## 3 LiCSAR Products: Current State and Future Trend
### Contents, Coverage and Update Strategy of LiCSAR Frame Products  
LiCSAR systematically uses Sentinel-1 IWS SLC data to generate large-scale multilooked interferograms, georeferenced to the ground resolution of a pixel size of \(10^{-3}\times 10^{-3}\) degrees in the WGS-84 geographic coordinate system (corresponding to \(\sim\)100 \(\times\) 100 m at the equator). Sentinel-1 datasets are processed, organised and catalogued in frame units. Default frames consist of 39 bursts (13 bursts within each of three observation swaths)--such a standard frame covers an area of around 220 \(\times\) 250 km. Our standard frame definitions include overlap of one burst per swath with each neighbouring frame along the orbital track. This enables us to seamlessly merge interferometric outputs from the frames. We have defined frames globally, but only carry out systematic LiCSAR InSAR analysis on a selection of frames within our current priority areas. The tectonic priorities are the Alpine-Himalayan Belt (572 frames) and East African Rift System (Figure 7). These frames are currently in the process of being systematic backfilled to a monthly 'rolling' status, in which data will be no more than 1 month out of date. This default status allows us to use the precise orbit ephemerides, which are available 21 days after each acquisition. Frames of a special interest can be switched to a weekly 'rolling' status with interferograms generated using the latest available data (using restituted orbit ephemerides). The LiCSAR system is also producing Sentinel-1 frame interferograms globally over 80% of the 1331 on-land volcanoes considered active during the Holocene [60]. Frames covering areas with volcanic activity are being updated three times per week and the list of these frames is updated based on new and ongoing volcanic activities reported by the Smithsonian Institution [60]. Figure 7 shows the global distribution of the active volcanoes and the number of interferograms for each of them. We develop routines to augment these frames into a 'live' status, i.e., to have interferograms generated as soon as a new acquisition appears at some of our source data stores. Interferograms related to recent seismic events are generated by the LiCSAR EIDP processes. Figure 7 includes locations of earthquakes where LiCSAR generated co-seismic frame interferograms. The frequent updates of earthquake-related frames (by EIDP) ensure their temporary 'live' status until a specified time after the earthquake (in order to also generate several post-seismic interferograms). Due to ESA's acquisition strategy for Sentinel-1, some of the data collected over certain small islands is acquired in SM mode. SM acquisitions are obtained in one of six possible beams. These beams cover a range of incidence angles of approx. 22-44\({}^{\circ}\) and acquire data in a finer pixel spacing of 1.5-3.1 \(\times\) 3.6-4.2 (slant range \(\times\) azimuth) [62]. LiCSAR automated processing produces interferograms for these regions, multi-looked to \(\sim\)30x30 m resolution, and the same output files and metadata as are generated for IWS acquisition mode products. We have added an automatic processing functionality for SM acquisitions to incorporate the following volcanic islands to the LiCSAR product database: La Reunion (French territory, Indian Ocean), Fogo (Cabo Verde), Tristan da Cunha (British Overseas Territory, south Atlantic Ocean) and Marion Island (South Africa, sub-antarctic Indian Ocean). To keep SM frames consistent with the LiCSAR system architecture originally designed for IWS data only, we use the geographic area of the SM image as a \"burst\" in the LiCSInfo database and a subset definition (geographic coordinates of corners covering area of observed island) as a \"frame\". One of the major limiting factors of the use of the InSAR in most of tectonic and volcanic applications is the spatiotemporal variability of tropospheric properties. This is of importance, especially in cases where deformation and topography are correlated [63].