PROBA-V Collection 2 Level-3 data are global composites on daily / five-daily or ten-daily basis. The aim is to optimally combine multiple observations into a single and cloud-free synthesis image. Level-2A data are first atmospherically corrected and these are the basis for the TOC synthesis products. The PROBA-V L3 products are available in 3 resolutions 1km, 300m and 100m.
Level-3 algorithm and data compositing
TOC directional reflectance estimates are obtained by applying the Simplified Method for Atmospheric Correction (SMAC, Rahman and Dedieu, 1994). The atmospheric correction is performed for each band separately and auxiliary data are used to compute the total gaseous transmission, the atmospheric path radiance, the atmospheric spherical albedo and the total downward and upward scattering transmissions. Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) data are used as input for atmospheric correction.
The compositing into synthesis images is performed by the Level 3 Processor. The aim is to optimally combine multiple observations into a single and cloud-free synthesis image. Atmospherically corrected (Level 2B) data are the basis for the TOC synthesis products. Cloud coverage is minimized through discarding pixels that were labelled as cloudy by the cloud detection algorithm. In addition, angular variations are minimized, while global coverage is maximized. The S10 compositing is applied to avoid spatial coverage gaps resulting from clouds and the non-global daily swath coverage in the tropical areas. Atmospherically corrected segment files are combined into a global Level-3 synthesis through application of a Maximum Value Composite (MVC) technique (see among others Holben, 1986 and Tarpley et al., 1984). This technique selects the maximum TOA NDVI (which is additionally calculated within the compositing algorithm) pixel values. The following TOC synthesis products are generated:
- S1 (1-day syntheses)
- S10 (10-day or dekad syntheses): with starting days at the 1st, 11th, or 21st day of a month. For months having 28, 29 or 31 days the S10 of the third dekad comprises the remaining days of that month.
- For the 100 m product, also S5 data files are available. PROBA-V 100 m S5 products are comparable with full-coverage 300 m S1 products and are not real syntheses. Due to the narrow swath of the 100 m camera, there is only overlap in observations for latitudes > ~40° . This means that only poleward of this latitude compositing rules can be applied and that within ~40° S – 40° N the reflectances observed at one of the five days are given.
The layers include:
TOC reflectance for bands Blue, Red, NIR and SWIR
Angular information: solar and viewing zenith and azimuth angles
Status map information
The TIME grid dataset in the S5 and S10 files provides per pixel information at which day the observations over specific regions was taken. This information is provided in minutes since the start of the synthesis period (day 1, 00:00 UTC). Check the Products User Manual more detailed information.
Level-3 Quality assurance
In the Level 3 S1, S5, and S10 product files, the quality indicator is located in the SM (Status Map) Dataset within the QUALITY Group. The SM Dataset contains a quality state indicator per pixel, consisting of an observation indicator (clear, cloud, ice, shadow, undefined), a land/sea flag, and a radiometric quality indicator. Check the Products User Manual for a list of the various quality bit values and how to read them. The Status Map information can be easily read in most programming languages.
A Quality Webpage is available and provides information on the Quality Assessment and the various methods applied to maintain PROBA-V’s data quality at the highest possible level, from the raw satellite observations through the value-added products available at the PROBA-V Data Portal.
Digital Object Identifier (DOI)
European Space Agency, 2023, PROBA-V Level-3 TOC reflectance Data (S1, S5, S10) Collection 2,
Spatial coverage: 75°N, 56°S, 180°W, 180°E
2013-10-16 – 2020-06-30 (for 1 km and 300 m)
2014-03-12 – 2020-06-30 (for 100 m)
Mission status: Complete
Orbit type: Sun-synchronous
European Space Agency, 2023, PROBA-V Level-3 TOC reflectance Data (S1, S5, S10)