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.
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To accomplish this, the IPF is composed of several software components as shown in the following figure.
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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).