid CDR/DDR data products, and returned the data to the SOC for storage and distribution. The MESSENGER SOC delivered data for the NS CDR/DDR archive 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 6.9. The following describes the electronic transfer process used in releasing data to PDS. In preparation for delivery the directory structure was compressed into a single 'zip archive' file for transmittal to the PDS node. The zip archive preserves the directory structure internally so that it can be recreated after electronic delivery to the PDS node. The 'zip archive' file was transmitted to the PDS node via FTP to an account set up by the receiving node. Also transmitted was a checksum file created using the MD5 algorithm. This provided an independent method of verifying the integrity of the zip file after it was sent. Within days of transmittal the PDS node acknowledged receipt of the archive and checksum file. If acknowledgement was not received, or if problems were reported, the MESSENGER SOC immediately took corrective action. After transmittal the PDS node uncompressed the zip archive file and checked for data integrity using the checksum file. The node then performed any additional verification and validation of the data provided and reported any discrepancies or problems to the MESSENGER SOC. After inspection was completed to the satisfaction of the PDS node, the node issued to the MESSENGER SOC acknowledgement of successful receipt of the data. Following receipt of a data delivery the PDS node organized the data into a PDS archive volume structure within its online data system. Newly delivered data are made available publicly from PDS once accompanying labels and other documentation are validated. Figure 1. MESSENGER Data Flow See PDF version of document for figure. 5.3.4 Labeling and Identification There is a corresponding detached PDS label file for each NS CDR/DDR data file. Detached means that the label file is separate from the data file, as opposed to being in the header portion of the data file. See sections 7.4 and 7.5 for sample PDS label and format files and section 6 for a complete description of the included keywords. The data set ID assigned by PDS to the NS CDR data set is "MESS-E/V/H-GRNS-3-NS-CDR-V2.0." The data set ID assigned by PDS to the NS DDR data set is "MESS-E/V/H-GRNS-4-NS-DDR-V2.0." 5.4 Standards Used in Generating Data Products 5.4.1 PDS Standards The NS CDR/DDR data products comply with Planetary Data System standards for file formats and labels as specified in the PDS Standards Reference. Each NS CDR/DDR data product includes the following: * Data File - A binary or ASCII table object containing the data. * Detached Label File - A high-level description of the parameters that correspond to the table object. * Format File - A detached file located in the LABEL directory which describes the structure of the table file. There is 1 format file for each of the 5 CDR standard data products and the DDR NCR data product. The DDR NCP does not have an associated format file. 5.4.2 Coordinate Systems There are two general coordinate systems in use for the MESSENGER project: * The celestial reference system used for target and spacecraft position and velocity vectors and camera pointing. * The planetary coordinate system for geometry vectors and target location. The celestial coordinate system is J2000 (Mean of Earth equator and equinox of J2000). The planetary coordinate system is planetocentric. For planetary orbital and flyby data, the NS-specific data also have two additional coordinate systems for expressing spacecraft velocity and attitude data: the nadir fixed coordinate system and the spacecraft fixed coordinate system. The nadir fixed coordinate system is defined as follows: * The z-axis is defined as the vector from the spacecraft center to the flyby or orbiting planet center. * The nadir fixed y-axis is defined as the cross product of the nadir z-axis and the spacecraft velocity vector (where both are expressed in the J2000 coordinate system). * The nadir fixed x-axis is defined as the cross product of the nadir fixed y-axis with the nadir fixed z-axis. The spacecraft fixed coordinate system is defined as follows: * The spacecraft fixed x-axis is the vector normal to the NS LG1 sensor and is parallel to the spacecraft solar panel booms. * The spacecraft fixed y-axis is in the direction from the spacecraft down the magnetometer boom. * The spacecraft fixed z-axis is the viewing direction from the instrument * deck. The list below describes the computational assumptions for the geometric and viewing data provided in the PDS label: * The beginning time of observation is used for the geometric element computations. * Label parameters reflect observed, not true, geometry. Therefore, light-time and stellar aberration corrections are used as appropriate. * The inertial reference frame is J2000 (also called EME2000). * Latitudes and longitudes are planetocentric. * The "sub-point" of a body on a target is defined by the surface intercept of the body-to-target-center vector. This is not the closest point on the body to the observer. * Distances are in km, speeds in km/sec, angles in degrees, angular rates in degrees/sec, unless otherwise noted. * Angle ranges are 0 to 360 degrees for azimuths and local hour angle. Longitudes range from 0 to 360 degrees (positive to the East). Latitudes range from -90 to 90 degrees. * SPICE kernel files are used in the geometric parameters (See Appendix A, Section 7.1). 5.4.3 Data Storage Conventions The data are organized following PDS standards and stored on hard disk and an SQL (Structured Query Language) relational database for rapid access during mission operations. The MESSENGER SOC transfers data to PDS via electronic transfer and delivery methods as detailed in section 5.3.3. After verification of the data transfer PDS provides public access to MESSENGER science data products through its online data distribution system. 5.5 Data Validation The NS CDR/DDR data products were validated by the NS Instrument Scientist for science content and for compliance with PDS archive standards [Applicable Document: MESSENGER Data Management and Archiving Plan]. The NS CDR/DDR data products and documentation have been approved by a peer review committee according to PDS policy. 5.6 Software No NS-specific software is required to read these data products. As PDS-compliant binary and ASCII tables, they can be read using the PDS-supplied program NASAView and other software designed to read PDS data. NASAView is available at no charge from the PDS web site http://pds.nasa.gov. The information in the PDS labels includes complete software-readable descriptions of data file formats, so that users may write custom software to read the products if desired. 6 Detailed Data Product Specifications 6.1 Common Elements of Calibrated and Derived Data 6.1.1 Handling Errors Even with data validation procedures applied to the archive volume, it is inevitable that errors are introduced. A plan is required to handle errors discovered in data volumes that have already been produced. As errors were discovered, they were reported to the NS data processing facility. An errata report file (errata.txt) was maintained to track and document all discovered errors, including any CDRs/DDRs that were revised during the course of the mission. Revised CDRs/DDRs or CDRs/DDRs that were missing from a previous PDS delivery were provided at the next scheduled PDS delivery or at the final PDS delivery as needed. The keywords PRODUCT_VERSION_ID and PRODUCT_CREATION_TIME were updated in the PDS labels of corrected files. 6.1.2 Geometric Elements The timing and spatial information that is packaged with the NS CDR/DDR data products are the timing and spatial values derived from the appropriate SPICE kernels collected for each day of the mission. SPICE is an acronym for Spacecraft, Planet, Instrument, C-matrix, and Event kernels. SPICE kernels are provided by the Navigational Ancillary Information Facility (NAIF) at the Jet Propulsion Laboratory, and are the standard for all timing and spatial data transformations. See Appendix A, Section 7.1 for more information. 6.1.3 PDS Label File Keywords Each NS CDR/DDR table is accompanied by a PDS label. See Appendix D, Section 7.4 for sample PDS label files. Below are the keyword definitions for the detached PDS label file, in alphabetical order: BYTES Indicates the number of bytes allocated for a particular data representation. COLUMNS Identifies the number of columns (fields) in the table. The NS_CDR_SPECTRA, NS_CDR_COUNTS, NS_CDR_GCR_SPECTRA, NS_CDR_GAB, NS_CDR_ENG, NS_DDR_NCR, and NS_DDR_NCP data products have 26, 25, 10, 11, 98, 29, and 13 columns, respectively. DATA_SET_ID The DATA_SET_ID element is a unique alphanumeric identifier for a data set or a data product. The DATA_SET_ID value for a given data set or product is constructed according to flight project naming conventions. The DATA_SET_IDs for the NS CDRs and DDRs are MESS-E/V/H-GRNS-3-NS-CDR-V2.0 and MESS-E/V/H-GRNS-4-NS-DDR-V2.0, respectively. DESCRIPTION Specifies a description of the table object. Each data product (NS_CDR_SPECTRA, NS_CDR_COUNTS, NS_CDR_GCR_SPECTRA, NS_CDR_GAB, NS_CDR_ENG, NS_DDR_NCR, NS_DDR_NCP) has a unique description. FILE_RECORDS The FILE_RECORDS element indicates the number of physical file records in the detached data file. ^HEADER Pointer to the external data file that contains the header object. HEADER_TYPE Identifies a specific type of header data structure. HEADER_TYPE = TEXT for the DDR NCP data products. INSTRUMENT_HOST_NAME The full name of the host on which the instrument is based: MESSENGER. INSTRUMENT_ID Unique ID associated with the instrument: NS. INSTRUMENT_NAME Full, unabbreviated name of the instrument: NEUTRON SPECTROMETER. INTERCHANGE_FORMAT Specifies the file format. NS_CDR_SPECTRA, NS_CDR_COUNTS, and NS_CDR_GCR_SPECTRA data products are in BINARY format. The NS_CDR_ENG, NS_CDR_GAB, NS_DDR_NCR, and NS_DDR_NCP data products are in ASCII format. MISSION_PHASE_NAME Provides the commonly used identifier of a mission phase. There are 19 possible phase names for MESSENGER: LAUNCH, EARTH CRUISE, EARTH FLYBY, VENUS 1 CRUISE, VENUS 1 FLYBY, VENUS 2 CRUISE, VENUS 2 FLYBY, MERCURY 1 CRUISE, MERCURY 1 FLYBY, MERCURY 2 CRUISE, MERCURY 2 FLYBY, MERCURY 3 CRUISE, MERCURY 3 FLYBY, MERCURY 4 CRUISE, MERCURY ORBIT, MERCURY ORBIT YEAR 2, MERCURY ORBIT YEAR 3, MERCURY ORBIT YEAR 4, and MERCURY ORBIT YEAR 5. OBJECT=HEADER Specifies the header portion of the DDR NCP table. The header references information and column headings to improve usability. The header object contains its own elements which are defined alphabetically in this section. NOTE: The end of the object definition is always marked with an END_OBJECT line. OBJECT=TABLE Specifies that the CDR/DDR is a PDS TABLE object. This object contains its own elements which are defined alphabetically in this section. NOTE: The end of the object definition is always marked with an END_OBJECT line. PDS_VERSION_ID Represents the version number of the PDS standards document that is valid when a data product label is created. PDS3 is used for the MESSENGER data products. PRODUCT_CREATION_TIME Stores the time that the data product was created, in UTC time. PRODUCT_ID The PRODUCT_ID data element represents a permanent, unique identifier assigned to a data product by its producer. For the NS_CDR_SPECTRA, NS_CDR_COUNTS, and NS_CDR_GCR_SPECTRA binary standard data products, the product_id is the file name with ".DAT" replaced by "_DAT." For the NS_CDR_ENG, NS_CDR_GAB, and NS_DDR_NCR ASCII standard data products, the product_id is the file name with ".TAB" replaced by "_TAB." For the NS_DDR_NCP special data product, the product_id is NS_DDR_NCP_TAB. Note: In the PDS, the value assigned to PRODUCT_ID must be unique within its data set. PRODUCT_TYPE Data products are identified as a CDR (Calibration Data Record) or DDR (Derived Data Record). PRODUCT_VERSION_ID Version number of an individual product within a data set. RECORDS Identifies the number of physical records in a file or other data object. RECORD_BYTES This element indicates the number of bytes in a physical file record, including record terminators and separators. RECORD_TYPE The RECORD_TYPE element indicates the record format of a file. The FIXED_LENGTH value is used for the table object used in the MESSENGER NS CDR/DDR data products. ROW_BYTES Specifies the number of bytes for each row in the table. ROWS Number of rows in the table. SOFTWARE_NAME Identifies the name of the software system that created the data products, NS_CDR_GEN or NS_DDR_GEN. SOFTWARE_VERSION_ID Version number of the program or program library used by the instrument to collect observations. SPACECRAFT_CLOCK_START_COUNT Clock count of the spacecraft computer at the start of the observation. SPACECRAFT_CLOCK_STOP_COUNT Clock count of the spacecraft computer at the end of the observation. STANDARD_DATA_PRODUCT_ID Used to link a NS file to one of the 7 types of standard data products defined in the NS CDR/DDR SIS: NS_CDR_SPECTRA, NS_CDR_COUNTS, NS_CDR_GCR_SPECTRA, NS_CDR_GAB, NS_CDR_ENG, NS_DDR_NCR, and NS_DDR_NCP. START_TIME Start time in UTC of the observation. STOP_TIME Time in UTC when the instrument stopped collecting measurements. ^STRUCTURE Pointer to the external file that provides the structure definition for the table object. For the NS_CDR_SPECTRA, NS_CDR_COUNTS, NS_CDR_GCR_SPECTRA, NS_CDR_GAB, NS_CDR_ENG, and NS_DDR_NCR standard data products, the external files are named NS_CDR_SPECTRA.FMT, NS_CDR_COUNTS.FMT, NS_CDR_GCR_SPECTRA.FMT, NS_CDR_GAB.FMT, NS_CDR_ENG.FMT, and NS_DDR_NCR.FMT, respectively. TARGET_NAME The target of the observation. The TARGET_NAME defines the reference frame for the geometry keywords listed in the data product tables. For TARGET_NAME = CALIBRATION, the reference frame is Mercury-centric, however these values are essentially meaningless for data interpretation purposes. ^TABLE Pointer to the external data file that contains the table object. 6.1.4 Format File Keywords With the exception of the DDR NCP, each NS CDR/DDR PDS label contains a pointer to the column format file. This file describes the structure of the NS binary or ASCII table that includes column name, byte size, data type, applicable units, and a description of the value assigned to the column. See Appendix E, Section 7.5 for the column format files. The following describes the keywords used in the format file, in alphabetical order: BYTES Specifies the total number of bytes allocated for this particular column element. COLUMN_NUMBER Identifies the location of the column within the larger table data object. For tables consisting of rows (I= 1, N) and columns (j = 1, M), the column_number is the j-th index of any row. DATA_TYPE Specifies the internal representation and/or mathematical properties of the value being stored in this column. DESCRIPTION Brief description of the value assigned to the column, including units where applicable. ITEMS Defines the number of multiple, identical occurrences of a single data item. ITEM_BYTES Represents the size of each individual item within the column field. NAME Indicates a literal value representing the common term used to identify an element or object. OBJECT=COLUMN Identifies the object as a column field within a table. START_BYTE Identifies the location of the first byte of the particular column, counting from 1. UNIT Unit of measurement in which the value is expressed. 6.2 NS Spectra - NS_CDR_SPECTRA 6.2.1 Data Product Structure and Organization The NS_CDR_SPECTRA are calibrated neutron spectra that have the timing, spatial and engineering readings taken at the beginning of the associated spectral collection period. Each NS_CDR_SPECTRA data product is organized as a binary data file containing calibrated spectra and associated data collected over a 24 hour time period, with a detached ASCII text PDS label file. The files are grouped by month (MM) within the DATA directory (see figure 2). Table 6.1 lists the values that make up the NS_CDR_SPECTRA files. Table 6.1. Data values for the NS_CDR_SPECTRA data product. See PDF version of document for table. 6.2.2 Data Format Descriptions The data format for the NS_CDR_SPECTRA is a 26-column binary table. Columns vary in width from 4 to 1024 bytes. Column structure and start byte are described in Appendix E, Section 7.5.1. The number of rows in a data table depends on the number of collection intervals during the time frame of the data file, i.e. one Earth Day. 6.2.3 File Naming Conventions The general form of the NS_CDR_SPECTRA file name is: "NS_CDR_ZZZYYYYDDDWWW.XXX", where NS instrument identifier: represents the NS instrument CDR data product identifier: CDR ZZZ data product name SPE - NS CDR Spectra with associated engineering, timing and spatial data. YYYY four-digit year corresponding to the start-time of the first record in the NS_CDR_SPECTRA data file. DDD three-digit day of the year corresponding to the start time of the first record in the NS_CDR_SPECTRA data file. WWW reserved character string to use during the course of the mission as necessary to identify "special" data products. Nominal data products are identified by ZZZ. .XXX the file extension (.DAT). 6.2.4 Label Description The NS_CDR_SPECTRA data product has detached PDS labels stored as ASCII text. A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification and for data object definitions. The label also contains descriptive information needed to interpret or process the data objects in the file. The detached label file has the same name as the data file it describes, except that it has the extension LBL instead of DAT. PDS labels are written in Object Description Language (ODL). PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects: ^object = location where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the name of the file that contains the data object. 6.3 NS Counts Data - NS_CDR_COUNTS 6.3.1 Data Product Structure and Organization The NS_CDR_COUNTS files contain NS counter data that have the timing, spatial and engineering readings taken at the beginning of the associated spectral collection period. Each NS_CDR_COUNTS data product is organized as a binary data file containing counting rates and associated data collected over a 24 hour time period, with a detached ASCII text PDS label file. The files are grouped by month (MM) within the DATA directory (see figure 2). Table 6.2 lists the values that make up the NS_CDR_COUNTS files. Table 6.2. Data values for the NS_CDR_COUNTS data product. See PDF version of document for table. 6.3.2 Data Format Descriptions The data format for the NS_CDR_COUNTS files is a 25-column binary table. Columns vary in width from 4 to 17 bytes. Column structure and start byte are described in Appendix E, Section 7.5.2. The number of rows in a data table depends on the number of collection intervals during the time frame of the data file, i.e. one Earth Day. 6.3.3 File Naming Conventions The general form of the NS_CDR_COUNTS file name is: "NS_CDR_ZZZYYYYDDDWWW.XXX", where NS instrument identifier: represents the NS instrument. CDR data product identifier: CDR ZZZ data product name CTS - NS CDR Counts with associated engineering, timing, and spatial data. YYYY four-digit year corresponding to the start-time of the first record in the NS_CDR_COUNTS data file. DDD three-digit day of the year corresponding to the start time of the first record in the NS_CDR_COUNTS data file. WWW reserved character string to use during the course of the mission as necessary to identify "special" data products. Nominal data products are identified by ZZZ. .XXX the file extension (.DAT). 6.3.4 Label Description The NS_CDR_COUNTS data product has detached PDS labels stored as ASCII text. A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification and for data object definitions. The label also contains descriptive information needed to interpret or process the data objects in the file. The detached label file has the same name as the data file it describes, except that it has the extension LBL instead of DAT. PDS labels are written in Object Description Language (ODL). PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects: ^object = location where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the name of the file that contains the data object. 6.4 NS Galactic Cosmic Ray Spectra - NS_CDR_GCR_SPECTRA 6.4.1 Data Product Structure and Organization The NS_CDR_GCR_SPECTRA are LG1 and LG2 64-channel spectra data taken when a coincidence condition is detected in both LG sensors and the BP sensor. Since only high energy charged particles (>~100 MeV) can penetrate all three sensors to provide a coincidence, these spectra are called GCR spectra for Galactic Cosmic Rays (GCR). Associated timing, spatial and engineering readings taken at the beginning of the associated spectral collection period are also provided in the NS_CDR_GCR_SPECTRA files. Each NS_CDR_GCR_SPECTRA data product is organized as a binary data file containing calibrated spectra and associated data collected over a 24 hour time period, with a detached ASCII text PDS label file. The files are grouped by month (MM) within the DATA directory (see figure 2). Table 6.3 lists the values that make up the NS_CDR_COUNTS files. Table 6.3. Data values for the NS_CDR_GCR_SPECTRA data product. See PDF version of document for table. 6.4.2 Data Format Descriptions The data format for the NS_CDR_GCR_SPECTRA is a 10-column binary table. Columns vary in width from 4 to 256 bytes. Column structure and start byte are described in Appendix E, Section 7.5.3. The number of rows in a data table depends on the number of collection intervals during the time frame of the data file, i.e. one Earth Day. 6.4.3 File Naming Conventions The general form of the NS_CDR_GCR_SPECTRA file name is: "NS_CDR_ZZZYYYYDDDWWW.XXX", where NS instrument identifier: represents the NS instrument. CDR data product identifier: CDR ZZZ data product name GCR - NS CDR Galactic Cosmic Ray spectra with associated engineering, timing and spatial data. YYYY four-digit year corresponding to the start-time of the first record in the NS_CDR_GCR_SPECTRA data file. DDD three-digit day of the year corresponding to the start time of the first record in the NS_CDR_GCR_SPECTRA data file. WWW reserved character string to use during the course of the mission as necessary to identify "special" data products. Nominal data products are identified by ZZZ. .XXX the file extension (.DAT). 6.4.4 Label Description The NS_ CDR_GCR_SPECTRA data product has detached PDS labels stored as ASCII text. A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification and for data object definitions. The label also contains descriptive information needed to interpret or process the data objects in the file. The detached label file has the same name as the data file it describes, except that it has the extension LBL instead of DAT. PDS labels are written in Object Description Language (ODL). PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects: ^object = location where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the name of the file that contains the data object. 6.5 NS Engineering Data - NS_CDR_ENG 6.5.1 Data Product Structure and Organization The NS_CDR_ENG data product is organized as an ASCII table containing a time series of engineering parameters taken over a 24 hour time period, with a detached ASCII text PDS label file. Individual records are a single data collection interval that is variable in duration. In general, temperatures are reported in Celsius, currents in Amps, and potentials in Volts. The files are grouped by month (MM) within the DATA directory (see figure 2). Table 6.4 lists the values that make up the NS_CDR_ENG files. In general, the data values in the NS_CDR_ENG files are carried over without correction from the NS EDR status files. Thus, the definitive explanations of these data are given in the NS EDR SIS. However, for quantities with physical units, a conversion has been made to change the engineering units to physical units. A description of how this conversion is done is given in the NS calibration document (messns_edr2cdr2ddr.pdf in the CALIB directory). Another change in these files compared to the EDR data is that UTC times, instead of the spacecraft clock values of MET, are appended to the data. This allows a simple, direct comparison in time of these engineering data with other NS spectra and counting rate data. Table 6.4 Data values for the NS_CDR_ENG data product See PDF version of document for table. 6.5.2 Data Format Descriptions The data format for the NS_CDR_ENG data product is a 98-column ASCII table. Columns vary in width from 8 to 18 bytes. Column structure and start byte are described in Appendix E, Section 7.5.4. The number of rows in a data table depends on the number of collection intervals during the time frame of the data file, i.e. one Earth Day. 6.5.3 File Naming Conventions The general form of the NS_CDR_ENG file name is: "NS_CDR_ZZZYYYYDDDWWW.XXX ", where NS instrument identifier: represents the NS instrument. CDR data product identifier: CDR ZZZ data product name ENG - Engineering data. YYYY four-digit year corresponding to the start-time of the first record in the NS_CDR_ENG data file. DDD three-digit day of the year corresponding to the start time of the first record in the NS_CDR_ENG data file. WWW reserved character string to use during the course of the mission as necessary to identify "special" data products. Nominal data products are identified by ZZZ. .XXX the file extension (.TAB). 6.5.4 Label Description The NS_CDR_ENG data product has detached PDS labels stored as ASCII text. A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification and for data object definitions. The label also contains descriptive information needed to interpret or process the data objects in the file. The detached label file has the same name as the data file it describes, except that it has the extension LBL instead of TAB. PDS labels are written in Object Description Language (ODL). PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects: ^object = location where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the name of the file that contains the data object. 6.6 NS Gamma Ray Burst - NS_CDR_GAB 6.6.1 Data Product Structure and Organization The NS_CDR_GAB data product is organized as an ASCII table containing a time series of gamma ray burst data taken over a 24 hour time period, with a detached ASCII text PDS label file. Individual records are a single data collection interval that is variable in duration. It contains the same data values as in the NS Gamma Ray Burst (GAB) EDR, only in ASCII form. This was done to provide a data product that was easy to analyze, such that the user did not have to develop tools to read clock kernels and keep track of which oscillator was being used. The data values in the NS_CDR_GAB files are carried over without correction from the NS GAB EDR. UTC date and time, derived from the spacecraft clock MET, are appended to the data. This allows a simple, direct comparison in UTC time of these engineering data with other external data sources. Table 6.5 Data values for the NS_CDR_GAB data product See PDF version of document for table. 6.6.2 Data Format Descriptions The data format for the NS_CDR_GAB data product is an 11-column ASCII table. Column structure and start byte are described in Appendix E, Section 7.5.5. The number of rows in a data table depends on the number of collection intervals during the time frame of the data file, i.e. one Earth Day. 6.6.3 File Naming Conventions The general form of the NS_CDR_GAB file name is: "NS_CDR_ZZZYYYYDDDWWW.XXX ", where NS instrument identifier: represents the NS instrument. CDR data product identifier: CDR ZZZ data product name GAB - Gamma-Ray Burst YYYY four-digit year corresponding to the start-time of the first record in the NS_CDR_GAB data file. DDD three-digit day of the year corresponding to the start time of the first record in the NS_CDR_GAB data file. WWW reserved character string to use during the course of the mission as necessary to identify "special" data products. Nominal data products are identified by ZZZ. .XXX the file extension (.TAB). 6.6.4 Label Description The NS_CDR_GAB data product has detached PDS labels stored as ASCII text. A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification and for data object definitions. The label also contains descriptive information needed to interpret or process the data objects in the file. The detached label file has the same name as the data file it describes, except that it has the extension LBL instead of TAB. PDS labels are written in Object Description Language (ODL). PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects: ^object = location where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the name of the file that contains the data object. 6.7 NS Net Neutron Count Rates - NS_DDR_NCR 6.7.1 Data Product Structure and Organization The NS_DDR_NCR files contain net neutron count rate data as derived from the LG and BP singles spectra. The net count rates are given in units of counts per second for each accumulation time interval. Derived uncertainty values for each count rate are also provided for each time step. Each NS_DDR_NCR file is organized as an ASCII text file and contains data collected over one Earth day. In addition to the count rates, spacecraft time and geometry information associated with each measurement are provided. These time and geometry values are the same as is given in the CDR files for each corresponding measurement. Three main processing steps are carried out for the derivation of the net neutron count rate data. First, data selections are made to exclude data taken during times of solar particle events when the charged particle flux is sufficiently high to affect the background in the NS sensors. The times of these exclusions are given in the data confidence notes associated with each delivery (see catalog/ ddr_ds.cat). Second, gain corrections are made to the NS spectra prior to deriving any net neutron counts. Finally, background subtraction algorithms are applied to the NS spectra through which the net neutron counts are derived. Details of the processing are given in the document messns_processing.pdf located in the CALIB directory. Please note that DDRs were generated for data collected during the "Mercury Orbit" phase only. Table 6.6 Data Values for the NS DDR NCR data product See PDF version of document for table. 6.7.2 Data Format Descriptions The data format for the NS_DDR_NCR data product is a 29-column ASCII table. Column structure and start byte are described in Appendix E, Section 7.5.6. The number of rows in a data table depends on the number of collection intervals during the time frame of the data file, i.e. one Earth Day. 6.7.3 File Naming Conventions The general form of the NS_DDR_NCR file name is: "NS_DDR_ZZZYYYYDDDWWW.XXX ", where NS instrument identifier: represents the NS instrument. DDR data product identifier: DDR ZZZ data product name NCR - Neutron Count Rates YYYY four-digit year corresponding to the start-time of the first record in the NS_DDR_NCR data file. DDD three-digit day of the year corresponding to the start time of the first record in the NS_DDR_NCR data file. WWW reserved character string to use during the course of the mission as necessary to identify "special" data products. Nominal data products are identified by ZZZ. .XXX the file extension (.TAB). 6.7.4 Label Description The NS_DDR_NCR data product has detached PDS labels stored as ASCII text. A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification and for data object definitions. The label also contains descriptive information needed to interpret or process the data objects in the file. The detached label file has the same name as the data file it describes, except that it has the extension LBL instead of TAB. PDS labels are written in Object Description Language (ODL). PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects: ^object = location where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the name of the file that contains the data object. 6.8 NS Neutron Composition Product - NS_DDR_NCP 6.8.1 Data Product Structure and Organization The NCP data product contains latitude-binned relative neutron count rates taken during the primary MESSENGER mission from 26 March 2011 to 25 February 2012. Specifically, these data are the exact data points given in Figure 2 and Figure 3A from Lawrence et al., Science, 339, 292-296, 2013. The delivered values include measured and simulated data for fast and epithermal neutron data within 2 degree wide latitude bins; the latitude values are the midpoint values within each bin and the data are the average values within each latitude bin. The simulated data include two cases: one case assumes there is no hydrogen in Mercury's north polar radar bright regions; the other case assumes that the north polar radar bright regions contain 100 wt. percent H2O. Table 6.7 lists the values that make up the NS_DDR_NCP file. Details of the processing are given in the document messns_processing.pdf located in the CALIB directory. Table 6.7 Data Values for the NS DDR NCP data product See PDF version of document for table. 6.8.2 Data Format Descriptions The data format for the NS_DDR_NCP data product is a 13-column ASCII table. Column structure and start byte are described in the data product label, ns_ddr_ncp.lbl. 6.8.3 File Naming Conventions The general form of the NS_DDR_NCP file name is: "NS_DDR_ZZZ.XXX ", where NS instrument identifier: represents the NS instrument. DDR data product identifier: DDR ZZZ data product name NCP - Neutron Composition Product .XXX the file extension (.TAB). 6.8.4 Label Description The NS_DDR_NCP data product has a detached PDS label stored as ASCII text. A PDS label is object-oriented and describes the objects in the data file. The PDS label contains keywords for product identification and for data object definitions. The label also contains descriptive information needed to interpret or process the data objects in the file. The detached label file has the same name as the data file it describes, except that it has the extension LBL instead of TAB. PDS labels are written in Object Description Language (ODL). PDS label statements have the form of "keyword = value". Each label statement is terminated with a carriage return character (ASCII 13) and a line feed character (ASCII 10) sequence to allow the label to be read by many operating systems. Pointer statements with the following format are used to indicate the location of data objects: ^object = location where the carat character (^, also called a pointer) is followed by the name of the specific data object. The location is the name of the file that contains the data object. 6.9 Directory Structure and Contents for NS CDR/DDR Archive Volume The following illustration (Figure 2) shows the directory structure overview for the NS CDR/DDR archive volume, which bears the PDS-assigned volume ID MESSNS_2101. Empty directories, which occur when no data are received for a given orbit or day in which data were expected, are not included on the volume. The archive volume was delivered to PDS with the first release of NS CDR products. Subsequent deliveries of NS CDR/DDR products consisted of a partial volume containing only new and changed files. ______________________________________|____________________________________ | | | | | | |