# FLATSIM: The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service
Other groups are making systematic small baseline differential interferograms over large areas available online, as in the framework of the Advanced Rapid Imaging and Analysis project (ARIA) from Jet Propulsion Laboratory, California Institute of Technology (JPL-Caltech) for California, Tibet and Afar areas [36], or of the Looking Into Continents from Space with Synthetic Aperture Radar (LiCSAR) project for the whole Alpine-Himalayan belt [37]. In these last two cases, the delivered interferograms can be used to recover, after network inversion, the tectonic ground deformation at large-scale, as no high-pass spatial filtering of the phase is performed [23]. Open source time series analysis packages can even be directly integrated with the interferograms production services as for LiCSBAS [38]. In France, the development of InSAR services adapted to Sentinel-1 data for the Earth sciences research community is among the objectives of ForM@Ter, a data and services center for the study of solid earth. ForM@Ter is one component of the national research infrastructure Data Terra ([[https://www.data-terra.org](https://www.data-terra.org)]([https://www.data-terra.org](https://www.data-terra.org)), accessed on 10 September 2021), which aims to promote an integrated approach for the study of the Earth System through multi-type observation data and services, in particular by enforcing data interoperability. ForM@Ter helps developing high-performance tools and services to access, process, and analyze satellite and in-situ data on solid earth, as well as their value-added products, in a unified and simplified way. In particular, ForM@Ter sets up a meta-catalog for unified search and access to data, as well as a web portal to make data, products, and services available. Two services dedicated to the measurement of ground motion by InSAR using Sentinel-1 data are being developed within ForM@Ter: the GDM-SAR and FLATSIM services. Ground deformation monitoring-synthetic aperture radar (GDM-SAR) is an on-demand processing service, which will be accessible to the national and European scientific community as part of the Thematic Core Service Satellite Data of the European solid earth research infrastructure, EPOS ([[https://www.epos-eu.org](https://www.epos-eu.org)]([https://www.epos-eu.org](https://www.epos-eu.org)), accessed on 10 September 2021). In this paper, we focus on the FLATSIM service. FLATSIM stands for ForM@Ter large-scale multi-temporal Sentinel-1 interferometry. This service, dedicated to massive, automatic, multi-temporal InSAR processing over large continental areas (250,000 km\({}^{2}\) minimum per study site), with an emphasis on the recovery of large-scale deformation processes. The FLATSIM service delivers interferograms, line of sight average ground velocity maps, time series of ground displacements, and numerous auxiliary information. The processed areas are selected through a series of call for scientific proposals presently open to the French scientific community. In the following, we first present the main processing steps implemented in FLATSIM, based on the MTInSAR NSBAS software [39; 40]. The FLATSIM parallel implementation on the CNES high performance computing infrastructure is then described together with the production and delivery modules. Next, we present the main products, including the auxiliary data that are provided for assessment of the products' quality. Finally, two FLATSIM case studies among the first selected ones are presented to discuss the qualification of the results.