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Sentinel-3 for Science Workshop
(Venice -Lido Palazzo del Casinò, Italy, 02–05 June '15)
100 m Workshop Probing Vegetation
Collection 1 Change Summary
As a result of major improvements to the cloud detection algorithm, a reprocessing campaign was planned and executed from August 2016 - January 2017. Together with the cloud detection algorithm improvements, several other modifications to the PROBA-V data and metadata were included. Reprocessed data (referred to as ‘Collection 1’) have become fully available in February 2017, while the previous data collection ('Collection 0') was discontinued as of 1 March 2017. Data files are identified as .v1xx in the filenames.
The reprocessing was carried out on the entire product chain from raw data through the synthesis products and covers the period 16 October 2013 till present. All data is stored on disk in HDF5 and GeoTiff format for fast access. Further, the intermediate Level 2A data were made available for all resolutions. The changes that were implemented during the reprocessing campaign are described below.
Improved cloud detection algorithm
A new cloud detection algorithm was developed to improve on major detection issues in the previous operational algorithm. This change gives the most significant differences between the Collection 1 and Collection 0 data products. More information on the new cloud detection methodology can be found in Appendix B of the PROBA-V Product User Manual, while an extensive evaluation of the new cloud detection algorithm is documented by Stelzer et al. (2016).
Updates to the radiometric ICP files
With changes to the radiometric ICP files, users benefit from improved reflectance values due to updated absolute calibration coefficients, a better inter-camera consistency, and an overall improvement of the radiometric pixel quality.
The changes that were made to the radiometric ICP files include:
- Inter-camera adjustments to the VNIR absolute calibration coefficients;
- The application of a degradation model to the SWIR absolute calibration coefficients;
- Improvement of the low frequency multi-angular coefficients (i.e., equalization) for the SWIR strips of the CENTER camera;
- Changes to the dark current values;
- Minor changes to the status of bad pixels.
Users that are interested in more details on the above mentioned changes are referred to Appendix C of the PROBA-V Products User Manual.
Update product metadata for Climate Forecast (CF) compliancy
Metadata was made compliant to the Climate and Forecast metadata conventions (CF v1.6). In Collection 0, metadata was already compliant to these conventions for data from 6 January 2016 onwards, while in Collection 1 all data from 16 October 2013 onwards are CF v1.6 compliant. More details on the CF conventions can be found in Section 4.5 of the PROBA-V Products User Manual.
Some issues in the processing facility and at platform level were solved:
- Bugfix to limit the impact of on-board compression errors for data before July 2015.
- Bugfix in the processing facility component to update the module that checks the satellite attitude data. Some data before 10 February 2016 might be incorrectly marked as ‘No data’.
In order to assess the impact of the various changes that were implemented during the reprocessing, Toté et al. (2016) performed an evaluation of differences between Collection 1 and Collection 0 on S1 and S10 data over six months (November 2013 - April 2014) for all spectral band reflectances and NDVI. The evaluation was carried out on tiles, as well as on subsampled global data. The study revealed that, as a result of the improved cloud detection, substantially less clear observations are yielded. Further, systematic differences between Collection 1 and Collection 0 surface reflectance and NDVI are generally small and similar for 300 m and 1 km data. The full evaluation methodology and results are described in the PROBA-V Reprocessing Evaluation Report:
An evaluation on the entire reprocessed archive is currently being performed and the results and final conclusions will be made available in due course.