Retrieval of 3-D Ground Displacement Time Series From Multitemporal/Multiangle Capella Space SAR Data Acquired From Mid-Inclination Orbits

In recent years, small synthetic aperture radar (SAR) satellite constellations have emerged as a viable solution due to their ease of design and relatively low launch costs. These next-generation systems aim to meet the growing needs of the differential interferometric SAR (DInSAR) community, including high spatial resolution and temporal acquisition frequency. Nevertheless, despite their benefits, small satellites face drawbacks such as low power budgets and limited imaging capabilities, needing the exploration of new orbital configurations to meet specific mission objectives. Among these, mid-inclination orbits (MIOs) offer the unique advantage of enabling the retrieval of North-South surface displacements, overcoming a key limitation of conventional sun-synchronous orbits. In this study, we analyze three SAR datasets acquired by Capella Space over the Campi Flegrei (CF) Caldera (Italy), exploiting a 45° MIO. The presented results, validated against GNSS measurements, show a mean standard deviation of 3–4 mm between DInSAR and GNSS LOS-projected time series, while the uncertainty for the North-South component is estimated to be less than 5 mm. Furthermore, we retrieve, for the first time, comprehensive North-South deformation products of the CF caldera, including both a high-resolution map and displacement time series. These outcomes represent a precursor for the upcoming Italian SAR constellation NIMBUS, part of the IRIDE program, which will be launched in a similar MIO configuration and become operational during 2027.