Tazio Strozzi

Interferometric point target analysis for deformation mapping

Interferometric Point Target Analysis (IPTA) is a method to exploit the temporal and spatial characteristics of interferometric signatures collected from point targets to accurately map surface deformation histories, terrain heights, and relative atmospheric path delays. In this contribution the IPTA concept is introduced, including the point selection criteria, the phase model and the iterative improvement of the model parameters. Intermediate and final results of an IPTA example using a stack of ERS-1 and ERS-2 data, confirm the validity of the concept and indicate a high accuracy of the resulting products.

Glacier motion estimation using SAR offset-tracking procedures

Two image-to-image patch offset techniques for estimating feature motion between satellite synthetic aperture radar (SAR) images are discussed. Intensity tracking, based on patch intensity cross-correlation optimization, and coherence tracking, based on patch coherence optimization, are used to estimate the movement of glacier surfaces between two SAR images in both slant-range and azimuth direction. The accuracy and application range of the two methods are examined in the case of the surge of Monacobreen in Northern Svalbard between 1992 and 1996. Offset-tracking procedures of SAR images are an alternative to differential SAR interferometry for the estimation of glacier motion when differential SAR interferometry is limited by loss of coherence, i.e. in the case of rapid and incoherent flow and of large acquisition time intervals between the two SAR images. In addition, an offset-tracking procedure in the azimuth direction may be combined with differential SAR interferometry in the slant-range direction in order to retrieve a two-dimensional displacement map when SAR data of only one orbit configuration are available.

Landuse mapping with ERS SAR interferometry

Two landuse maps and a forest map of three different areas in Europe were completed with ERS SAR interferometry. The test sites represent various geomorphological regions with different cover types. In this article, the mapping algorithms are presented, the results are summarized, and the potential and limitations of ERS SAR interferometry for landuse mapping are discussed. Overall, the results suggest that landuse classification accuracies on the order of 75% are possible with, in the best case, simultaneous forest and nonforest accuracies of around 80-85%. The presence of topography reduces the performance.

SAR interferometric and differential interferometric processing chain

The authors have developed a SAR and an interferometric processor suitable for all current SAR systems. The main modules of the processor are the Modular SAR Processor (MSP), the Interferometric SAR Processor (ISP), and the Differential Interferometry and Geocoding Module (DIFF&GEO). The potential and limitations of the selected algorithms and processing techniques are discussed. Typical results are shown.

Detecting and quantifying mountain permafrost creep from in situ inventory, space-borne radar interferometry and airborne digital photogrammetry

In this paper three different techniques for detecting and quantifying mountain permafrost creep are compared: (1) rock glacier inventory and characterization from in situ indicators, (2) space-borne radar interferometry, and (3) digital processing of repeated airborne imagery. The specific characteristics of the three methods and their complementarity are investigated for the Fletschhorn mountain range in the Simplon/Saas valley region, Swiss Alps. We found that radar interferometry is suitable to quantify the degree of activity and the order of surface velocity of rock glaciers over large areas in one process, with the possibility to also detect very small movements of inactive and relict rock glaciers. On the other hand, aero-photogrammetry represents a valuable base for additional interpretation of the three-dimensional surface flow field (including speed, direction and change in thickness) of the most active rock glaciers. Results from radar interferometry can also form the basis for further detailed in situ investigations.

JERS SAR interferometry for land subsidence monitoring

In this paper, the potential of L-band repeat-pass differential synthetic aperture radar (SAR) interferometry for land subsidence monitoring is evaluated using Japanese Earth Resources Satellite (JERS) SAR data. Bologna, Mexico City, and the Ruhrgebiet are selected as application sites representing slow to fast deformation velocities. The investigation includes feasibility aspects such as data availability, the temporal decorrelation over different landcover classes and the range of useful spatial baselines, an analysis of the achieved deformation accuracy, and considerations on the complementarity to European Remote Sensing satellite (ERS) SAR interferometry and leveling surveys. In spite of the rather limited data availability, land subsidence maps could be generated for the three selected application sites. In contrast to ERS C-band SAR data, JERS L-band interferometry permitted the retrieval of subsidence values over vegetated areas and forest when using interferograms of less than one year acquisition time interval and short baseline. In addition, the longer L-band wavelength was found to be superior in the case of large deformation gradients that lead to phase-unwrapping problems in C-band interferometry.

Ionospheric Electron Concentration Effects on SAR and INSAR

The launch of ALOS and the high potential expected for the L-band PALSAR motivated us to investigate ionospheric electron concentration effects using JERS L-band SAR data acquired at high latitudes. An important focus of our work was on the identification of ionospheric effects and resulted in methodologies to detect ionospheric effects in single SAR acquisitions as well as in repeat-orbit pairs. For cases where significant ionospheric anomalies are present, procedures to improve SAR offset tracking and interferometric results are proposed and the retrieval of free electron density maps is discussed.

Natural versus anthropogenic subsidence of Venice

We detected land displacements of Venice by Persistent Scatterer Interferometry using ERS and ENVISAT C-band and TerraSAR-X and COSMO-SkyMed X-band acquisitions over the periods 1992–2010 and 2008–2011, respectively. By reason of the larger observation period, the C-band sensors was used to quantify the long-term movements, i.e. the subsidence component primarily ascribed to natural processes. The high resolution X-band satellites reveal a high effectiveness to monitor short-time movements as those induced by human activities. Interpolation of the two datasets and removal of the C-band from the X-band map allows discriminating between the natural and anthropogenic components of the subsidence. A certain variability characterizes the natural subsidence (0.9 ± 0.7 mm/yr), mainly because of the heterogeneous nature and age of the lagoon subsoil. The 2008 displacements show that man interventions are responsible for movements ranging from −10 to 2 mm/yr. These displacements are generally local and distributed along the margins of the city islands.

Mapping wet snowcovers with SAR interferometry

Abstract The capability of mapping wet snowcovers by means of Synthetic Aperture Radar (SAR) is well known. However, using only the backscattering intensity at C-band, there still remain some incertitudes regarding the effect of either rough snow surfaces or very small liquid water contents for measurements performed at small incidence angles. Since the European remote sensing (ERS) satellites usually operate at 23 incidence angle, it is important to consider these effects. This paper shows that these difficulties can be overcome using repeatpass SAR interferometry. ERS data over a part of the Netherlands and a part of Switzerland are used as illustrative examples. In the situations examined the occurrence of wet snow could not be directly observed by means of the backscattering intensity, but the use of the degree of coherence allowed an easy discrimination. The results are validated with in situ measurements.

The initiation of glacier surging at Fridtjovbreen, Svalbard

Abstract Glacier surges in Svalbard have long durations and multi-year terminations, but much less is known regarding surge initiation in the archipelago. Fridtjovbreen, a 12 km long glacier in central Spitsbergen, advanced ∼ 2.8 km during a surge in the 1990s at a maximum rate of ∼ 4. 2 m d–1 . Differential dual-azimuth satellite radar interferometry (SRI) is used to produce ten snapshots of three-dimensional surface dynamics and four digital elevation models covering the period October 1991–October 1997. The glacier velocity rose slowly and uniformly until June 1995. It then increased dramatically to a measured maximum of ∼ 2.5 m d–1 during February and May 1996, and by October 1997 it had dropped. We attempt to evaluate errors in the calculated velocities. Systematic errors are evaluated using the apparent displacement of bedrock, ∼0.03 m d–1 . Errors arise from assumptions during processing, for example that ice-flow direction does not change during the surge. Two independent measurements using dual-azimuth processing show the mean absolute change in flow direction was ∼1.2°. This study covers fast-flow initiation and peak flow, but not the deceleration phase. The SRI observations show a progressive acceleration phase to the surge, with no evidence of a surge front propagating down-glacier.