## 2 LiCSAR System Architecture
### LiCSInfo Metadata Database  
The LiCSInfo metadata database has been developed as the core for our autonomous Sentinel-1 processing system. It contains information on the original Sentinel-1 SLC data files, the LiCSAR frame definitions and the links between them through common burst units. It also stores basic information on processed interferometric products (e.g., file paths, perpendicular baseline) and other useful information (e.g., number of unwrapped pixels as a measure of the product quality). The database is also used to maintain frame update triggers if a frame is set as 'active'. The base structure of the database is depicted in Figure 4.  
Sentinel-1 IWS acquisitions in the form of SLC data are originally distributed as a set of focused burst units (or bursts) within three swaths. Burst metadata, including the geographic coordinates of each burst, can be directly read or inherited from Sentinel-1 annotation files provided within the distributed data. We generate custom unique LiCSAR burst identifiers based on the Zero Doppler azimuth time of the first line of the burst relative to the Ascending Node Crossing (ANX) time. The information is ingested to the table bursts. In the case of Sentinel-1 SM mode acquisitions, the whole areal coverage of the image is set as a burst.  
Frame definitions are stored in the table polyps. The table includes the generated frame identifier (the naming convention is explained in Section 3) and geographic coordinates of frame corners, among other metadata. The geographic coordinates are generated either from the set of bursts comprising the frame in the case of IWS products or they are set to cover a particular area of interest in the case of SM  
Figure 4: Base structure of LiCSAR databases—LiCSInfo metadata database for storing information on burst and frame definitions, related input files and output products, and earthquake frame data (**left**) and LiCSinfo batch processing database for storing temporary information used for LiCSAR FrameBatch processing chain (**right**).  
frames. The bursts are linked to the related frames through a lookup table polyps2 bursts. Geodatabase functions are enabled through tables bursts2 geom and polyps2 geom, for both bursts and frames.  
Having the basic information about ingested SLC files stored in the table files and linked to bursts contained within the files through the lookup table files2 bursts, it is possible to perform SQL queries such as identifying files related to requested epochs within a selected frame. These structures are also linked to a concurrent LiCSInfo batch processing database (LiCSBatch database) that is used within the LiCSAR FrameBatch processing chain (see Section 2.3). Here, temporary fields linking job-relevant files and bursts are stored in interconnected LiCSBatch tables, as shown in the right panel of Figure 4. Final product information can be stored in product metadata tables (coherence, rslc, ifg).  
Finally, the Earthquake Data Provider tables include basic information on earthquakes and related frames that are ingested to processing by the LiCSAR Earthquake InSAR Data Provider system (see Section 2.4). These tables keep track of processing stages for generating pre-seismic, co-seismic and post-seismic interferograms.