Francesco Casu

Satellite radar interferometry time series analysis of surface deformation for Los Angeles, California

[1] The Los Angeles, California, metropolitan area is a tectonically active region with surface deformation that is a combination of fault related tectonics plus a variety of natural and anthropogenic signals. We apply the small baseline subset (SBAS) algorithm to produce an interferometric synthetic aperture radar (InSAR) time series analysis for the Los Angeles area using data acquired by the ERS satellites from late 1995 into 2002. The result is a space-time deformation product that can be exploited to view not only the smoothly varying long-term surface motion, but also its time varying patterns. Large seasonal oscillations of the Santa Ana aquifer observed in Southern California Integrated GPS Network (SCIGN) data are accurately matched in the InSAR time series, moreover, correlations of the InSAR time series with an annual sinusoid allows us to investigate the dynamics of the hydrologic system. INDEX TERMS: 1243 Geodesy and Gravity: Space geodetic surveys; 1294 Geodesy and Gravity: Instruments and techniques; 1803 Hydrology: Anthropogenic effects. Citation: Lanari, R., P. Lundgren, M. Manzo, and F. Casu (2004), Satellite radar interferometry time series analysis of surface deformation for Los Angeles, California, Geophys. Res. Lett., 31, L23613, doi:10.1029/2004GL021294.

Deformation and eruptions at Mt. Etna (Italy): A lesson from 15 years of observations

This work was partly funded by INGV and the Italian DPC and was supported by ASI, the Preview Project and CRdC-AMRA. DPC-INGV Flank project providing the funds for the publication fees.

Deformation Time-Series Generation in Areas Characterized by Large Displacement Dynamics: The SAR Amplitude Pixel-Offset SBAS Technique

We exploit the amplitude information of a sequence of synthetic aperture radar (SAR) images, acquired at different times, in order to generate displacement time-series in areas characterized by large and/or rapid deformation, the size of which is on the order of the images pixel dimensions. We follow the same rationale of the Small BAseline Subset (SBAS) differential SAR interferometry (DInSAR) approach, by coupling the available SAR images into pairs characterized by a small separation between the acquisition orbits. We exploit the amplitudes of the selected image pairs in order to calculate the relative across-track (range) and along-track (azimuth) pixel-offsets (PO). Finally, we apply the SBAS inversion strategy to retrieve the range and azimuth displacement time-series. This approach, referred to as pixel-offset (PO-) SBAS technique, has been applied to a set of 25 ENVISAT SAR observations of the Sierra Negra caldera, Galápagos Islands, spanning the 2003-2007 time interval. The retrieved deformation time-series show the capability of the technique to detect and measure the large displacements affecting the inner part of the caldera that, in correspondence to the October 2005 eruption, reached several meters. Moreover, by comparing the PO-SBAS results to continuous GPS measurements, we estimate that the accuracy of the PO-SBAS time-series is on the order of 1/30th of a pixel for both range and azimuth directions.

Magma injection beneath the urban area of Naples: a new mechanism for the 2012–2013 volcanic unrest at Campi Flegrei caldera

We found the first evidence, in the last 30 years, of a renewed magmatic activity at Campi Flegrei caldera from January 2012 to June 2013. The ground deformation, observed through satellite interferometry and GPS measurements, have been interpreted as the effect of the intrusion at shallow depth (3090 ± 138 m) of 0.0042 ± 0.0002 km3 of magma within a sill. This interrupts about 28 years of dominant hydrothermal activity and occurs in the context of an unrest phase which began in 2005 and within a more general ground uplift that goes on since 1950. This discovery has implications on the evaluation of the volcanic risk and in the volcanic surveillance of this densely populated area.

Ground deformation and source geometry of the 24 August 2016 Amatrice earthquake (Central Italy) investigated through analytical and numerical modeling of DInSAR measurements and structural-geological data

We investigate the ground deformation and source geometry of the 2016 Amatrice earthquake (Central Italy) by exploiting ALOS2 and Sentinel-1 coseismic differential interferometric synthetic aperture radar (DInSAR) measurements. They reveal two NNW-SSE striking surface deformation lobes, which could be the effect of two distinct faults or the rupture propagation of a single fault. We examine both cases through a single and a double dislocation planar source. Subsequently, we extend our analysis by applying a 3-D finite elements approach jointly exploiting DInSAR measurements and an independent, structurally constrained, 3-D fault model. This model is based on a double fault system including the two northern Gorzano and Redentore-Vettoretto faults (NGF and RVF) which merge into a single WSW dipping fault surface at the hypocentral depth (8 km). The retrieved best fit coseismic surface deformation pattern well supports the exploited structural model. The maximum displacements occur at 5–7 km depth, reaching 90 cm on the RVF footwall and 80 cm on the NGF hanging wall. The von Mises stress field confirms the retrieved seismogenic scenario.

SBAS-DInSAR Parallel Processing for Deformation Time-Series Computation

The aim of this paper is to design a novel parallel computing solution for the processing chain implementing the Small BAseline Subset (SBAS) Differential SAR Interferometry (DInSAR) technique. The proposed parallel solution (P-SBAS) is based on a dual-level parallelization approach and encompasses combined parallelization strategies, which are fully discussed in this paper. Moreover, the main methodological aspects of the proposed approach and their implications are also addressed. Finally, an experimental analysis, aimed at quantitatively evaluating the computational efficiency of the implemented parallel prototype, with respect to appropriate metrics, has been carried out on real data; this analysis confirms the effectiveness of the proposed parallel computing solution. In the current scenario, characterized by huge SAR archives relevant to the present and future SAR missions, the P-SBAS processing chain can play a key role to effectively exploit these big data volumes for the comprehension of the surface deformation dynamics of large areas of Earth.

SBAS-DInSAR Analysis of Very Extended Areas: First Results on a 60 000-

We present the results of the first experiment to survey the temporal evolution of the deformation affecting very large areas using the small baseline subset (SBAS) differential synthetic aperture radar interferometry (DInSAR) algorithm. In particular, we have analyzed a set of 264 descending European Remote Sensing (ERS) SAR data frames from 1992 to 2000; these data are relevant to an area in central Nevada (U.S.) that extends for about 600times100 km. The starting point of our study has been the generation of an appropriate set of small baseline multilook interferograms computed from long SAR image strips, which were obtained by jointly focusing six contiguous raw data frames. Following their generation, the selected interferograms, which are computed on a spatial grid of 160times160 m, have been inverted via the SBAS technique to retrieve, for each coherent pixel, the displacement time series and the corresponding mean deformation velocity. The presented results are, to our knowledge, the first ones with such an extended multitemporal SAR data set, and they demonstrate the effectiveness of the approach to analyze the deformation of the investigated zone.

\hbox{km}^{2}

Time-series interferometric synthetic aperture radar (InSAR) methods estimate the spatiotemporal evolution of deformation over large areas by incorporating information from multiple SAR interferograms. Persistent scatterer (PS) and small baseline (SB) methods, which identify areas where the surface is least affected by geometric and temporal decorrelation, represent two families of time-series InSAR techniques to study successfully a wide spectrum of ground deformation phenomena worldwide. However, little is known comparatively about the performance of PS and SB techniques applied to the same region. Here, we compare quantitatively and cross validate the time-series InSAR results generated using two representative algorithms-the maximum likelihood PS method and the small baseline subset algorithm-in selected test sites, over the San Francisco Bay Area imaged by European Remote Sensing (ERS) sensors during 1995-2000. We present line of sight (LOS) velocities and deformation time series using both techniques and show that the root mean squared differences of the estimated mean velocities and deformation from each method are about 1 mm/year and 5 mm, respectively. These values are within expected noise levels and a characteristic of the pixel selection parameters for both the time-series techniques. We validate our deformation estimates against creep measurements from alignment arrays along the Hayward Fault and show that our estimates agree to within 0.5 mm/year LOS velocity and 1.5 mm LOS displacement.

Test Site

Long-term and high temporal resolution gravity and deformation data move us toward a better understanding of the behavior of Mt Etna during the June 1995 – December 2011 period in which the volcano exhibited magma charging phases, flank eruptions and summit crater activity. Monthly repeated gravity measurements were coupled with deformation time series using the Differential Synthetic Aperture Radar Interferometry (DInSAR) technique on two sequences of interferograms from ERS/ENVISAT and COSMO-SkyMed satellites. Combining spatiotemporal gravity and DInSAR observations provides the signature of three underlying processes at Etna: (i) magma accumulation in intermediate storage zones, (ii) magmatic intrusions at shallow depth in the South Rift area, and (iii) the seaward sliding of the volcanos eastern flank. Here we demonstrate the strength of the complementary gravity and DInSAR analysis in discerning among different processes and, thus, in detecting deep magma uprising in months to years before the onset of a new Etna eruption.

Comparison of Persistent Scatterers and Small Baseline Time-Series InSAR Results: A Case Study of the San Francisco Bay Area

Monitoring of deformation phenomena affecting urban areas and man-made structures is of key relevance for the preservation of the artistic, archaeological and architectural heritage. The differential SAR interferometry (DInSAR) technique has already been demonstrated to be an effective tool for non-invasive deformation analyses over large areas by producing spatially dense deformation maps with centimetre to millimetre accuracy. Moreover, by exploiting long sequences of SAR data acquired by different sensors, the advanced DInSAR technique referred to as the small baseline subset (SBAS) approach allows providing long-term deformation time series, which are strategic for guaranteeing the monitoring of urban area displacements. In this work, we investigate the effectiveness of the two-scale multi-sensor SBAS-DInSAR approach to detect and monitor displacements affecting historical and artistic monuments. The presented results, achieved by applying the full resolution SBAS technique to a huge set of ERS-1/2 and ENVISAT data, spanning the 1992–2010 time interval and relevant to the city of Rome (Italy), show the capability of this approach to detect and analyse the temporal evolution of possible deformation phenomena affecting historical buildings and archaeological sites. Accordingly, our analysis demonstrates the effectiveness of the full resolution multi-sensor SBAS approach to operate as a surface deformation tool for supporting the study and conservation strategies of the historical, cultural and artistic heritage.