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Metadata & MetaSat

What is Metadata?

Without context data has no meaning. Take for example, the following table:

Figure 1

Without context the values in columns A, B, and C are ambiguous; the answer to whether or not the table’s content refers to the same thing (e.g., a satellite, an asteroid, etc.) is uncertain. 

  • Metadata, or simply, data that describes data, provides the context necessary for the table’s values to have meaning.

With basic metadata, the columns can be given context and are no longer ambiguous (Figure 2). The table can now be interpreted and recognized for what it is (e.g., orbital elements) and the data is therefore meaningful and useful.

Figure 2

One issue with metadata is that it is rarely consistent. Two tables that describe the same thing, for example, may use very different metadata (Fig. 3).

Figure 3

The need for a metadata schema, or a common way of describing and organizing metadata, is therefore needed when working with more than one dataset, sharing information with other people, or searching across different systems using tools like APIs. In this way metadata helps facilitate the sharing of lessons learned and access to information.

Different, existing metadata standards can be “crosswalked” (Fig. 4) and incorporated into a single metadata schema. One group may choose to implement a schema using Standard 1, while another may choose to use a Standard 2. The metadata crosswalk makes these standards translatable, while the schema itself makes it clear which standard is being used and in what context.

Figure 4: Simplified Orbital Elements Crosswalk


What is MetaSat?

MetaSat, as a common way of describing small satellite missions, aims to improve interoperability and access to mission outputs by removing ambiguity and providing the digital infrastructure necessary for crosswalking mission-related metadata and standards. In this way the schema is like a recipe card that can be filled out by people participating in missions and recording information about missions. The schema does not include small satellite mission data itself, but rather, data about mission data. In this way the schema remains a highly flexible tool regardless of its specific use case (e.g., maintaining a database, running a ground station network). 

Consider how a recipe card could be used to describe a recipe on a website, in a cookbook, or in a script for a cooking show — in each case the same schema could be implemented. In one case certain metadata elements may not be required, and in another case it may be necessary to add new elements to the schema. For instance, it may be necessary to include elements about a recipe’s cultural origin (e.g. geographic region) or the type of oven required to prepare the dish, but in other cases these metadata elements may not be necessary.

Similarly, a schema to describe small satellite missions may need elements to record or link to standardized metadata about images taken by a specific instrument, but not all satellite missions would need to use those elements. Likewise, if the schema was implemented on a dashboard to monitor an on-going mission, fields related to a satellite’s orbit would be essential, but that information may be less essential if the schema is being used to build an archive of software used by missions funded through a specific program.

  • For this reason, MetaSat is open and publically available so that it can be implemented for any purpose.

MetaSat

Introducing MetaSat

The MetaSat team is working on creating a metadata schema to describe small satellite (SmallSat) missions. Our schema will help facilitate the ease of sharing information between missions and lower the barrier of entry into the field.

Why metadata?

Metadata is most simply defined as data about data. For example, a book contains data: the words on the page. The metadata is information about the book, such as the title, author, page count, publisher, and more. Space missions also have data—for example, the information a satellite collects and sends back to earth. The metadata about a space mission might include information about the satellite components, people and organizations involved with the mission, the launch date, or information about any ground stations receiving information from the spacecraft.

Right now, space mission metadata is not standardized, which makes it hard for different teams to talk to each other, collaborate, or share advice about what works or doesn’t work in SmallSat missions. Our goal with MetaSat is to create a metadata schema that can be shared and expanded upon, and which will eventually facilitate information sharing between satellite missions.

Why linked data?

MetaSat will also incorporate linked data into its schema. Linked data is used by the web to link together related information. This facilitates both the sharing of information and the synthesis of new ideas. For more information on linked data, visit linkeddata.org.

Our work so far

The Wolbach library is working closely with the Libre Space Foundation (LSF) to create our metadata schema. LSF has direct experience working on SmallSat missions and runs SatNOGS, a global network of ground stations that collects satellite observations and stores them in a database. The SatNOGS Network stores information about both the ground stations in the network and their observations, and the SatNOGS database (SatNOGS DB) stores information about active satellites. SatNOGS will be one of the earliest adopters of the MetaSat schema.

We are currently basing our schema off of four use cases: Missions, Spacecraft, Observations, and Ground Stations. Users will be able to mix and match the use cases as they see fit. For example, a user scheduling an observation on their ground station can link the Observation metadata to Ground Station metadata and Spacecraft metadata in a single JSON-LD file. A ground station owner can link their Ground Station metadata to several instances of Observation metadata to reflect the observations taken by their ground station. Our hope is that the modular nature of the schema will allow a high degree of flexibility for our users.