Level-1 Algorithm Overview - Sentinel-1 SAR Technical Guide - Sentinel Online
The SENTINEL-1 Payload Data Ground Segment (PDGS) is responsible for:
- implementing the SENTINEL-1 mission observation scenario
- X-band data reception
- generating the operational core ground segment products
- reacting to emergency orders with rush instrument tasking and processing
- providing access to SENTINEL-1 data
- ensuring long term mission data archiving
- monitoring the instrument and mission performance
- ensuring SENTINEL-1 core operational user products meet the expected quality, with necessary calibration and validation activities.
Within the PDGS, the Instrument Processing Facility (IPF) is responsible for the generation of Level-1 and Level-2 products. In addition to SENTINEL-1, the IPF uses the same processing system and mostly the same algorithms for processing of ENVISAT ASAR stripmap and wave mode data. Level-0 data from SENTINEL-1 and ENVISAT ASAR are ingested into the system where different pre-processing steps are performed for the respective mission data. The system then applies the Single Look Complex (SLC) image processing for Doppler centroid estimation and focusing, as well as mode-specific processing for assembling of multi-swath products. The Level-1 post-processing then generates the output Level-1 SLC products and the Level-1 Ground Range Detected (GRD) products. From internally generated Level-1 SLC and GRD products, the Level-2 Ocean (OCN) products are produced.
To accomplish this, the IPF is composed of several software components as shown in the following figure.
The algorithms applied by the IPF to generate Level-1 products from Level-0 data include:
- Level-1 pre-processing
- Special handling for TOPSAR mode
- Doppler centroid estimation
- Level-1 SLC processing
- Level-1 post-processing
- Level-1 Radiometric Calibration.
Processing of each polarisation is essentially the same. A separate image is generated for each polarisation, and polarisation-specific correction and calibration factors are applied during the processing of each polarisation The Doppler Centroid (DC) from the co-polarisation channel is used for processing both polarisations, so that the two resulting images are accurately co-registered.
For further details on the SENTINEL-1 Level-1 algorithms, please refer to the SENTINEL-1 Level-1 Detailed Algorithm Definition document (S1-TN-MDA-52-7445).