Synthetic Aperture Radar (SAR) tomography is an advanced technique for monitoring deformations of the Earth’s surface. However, the computational complexity of SAR tomography algorithms often restricts their application to large-scale datasets. To address this issue, we introduce a multi-level parallel implementation of a single scatterer detection algorithm specifically designed to exploit the capabilities of modern heterogeneous High-Performance Computing (HPC) systems. By efficiently distributing the computational workload at different levels across multiple processing units, our parallel approach significantly reduces processing time, facilitating the analysis of extensive SAR datasets. We assess the performance of our parallel implementation using real-world SAR data, showcasing its effectiveness in enhancing both the efficiency and scalability of SAR tomography. Our work contributes to advancing remote sensing techniques and offers valuable insights into the application of HPC for large-scale environmental monitoring.

Airborne SAR data are typically affected by phase distortions arising from subwavelength residual positioning uncertainties (known as the phase screen) when acquired along different tracks. Existing methods commonly leverage on disjoint estimation of the phase screens affecting the phase information of multibaseline acquisitions. An innovative approach for jontly estimating the phase screens across multiple baselines is presented. The outcomes of the applied phase calibration are evaluated through tomographic inversion, thus obtaining a 3D image that captures the vertical characteristics of the scene’s scattering. Specifically, the proposed method was applied to multibaseline P-band SAR data obtained through the AfriSAR campaign conducted over the Lopé tropical forests in Gabon (Africa). A reference LIDAR data acquired over the area of interest has also been used for a qualitative evaluation.

We propose a novel formulation for layover regions identification in SAR imaging, by employing an appropriate parametrization of the ground profile and utilizing differential geometry. It enables the rigorous identification of both the regions undergoing direct and indirect layover. Specifically, the adopted ray casting based approach results in an efficient implementation, since the sequential exploration always remains confined only to regions (which are adjacent to direct regions) actually affected by indirect layover, thus minimizing unnecessary computation. The implemented algorithm for SAR layover regions simulation results to be robust, efficient, and easy to be implemented. High-resolution Cosmo Skymed (CSK) C-band SAR data acquired over the mountainous area is used to illustrate the capabilities of the proposed approach.

Airborne interferometric data is typically affected by phase distortions originated from subwavelength residual positioning uncertainties (phase screen) when acquired along different tracks. Available methods estimate the phase screen affecting stacks of multibaseline acquisitions, mainly by exploiting single interfograms separately. A novel method for the joint estimation of the multibaseline phase screens is proposed. The results of the implemented phase calibration are analyzed via a tomographic inversion, allowing to obtain a 3-D imaging estimating the vertical characteristics of the scene scattering. Specifically, we processed the multibaseline, fully polarized P-band synthetic aperture radar (SAR) data collected during the AfriSAR campaign in July 2015 over the Lopé tropical forests in Gabon, West Africa. Validation of the 3-D imaging results, supported by reference LiDAR (NASA LVIS) data, allowed demonstrating that the proposed joint estimation method overcomes the classical disjoint estimation solutions.

In the last two decades, satellite Multi-Temporal Differential Interferometric SAR (DInSAR) techniques have become consolidated tools for studying slow-moving landslides. Moreover, the availability of sensors using different band frequencies and the development of advanced processing algorithms have constantly improved. In this work we discuss the first results of an experimental analysis carried out on multi-temporal multi-baseline L-Band data acquired by the newly launched SAOCOM satellites in the framework of the MEFISTO project founded by the Italian Space Agency (ASI), one of the main aims of which was to test the potentiality of multi-frequency (X, C and L bands) DInSAR data processed with different methodologies applied to a multi-scale slow-landslide analysis.

Among the several applications of multipass InSAR, monitoring of landslides represents one of the most challenging case because of the topographic characteristics, the heterogeneous displacement rates and the frequent presence of vegetation. In this study, we consider the use of multi-frequency InSAR data for the application to case studies located in the North and South Italy.

An innovative method for radiometric calibration of SAR images affected by induced-topography distortions is proposed. The analytical formulation underlying the proposed method is rigorously obtained by using the fundamental concepts of the differential geometry of the surface. It encompasses a suitable 3D geometric description based on a trajectory-centric cylindrical coordinate system, a convenient parametrization of the illuminated terrain surface, and an inverse mapping approach. The practical effectiveness of the GICAL method is successfully demonstrated by using COSMO-SkyMed SAR data.

A novel look-angle function based formulation of the topography-induced backscattering matrix rotation is proposed in this paper. The proposed formulation is obtained by relying on a suitable cylindrical coordinate system and a suitable parametric representation of the illuminated surface. A concise functional form for the polarization orientation angle shifts, whose expression is given uniquely in terms of the partial derivative of the look-angle function along the azimuthal (or along track) direction, is derived. As a result, a unifying analytical approach for the calibration of polarimetric SAR data, which incorporates consistently within a common formalism both area-stretching radiometric compensation and polarization orientation angle shifts compensation, is developed. The validity of the proposed method is demonstrated by using real polarimetric SAR data.

About 54% of world population nowadays lives in urban areas and this percentage is expected to increase up to 66% by 2050. Therefore, it is crucial to manage this social and cultural change by collecting, integrating and sharing reliable and open spatial information concerning the urban environments where we leave in. The present availability of huge archives of synthetic aperture radar (SAR) data collected since 1992 by ESA, in conjunction with the available Earth-Observation (EO) optical data, represents a unique possibility to derive valuable information for the understanding of the ongoing urban processes. In this framework, the three-year project financed by the Italian Ministry of Instruction, Research and University, entitled “URBAN GEOmatics for bulk information generation, data assessment and technology awareness” may play a role for the assessment and the development of new replicable methodologies for the study of soil consumption and mobility in urban zones. The paper aims to present some preliminary results achieved during the project, clarifying how the new emerging technologies for managing big EO data are proficient for the investigation of urban processes.

This paper aims at investigating the use of microwave and optical images for the detection and characterization of fire scars in vegetated areas. To cope with this issue, Sentinel-l (S-1) C-band synthetic aperture radar (SAR), and multispectral Sentinel-2 (S-2) multispectral data are used. First, a consolidated fuzzy-based methodology, specifically designed for retrieving burned areas, is considered. Then, an investigation based on the analysis of the maps of backscattering coefficients, as obtained by processing stacks of SAR images, is performed. The outcomes obtained with SAR data are validated by comparison with the results obtained with the optical multispectral data. Presented experiments are related to the Soberanes fires, California, which ignited on July 22,2016, and affected more than 400 square kilometers. In addition, we explore the potential use of stacks of spatial coherence maps generated from pairs of complex-valued SAR images that encompass a fire event to recover new, additional information on the vegetation state and extent of the fire scars. To the purpose, stacks of S-1 SAR images acquired at different polarizations over the Mt. Vesuvius, Italy, in the 2017 summer season has been used. Some preliminary results, which evidence how the variations of the spatial coherence values can be somehow related to a fire and used to recover additional pieces of information, are presented.

This letter aims to investigate the applicability of the hybrid stripmap-ScanSAR differential synthetic aperture radar interferometry to data collected by the X-band RADAR sensors of the Italian COSMO-SkyMed (CSK) constellation. The presented analysis relies on the experiments carried out on two sets of stripmap and ScanSAR CSK images collected over the Chuquicamata copper mine in Chile and the Mojave Desert in Southern California, respectively. As a result of our investigation, a spurious phase modulation has been recognized in the generated hybrid stripmap-ScanSAR interferograms along the azimuth direction. This effect is due to the specific staggered topology of the used active phased array antennas that introduces half-wavelength residuals during the electronic antenna steering in the elevation plane. A straightforward solution to compensate for such spurious phase modulation effects has been provided, and the achieved results demonstrate its effectiveness. The outcomes of our analysis may be relevant in the perspective of the future CSK Second Generation Program.

This paper describes a general-purpose parallel scheme for efficiently focusing synthetic aperture radar (SAR) data on multicore-based shared-memory architectures. The rationale of the proposed tiling-based parallel focusing model is first discussed, and then, its implementation structure is illustrated. The adopted parallel solution, which is based on a canonical processing pattern, exploits a segmented-block-based approach and works successfully on data acquired by different spaceborne SAR platforms. Insofar as a significant portion of the focusing algorithm is amenable to tiling, our approach decomposes the problem into simpler subproblems of the same type, also providing a suitable mechanism to explicitly control the granularity of computation through the proper specification of the tiling at the different stages of the algorithm itself. Relevant implementation makes use of multithreading and high-performance libraries. Achievable performances are then experimentally investigated by quantifying the benefit of the parallelism incorporated into the prototype solution, thus demonstrating the validity of our approach. Accordingly, canonical performance metrics have been evaluated, and the pertinent scalability has been examined on different multicore architectures. Furthermore, in order to emphasize the practical ability of the proposed parallel model implementation to efficiently deal with data of different SAR sensors, a performance analysis has been carried out in different realistic scenarios including data acquired by the Envisat/ASAR, RADARSAT-1, and COSMO-SkyMed platforms.

A general-purpose parallel scheme for efficiently focusing synthetic aperture radar (SAR) data on multicore-based shared-memory architectures is presented. The proposed parallel solution is based on a canonical processing pattern that exploit a segmented-block-based approach, and it works successfully on data acquired by different SAR platforms. Insofar as significant portion of the focusing algorithm is amenable to tiling, our approach decomposes the problem into simpler subproblems of the same type, also providing a suitable mechanism to explicitly control the granularity of computation through the proper specification of the tiling. Relevant implementation makes use of multithreading and high-performance libraries. Achievable performances are then experimentally investigated by quantifying the benefit of the parallelism incorporated into the prototype solution, thus demonstrating the validity of our approach.

A parallel model for the solution of the computationally intensive multichannel phase unwrapping (MCh-PhU) problem is proposed. Emphasis is placed on those methodological and practical aspects, which lead to a parallel reformulation of the Extended Minimum Cost Flow (EMCF) algorithm. Thus, a novel dual-level parallel computational model, in which the parallelism is hierarchically implemented at two different (i.e., process and thread) levels, is presented. The validity of our approach has been demonstrated through a series of experiments that have revealed a significant speedup. Therefore, the attained high-performance prototype is suitable for the solution of large-scale phase unwrapping problems in reasonable time frames, with a significant impact on the systematic exploitation of the existing, and rapidly growing, large archives of SAR data.

The application of an integrated monitoring tool to assess and understand the effects of annually occurring forest fires is presented, with special emphasis to Mediterranean and Temperate Continental zones of Europe. The distinctive features of the information conveyed by optical and microwave remote sensing data have been firstly investigated, and pertinent information have been subsequently combined to identify burned areas at the regional scale. We therefore propose a fuzzy-based multisource framework for burned area mapping, in order to overcome the limitations inherent to the use of only optical data (which can be severely affected by cloud cover or include low albedo surface targets). The relevant experimental validation has been carried out on an extensive area, thus quantitatively demonstrating how our approach successes in identifying areas affected by fires. Furthermore, the proposed methodological framework can also be profitably applied to Sentinel (optical and SAR) data.

In the theoretical purview of the discrete Calculus, a rigorous gradient-based formulation of the multichannel phase unwrapping (MCh-PhU) problem is systematically established in terms of discrete differential operators, which are defined by the topology of the intrinsically discrete spaces upon which they act, thus capturing the essential topological character of the problem within a suitable matrix formalism and providing interesting implications. Within this methodological framework, the extended minimum cost flow (EMCF) algorithm, which provides an effective strategy aimed at solving the MCh-PhU problem, is revised, and its computational structure is analyzed. A parallel formulation of the computational-intensive EMCF algorithm is then presented. Emphasis is placed on the methodological and practical aspects leading to a novel dual-level parallel computational model in which the parallelism is hierarchically implemented at two different levels. Performance evaluation relevant to the implemented prototype solution is also carried out, thus quantifying the benefit of parallelism at different levels. The significant experimentally achieved speedup demonstrates the validity of our approach. As a result, the attained parallel prototype enables the large-scale solution of the MCh-PhU problem in a reasonable time frame, with a great impact on systematic exploitation of the available SAR archives.

The effective exploitation of the available huge SAR data archives in reasonable time-frames has motivated the development of P-SBAS, a parallel computing solution for the SBAS (Small BAseline Subset) processing chain. Hence, P-SBAS parallel solution represents a valuable tool for the analysis of the complex phenomena characterizing the surface deformation dynamics of Earth large areas, since it permits to exploit the parallelism offered by the modern computational platforms. In this paper, the performance of the parallel algorithm P-SBAS is investigated. The quantitative evaluation of the computational efficiency of the implemented parallel prototype in terms of achieved speedup is addressed to demonstrate the effectiveness of the proposed approach. An experimental analysis has been carried out on real data by employing a computational platform comprising 32 processors. In particular, the performance analysis has been conducted by exploiting different SAR datasets pertinent to different sensors (Envisat and Cosmo Sky-Med) and the factors limiting the inherent scalability are discussed.

This paper proposes a parallel model for the Differential Interferometry Synthetic Aperture Radar approach referred to as Small BAseline Subset (SBAS) algorithm. This new computational model has been designed to be specifically exploited within the emerging cloud computing environments. An experimental analysis, involving two different case studies, has been carried out to demonstrate the effectiveness of the methodology. The major novelty of the proposed Parallel SBAS (P-SBAS) model consists in the capability of processing large SAR data sets in reasonable time-frames. This key feature may be of great impact not only for hazard monitoring and risk mitigation activities but also for data sharing and knowledge spreading within the scientific community.

We present a research project, funded by the Italian Space Agency (ASI), aimed at performing 2D and 3D Focusing of COSMO/SkyMed (CSK) SAR Data. We describe the main objectives of the project, briefly illustrate employed techniques, and finally present the obtained results. The latter show that sub-meter resolution can be achieved in the enhanced spotlight CSK acquisition mode, and that by using 3D focusing it is possible to resolve scatterers at different slant heights within the same range-azimuth resolution cell, even in areas characterized by severe height discontinuities and large thermal dilations effects.

Backscattering from natural rough multilayers is addressed. In order to characterize the radar response patterns of natural rough multilayer, the closed-form solution of the Boundary Perturbation Theory (BPT), specialized to backscattering configuration, is employed in conjunction with a fractal description of the interfacial roughness, involving the fractional Brownian motion (fBm) process. Furthermore, numerical examples are presented and discussed with reference to layered structure of interest for remote sensing scenarios. As a result, BPT-fBm model offers a consistent and plausible explanation of the scattering dependency on the involved parameters, so providing a rationale for understanding the basic scattering properties of natural rough multilayers.

This paper is primarily aimed at formally resolving the seeming discrepancy between the corresponding regimes of validity of two different kinds of perturbative formulations based on boundary perturbation (BPT) and volumetric perturbation (VPRT), respectively. Instead of resorting to purely intuitional considerations, the VPRT regime of validity is obtained by using a formal derivation, which also permits to understand in detail the meaning of the involved approximation. As a result, we demonstrate that these two theoretical constructs addressed to rough multilayer scattering can be now regarded in a conceptually coherent frame. Theoretical analysis is also supported by numerical results.

We propose a comprehensive analysis for the evaluation of the scattering from randomly inhomogeneous semi-infinite media, including both interfacial roughness and volume inhomogeneities, by applying the methodological approach of the Volumetric Perturbative Reciprocal Theory (VPRT). An unifying perspective on the scattering phenomenon considered in its entirety is gained and an analytic scattering model is obtained.

Second-order volumetric perturbative reciprocal theory (VPRT), which has a direct theoretical interest to scattering in random media including up to second-order effects, is presented. Expression for the scattering field are directly given in terms of meaningful reactions, i.e. involving physical observable quantities. Distribution theory for discontinuous test functions provides the rigorous mathematical backbone of the general VPRT formulation, so conferring conceptual elegance to the theoretical construct. In this paper, a conceptual and mathematical new approach of interest in electromagnetic scattering analysis is then introduced and discussed.

This paper presents the main scientific novel outcomes of the research activities included in the project “Buildings Feature Extraction from Single SAR Images: Application to COSMO-SkyMed High Resolution SAR Images”. The project was conceived by the authors of this paper and financed by the Italian Space Agency under the Announcement of Opportunity for the COSMO/SkyMed mission.

We present a theoretical model for the evaluation of electromagnetic transmission through a gently rough wall. The pertinent closed-form solution is obtained in the theoretical framework of the boundary perturbation theory (BPT). Specifically, for a slab with rough interfaces we derive a compact polarimetric solution directly expressed in terms of the (Fresnel) ordinary reflection coefficient only. Numerical results are carried out with reference to the canonical structure by considering two-dimensional Gaussian rough interfaces, and relevant scattering patterns are presented.

A closed-form first-order perturbative solution to the problem of electromagnetic scattering from a layered structure with an arbitrary number of rough interfaces is presented in this paper. Following the classical scheme employed to deal with a rough surface, a perturbative expansion of the fields in the rough-interface layered structure is performed, assuming that roughness heights and slopes are small enough. In this manner, in the first-order approximation, the geometric randomness of the corrugated interfaces is translated into random current sheets imposed on the unperturbed (flat) interfaces and radiating in the unperturbed (flat boundaries) layered media. The scattered field is then represented as the sum of up- and down-going waves, and a systematic approach that involves the use of matrix formalism and generalized reflection/transmission coefficients is employed. This approach permits us to avoid the necessity of the cumbersome Green function formalism. The demonstration of the consistency of the presented solution is analytically provided, showing that the proposed solution reduces to the corresponding existing ones when the stratification geometry reduces to the simplified ones considered by the other authors.

In this paper, we present an elegant closed form solution obtained applying perturbation theory to three-dimensional layered structures with an arbitrary number of rough interfaces. A general method has been developed to treat layered structures that can be described by small changes with respect to an idealized (unperturbed) structure, whose associated problem is exactly solvable. The final expression, beyond the compactness, allows us to directly prove that our formulation satisfies the reciprocity principle.

In this paper the focus is on the intrinsic significance of the first-order perturbative scattering solution for the scattering from layered structures with an arbitrary number of rough interfaces. An exact analytic decomposition of the solution in terms of local interactions is carried out. Consequently, the suitably expanded solution can be expressed as an optical geometric series, where each term of the series is susceptible of a direct physical interpretation. Therefore, the obtained interpretation enables the global scattering phenomenon involved to be visualized as a superposition of local interactions, emphasizing the role of the interference effects in the structure as well. The interpretation opens the way to new techniques for solving the inverse problem, for designing SAR processing algorithms, and for modelling the time-domain response of complex layered structures.

In this paper, we investigate analytically the connection between the existing first-order small perturbation method solutions for the scattering from a layered structure with one rough interface. First of all, by using effectively the concept of generalized reflection coefficients, we cast the existing models in a unified more compact formulation and point out the connection between the different analytical solutions. The obtained reformulations of the available analytical solutions allow us to subsequently prove the consistency of the considered models. Finally, a suitable expansion is performed that leads us to understand the physical meaning of the analytical expressions. The obtained unified formulation also opens the way toward a general closed-form solution for the problem of scattering by a layered structure with an arbitrary number of corrugated interfaces.

In this paper we show that existing small perturbation-based methods for computation of scattering from a layered structure with a single rough interface are substantially equivalent. In addition, a further reformulation of the scattered field expression allows us to express the final solution in series form: we then show that each term of the series has a direct physical interpretation.