ARD Production

The following sections give a brief overview of the major package components for creating an ARD product.

MGRS Gridding

The basis of the processing chain builds the Sentinel-2 Military Grid Reference System (MGRS) tiling system. Hence, a reference file is needed containing the respective tile information for processing ARD products. A KML file is available online that will be used in the following steps:

S2A_OPER_GIP_TILPAR_MPC__20151209T095117_V20150622T000000_21000101T000000_B00.kml

This file contains all relevant information about individual tiles, in particular the EPSG code of the respective UTM zone and the geometry of the tile in UTM coordinates. This file is automatically downloaded to ~/.cesard by the function cesard.ancillary.get_kml(). The function cesard.tile_extraction.aoi_from_tile() can be used to extract one or multiple tiles as spatialist.vector.Vector object.

Scene Management

The source products are managed in a local SQLite database to select scenes for processing (see pyroSAR’s section on Database Handling) or are directly queried from a STAC catalog (see s1ard.search.STACArchive).

After loading an MGRS tile as an spatialist.vector.Vector object and selecting all relevant overlapping scenes from the database, processing can commence.

DEM Handling

cesard offers a convenience function cesard.dem.mosaic() for creating scene-specific DEM files from various sources. The function is based on pyroSAR.auxdata.dem_autoload() and pyroSAR.auxdata.dem_create() and will

  • download all tiles of the selected source overlapping with a defined geometry

  • create a GDAL VRT virtual mosaic from the tiles including gap filling over ocean areas

  • create a new GeoTIFF from the VRT including geoid-ellipsoid height conversion if necessary (WGS84 heights are generally required for SAR processing but provided heights might be relative to a geoid like EGM2008).

ARD Formatting

During SAR processing, files covering a whole scene are created. In this last step, the scene-based structure is converted to the MGRS tile structure. If one tile overlaps with multiple scenes, these scenes are first virtually mosaiced using VRT files. The files are then subsetted to the actual tile extent, converted to Cloud Optimized GeoTIFFs (COG), and renamed to the ARD naming scheme. All steps are performed by satellite-specific format functions, e.g. s1ard.ard.format().