The remarkable performance achieved by Large Language Models (LLM) has driven research efforts to leverage them for a wide range of tasks and input modalities. In speech-to-text (S2T) tasks, the emerging solution consists of projecting the output of the encoder of a Speech Foundational Model (SFM) into the LLM embedding space through an adapter module. However, no work has yet investigated how much the downstream-task performance depends on each component (SFM, adapter, LLM) nor whether the best design of the adapter depends on the chosen SFM and LLM. To fill this gap, we evaluate the combination of 5 adapter modules, 2 LLMs (Mistral and Llama), and 2 SFMs (Whisper and SeamlessM4T) on two widespread S2T tasks, namely Automatic Speech Recognition and Speech Translation. Our results demonstrate that the SFM plays a pivotal role in downstream performance, while the adapter choice has moderate impact and depends on the SFM and LLM.

This work describes the airborne Synthetic Aperture Radar (SAR) infrastructure developed at the Institute for Electromagnetic Sensing of the Environment (IREA) - National Research Council of Italy (CNR), Naples, Italy.The current infrastructure consists of a flight and a ground segment, including: a multi-frequency airborne SAR sensor operating at X- and L-band, owned by IREA-CNR; an IT platform for data storage and processing, located at the laboratories of IREA-CNR; an airborne SAR data processing chain, completely developed at IREA-CNR and University Parthenope, Naples, Italy.To show the current capabilities of this infrastructure in terms of characteristics of the final products as well as of quick response in emergency cases, a real world application scenario, namely, the monitoring of the volcanic area of Stromboli, Italy, in the frame of an agreement between IREA-CNR and the Department of Civil Protection of the Italian Presidency of the Council of Ministers, is presented.The short-term future perspectives related to the exploitation of this airborne SAR infrastructure are finally drawn, according to ongoing strengthening actions supported by already assigned fundings.

The SAOCOM-1 space-borne mission, developed by the Space Agency of Argentina (CONAE), involves two Synthetic Aperture Radar (SAR) sensors operating at L-band with different acquisition modes. Among them, the TOPSAR mode lacks burst synchronization, thus making more difficult the selection of repeat pass datasets suitable for interferometric purposes.This work shows that, despite the lack of burst synchronization, SAOCOM-1 TOPSAR data can be in any case successfully used for interferometric applications due to the large number of available acquisitions carried out with this mode.

In this work we focus on the estimation of the soil permittivity from L-band polarimetric Synthetic Aperture Radar (SAR) data. To this aim, we consider SAOCOM-1 data collected in December 2021, over the province of La Pampa, in Argentina. The soil permittivity estimates, obtained through the Polarimetric Two-Scale Model (PTSM), are compared with the in-situ measurements collected at the same time of the SAR acquisition. Our results of the dielectric constant retrieved for the full scene are in accordance with a semi-arid landscape where the mode of the retrieved estimates is around εr~4 and a 2.41% relative error was found for ground data.

This work is focused on the forthcoming ROSE-L mission, developed by the European Space Agency (ESA) as part of the Copernicus Expansion Programme. Among the different advanced engineering solutions that will be exploited by the system, we concentrate on the ScanSAR acquisition mode and show how to enable ROSE-L for a high gain two-look configuration. More specifically, we propose a solution aimed at achieving different goals.The first goal is focused on better tailoring the ROSE-L system, originally designed for a one-look ScanSAR mode configuration, to a more attractive two-look one. The second goal is to retain the azimuth resolution and the range swath of the original system design. The third goal is to be compliant with the main system specifications, with respect to the one- look mode configuration.To achieve these goals, we propose to properly shape the radiated azimuth beam, without upsetting the original design of the ROSE-L radar antenna and taking advantage of the degrees of freedom offered by its current layout.

The problem of the identification of Radio Frequency Interferences (RFI) that corrupt Synthetic Aperture Radar (SAR) data is addressed in this work.In particular, we propose a new approach based on the minimization of the Bayesian Information Criterion (BIC) able to detect, on a pixel-by-pixel basis, the RFI signals within the considered SAR data.The performance of the proposed approach is assessed by means of both simulated and real-world airborne L-band SAR data corrupted by RFI signals.

SAOCOM-1 constellation operates in three acquisition modes: Stripmap (SM), TOPSAR Narrow (TNA and TNB) and TOPSAR Wide (TW). Since repeat pass SAOCOM-1 TOPSAR acquisitions are not synchronized, the generation of the related interferometric products is not guaranteed, as it happens instead for the synchronized repeat pass TOPSAR acquisitions, such as those of Sentinel-1. In this work, we assess the suitability of SAOCOM-1 TOPSAR acquisitions for generating interferometric products. To this aim, we first discuss the constraints that must be fulfilled by the repeat pass non-synchronized TOPS acquisitions in order to make it feasible the generation of usable interferograms. Then, we verify if SAOCOM-1 TOPSAR acquisitions fulfill these constraints. For this purpose, we present an analysis based on the use of a data set composed by 18 TNB images relevant to a single subswath illuminating a region located in the South-West of Argentina. From this data set, we were able to select 48 pairs that guarantee the spectral superposition needed for interferometric purposes. We verified that the 50% of these 48 pairs fulfill the constraint required to avoid in the corresponding interferograms the presence of non-coherent azimuth stripes, whose azimuth extension depends on one side on the mis-synchronization percentage between the repeat pass acquisitions, and on the other side on the overlapping percentage between adjacent bursts of the same acquisition. Summing up, the presented analysis proves the potential of SAOCOM-1 TOPSAR acquisitions to obtain interferometric products, despite the absence of bursts synchronization between repeat pass acquisitions.

This work shows that additional ScanSAR capabilities, with respect to those achievable through the current synthetic aperture radar (SAR) system of the forthcoming Radar Observation System for Europe at L-band (ROSE-L) mission, may be easily enabled through a proper shaping of the azimuth pattern of the TX radar antenna. In particular, we show that by properly acting only on the distribution of the input excitations of the elements of the currently designed TX antenna array, we can move from a single azimuth-look ScanSAR configuration to a more attractive two-look one. This result is achieved without upsetting the current system architecture and without changing the current mission parameters [such as azimuth resolution, range swath, and pulse repetition frequency (PRF)], all tailored to a one-look ScanSAR configuration. On the other hand, the proposed two-look mode requires to double the azimuth beamwidth with respect to the one-look mode, thus leading to an unavoidable antenna gain decrease, whose amount is approximately 3 dB. The presented analysis also shows that, by still acting on the distribution of the input excitations of the TX antenna array, the scalloping effect can be significantly mitigated with respect to that of the current system design, in both scenarios relevant to the original one-look ScanSAR configuration and the proposed two-look one.

The retrieval of the topographic changes induced by the eruptive activity of the Stromboli volcano, located in the Tyrrhenian Sea off Sicily (Italy), is the main topic of this contribution. In particular, we focus on the Stromboli activity during the July 2019 - October 2022 time period that was characterized by two violent explosions and months of lava emission inducing topography changes. These variations have been measured through the comparison of the generated airborne single-pass interferometric Synthetic Aperture Radar Digital Elevation Models.

We investigate in this work the soil moisture retrieval from P-band polarimetric Synthetic Aperture Radar (SAR) data. In particular, the analyzed SAR data were collected during a helicopter-borne campaign conducted over the Apulian Tavoliere plain, Southern Italy, on July 2021. The soil moisture estimates, obtained through the Polarimetric Two-Scale Model (PTSM), are then synthetically compared with in-situ measurements collected at the same time of the radar survey.

It is widely recognized that SAR images can suffer from the presence of RFI, especially at the low frequencies of the microwave spectrum. Such nuisance signals can significantly impair the quality of the SAR data with unwanted effects on the final products. This paper describes a processing strategy for the detection and cancellation of RFI signals corrupting airborne SAR raw-data. In addition, the performance of the proposed strategy is assessed by exploiting airborne L-band FMCW-SAR data.

Airborne synthetic aperture radar (SAR) data focusing in presence of highly variable squint angles is addressed in this work. To do this, a time-domain SAR focusing algorithm has been developed to account for the target-dependent nature of the acquisition squint angle. For comparison purposes, we have considered also a SAR processor based on the use of an azimuth-invariant processing squint angle. Moreover, real data acquired by two different X-band airborne SAR systems have been analyzed. The aims of the work are twofold. First, we show that the adoption of an azimuth-invariant processing squint angle, typically pursued by computationally efficient focusing strategies, may become inappropriate in several airborne missions, which are typically corrupted by motion errors induced by atmospheric turbulence. On the contrary, these problems are circumvented through the developed time-domain focusing strategy, which exploits a target-dependent processing squint angle that is coincident with the acquisition one. Second, we show that the proposed focusing strategy must be properly revised in the case of interferometric processing. In particular, we show that if the (target-dependent) acquisition squint angle is different for the two interferometric channels used, we have to move toward a different focusing paradigm, say, an interferometric focusing solution. This is again based on considering a target-dependent processing squint angle, but for each target, this processing angle should be equal neither to the acquisition squint angle of the “master” acquisition nor to that of the “slave” one: it must instead lie halfway between them. We prove that this approach is appropriate to obtain high interferometric coherence, and it is sub-optimal to separately focus the interferometric channels.

In recent years, airborne Synthetic Aperture Radar (SAR) remote sensing is becoming more and more attractive, thanks to the operational flexibility and observation capabilities provided by aerial SAR systems, and also due to the comparatively low-cost of these radar devices. In this work, we show the preliminary results relevant to the first acquisition campaign of the new Italian airborne Multiband Interferometric and Polarimetric SAR (MIPS) system, which is based on the Frequency Modulated Continuous Wave (FMCW) technology, and is able to operate at both X- and L-band.

In the future ROSE-L mission, supported by the European Space Agency (ESA) as part of the Copernicus Expansion Programme, different advanced acquisition techniques will be simultaneously experienced, namely, ScanSAR, Scan On Receive and Digital Beam Forming on receive. This work shows that additional ScanSAR capabilities with respect to those achievable through the current ROSE-L system design may be enabled through proper shaping of the azimuth pattern of the TX radar antenna. In particular, we show that without upsetting the current system architecture, and properly acting only on the distribution of the input excitations of the elements of the currently designed TX array antenna, we can obtain a significant mitigation of the scalloping effect and/or move from a single azimuth look ScanSAR configuration to a more attractive two-look one.

Abstract Modern programming languages typically provide some form of comprehension syntax which renders programs manipulating collection types more readable and understandable. However, comprehension syntax corresponds to nested loops in general. There is no simple way of using it to express efficient general synchronized iterations on multiple ordered collections, such as linear-time algorithms for low-selectivity database joins. Synchrony fold is proposed here as a novel characterization of synchronized iteration. Central to this characterization is a monotonic isBefore predicate for relating the orderings on the two collections being iterated on and an antimonotonic canSee predicate for identifying matching pairs in the two collections to synchronize and act on. A restriction is then placed on Synchrony fold, cutting its extensional expressive power to match that of comprehension syntax, giving us Synchrony generator . Synchrony generator retains sufficient intensional expressive power for expressing efficient synchronized iteration on ordered collections. In particular, it is proved to be a natural generalization of the database merge join algorithm, extending the latter to more general database joins. Finally, Synchrony iterator is derived from Synchrony generator as a novel form of iterator. While Synchrony iterator has the same extensional and intensional expressive power as Synchrony generator, the former is better dovetailed with comprehension syntax. Thereby, algorithms requiring synchronized iterations on multiple ordered collections, including those for efficient general database joins, become expressible naturally in comprehension syntax.

In recent years, airborne Synthetic Aperture Radar (SAR) systems based on the Frequency Modulated Continuous Wave (FMCW) technology are becoming very popular thanks to their simple architecture and low cost. When FMCW SAR data are processed, it is essential to accurately know the electronic parameters of the system. In particular, the use of an incorrect value of the Frequency Sweep Rate (FSR) introduces geometric distortions in the focused images. In this work we provide the assessment of the performances of the FSRETC algorithm, recently proposed with the aim of estimating the correct FSR from the radar data. The presented analysis is conducted through the use of real data acquired by an airborne FMCW SAR system.

In this work, a time-domain procedure is presented to focus airborne Synthetic Aperture Radar (SAR) data collected in the presence of strong variations of the squint angle during the radar acquisition. The approach is tested on two datasets acquired by two different X-band airborne SAR systems.

In this work, we present some results of the flight-test campaign carried out with the AXIS system, which is an Italian single-pass interferometric airborne X-Band Synthetic Aperture Radar (SAR) based on the frequency modulated continuous wave technology. The system has recently been developed in the frame of a cooperation between a public research institute (IREA-CNR) and a private company (Elettra Microwave). The campaign was performed in 2018 over the Salerno area, South of Italy, and some corner reflectors (CRs) were deployed over the illuminated area with the aim of verifying the system performances in terms of geometric resolution and target location.

The retrieval of soil moisture and surface roughness from P-Band Synthetic Aperture Radar (SAR) data is here addressed. In particular, the presented methodology is based on the Polarimetric Two Scale Model (PTSM) recently proposed in the literature, and exploits the combination of SAR data collected along two antiparallel flight-tracks flown on the same area with a very short revisit time. Some considerations about the effects of the SAR acquisition geometry on the retrieval results are also provided. The used dataset is relevant to a desert campaign carried out in 2018 with the helicopter-borne P-band SAR system owned by the Italian Space Agency.

The Italian Space Agency (ASI) has recently entrusted CO.RI.S.T.A. with the development of a radar system that can be mounted onboard small airplanes or helicopters and may operate, at different frequencies belonging to the P-Band, either as Synthetic Aperture Radar (SAR) or as Sounder. In this work, we present preliminary results of the helicopter-borne desert campaign carried out with this system in 2018 over the Erfoud area, Morocco, in the frame of a project that has involved different public Italian Research Institutes and Universities.

MOTIVATION: We previously proposed a paradigm shift in genomic data management, based on the Genomic Data Model (GDM) for mediating existing data formats and on the GenoMetric Query Language (GMQL) for supporting, at a high level of abstraction, data extraction and the most common data-driven computations required by tertiary data analysis of Next Generation Sequencing datasets. Here, we present a new GMQL-based system with enhanced accessibility, portability, scalability and performance. RESULTS: The new system has a well-designed modular architecture featuring: (i) an intermediate representation supporting many different implementations (including Spark, Flink and SciDB); (ii) a high-level technology-independent repository abstraction, supporting different repository technologies (e.g., local file system, Hadoop File System, database or others); (iii) several system interfaces, including a user-friendly Web-based interface, a Web Service interface, and a programmatic interface for Python language. Biological use case examples, using public ENCODE, Roadmap Epigenomics and TCGA datasets, demonstrate the relevance of our work. AVAILABILITY AND IMPLEMENTATION: The GMQL system is freely available for non-commercial use as open source project at: http://www.bioinformatics.deib.polimi.it/GMQLsystem/. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

This paper shows the design parameters and specifications of the AXIS system, which is an Italian single-pass interferometric airborne X-Band Synthetic Aperture Radar (SAR) based on the frequency modulated continuous wave technology. The activity is framed within a cooperation agreement signed between Elettra Microwave S.r.l and the Institute for Electromagnetic Sensing of the Environment (IREA) of the Italian National Research Council (CNR).

In this paper we derive a simple model to describe the distortions on focused airborne SAR data rising from the usage of inaccurate external information of the topography of the illuminated area. The model is based on the assumption that an accurate time-domain strategy is applied to focus the data. Moreover, perfect knowledge of the aircraft trajectory is also assumed, in order to better highlight the relation between true topography and airborne SAR focused data. The presented model takes into account the coupling between the trajectory deviations affecting the aircraft flight track and the topography errors. A closed form expression for both the amplitude and phase distortions corrupting the focused signal is provided. To validate the presented analysis some simulation results relevant to a realistic SAR acquisition scenario are finally shown.

We present a solution for simplifying a recently proposed two-step processing technique that allows to retrieve the constant phase offset present in the unwrapped synthetic aperture radar (SAR) interferograms by exploiting an external, even low-accuracy, digital elevation model (DEM) of the illuminated area and without using corner reflectors. In particular, we show in this letter that the second processing step, namely, the slope-topography-based estimate, can be avoided without impairing the accuracy of the final phase offset estimate. To this aim, we introduce a simple modification to the first step, referred to as phase-based estimate, by considering the vertical bias of the available external DEM as the second unknown parameter in the carried out estimation. The simplified algorithm is very easy to implement and is particularly suitable for airborne SAR interferometry. It has been tested on real airborne SAR data and the obtained results show that the achieved accuracy is the same or better than that achieved through the original two-step approach.

This work aims to describe the characteristics and the status of development, including the results of a first preliminary testing campaign, of a low frequency airborne imaging radar developed in Italy for the Italian Space Agency.

In order to generate a Digital Elevation Model (DEM) by exploiting the Synthetic Aperture Radar (SAR) Interferometry (InSAR) technique, it is necessary to properly estimate an unknown phase offset present in the unwrapped interferogram.

The paper presents the results of an experiment carried out with a hybrid along-track (AT) / across-track (XT) interferometric Synthetic Aperture Radar (SAR) configuration in order to simultaneously estimating the velocity and the elevation pattern of the illuminated sea surface. In particular, the experiment has been carried out in 2013 with the X-band InSAeS4 airborne SAR system, which is equipped with three antennas installed in such a way to allow the simultaneous presence of three AT baselines and three XT baselines. The test-site is the coastline stretch of the Campania region, in the South of Italy, close to the Volturno river.

In order to retrieve information about the sea surface velocity in coastal Mediterranean regions from Synthetic Aperture Radar (SAR) data, in this work we exploit spaceborne as well as airborne data. In particular, we apply two different processing techniques. The first one exploits a single SAR image, whereas the second one, referred to as Along-Track SAR Interferometry, exploits SAR data pairs. The first technique has been applied to spaceborne ENVISAT-1 SAR data, whereas the second one has been applied to airborne data acquired by the Italian InSAeS4 X-band SAR system.

Synthetic Aperture Radar Interferometry (InSAR) exploits the phase differences (interferogram) of SAR data pairs relevant to the same illuminated area and received by slightly different look angles. Within the InSAR processing chain, it is necessary to calculate a proper phase offset (PhOff) value to add to the unwrapped SAR interferogram. To this aim, different algorithms have been proposed in the literature, which typically exploit the external topography information provided by proper Ground Control Points (GCPs) relevant to the observed scene. In this paper we present a Maximum Likelihood (ML) approach for the InSAR PhOff estimation. It is based on the use of GCPs represented either by Corner Reflectors (CRs) or by the pixels of an available external Digital Elevation Model (DEM) of the observed area. The effectiveness of the proposed approach is assessed on simulated data.

InSAeS4 is an Italian X band airborne SAR system, recently upgraded to a multi-antenna interferometric configuration. The system is able to acquire single pass across-track and along-track multi-baseline data with different acquisition modes characterized by different geometric resolutions and across-track swaths. In recent work we have analyzed the high resolution InSAeS4 products (obtained by transmitting 400 MHz bandwidth pulses), characterized by the narrowest across-track swath (1.5 Km wide). In this work, we focus on the InSAeS4 products characterized by the widest across-track swath, at expenses of the lowest geometric resolution. To this aim we show some results achieved with an interferometric dataset acquired by the system in 2013 over the Napoli area, Italy.

Digital elevation model (DEM) generation through interferometric processing of synthetic aperture radar (SAR) data requires the calculation of a constant phase offset present in the unwrapped interferograms. This operation is usually carried out by exploiting the external information provided by GPS measurements in correspondence of corner reflectors (CRs) properly deployed over the illuminated area. This is, however, expensive in terms of cost and time. Moreover, deployment of CRs along with the corresponding in situ GPS measurements can be difficult (if not impossible) in unfriendly areas or in natural disaster scenarios. To circumvent these limitations, we address in this work the estimation of the required phase offset by exploiting a low-accuracy external DEM, without using CRs. More specifically, a two-step approach is proposed. The first step exploits the synthetic phase computed by means of the external DEM and represents a straightforward extension of the procedure that is usually applied in the presence of CRs. Subsequently, in order to refine the achieved solution, a second step is introduced. It is based on a least squares approach that properly exploits the difference between the available low-accuracy DEM and the interferometric DEM generated by means of the phase offset value roughly estimated through the first step. The presented approach is very easy to implement and allows us to achieve an accurate and fast estimate of the needed phase offset, even in the presence of an external DEM affected by a vertical bias and/or a planar shift. The algorithm performances improve in the presence of a large variation of the look angle, as it generally happens in airborne systems. On the other side, the effectiveness of the algorithm may be impaired by the possible presence of artifacts in the unwrapped interferograms, such as those due to the residual motion errors typical of repeat-pass airborne SAR scenarios. Accordingly, the proposed solution is particularly suitable for single-pass interferometric airborne SAR systems, as demonstrated through the presented experimental results achieved on real data.

TELAER is an Italian airborne X-Band Synthetic Aperture Radar (SAR) system recently upgraded to the interferometric mode thanks to an Italian National Research Council (CNR) funding. This system upgrading has been completed at the beginning of 2013 with a flight-test campaign carried out over the Napoli area, Italy. In this paper we present some results relevant to a single-pass interferometric dataset acquired during these flight-tests.

Synthetic Aperture Radar Interferometry (InSAR) allows the generation of Digital Elevation Models (DEMs) exploiting the phase difference (interferogram) of SAR data pairs relevant to the same illuminated area and received by slightly different look angles. Within the processing chain leading from the acquired SAR data pair to the final InSAR DEM, it is necessary to calculate a proper phase offset value to add to the unwrapped SAR interferogram. Moreover, in the airborne case, it can be necessary also the compensation of the residual motion errors not perfectly removed by the exploited Motion Compensation (MOCO) procedures during the focusing step. In this paper we present a novel algorithm for joint InSAR phase offset calculation and residual motion error compensation based on the use of an external low accuracy DEM. The effectiveness of the proposed algorithm is assessed on real data acquired by the multi-antena airborne OrbiSAR and TELAER system, both operating at X-band.

Accurate evaluation of the Antenna Phase Center (APC) position is a key issue in radar applications. In this work we propose an approach for the APC position measurement in anechoic chamber. The presented method allows overcoming some limitations of the classical algorithm known as Two Point Approach, and it has been tested on two X-band antennas: a standard horn antenna and the three-horn array antenna mounted onboard the TELAER airborne Synthetic Aperture Radar system.

Multidimensional synthetic aperture radar (SAR) imaging is a technique based on coherent SAR data combination for space (full 3-D) and space/deformation-velocity (4-D) analysis. It extends SAR interferometry and differential interferometry concepts, offering new options for the analysis and monitoring of ground scenes. In this paper, we consider the problem of detecting scatterers showing partial correlation properties induced by simultaneous acquisitions from satellite formations or an uneven temporal distribution of satellite constellations. To this end, we first provide a general model for the pixel imaged by a multidimensional SAR system. Then, we design a constant false alarm rate (CFAR) decision rule accounting for the presence of partially coherent scatterers. At the analysis stage, we assess the performance of the new detector also in comparison with a previously proposed CFAR scheme, developed in the context of SAR tomography for fully coherent scatterers.

In this work we focus on the Precise Topography- and Aperture-dependent algorithm, briefly PTA, proposed in the recent literature to remove the residual errors still affecting airborne SAR data focused with standard two-step Motion Compensation algorithms. More specifically, we first show that the azimuth-to-frequency mapping used by the PTA procedure is not fully appropriate, because it does not account for the presence of the residual motion errors themselves. Then, we show how to calculate the correct azimuth-to-frequency mapping able to fully account for the presence of the residual motion errors. Finally, we show how to modify the original PTA in such a way to properly exploit the correct azimuth-to-frequency mapping previously discussed.

Synthetic Aperture Radar Interferometry (InSAR) allows the generation of Digital Elevation Models (DEMs) exploiting the phase difference (interferogram) of SAR data pairs relevant to the same illuminated area and received by slightly different look angles. Within the processing chain leading from the acquired SAR data pair to the final InSAR DEM, it is necessary to calculate a proper phase offset value to add to the unwrapped SAR interferogram. To this aim, different algorithms have been proposed in the literature: most of them make use of very accurate information on the position of Ground Control Points (GCPs), such as Comer Reflectors (CRs), properly deployed over the observed scene. In this paper we present a novel algorithm for InSAR phase offset calculation without using CRs. The effectiveness of the proposed algorithm is assessed on real data acquired by the multi-antenna airborne OrbiSAR system operating at X-Band.

Airborne synthetic aperture radar (SAR) raw data are affected by motion errors. These are commonly accounted for via standard two-step motion compensation (MOCO) algorithm followed by the Precise Topography- and Aperture-dependent (PTA) procedure proposed some years ago. In this letter, we show how the azimuth-to-frequency mapping used by the PTA approach should be modified to fully account for the presence of uncompensated motion errors.

This paper describes the capabilities of the TELAER X-Band airborne SAR system, which has been upgrading according to a Italian National Research Council (CNR) funding. Such a system upgrading consists first of all in the realization of a multi-antenna system able to carry out, simultaneously, Across-Track (XT) and Along-Track (AT) SAR Interferometry (InSAR). Moreover, the system upgrading is also aimed at improving the performances achievable in repeat-pass applications, such as Differential SAR Interferometry, (DInSAR), which require very precise measurement of the tracks described during the flight by the SAR antennas.

In this paper we discuss the extension of an algorithm for efficient processing of SAR data acquired in sliding spotlight mode based on a two-step approach. The two-step spotlight data processing procedure, already introduced in the literature, is a very simple and effective procedure because it is based on a plain use of classical (i.e. stripmap mode) SAR processing codes. The algorithm here proposed extends the two-step approach in such a way t account for the presence of squint. Experiments have been carried out on simulated data to clarify the rationale of the method and to confirm its validity. Results obtained by processing real data of the COSMO-SKYMED constellation are also presented.

Airborne SAR focusing is affected by motion errors corrupting data acquired onboard. In order to account for these errors, MOtion COmpensation (MOCO) algorithms are necessary. However, efficient implementation of such MOCO algorithms requires use of proper approximations in the sensor-to-target distance history, which may impair the accuracy of the final SAR images. To circumvent this problem, some methods, such as the PTA (which stands for Precise Topography- and Aperture- dependent) algorithm, have been recently devised in the literature. This paper discusses limits of the PTA algorithm and provides some modifications aimed at improving its performances.

In recent years, it has been shown that use of the Kirchhoff approximation allows expressing the field scattered by a fractal surface in terms of two series expansions. A rigorous analysis of the properties of such two series has been addressed in the recent literature, aimed at finding suitable truncation criteria to compute, with a controlled absolute error, the field scattered by a fractal surface. In this paper, we first of all note that aforementioned analysis applies not only to the Kirchhoff approach, but also to more advanced approaches for surface scattering evaluation. Then, we address the use of the aforementioned series and truncation criteria to achieve a controlled relative rather than absolute error. According to such an analysis, an algorithm is provided, which allows to automatically choose which of the two series, if any, can be used, and how it can be properly truncated for efficient and effective (i.e., with a controlled relative error) computation of the field scattered by natural surfaces. An example of the application of the proposed algorithm to synthetic aperture radar data simulation is also provided.

Differential SAR Interferometry (DInSAR) is a remote sensing technique which allows monitoring ground deformation with accuracy of the order of the transmitted wavelength by exploiting the phase difference (interferogram) of two temporally separated SAR images relevant to the same area. In addition, when more than two multi-pass acquisitions relevant to the same area are available, they can be properly combined by means of recent multitemporal DInSAR algorithms, in order to detect and follow the temporal evolution of ground deformation via the generation of spatially dense time series. Such a multitemporal DInSAR technique is nowadays developed and operative with space-borne SAR data, whereas specific problems may limit its application to airborne data. In this work, starting from the results already shown in previous works and relevant to an X-Band airborne DInSAR experiment carried out over the Perugia area (center of Italy) by using the OrbiSAR system, we carry out a DInSAR multitemporal analysis of data relevant to a 16 km (in azimuth) by 4 km (in range) region.

This paper presents the interferometric airborne repeat-pass mode results at X-band after applying a complete residual motion compensation (MoCo) strategy. The data were acquired, over the Perugia area, Italy, by the OrbiSAR sensor from OrbiSat, Brazil, and the first X-Band D-InSAR results were published, where a space-invariant topography-dependent MoCo was applied after focusing with smoothed elevation model. Now, in this paper, we apply to the same X-band data the precise topography- and aperture-dependent (PTA) MoCo and the weighted phase curvature autofocus (WPCA) to account for high-order residual motion errors. We compare the differential interferograms and coherence map obtained after PTA-WPCA to the formerly results. The results show improvement in the interferometric accuracy after PTA-WPCA processing. The need of such complete processing chain for narrowband systems is discussed.

Differential synthetic aperture radar interferometry (DInSAR) is a remote sensing technique that allows monitoring ground deformation with accuracy of the order of fractions of the radiated wavelength, by means of proper combination and processing of repeat-pass data. In contrast to the satellite case, application of such a technique to airborne data is not, today, a well-established task. Several airborne campaigns, involving mainly C/L-band data, have been planned in the last years to exploit the potentialities of these more flexible platforms for deformation monitoring. In this paper, we show the results of an airborne DInSAR X-band experiment carried out over the Perugia area (center of Italy) by using the OrbiSAR system. We discuss the processing chain applied to the acquired data, which allows achieving a satisfactory compromise between accuracy and efficiency. Eleven repeated passes were carried out in two days; two corner reflectors were located on the ground in a hilly region. One corner reflector was vertically moved between the two days to evaluate the system detection capability. Moreover, we carry out an analysis of all possible differential interferograms for a region 2 4 km wide.

In this paper we show the results of an airborne differential SAR interferometry (DInSAR) experiment carried out over the Perugia area, center of Italy, by using the X-Band OrbiSAR system. Measurements on corner reflectors allowed us evaluating the system detection capability.

This work provides a geometrical analysis to assess the effects of center-beam approximation, crucial for efficient airborne raw data focusing, on the final image.

Synthetic aperture radar (SAR) raw signal simulation is a useful tool for SAR system design, mission planning, processing algorithm testing, and inversion algorithm design. A two-dimensional (2-D) Fourier domain SAR raw signal simulator, exploiting the efficiency of fast Fourier transform algorithms, has been presented some years ago and is able to generate the raw signal corresponding to extended scenes. However, it cannot account for the effects of sensor trajectory deviations with respect to the nominal straight-line path. This paper explores the possibility of extending the efficient Fourier domain simulation approach to the case of sensor trajectory deviations, which is more realistic for airborne SAR systems. We first of all obtain a general and compact Fourier domain formulation of the SAR raw signal in the presence of arbitrary trajectory deviations, and show that in this general case no efficient simulation scheme can be devised. However, we demonstrate that, if a narrow beam and slow trajectory deviation assumption is made, a full 2-D Fourier domain simulation can be used. This approach can be applied only to some SAR systems and/or trajectory deviations, but it has the advantage that processing time is practically not increased with respect to the nominal trajectory case. The validity limits of the approach are analytically evaluated. Some simulation results are finally presented in order to verify the effectiveness of the proposed simulation scheme. In another paper, which is the second part of this work, it will be shown that the narrow beam-slow deviation assumption can be relaxed, at the expense of computation efficiency, if a one-dimensional azimuth Fourier domain processing followed by a range time-domain integration is used

In a previous paper, a two-dimensional Fourier domain synthetic aperture radar (SAR) raw signal simulator that exploits the efficiency of fast Fourier transform algorithms was presented. It accounts for the effects of sensor trajectory deviations and is able to generate the raw signal corresponding to extended scenes in a few seconds. However, a narrow-beam-slow-deviation assumption is made; hence, the approach can be applied only to some SAR systems and/or trajectory deviations. To overcome this limitation, in this paper, we show that the narrow-beam-slow-deviation assumption can be relaxed, at the expense of computation efficiency, if use is made of one-dimensional azimuth Fourier domain processing followed by range time-domain integration. The latter approach only requires some reasonable assumptions on the sensor motion and on the SAR system features; hence, it can be used for airborne SAR systems, and turns out to be still much more efficient than the time-domain one; hence, extended scenes can still be considered. Validity limits of the approach are also analytically evaluated, and several simulation results are finally presented to verify the effectiveness of the proposed simulation scheme

An extended scene SAR raw signal simulator accounting for sensor trajectory deviation is here presented. A general Fourier Domain formulation of the SAR raw signal in presence of arbitrary trajectory deviations is obtained, and it is shown that, under the assumption that the radar beam is sufficiently small and the trajectory deviations are sufficiently slow, a very efficient full 2-D Fourier domain simulation can be used. © 2005 IEEE.

We discuss the role of processing geometry and the problem of motion compensation for non zero squint in airborne SAR processing.

In this work we present the results of an airborne differential interferometry experiment carried out by using the ORBISAR X-band system. Use of a high track measurement accuracy allowed us to fulfill the requirements of Fornaro et al. (2003), where repeat pass phase accuracy has been quantified in terms of position measurement errors. The presented experiment can be considered a first step towards the development of operative airborne differential interferometry for accurate ground deformation monitoring.

We study the effects of residual uncompensated trajectory deviations on the phase accuracy of motion compensated SAR images. We show that linear and quadratic deviations interact with the SAR processing and generate additional phase artifacts with respect to what is expected by simple geometric considerations.