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In this paper, some results obtained through the processing of data acquired from the Argentinian L-band SARAT system are presented. SARAT is an airborne system that was developed as a first conceptual step toward the design of the Argentinian L-Band satellite mission SAOCOM-1. In particular, some studies relevant to the data focusing, and also regarding the interferometric and polarimetric capabilities of the SARAT system are hereby shown. The considered dataset, relevant to an area located in the Cordoba province, Argentina, has been provided by the National Commission of Space Activities of Argentina (CONAE). This work has been developed in the framework of a collaboration between the Italian Space Agency (ASI) and CONAE.

The SARSense campaign in the Jülich area (Germany) in summer 2019 was performed to support the ESA Copernicus high priority mission ROSE-L. Airborne SAR signals in C- and L-band, drone imagery, in situ soil and plant parameters, as well as biophysical variables in the lab were measured to provide a comprehensive data set to study details of the mission design for agricultural applications. Although an in depth analysis will be performed soon, the preliminary outcome of the dry summer example campaign is as follows: - An L-band SAR monitoring in the Copernicus program will provide an added value to the existing C-band capacities of Sentinel-1 (A/B). - Simultaneous C- and L-band observations may help to disentangle the different processes in the plant and the soil. Single frequency observations may tend to be misinterpreted. The main objectives of SARSense are: - investigate the use of L & C-band SAR data for soil moisture retrieval at high resolution (i.e., 0.1-1.0 km). Both the case of temporally collocated L & C-band SAR time series and that of independent acquisitions will be investigated. - extend the existing airborne SAR programme to new test sites (Jülich, Germany) and acquire reference L- and C-band airborne SAR datasets collocated in time and space over different well-defined land-cover including agricultural and forested regions. - document the added value of L-band SAR in addressing current EO measurement gaps (soil moisture, vegetation biomass, etc.) and enhanced continuity together with other missions such as Sentinel-1. - support specification of the time interval/latency between Sentinel-1 and L-band SAR coverage for time-critical application products such as soil moisture. - support trade-off and definition of other key missions parameters in Phase-A/-B1 (noise floor, resolution). The objectives shall be addressed through the design of the campaign acquisitions, the data acquisition, processing and documentation and preliminary analyses to provide first answers to key mission design needs. The later includes documenting the unique value of L-band SAR and trade-offs on the C- and L-band time-latency between acquisitions. The flight configuration is 2 fully polarimetric L- and C-band SAR on 1 aircraft. The SARSense campaign will cover a number of vegetation types focussing on agricultural and forest areas in order to satisfy all of the campaign objectives.

In last years the Frequency Modulated Continuous Wave (FMCW) technology has been playing an ever greater role in the realization of compact, lightweight and cheap Synthetic Aperture Radar (SAR) systems to be mounted onboard small, low altitude platforms such as airplanes, helicopters and drones. In this work, we present the imaging capabilities of the AXIS (Airborne X-band Interferometric SAR) system, which is an Italian airborne interferometric SAR system operating at X- Band and based on the FMCW technology. The system has been developed in the frame of a cooperation between a public research institute (IREA-CNR) and a private company (Elettra Microwave S.r.l.). The first flight tests of the system have been carried out at the end of April 2018 over the Salerno coastline, in the South of Italy, onboard a Cessna 172 aircraft. In this paper, we show a preview of the obtained preliminary results, comprising a description on the mission, an analysis of both the SAR images and the interferometric products.

In May-June 2015 UAVSAR was flown to Europe to collect data in support of experiments in Iceland, Norway and Ger-many. The deployment in Germany was focused on PolIn-SAR and tomographic data collections at the Traunstein Forest and in the Munich urban area. In this paper we describe tomographic processing of the Munich data and comparison with in situ ground truth data.

We present detailed maps of local-scale 3D deformation preceding the 2018 phreatic eruption at Iwo-yama volcano (south of Kyushu Island, Japan), using a combination of airborne and spaceborne Interferometric Synthetic Aperture Radar (InSAR) data. The 3D and 2.5D deformation maps obtained at different periods allow us to successfully track their spatiotemporal evolution and to infer the transition of subsurface conditions responsible for the precursory deformation observed from 2014 to 2018. From 2014 to 2016, ground inflation depicted an axisymmetric pattern with the maximum displacement at the center of the deformed area. However, from 2016 to 2018, an inflation peak moved to the southern edge of the area deformed during 2014–2016 and became more localized, which was close to the newly generated vents in the 2018 eruption. Modeling of the inflations suggests that pressurization within a crack at a depth of 150 m beneath the Iwo-yama geothermal area caused the 2014–2016 deformation and had continued until the 2018 eruption. Modeling results highlight the persistence of the local ground inflation pattern just above the southern edge of the crack, which suggests the presence of a shallower inflation source contributing to the local inflation. Consequently, we interpret the sequence of these deformations as follows: from 2014, deeper-rooted fluid started to inject into a fluid-saturated crack at 150-m depth, which caused the 2014–2016 deformation. Then, after 2016, the crack inflation continued because of the continuous fluid injection and formed another pressurized part directly above the southern tip of the crack. Additionally, the results of the time-series analysis of the satellite InSAR data revealed that the local inflation started around April 2017 for which thermal activity including a mud emission became pronounced around the location of the local inflation. As a result of an episodic increase in supply rate of magmatic fluids from a deep magma reservoir from early 2018, a phreatic eruption finally occurred in the vicinity of the most deformed point, providing a clue for predicting future eruption sites, as was also observed in the Hakone 2015 eruption.

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.

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.

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.

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.

It is difficult to estimate the Doppler frequency and modulating rate for airborne SAR by using traditional vector method due to instable flight and complex terrain. In this paper, it is qualitatively analyzed that the impacts of POS, DEM and their errors on airborne SAR Doppler parameters. Then an innovative vector method is presented based on the range-coplanarity equation to estimate the Doppler centroid taking the POS and DEM as auxiliary data. The effectiveness of the proposed method is validated and analyzed via the simulation experiments. The theoretical analysis and experimental results show that the method can be used to estimate the Doppler centroid with high accuracy even in the cases of high relief, instable flight, and large squint SAR.

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.

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).

A simple algorithm for determining the location of the antenna phase center is presented. The algorithm exploits amplitude and phase measurements, carried out in anechoic chamber, of the electromagnetic field received by the antenna under test. It is based on an accurate model able to account for the possible (unknown) misalignment between the axis of symmetry of the antenna under test and the rotation axis of the rotating column of the anechoic chamber. The proposed method has been applied to calculate the phase center of a microstrip antenna of an airborne synthetic aperture radar system operating at X-band. The presented results clearly show the effectiveness of the proposed algorithm.

The F-SAR instrument represents DLR’s advanced airborne SAR testbed for technology and remote sensing applications. The development of the instrument was triggered by a strong demand for data being simultaneously acquired at different wavelengths and polarizations as well as by the demand for very high range resolution. F-SAR is a modular development utilizing modern hardware and commercial of the shelf components. For the purpose of experiments and operational data acquisition campaigns the system is being installed on board a DLR Dornier DO228 research aircraft. This paper gives an overview of the instrument’s capabilities and performance, based on the multi-frequency and fully polarimetric imagery acquired during campaigns in the last two years. More specifically, campaigns in Greenland in 2015 (ARCTIC) and Gabon in 2016 (AfriSAR) are presented.

In the last years the Frequency Modulated Continuous Wave (FMCW) technology has been playing an ever greater role in the realization of compact, light and cheap Synthetic Aperture Radar (SAR) systems to be mounted onboard small, low altitude platforms such as airplanes, helicopters and drones. To correctly focus FMCW SAR images, it is necessary to accurately know some system parameters, including the frequency sweep rate of the signal transmitted by the radar. It may happen, however, that this frequency sweep rate is not very accurately measured by the radar provider, and thus an incorrect value of this parameter is used during the SAR data focusing procedure. This may produce serious geometric distortion effects in the focused FMCW SAR images. To circumvent these problems, in this work we present a procedure that estimates the frequency sweep rate actually employed by the FMCW radar, thus providing a key information that can be then profitably used to achieve the correct focusing of the SAR data acquired by the radar system at hand. More specifically, we propose an algorithm that exploits on one side the focused SAR images corrupted by the geometric distortion effects induced by the inaccurate knowledge of this radar parameter, and on the other side the very precise in-situ measurements of the positions of a limited number of Corner Reflectors (CRs) properly deployed over the observed scene. The effectiveness of the proposed algorithm has been tested on real data acquired by an airborne X-band FMCW SAR system.

The present contribution is aimed at showing the high resolution imaging capabilities of the InSAeS4 airborne Synthetic Aperture Radar. After a brief description of the main characteristics of such system, some high resolution SAR and single-pass interferometric SAR products on an urban area are shown.

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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.

The paper provides the description of a flexible frequency domain background clutter simulator for GMTI applications. The clutter module is able to simulate different acquisition geometries, including very high squint cases, and accounts for scene temporal decorrelation. The clutter simulator operates in frequency domain allowing good computational performance. Details on the simulation algorithm and an overview of the simulator results are provided.

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.

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.

Snow accumulation is a significant factor for hydrological planning, flood prediction, trafficability, avalanche control, and numerical weather/climatological modeling. Current snow depth methods fall short of requirements. This research explores a new approach for determining snow depth using airborne interferometric synthetic aperture radar (InSAR). Digital elevation models (DEM) are produced for Snow Off and Snow On cases and differenced to determine elevation change from accumulated snow. Interferograms are produced using Multi-pass Single Look Complex airborne Ku-band SAR. Two approaches were attempted. The first is a classical method similar to spaceborne InSAR and relies on determining the baseline of the interferometric pair. The second used a perturbation method that isolates and compares high frequency terrain phase to elevation to generate a DEM. Manual snow depth measurements were taken to verify the results. The first method failed to obtain a valid baseline and therefore failed. The second method resulted in representative DEMs and average snow depth errors of -8cm, 95cm, -49cm, 176cm, 87cm, and 42cm for six SAR pairs respectively. Furthermore, Ku-band appeared to be a high enough frequency to avoid significant penetration of the snow. Results show that this technique has promise but still requires more research to refine its accuracy. http://archive.org/details/determiningsnowd1094537622 Lieutenant Colonel, United States Air Force Approved for public release; distribution is unlimited.

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.

A new method for moving target detection, localization, and velocity estimation using SAR raw data is presented which allows the determination of the target's complete velocity vector. The method is applicable if the target has either a tangential velocity (/spl mu//sub T//spl ne/0) or a radial acceleration (/spl nu//spl dot//sub R//spl ne/0), or both. It is based on the analysis of the Doppler rate map which is obtained from the range compressed raw data, applying the reflectivity displacement method (RDM). The tangential velocity of each moving target is obtained from its own Doppler rate and the radial velocity from its own linear range migration. A velocity accuracy better than 3 m/s can be achieved for the airborne case. The method is validated experimentally by the use of real SAR data obtained by DLR's E-SAR. The paper gives a short description of the state of the art of moving target velocity measurements, introduces the RDM for stationary targets and its extension to the application for moving targets. It furthermore shows experimental results. >

This paper presents the very first assessment of the permanent scatterer (PS) technique for airborne data. A data set of 14 SAR images at L-band, acquired over the Oberpfaffen-hofen area on the same day with the E-SAR system of the German Aerospace Center (DLR), is used for the first airborne time series analysis with PS. The paper shows the importance of mitigating the residual motion errors through the use of precise motion compensation strategy before PS analysis. The target velocity and DEM error results are obtained by a periodogram-based estimation considering the linear displacement model. Due to the small number of images in our data set, the displacement velocity and DEM error results are presented on a PS basis. Target structures related to selected reliable PSs are shown and the corresponding periodograms highlighted.

F-SAR identifies the successor of the well-known E-SAR system. The system is under development at the Microwaves and Radar Institute. The development was triggered by the demand for data being simultaneously acquired at different wavelengths and polarisations as well as by the demand for very high range resolution.

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.

This paper analyzes the multi-path component effect in the airborne SAR context, proposing a model as an approach to correct the generated disturbances in the processed phase and amplitude images. The method assumes along-track interferometric or polarimetric data to estimate the unknowns of the model. Airborne data acquired by the F-SAR system of DLR are used to evaluate the performance of the proposed approach.

The study of data acquired over a circular trajectory has raised an increasing interest in the SAR community. Two main reasons summarize the interest in such geometry. First, sub-wavelength resolution can be achieved, as the targets in the spotted area are observed under a 360o aperture. Second, the use of the information from different azimuthal directions allows one to obtain information of the scene in the third dimension, making possible a 3D target reconstruction. In any case, both applications require certain target reflectivity homogeneity. This paper shows several processing results and analyzes the potentials and limitations of circular SAR to perform tomography of semi-transparent media. Special processing aspects, like the estimation of residual motion errors due to inaccuracies in the navigation data, are also addressed. Data acquired at L-band by DLR's E-SAR system are used to demonstrate the high resolution and tomographic imaging capabilities of circular SAR. The results include the tomogram of a Luneburg lens, as well as preliminary results over man-made targets and vegetation.

Detection of traffic congestion is an important issue both for the transportation research community and everyday life of the motorists. A new type of information is needed for a more efficient use of road networks. Remote sens-ing sensors installed on aircrafts or satellites enable data collection for various traffic applications over large ar-eas, especially areas not covered with other, e.g. terrestrial sensors, or difficult accessible areas. Synthetic aper-ture radar (SAR) systems seem to be very promising due to their all-weather capability. We approach the traffic congestion detection problem with a two-channel SAR sensor flying in along-track (ATI) the motorway by com-bining various techniques: look processing, channel balancing, coherent change detection, e.g. displaced phase center array (DPCA), image processing and incorporation of a priori information such as traffic model and road network. The potential of the proposed method is demonstrated with airborne E-SAR data collected during sev-eral campaigns over highways in Germany. Method application for future tight formation of space satellites is discussed.