Unit 2: Batch processing Copernicus Sentinel-3 OLCI with SNAP

For operational oceanographic applications of satellite data, it is often necessary to process data regularly, and/or large volumes of data in a batch. Whilst offering an excellent platform for learning about and exploring individual satellite data products, the Sentinel Applications Platform (SNAP) also has powerful functionalities for processing images in a more routine fashion, programmatically.

Using SNAP

SNAP is an extremely powerful tool for viewing, analysing, processing and exporting image-based Earth observation products. We will briefly highlight some of the main capabilities of SNAP in our training course. SNAP offers excellent user support through its forum Links to an external site.. If you are having a problem with SNAP, or have questions about it's functionalities it's worth searching the forum to see if someone has already raised the topic. Otherwise you can make your own post to receive support from the community and the SNAP developers.

If you wish to learn more about how to use the software package, we recommend the following video.

Note: You may note some small differences between the SNAP version in the video and your own, as SNAP has recently updated to version 9. Do not worry, no capability has been removed!

SNAP and the Graph Processing Tool

The Graph Processing Tool (GPT) allows for SNAP commands to be executed on a batch of images, without needing to use the usual graphical interface (GUI). An xml 'graph' can be written, creating a workflow including input and output functions, and between them, a configurable array of operation 'nodes' that process data in various ways. This includes various practical 

Example graphs come with the SNAP software, and a user can edit these directly. However, for inexperienced users, or for the creation of new workflows, the 'Graph Builder Tool' can also be used from the SNAP GUI to create these files.

The following video will walk you through the creation of an XML graph using the graph builder tool in the SNAP GUI.

Once you have the graph, you can use various programming languages to manage the execution of the graph as part of a routine and or/expanded workflow. We provide some examples on the EUMETSAT Gitlab Links to an external site. that will also be demonstrated in person at the OSOS training.

For further information on SNAP and GPT you can check out their wiki Links to an external site. or the SNAP forum Links to an external site. where there are many existing posts that may help you, or you can ask new questions of the developers.