Sentinel-2 Level 3A

Description

Levels 3A are a monthly syntheses of cloud surface refectances. A short documentation about the product is available at CESBIO’s multitemp blog.

Also, the ESA’s document provide explanations about algorithms used to generate L3A products.

Download data

Data are downloadable from : https://theia.cnes.fr

iota2’s cook

Configuration file parameter

chain.s2_l3a_path is the parameter to enable the use of L3A products

chain:
{
    ...
    s2_l3a_path:"/absolute/path/to/Storage_directory"
    ...
}

Data storage

Data must be stored by tiles as the following tree :

└── Storage_directory
    ├── T31TCJ
    │   ├── SENTINEL2X_20181015-000000-000_L3A_T31TCJ_D_V1-1
    │   │   ├── MASKS
    │   │   │   └── *.tif
    │   │   └── *.tif
    │   └── ...
    ├── T31TDJ
    │   └── ...
    └── ...

Where tiles are T31TCJ, T31TDJ …

Data usage

Time series

Every dates are chronologically stacked together in order to provide a temporal series to the learning / classification system. Then, if the configuration file parameter sensors_data_interpolation."use_gapfilling is set to True, the gapfilling is processed.

Note

Every bands are resample to a 10m resolution.

GapFilling

GapFilling allow iota2 the interpolation of clouds and resample every tile’s temporal series on the same temporal grid. The cloud interpolation is based on masks provided by L3A products.

Masks usage

A BINARY_MASK raster is generated for each L3A dates and place next to native data. BINARY_MASK is the raster provided to the gapFilling algorithm to know pixels to interpolate by dates. iota2 use _FLG_R1.tif raster to determine pixels to flag as to be interpolated. Every pixels under 0 and 1 respectively NODATA and Cloud / Cloud's shadow will be interpolated.

Features

Once the gapFilling is done, if the configuration file parameter arg_train.features is different from [] then features are compute from the the gapfilled time series. NDVI, NDWI and brightness are automatically computed. Also, users could provide a set of features describe as a BandMath expression using : Sentinel_2_L3A.additional_features configuration file parameter. By default every bands are use as features and use by the classification process to find pixels label, but with the joint use of Sentinel_2_L3A.keep_bands and iota2_feature_extraction.extract_bands only targeted bands will be used.

Available bands

Every bands provided by THEIA L3A product are availble.

Sentinel_2_L3A:
{
    keep_bands:["B2", "B3", "B4", "B5", "B6", "B7", "B8", "B8A", "B11", "B12"]
}