# FLATSIM: The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service
## 6 Conclusions and Future Work  
The FLATSIM service is dedicated to the monitoring of surface deformation of broad areas (i.e., larger than 250,000 km\({}^{2}\)). It aims at providing accurate measurements of ground displacements for a large range of geophysical applications, as pointed out in Sections 5.2 and 5.3, mostly in natural environments. The service is a collaborative effort between InSAR experts, researchers in geophysics, and CNES engineers. Scientists provide their expertise on multi-temporal InSAR processing with a state of the art processing chain (NSBAS v2.0) and on geophysical processes, while CNES supports the implementation and deployment of this service in an operational mode. Taking advantage of the CNES mirroring of the Sentinel-1 data, as part of the PEPS infrastructure, this service benefits from rapid access to large volumes of imagery, a prerequisite for the efficient execution of the processing chain. The success of the implementation relies (1) on the algorithm of the NSBAS stack processing, with a single reference image for the whole image stack, avoiding redundant copies of input data, together with optimizations for a large number of steps, but more importantly, (2) on the specific, parallel NSBAS chain implementation on the CNES HPC infrastructure, with local transfer of input-output data on cluster nodes, allowing very fast I/O between disk and processors. Since the goal of the service is to serve scientific purposes, the processed regions are selected according to scientific criteria. FLATSIM thus provides a set of products (e.g., the DTs product) that allows the end-users that do not have large computational capabilities to take advantage of the MTInSAR methodology, making an optimal use of the wealth of data provided by the Sentinel-1 mission. Moreover, a set of auxiliary data is also provided, which allows for assessing the quality of the delivered products. The product versatility makes possible their direct use by the end-users: for example by using the velocity maps as provided, ingesting the time-series in signal detection algorithms (e.g., principal component analysis, independent component analysis, geophysical modeling,...), or even by reprocessing individual interferograms or reinverting the time-series. Since the products are given a DOI, they can be cited. Figure 18: Zoom on three geophysical signals. Areas of interest are indicated by the black rectangles in Figure 17.  
In the future, the NSBAS processing chain will continue to evolve to integrate the most recent advances in InSAR processing. As the FLATSIM service has entered its operational phase, the core processing chain is anticipated to be updated at most twice a year. Another step will consist in providing the user with visualization capabilities, either online or with stand-alone tools, that will allow to explore more deeply into the delivered products. Conceptualization, M.-P.D., and C.L. ([PERSON]); Funding acquisition, E.D.-O., and C.P. ; Project administration, C.P. ; Software, F.T., D.C., M.-P.D., C.L. ([PERSON]), E.P. ([PERSON]), E.P. ([PERSON]), and B.S. ; Supervision, F.T., M.-P.D., and J.D. ; Validation, M.-P.D., P.D., R.G., and C.L. ([PERSON]); Writing--original draft, F.T., D.C., M.-P.D., J.D., P.D., R.G., C.L. ([PERSON]), C.L. ([PERSON]), E.D.-O., E.P. ([PERSON]), E.P. ([PERSON]), C.P., and B.S. ; Writing--review and editing, F.T., and M.-P.D. Except for the first author, who has supervised the writing of the paper, authors have been listed by alphabetical order. All authors have read and agreed to the published version of the manuscript. This research was funded by CNES and ForM@Ter (internal funding). The development, automation and optimization of the NSBAS chain necessary for this work was supported by CNES, focused on Sentinel-1 mission, under the project \"DAT-S1: Deformation actuelle au Tibet mesuree par Sentinel-1\". Copernicus Sentinel data 2014-2020, processed by ESA, were retrieved from CNES PEPS platform.