Sentinel 3A Ocean and Land Colour Instrument (OLCI) Land Reduced Resolution (LRR) Level 2 data
This dataset contains ocean and land colour imagery data from the Ocean and Land Colour Instrument (OLCI) aboard the European Space Agency (ESA) Sentinel 3A Satellite. Sentinel 3A was launched on the 16th February 2016. Data are provided by ESA and are made available via CEDA to any registered user. The OLCI radiometer images using 21 spectral bands ranging from 400nm to 1020nm.
The OLCI Level-2 Land Reduced (OL_2_LRR) Resolution products are outputs from the OLCI Level-2 processor and contain land and atmospheric geophysical products at Reduced resolution.
The content of these files depends on several switches included in the OLCI configuration parameters. Each geophysical parameter format is only triggered if the corresponding switch is set to ‘1'. Note that all pixels flagged as cloudy are discarded from OLCI Level-2 processing.
OL_2_LRR products have a spatial sampling of approximately 1.2 km for Reduced Resolution. The products are assumed to be computed in Near Real Time (NRT) (i.e. delivered to users less than 3 hours after acquisition), in Non-Time Critical (NTC) (i.e. within 1 month after acquisition) or in re-processed NTC.
Each product provides as measurement data files:
- Surface product as Green Instantaneous Fraction of Absorbed Photosynthetically Active Radiation (GI-FAPAR) and Terrestrial Chlorophyll Index (OTCI)
- Atmosphere by-products as Integrated Water Vapour (IWV) column (this product also contains information for water pixels and is identical to that included in OL_2_WRR and OL_2_WFR)
- Error estimates for all products.
Several associated variables are also provided in the annotations data files:
- Rectified reflectance for red and NIR channels (RC681 and RC865)
- Classification, quality and science flags (LQSF)
- Common data such as the ortho-geolocation of land pixels, solar and satellite angles, atmospheric and meteorological data, time stamp or instrument information. These variables are inherited from Level-1B products.
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Access to these data is available to any registered CEDA user. Please Login or Register for an account to gain access.
Use of these data is covered by the following licence: https://sentinel.esa.int/documents/247904/690755/Sentinel_Data_Legal_Notice. When using these data you must cite them correctly using the citation given on the CEDA Data Catalogue record.
Data collected and prepared by European Space Agency (ESA). Downloaded from the ESA hubs for use by the UK scientific community.
Data are as given by the data provider, no quality control has been performed by the Centre for Environmental Data Analysis (CEDA).
These image files are in NETCDF4 format.
|Sentinel 3 Ocean and Land Colour Instrument (OLCI)||Deployed on: Sentinel 3A|
Computation Element: 1
|Title||Level 2 processing algorithm applied to Sentinel 3 Ocean and Land Colour Instrument (OLCI) raw data|
|Abstract||In addition, a common pre-processing and product formatting process aims to read, check the input, and define and write the outputs. It is important to note that, for each geophysical parameter included in the OLCI Level-2 product, a switch has been defined in the OLCI Level-2 configuration file. Each parameter and its associated flags are produced only if the associated switch is set to '1'. As a consequence, the module generating each parameter is triggered only if the appropriate switch is set to '1'. The pre-processing module, starting from the Level-1B TOA radiances, derives reflectances corrected for gaseous absorption. The consolidation of pixel classifications from Level-1B and the definition of water vapour retrieval are included in this module. The algorithm is divided into five successive steps: 1. The conversion from radiances to reflectances step-checks the Level-1B products and converts radiances into reflectances (also known as first instrumental correction). 2. To be correctly taken into account or to be rejected from the algorithm, pixels have to be differentiated according to four criteria: cloud, land, water and invalid pixels. The first pixel classification focuses on identification of cloudy pixels. This Cloud masking will be improved in the frame of coming evolutions, including the improvement tested and validated during the MERIS 4th reprocessing. 3. Gaseous correction: correcting reflectances for gaseous absorption (i.e. O2, H2O and O3). Five OLCI bands are dedicated to this correction and are not used after this step: Oa13 to Oa15, Oa19 and Oa20. 4. The second-pixel classification estimates glint reflectance and completes pixel classification starting at the second step by consolidating the classification of land and water pixels. 5. The water vapour process retrieves atmospheric water vapour content from clear sky pixels. The land processing module consists of two independent sections (one for each product): 1. The Green Instantaneous Fraction of Absorbed Photosynthetically Active Radiation (GI-FAPAR) section combines the information contained in the blue band with that contained in the bands at 681 and 865 nm to generate "rectified channels" at these latter two wavelengths. 2. The OLCI Terrestrial Chlorophyll Index (OTCI) section uses Rayleigh correction to produce the necessary index. This step accounts for the spectral smile i.e. the in-FOV variation of the central wavelengths of OLCI channels. For more information please see the OLCI user guide in the docs tab.|