# FLATSIM: The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service
## 4 Description of Products  
### General Description  
The choice of the number of products and their processing level delivered by the FLATSIM service was a trade-off between providing only a few small-size high-level products ready-to-use for users non-expert in InSAR and providing the huge amount of all intermediate and final products along with processing logs, most of which are only potentially useful to user experimented in InSAR processing and require large storage and download capabilities on both the provider and user sides.  
Compared to other MTInSAR services, such as LicSAR or P-SBAS on GEP, we have chosen to put the slider more on the side of a rather large product set giving great flexibility for post-processing and analysis of results. This choice results from our long InSAR processing experience showing that starting from the coregistered stack of wrapped interferograms (that is a large burden of the processing) some processing steps can be optimized a-posteriori based on the analysis of the first time-series results.  
The details of the products made available by FLATSIM are described here: [[https://formater.pages.in2p3.fr/flatsim/](https://formater.pages.in2p3.fr/flatsim/)]([https://formater.pages.in2p3.fr/flatsim/](https://formater.pages.in2p3.fr/flatsim/)) (accessed on 10 September 2021). Here, we give insights on the main types of products that are delivered, including quality assessment products and auxiliary products useful for controlling how successfully the automated workflow proceeded. Except for the DEM which is provided only in radar geometry, all the products are delivered in both radar and ground geometries. For instance, this allows the user to re-run with his own computing resources the unwrapping step, or the time series inversion, before geocoding. We give all the necessary information so that the user can redo the processing from the merged, 2-looks, wrapped interferograms, if needed.  
Figure 10: Catalog access architecture.  
The products are delivered separately for each processed track as three types of packages: interferogram, time-series, and auxiliary data. Filenames are formed according to the following naming convention:  
\[\text{{{CNES\_TYPE\_GEOMETRY\_[DATE1\_DATE2]\_LOOKSrIKs.EXT}}}\]  
in which  
**TYPE**: points toward the file type (i.e., wrapped interferograms, coherence, etc.). See hereafter for a more detailed description.
**GEOMETRY**: is set either to _radar_ for radar geometry or _geo_ for ground geometry.
**DATE1**: (DATE2, respectively). These optional fields corresponds to the date at which the first (second or last, respectively) image has been taken.
**LOOKS**: is the number of looks used to downsample the image (note there is a factor 4 between the number of range and azimuth looks, i.e., 2 looks means 8 looks in range and 2 looks in azimuth).
**EXT**: is the extension of the file that defines its type:  
**tiff**: contains the data;
**png**: a preview file. It comes with a _legend_ file, typically a colorbar with the scale information.
**meta**: a file that contains additional metadata. It contains for example information about the parameters of the processing chain, or about the product itself like its DOI, or about the satellite geometry, like the orbit direction, the relative orbit number, etc.  
In each package, in addition to the main products, previews, graphs and small text files that contains statistics allow a quick quality assessment of different processing steps. The size of large products is also given in the next subsections. Although some files can be particularly large (>10 Gbytes), Geospatial Data Abstraction Library (GDAL) or GDAL API for example can easily manipulate them and extract sub-grids with lower spatial or temporal resolution. These sub-grids can be used in data analysis packages performing, for example, principal or independent component analysis, if these packages have data size limitations.