Minimize Validation

According to the Working Group on Calibration and Validation (WGCV) of the international Committee on Earth Observation Satellites (CEOS), validation is the process of assessing, by independent means, the quality of the data products derived from the system outputs.

The SENTINEL-1 phase E1 is planned for a period of 3 months from the time of launch. After a successful In-Orbit Commissioning Review (IOCR), the satellite is declared ready for routine operation in phase E2. The SENTINEL-1 core product verification, calibration and geophysical validation is not expected to be completed before IOCR but instead will continue during phase E2 until the final review, 9 months after launch.

The core product commissioning starts immediately after launch and encompasses verification, calibration and geophysical validation of the core SENTINEL-1 products:

IPF and product verification includes:

  • verification of the Level-1 and Level-2 product format and main annotations
  • verification of the main processing algorithm (Doppler estimation, focusing, ground range projection, de-bursting, swath stitching) and radiometric correction (EAP, TOPS scalloping, RSL, de-noising, etc.)
  • IPF normalization including verification of the image dynamic and IPF gain setting, sub-swath radiometric merging and product performance assessment
  • point target IRF (resolution, ISLR, PSLR, SSLR. PTAR, ENL, DTAR, NESZ)
  • geometric assessment.

Level-1 product calibration includes:

  • absolute and relative radiometric calibration
  • polarimetric calibration
  • geometric calibration.

Level-2 geophysical validation includes verification of the geophysical variables against independent external measures like modal data, buoys or other EO data sources.

Level-1 Product Verification

Product verification for Level-1 includes:
  • verification of the IRF performance parameters (resolution, ISLR, PSLR, SSLR and point target ambiguity) using mainly the SENTINEL-1 transponders
  • verification of the radiometric performances (ENL, NESZ, DTAR) using targets of occasions with peculiar radiometric characteristics
  • swath verification parameters (swath extent, incidence angle, (sub-) swath overlap, vignette size, distance between vignettes)
  • verification that there is no radiometric scalloping effect arising
  • burst synchronisation using the OBS product
  • visual inspection
  • product family consistency, e.g. verification of the consistency of measurement for GRD HR, FR and MR.

Level-2 Product Verification

Level-2 product verification consists of verifying the main quality of the engineering parameters prior to the inversion steps. OSW verification consists mainly of measuring the performance parameters related to the input imagette or the cross-spectra. OWI verification consists of verifying the calibration constant obtained from the transponders against a geophysical calibration constant and deriving the NESZ. RVL verification is mainly to verify the accuracy of the Doppler anomaly estimation.

Level-2 Geophysical Validation

The geophysical validation of SENTINEL-1 Level-2 products consists of comparing retrieved Level-2 products using a geophysical model function from SENTINEL-1 measurements with independent 'equivalent' measurements. This allows assessment of the information content and the quality of the SENTINEL-1 Level-2 products.

The geophysical validation of the OSW component consists of characterising the performance of wave spectral parameters derived from the SENTINEL-1 SAR with other independent sources (buoys, NWPM), followed by an estimation of RMS error and bias. The comparison is made possible through the collocation of the NWPM and buoys with SAR.

OWI validation assesses the radiometric calibration performance for all combinations of mode, swath and polarisation. It also characterises wind retrieval performance as a function of the mode, incidence angle (swath), polarisation and wind conditions:

  • geophysical validation is undertaken globally against collocated NWPM and in situ (buoys)
  • inter-comparison of wind measurements from the different SENTINEL-1 modes
  • inter-comparison with global winds retrieved from scatterometers (ASCAT).

The RVL component is less mature than OSW and OWI. The experiment performed on ASAR has demonstrated that the operational current extraction requires stringent performance on the accuracy of the Doppler shift anomaly estimation. It has been demonstrated that several biases or trends were present in the ASAR Doppler estimation impeding a straightforward RVL estimation without performing heavy Doppler calibration steps for fixing the biases.