Level-0 Algorithms and Products – Sentinel-3 SLSTR Technical Guide – Sentinel Online
Level-0 Algorithms and Products
Level-0 processing generates time sorted and annotated Level-0 data products from Instrument Source Packets (ISP).
The first part of processing involves unpacking the ISP, performing a quality check and appending annotation data. Once the input raw data files have been read, all necessary data are extracted and parsed. The ISPs are then sorted and checked. This includes checks for missing and duplicate packet numbering.
The final part of the processing is Level-0 product generation. Several quality flags are computed and included in the associated metadata and the time sorted and annotated raw data are included in the Level-0 package.
During Level-0 processing, several activities have to be completed:
- Leap second management should be handled.
- Product quality flags should provide information concerning nominal processing, satellite manoeuvring, contingency processing and degraded processing.
- The total number of missing ISPs should be reported.
- No duplicated packets should be included in Level-0 products.
Level-0 Products Description
The SLSTR Level-0 product, SL_0_SLT, is produced during Level-0 processing and is an internal product. It is not available to users and is considered only as input to SLSTR Level-1 processing.
This packet includes, in a measurement data file, raw Instrument Source Packets (ISP), error corrected and sorted by acquisition time to ensure unity. There are 13 distinct types of ISP defined:
- one for each SLSTR optical channel (S1-S9)
- one for each fire SLSTR channel (F1 and F2)
- one dedicated to scan information
- one dedicated to ancillary ("house-keeping") parameters.
Apart from the ancillary packets, all other ISPs are provided in a separate file for each of the eight targets (Earth view, VISCAL, Black Body-Y and Black Body+Y, for nadir and oblique view), giving a total of 97 distinct ISPs. A total of 10 packets are generated for each optical channel and for the scan position in each "cycle", corresponding to two complete revolutions ("scans") of the scan mirrors. One ancillary packet is generated per scan, or two per cycle.
Annotation data files included in this Level-0 product include ISP annotations such as sensing time, packet size, packet ID, and Front End Processor (FEP) quality information.