Product Slice Handling - Sentinel-1 SAR Technical Guide - Sentinel Online
Product Slice Handling
The SENTINEL-1 SAR is capable of operating up to 25 minutes per orbit in any of the three high bit rate modes (SM, IW, EW). To avoid distributing unwieldy products to end users, the Level-0 and Level-1 products are segmented into slices of defined length along a track. Product slices make the data more manageable for users.
Feeding sliced Level-0 data to the processing facility enables the ground segment to process slice data in parallel, resulting in a more efficient use of resources and more timely product delivery.
The Instrument Processing Facility (IPF) is able to generate a Level-1 product that covers the entire Level-0 segment or it can divide the Level-0 segment, in azimuth, into multiple slices. Each product slice is a stand-alone product that can be processed independently. Slices are approximately 25 seconds in length for SM and IW and approximately 60 seconds in length for EW. Each GeoTIFF band within a product slice will be no larger than 2 GB. Since a product could contain several bands for swaths and polarisations, the overall product size could be much larger.
From each Level-0 segment, all Level-1 slices are generated using the same set of processing parameters. The image data is continuous in terms of geometry, radiometry and phase, and the annotations are coherent in terms of update rate and grid spacing.
The amount of black-fill at near and far range of the Level-1 image can vary with the segment length. The longer the segment the more black-fill is potentially needed.
Slice products can be combined to form an assembled Level-1 product with the same product characteristics covering the complete segment. Assembly is performed following the three strategies of Include, Merge and Concatenate.
- Include - the value of the information is identical for all slices and a single occurrence of the value is copied into the assembled product.
- Merge - the value of the information may differ between slices and a single value must be amalgamated into the assembled product using the values from all slices. This can be accomplished by means of averaging, majority polling, summing, etc.
Concatenate - the information is stored in list format and the values from each slice are appended to the appropriate list in the assembled product in Zero Doppler Time (ZDT) ordered sequence and the list count attribute is updated to contain the number of items in the concatenated list. This applies to both binary image data and XML lists.
Concatenation of Level-1 GeoTIFF Measurement Data Set Slices
Fields in the annotations should be included, merged and concatenated in accordance with the SENTINEL-1 Product Specification document.