PDS3 and PDS4 Data Standards

The Orbital Data Explorer (ODE) catalogs and provides access to NASA’s Planetary Data System (PDS) archives of observational data of Mars, Mercury, Venus, and the Moon. The data are archived by the PDS in standardized file formats and directory structures to support the long-term preservation of the information. Observational data are stored in non-proprietary formats to eliminate a reliance on commercial software.

The PDS currently supports two PDS standards: PDS3 and PDS4. The legacy PDS3 standard has been in place for many years and is still used by several active missions. Planetary missions confirmed for flight after November 1, 2011 are required to archive in PDS4. Active missions that were archiving in PDS3 before that date have continued to use the PDS3 standard. These archives will be converted to PDS4 according to the PDS migration policy. Proposals to new R&A programs should include archiving in PDS4.

Both PDS3 and PDS4 specify the contents of a quality archive, including data, documentation, and ancillary material, with metadata for each product stored in a PDS label. A key concept of both PDS3 and PDS4 is the PDS data product. A data product consists the observational data, which may consist of one or more files, and the metadata that describes the observational data.

In PDS3, the metadata could be attached to the data file as a defined header section of ASCII text or in a separate .lbl text file. The metadata “label” describes the context of the observation and can reference additional format files, calibration files, and one or more files containing the observational data. The label information is stored as ASCII text in Object Description Language (ODL) format - easily read by humans with keyword value pairs.

PDS3 ODL Metadata Example:

/* Image Description */

SPACECRAFT_NAME = VOYAGER_2

TARGET_NAME = IO

IMAGE_ID = "0514J2-00"

IMAGE_TIME = 1979-07-08T05:19:11Z

INSTRUMENT_NAME = NARROW_ANGLE_CAMERA

EXPOSURE_DURATION = 1.9200 <SECONDS>

NOTE = "Routine multispectral longitude coverage, 1 of 7 frames"

The PDS4 standard is designed to produce higher quality, more accessible archives using modern software capabilities. PDS4 metadata (labels) are represented in an XML (eXtensible Markup Language) format, for improved software reading and system integration. The number of accepted data formats has been reduced for improved standardization and simplification. While PDS3 labels used a keyword=value format, PDS4 labels are written in XML, enabling more complete and consistent metadata while allowing the use of existing XML language tools.

PDS4 XML Metadata Example:

<Time_Coordinates>

<start_date_time>2009-10-06T00:11:01.684Z</start_date_time>

<stop_date_time>2009-10-06T15:51:01.686Z</stop_date_time>

</Time_Coordinates>

<Investigation_Area>

<name>MESSENGER</name>

<type>Mission</type>

<Internal_Reference>

<lid_reference>urn:nasa:pds:context:investigation:mission.messenger</lid_reference>

<reference_type>data_to_investigation</reference_type>

</Internal_Reference>

</Investigation_Area>

<Observing_System>

<Observing_System_Component>

<name>MESSENGER</name>

<type>Spacecraft</type>

<Internal_Reference>

<lid_reference>urn:nasa:pds:context:instrument_host:spacecraft.mess</lid_reference>

<reference_type>is_instrument_host</reference_type>

</Internal_Reference>

</Observing_System_Component>

<Observing_System_Component>

<name>Gamma Ray Spectrometer</name>

<type>Instrument</type>

<Internal_Reference>

<lid_reference>urn:nasa:pds:context:instrument:grs.mess</lid_reference>

<reference_type>is_instrument</reference_type>

</Internal_Reference>

</Observing_System_Component>

</Observing_System>

Another noteworthy difference between PDS3 and PDS4 is the online archive structure. In PDS3, data products are associated with data sets and volumes. PDS4 associates data products with bundles and collections. This concept is not very relevant to interacting with PDS products through ODE as it primarily appears when using the ODE cart and selecting the file organization of “maintain original PDS archive directory structure”. In this case, PDS products will be grouped by their PDS3 volume or PDS4 collection for user download. More information about the archive structure can be found in the archive standards links below.

Both PDS3 and PDS4 archives include details about included product formats in data product SIS (Software Interface Specification) files. These files are found in the documentation directories of the PDS3 volumes and the PDS4 bundles’ documentation collections. Links to these files are found on ODE product detail pages under “Product Description and Supporting Documents”.

What’s in ODE?

ODE supports both PDS standards. The PDS product metadata is displayed in the same manner through the ODE interface. If the product was converted from PDS3 to PDS4 standard, the original PDS3 label will still be available for download through ODE. In this case, an ODE cart order will provide the original PDS3 label and the new PDS4 label. The user can use whichever metadata format preferred when working with the unaltered data product.

MESSENGER data are currently being migrated to the PDS4 standard. As part of this migration, the existing PDS3 label files and documentation files will remain online in their PDS3 archive structure. New PDS4 product labels are added, along with additional PDS4 archive files where required. MESSENGER users can continue to use their existing scripts and software that utilize the PDS3 labels. Those files will remain in the archive. New users are encouraged to use the PDS4 XML labels.

Helpful Links

PDS3

PDS4

PDS Tools

  • PDS Tools Registry – For a full list of software packages related to the access and use of planetary data.

Highlighted Tools from the PDS Tools Registry

  • Transform Tool – Software for transforming PDS3 to PDS4 product labels and product data into common formats.

  • PDS4 Viewer – A general read-in and visualization GUI tool for PDS4 data.

  • NASAView – A PDS3 product display program that runs on multiple platforms in a GUI environment.

Getting Help

We are here to help. Questions can be posted online through the PDS Geosciences Node forum. Geosciences Node staff monitors the forum to answer questions. You can also email us at geosci@wunder.wustl.edu for general PDS questions. ODE specific questions are best directed to ode@wunder.wustl.edu.