Mars Global Surveyor
Mars Orbiter Laser Altimeter

MOLA STANDARD PRODUCT
ARCHIVE VOLUME
SOFTWARE INTERFACE SPECIFICATION

(MOLA Archive Volume SIS)

Version 4.4
rev. May 16, 2000

Each MOLA-AEDR product is an aggregation of MOLA telemetry packets for a single orbit (i.e., the raw data). Each MOLA-PEDR product contains AEDR data that has been converted to engineering and physical units using precision orbit data. AEDRs and PEDRs from the Orbit Insertion mission phases contain one orbit's worth of data per product. Products from the Mapping Phase contain one day's worth of data, covering several orbits. The MOLA-IEGDR and MOLA-MEGDR products, together known as the gridded products, are sets of global maps  at different resolutions created by binning the MOLA-PEDR products. The MOLA standard data products are generated by the MOLA Instrument Team and archived by the Planetary Data System (PDS). The PDS Geosciences Node is responsible for compiling the MOLA archive volumes on CD-ROM media.

This Software Interface Specification (SIS) describes the format, content, and generation of the MOLA Standard Product Archive Volumes. Section 3, Archive Volume Generation, describes the procedure for transferring data products to archive media. Section 4, Archive Volume Contents, describes the structure of the archive volumes and the contents of each file. Section 5, Archive Volume Format, describes the file formats used on the archive volumes. Finally, Section 6, Support Staff and Cognizant Persons, lists the individuals responsible for generating the archive volumes.

2.2 Scope

The specifications in this document apply to all MOLA standard product archive volumes that are produced on compact disk media during the Mapping Phase of the Mars Global Surveyor mission. Most of the specifications in this document also apply to MOLA archive volumes containing data acquired during the Orbit Insertion Phase of the mission, prior to the Mapping Phase. The chief difference between the Orbit Insertion Phase and Mapping Phase volumes is that AEDRs and PEDRs are archived together on Orbit Insertion Phase volumes, while during the Mapping Phase they are archived on separate volumes.

ISO 9660-1988, Information Processing - Volume and File Structure of CD-ROM for Information Exchange, April 15, 1988.

Arvidson, R., E. Guinness, and S. Slavney, Mars Global Surveyor Project Archive Generation, Validation, and Transfer Plan, MGS Document #542-312, 1998.

Mars Global Surveyor MOLA (Mars Orbiter Laser Altimeter) Aggregated Experiment Data Record Software Interface Specification (MOLA AEDR SIS), September 24, 1998, Version 2.1, NASA Goddard Space Flight Center.

Planetary Science Data Dictionary Document, July 15, 1996, Planetary Data System, JPL D-7116, Rev. D.

Planetary Data System Data Preparation Workbook, February 1995, Version 3.1, JPL D-7669, Part 1.

Planetary Data System Standards Reference, July, 1995, Version 3.2. JPL D-7669, Part 2.

This specification is useful to those who wish to understand the format and content of the MOLA Standard Product Archive Collection. Typically, these individuals would be software engineers, data analysts, or planetary scientists.

3.1 Data Transfer and Validation Methods

The MOLA Standard Product Archive Collection is produced by the PDS Geosciences Node at Washington University, in conjunction with the MOLA Instrument Team. The Washington University activities is funded by the Mars Global Surveyor Project.

The Archive Collection includes data acquired during the Orbit Insertion and Mapping Phases of the MGS mission. The archive validation procedure described in this section applies to volumes generated during the Mapping Phase of the mission. The few volumes produced with Orbit Insertion data, before mapping begins, are validated using PDS peer review procedures.

During the Mapping Phase of the MGS mission, two archive volume sets of MOLA data are produced: one contains the MOLA-AEDR products, and the other contains the MOLA-PEDR and gridded products. (see Figure 1, Generation of MOLA Standard Product Archive Volumes). Upon notification by the MOLA Team, the Geosciences Node extracts standard products by electronic file transfer from the MOLA Team's processing facility and generates associated documentation and ancillary products (e.g. index tables). Each volume of standard products, documentation and ancillary products is stored on a write-once CD-ROM (CD-WO) generated at Washington University. All data formats are based on the Planetary Data System standards as documented in the PDS Standards Reference [section 2.3, Applicable Documents].

Four copies of each volume are produced. Two are sent to the MOLA Team and the SDVT for review, along with a Manifest that lists the contents of the volume in detail, and an Error Report Log that describes any known deviations from the Manifest or other anomalies. A third copy remains at Washington University for backup. Upon approval of a volume from the MOLA Team and the SDVT, the volume is considered officially released to the PDS as defined by the Mars Global Surveyor data release policy [Arvidson et al., 1998]. The Geosciences Node then sends the fourth copy of the volume to a CD-ROM vendor for replication.

The Geosciences Node provides the vendor with a mailing list for distribution of copies. The list includes MGS personnel who have expressed interest in receiving the data, the Planetary Data System, and the National Space Science Data Center (NSSDC). The PDS requests enough copies to serve its anticipated user needs, and funds those copies. The PDS is responsible for making additional future copies as needed.

In the event that a volume is found to contain errors, the reviewers can recommend one of two courses of action: (1) if the errors are minor, the volume may be published anyway, with an explanatory note added to the volume's errata file and the errors corrected on subsequent volumes; (2) if the errors are major, the volume must be re-generated to correct them.

Table 2 summarizes expected sizes and delivery rates for the MOLA Standard Products.

Each MOLA Standard Product Archive Volume contains at most 650 Mbytes of data, including documentation and ancillary files, based on the storage capacity of CD-ROMs readable by most CD-ROM drives.

The Archive Volumes are produced as enough data are accumulated to fill each disk. The MOLA-AEDRs are accumulated at the rate of about 56 Mb per week, so CD-WO volumes containing these data are produced about every 11 weeks. The MOLA-PEDRs are accumulated at the rate of about 238 Mb per week, resulting in a new volume every 2 to 3 weeks. The MOLA IEGDR consists of a single product generated after the first 30 days of mapping, and the MOLA MEGDR is a single product generated after the primary mission is completed. As they become available, these products are included on PEDR volumes, as their small size does not justify placing them on separate volumes.

The MOLA Team expects to issue revised versions of PEDR products as more precise orbit information is obtained in the course of the mission. The plan is for three revisions of the orbit information, although the number of versions of an individual PEDR product may vary. The EGDR products may also be revised using increasingly higher resolutions.

All volumes in the MOLA Standard Product Archive Collection conform to ISO 9660 standards [ISO 9660, 1988].

Washington University keeps a backup copy of each CD-WO volume. The backup copy can be used if the CD-WO sent to the vendor becomes lost or damaged. The two CD-WO volumes sent to the MOLA Team and the SDVT for review do not need to be returned to Washington University.

Each MOLA CD-WO bears a volume ID using the last two components of the volume set ID [PDS Standards Reference, 1995]. For archive volumes containing data acquired during the Mapping Phase, the AEDR volume set ID is USA_NASA_JPL_MGSL_1nnn, and the PEDR/gridded product volume set ID is USA_NASA_JPL_MGSL_2nnn, where nnn is the sequence number of the individual volume. Hence the first AEDR volume has the volume ID MGSL_1001, and the first PEDR and gridded products volume has the volume ID MGSL_2001. For archive volumes containing pre-Mapping Phase data, AEDR and PEDR products will be combined on the same volume. The volume set ID is USA_NASA_JPL_MGSL_0nnn.

4. Archive Volume Contents

This section describes the contents of the MOLA Standard Product Archive Collection volumes, including the file names, file contents, file types, and organization responsible for providing the files. The complete directory structure is shown in Appendix A. All the ancillary files described herein appear on both the AEDR volumes and the PEDR / gridded products volumes, except where noted. See the MOLA Data Product SIS documents [MOLA AEDR SIS, 1998; MOLA Any-EGDR SIS, 1997; MOLA PEDR SIS, 1998] for examples of PDS labels for each type of product.

4.1 Root Directory Contents

The following files are contained in the Root Directory, and are produced by the Geosciences Node at Washington University:

4.2 Index Directory Contents

The following files are contained in the Index Directory and are produced by the Geosciences Node.

4.3 Document Directory Contents

The following files are contained in the Document Directory and are produced or collected by the MOLA team.

4.4 Label Directory Contents

The following files are contained in the Label Directory and are produced by the MOLA team.

4.5 Catalog Directory Contents

The files in the Catalog directory provide a top-level understanding of the Mars Global Surveyor Mission, spacecraft, instruments, and data sets in the form of completed PDS templates. The files are produced or collected by the MOLA team. The files in this directory are coordinated with the PDS data engineer.

4.6 Software Directory Contents

Two programs are provided on the PEDR/EGDR volumes for accessing PEDR data. They are:

These programs are also available from the PDS Geosciences Node web site, http://wwwpds.wustl.edu,  and from the MOLA Team web site, http://ltpwww.gsfc.nasa.gov/tharsis/mola.html. They are subject to change during the course of the mission. The MOLA site may include variants of the software for computer platforms other than those listed here. Updates to the software, as well as additional programs, are posted on the web sites as they become available. The archive volumes contain the latest version of programs available at the time the volume is generated.

The Software Directory is divided into subdirectories for each program, and then further divided by computer platform. The Software Directory appears only on PEDR/EGDR volumes, not on AEDR volumes.

4.7 Standard Products Data Directory Contents

The Standard Products data directories contain the actual data products produced by the MOLA team.

Two volume sets are produced during the Mapping Phase of the mission, one containing raw data (AEDRs) and one containing derived data (PEDRs and the gridded products, IEGDRs and MEGDRs). The contents of data directories on these two volume sets are described below. Volumes containing Orbit Insertion Phase data will have the same contents as Mapping Phase volumes, the only difference being that AEDR and PEDR products are combined on the same volume.

4.7.1 AEDR Data Directory Contents and Naming

The AEDR Data Products are aggregations of MOLA telemetry packets. Each file contains one day's worth of data, with one telemetry packet per record. The maximum number of packets in one orbit is approximately 486 [MOLA PEDR SIS, 1998]. Files are named according to the form AAnnnnnv.B, where the first A stands for Altimeter, the second A stands for the product type, AEDR, nnnnn is the number of the first orbit covered in the product, and v indicates the version. For example, the file AA10134F.B contains AEDR data starting with orbit 134, version F.

Note that during the Mapping Phase the MOLA Team uses a different orbit numbering scheme than the MGS Project. The Project reset the orbit count to 1 at the beginning of mapping, at the descending equator crossing of actual orbit 1683. To preserve a unique orbit number for identifying MOLA products, the MOLA Team adds 10000 to the Project orbit number for products created during the Mapping Phase.

The AEDR Data Products are contained in the DATA directory. If a large number of products are present on a volume, they are organized into subdirectories by groups of orbits. These subdirectory names are of the form AAnnnXX where nnnXX is the number of the first orbit in the directory. For example, the subdirectory AA001XX is the subdirectory of AEDR products covering orbits 100 through 199.

4.7.2 PEDR Data Directory Contents and Naming

The PEDR Data Products contain corrected along-track, time series range and planetary radius data in engineering and physical units, created from the raw telemetry data (AEDRs) using precision orbit information. The products also contain engineering and housekeeping data from the telemetry packets, as well as data correction values that were used to process the telemetry data into the PEDR data. Each record covers a two-second time span, called a frame, that is retrieved from the 14-second AEDR telemetry packet. Hence for every AEDR record, seven PEDR records will be generated. The names of PEDR files follow the format Apnnnnnv.B, where A is for Altimeter, P is for PEDR, nnnnn is the number of the first orbit covered in the product, and v is the version. For example, the file AP00125K.B contains the PEDR product from orbit 125, version K.

The PEDR Data Products are contained in the PEDR directory. If a large number of products are present on a volume, they are organized into subdirectories by groups of orbits. These subdirectory names are of the form APnnnXX where nnnXX is the number of the first orbit in the directory. For example, the subdirectory AP001XX is the subdirectory of PEDRs covering orbits 100 through 199.

4.7.3 Gridded Product Data Directory Contents and Naming

The gridded products are located in the data directory EGDR. Tabular data files are named according to the convention xEGddd[d]v.TAB, where x is replaced by I or M; ddd or dddd is a decimal fraction indicating the product's resolution (bin size), such as 025 for one-quarter degree bins; and v is a letter indicating the version. Image data files are named according to the convention xEGddd[d]z.IMG, where x is replaced by I or M, ddd or dddd is the resolution, and z is a letter indicating the data type: a for areoid, c for counts, r for radius, and t for topography. Each product has a detached PDS label in a separate file with the same name, extension .LBL. See section 5.2.6.3 for a description of the format of the gridded products.

4.8 Special Products Data Directory Contents

The MOLA Team may create special data products derived from the standard MOLA products. The Team may choose to publish the special products on the standard product archive volumes if appropriate; for example, if the special product is so small that publication on a separate CD volume is not practical. Special products published on standard product volumes will be fully compatible with PDS standards, accompanied by a data product SIS, and described by a PDS catalog object. A special product will be stored on the archive volume in a separate directory appropriately named for the product.

5. Archive Volume Format

This section describes the format of MOLA Standard Product Archive Volumes. Data that comprise the MOLA Standard Product Archives will be formatted in accordance with Planetary Data System specifications [Planetary Science Data Dictionary, 1996; PDS Data Preparation Workbook, 1995; PDS Standards Reference, 1995].

5.1 Disk Format

Archive Volumes have a compact disk format that is compatible with the computer operating systems MS-DOS, Macintosh, and SunOS. The MOLA CD-ROM format is in accordance with ISO 9660 level 1 Interchange Standard [ISO 9660, 1988].

5.2 File Formats

The following section describes file formats for the kinds of files contained on Archive Volumes. For more information, see the PDS Data Preparation Workbook [1995] and Appendix B.

5.2.1 Document File Format

Document files with the .TXT suffix exist in the Root, Index, Software, Catalog, and Label directories. They are ASCII files with embedded PDS labels. All document files contain 80-byte fixed-length records, with a carriage return character (ASCII 13) in the 79th byte and a line feed character (ASCII 10) in the 80th byte. This allows the files to be read by the MacOS, DOS, Unix, OS2, and VMS operating systems.

Documents in the Document directory contain formatting and figures that cannot be rendered as ASCII text. Therefore each document is given in two formats, hypertext and PDF. The hypertext file contains ASCII text plus hypertext markup language (HTML) commands that enable it to be viewed in a Web browser such as Netscape Navigator or Microsoft Internet Explorer. The hypertext file may be accompanied by ancillary files such as images and style sheets that are incorporated into the document by the Web browser. The second format, PDF (Portable Document Format) is a proprietary format of Adobe Systems Incorporated that is frequently used for distributing documents. Adobe offers free software, Acrobat Reader, for viewing PDF files.

5.2.2 Tabular File Format

Tabular files (.TAB suffix) exist in the Index directory. Tabular files are ASCII files formatted for direct reading into many database management systems on various computers. All fields are separated by commas, and character fields are enclosed in double quotation marks ("). (Character fields are padded with spaces to keep quotation marks in the same columns of successive records.) Character fields are left justified, and numeric fields are right justified. The "start byte" and "bytes" values listed in the labels do not include the commas between fields or the quotation marks surrounding character fields. The records are of fixed length, and the last two bytes of each record contain the ASCII carriage return and line feed characters. This allows a table to be treated as a fixed length record file on computers that support this file type and as a text file with embedded line delimiters on those that don't.

All tabular files are described by PDS labels, either embedded at the beginning of the file or detached. If detached, the PDS label file has the same name as the data file it describes, with the extension .LBL; for example, the file AEDINDEX.TAB is accompanied by the detached label file AEDINDEX.LBL in the same directory.

5.2.3 PDS Label Format

All data files in the MOLA Standard Product Archive Collection have PDS labels [Planetary Science Data Dictionary, 1996; PDS Standards Reference, 1995]. For AEDR and PEDR products, these labels are embedded at the beginning of the data files. The IEGDR and MEGDR products have detached PDS labels. For examples of PDS labels for each type of data product, see the Data Product SISs [MOLA AEDR SIS, 1998; MOLA PEDR SIS, 1998; MOLA Any-EGDR SIS, 1997].

A PDS label, whether embedded or detached from its associated file, provides descriptive information about the associated file. The PDS label is an object-oriented structure consisting of sets of 'keyword=value' declarations. The object to which the label refers (e.g. IMAGE, TABLE, etc.) is denoted by a statement of the form:

^object = location

in which the carat character (^, also called a pointer in this context) indicates where to find the object. In an embedded label, the location is an integer representing the starting record number of the object (the first record in the file is record 1). In a detached label, the location denotes the name of the file containing the object, along with the starting record or byte number, if there is more than one object in the file. For example:

^HEADER = ("F01.IMG",1)

^IMAGE = ("F01.IMG",1025 <BYTES>)

indicates that the IMAGE object begins at byte 1025 of the file F01.IMG, in the same directory as the detached label file. Below is a list of the possible formats for the ^object definition.

^object = n

^object = n<BYTES>

^object = "filename.ext"

^object = ("filename.ext",n)

^object = ("[dirlist]filename.ext",n)

^object = ("filename.ext",n<BYTES>)

^object = ("[dirlist]filename.ext",n<BYTES>)

where

All detached labels contain 80-byte fixed-length records, with a carriage return character (ASCII 13) in the 79th byte and a line feed character (ASCII 10) in the 80th byte. This allows the files to be read by the MacOS, DOS, Unix, OS2, and VMS operating systems.

5.2.4 Software File Format

Two programs are provided for accessing PEDR data products. MPROF is a script for use with the commercial software IDL. It is provided as an ASCII text file in two versions, one for use on Sun/UNIX computers and one for PC/Windows computers. PEDR2TAB is a Fortran program for use on Sun/UNIX and PC computers. Binary executable files compiled for Solaris 2.4 and MS-DOS/Windows are also provided. Documentation for both MPROF and PEDR2TAB is provided as ASCII text files.

5.2.5 Catalog File Format

Catalog files (suffix .CAT) exist in the Root and Catalog directories. They are formatted in an object-oriented structure consisting of sets of 'keyword=value' declarations.

5.2.6 Science Data File Formats

5.2.6.1 AEDR Data Product Format

An AEDR product is organized as a table of binary data for a single day. Each record contains one packet of telemetry data. For information about the format and contents of an AEDR product, see the MOLA AEDR SIS [1998].

5.2.6.2 PEDR Data Product Format

A PEDR product is organized as a table of binary data for a single day. Each record represents a 2-second time span, called a frame, that is generated from the 14-second telemetry packet (the AEDR). For information about the format and contents of a PEDR product, see the MOLA PEDR SIS [1998].

5.2.6.3 Gridded Data Product Format

Gridded products are global maps of planetary radius, areoid radius, topography, and number of observations, derived from the PEDRs and aggregated into latitude-longitude bins. The values are stored either as columns in a table, with each row in the table representing a latitude-longitude bin, or as images. Multiple versions of each gridded product may be released at increasingly higher resolutions.

For information about the format and content of the gridded products, see the MOLA Any-EGDR SIS [1997].

6. Support Staff and Cognizant Persons

Table 3 – MOLA Archive Collection Support Staff

Figure 1 – Generation of MOLA Archive Volumes During Mapping. The MOLA Team generates MOLA standard data products. The Geosciences Node extracts MOLA standard products from the MOLA Team's processing facility and generates archive volumes on write-once CD-ROM media. Four copies of each archive volume are made. One is sent back to the MOLA Team and another to the MGS Science Data Validation Team (SDVT) for validation. A third copy is kept as a backup at the Geosciences Node. The SDVT sends validation reports to the MGS Project Science Group, who recommends either that the volume be released or, in case of errors, that it be regenerated. When a volume passes validation and is approved by the MGS Project for release, the fourth CD-WO copy is delivered to a CD-ROM vendor for replication. The vendor mails the CD-ROM archive volumes to a distribution list including planetary scientists, the PDS, and the NSSDC.