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The 2-D frequency-based omega-K method is known to be a suitable algorithm for fully focused SAR (FF-SAR) radar altimeter processors, as its computational efficiency is much higher than equivalent time-based alternatives without much performance degradation. In this article, we provide a closed-form description of a 2-D frequency-domain omega-K algorithm specific for instruments such as Poseidon-4 onboard Sentinel-6. The processor is validated with real data from point targets and over the open ocean. Applications such as ocean swell retrieval and lead detection are demonstrated, showing the potentiality of the processor for future operational global-scale products., This work was supported by the Industrial Doctorates Plan from the Secretary of Universities and Research of the Department of Business and Knowledge of the Government of Catalonia through Project SA.45217 with Expedient Number 094 under Grant Doctorats Industrials 2020., Peer Reviewed, Postprint (published version)

In the framework of a feasibility study in support of the Hydroterra mission, a high resolution radar has been setup to monitor continuously a crop field with high resolution synthetic aperture radar images. In parallel, ground-truth data is acquired such as soil roughness, soil moisture and crop biological parameters. From this experimental data set the possibility to monitor soil moisture and crop biological parameters from back-scattering radar measurements will be assessed. To use the phase information of SAR images it is interesting to compensate the atmospheric phase screen induced by tropospheric refractive index. The paper presents a study of the atmosphetric phase drift prediction and compensation based on the local measurement of meteorological parameters., Peer Reviewed, Postprint (author's final draft)

HydroSoil is a measurement campaign, funded by the European Space Agency (ESA), where the temporal evolutions of two crops, barley and corn, have been continuously monitored during the whole crop period by means of a C-band Fully Polarimetric C-band Ground-Based Synthetic Aperture Radar (GB-SAR). SAR data has been collected together with ancillary data, and both are being processed to demonstrate the retrieval of soil moisture and vegetation parameters in an agricultural field under controlled conditions, to simulate the frequent acquisitions of GeoSAR missions., This work was funded by the European Space Agency (ESA Contract No. 4000132509/20/NL/FF/ab with UPC) and supported by the Spanish MCYT funds Unidad de Excelencia Maria de Maeztu MDM-2016-0600 and under project TEC2017-85244-C2-2-P. Special thanks to the Barcelona School of Agri-Food and Biosystems Engineering (EEABB) for making possible the radar deployment and the use of the experimental field., Peer Reviewed, Postprint (author's final draft)

The advent of geosynchronous remote sensing missions requires the development of precise orbit determination techniques at high orbits. Geosynchronous satellites require station-keeping manoeuvres to be performed periodically. Dynamical models do not consider artificial forces. Therefore, the tracking system must be able to detect them in order to keep track of the spacecraft autonomously. A compact baseline interferometer is deployed in order to track the signals of opportunity from the ASTRA 19.2?E geostationary constellation. The system is capable of autonomously estimate the trajectory of the satellite for a period of 22 days. Even after artificial orbital manoeuvres are performed. These results show that interferometry is a valid alternative for future geosynchronous remote sensing missions which require precise orbit determination. © 2021 IEEE, This work has been supported by the Spanish Science, Research and Innovation Plan (MINECO) with Project Codes TIN2014-55413-C2-1-P and TEC2017-85244-C2-2-P and by Unidad de Excelencia Maria de Maeztu MDM-2016-0600 financed by the Agencia Estatal de Investigacion, Spain., Peer Reviewed, Postprint (published version)

The orbit accuracy requirements for a Geosynchronous Synthetic Aperture Radar (GEOSAR) are studied. Compared to telecommunication GEO satellites' station keeping needs, focusing the GEOSAR synthetic aperture demands a more accurate orbital determination. For this reason, the most suitable Precise Orbit Observation (POB) techniques are considered. Several radar tracking techniques fulfil the accuracy requirements while presenting a trade-off problem in terms of cost an operation. GNSS allow for precise autonomous navigation even at high orbits like GEO. Optical observation techniques perform well in order to calibrate other tracking systems. Interferometry stands out since it can be used taking advantage of present illuminators of opportunity. A ground interferometer is being designed and built in order to provide experimental measurements which will serve as proof of concept., This work has been supported by the Spanish Science, Re-search and Innovation Plan (MINECO) with Project Codes TIN2014-55413-C2-1-P and TEC2017-85244-C2-2-P and by Unidad de Exce-lencia Maria de Maeztu MDM-2016-0600 financed by the AgenciaEstatal de Investigaci ́on, Spain., Peer Reviewed, Objectius de Desenvolupament Sostenible::6 - Aigua Neta i Sanejament, Objectius de Desenvolupament Sostenible::3 - Salut i Benestar, Objectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura, Objectius de Desenvolupament Sostenible::15 - Vida d'Ecosistemes Terrestres, Objectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles, Objectius de Desenvolupament Sostenible::13 - Acció per al Clima, Postprint (published version)

Orbit determination errors are expected to be a major threat for obtaining focused images on Geostationary Synthetic Aperture Radar (GeoSAR) missions. A ground-based interferometer system is presently being under research to determine the satellite orbit with the required precision. However, from that system, it must be addressed which orbit determination techniques offer better results for that purpose. This paper provides a comparison between two differential correction techniques: the least squares (LS) and the extended Kalman filter (EKF) techniques., Peer Reviewed, Postprint (published version)

Technological developments in low-power mmW radar allow the measurement of deformations in the order of few micrometers and monitoring dynamic processes like structural vibration. This paper presents a fast acquisition FMCW radar operating at 94 GHz and recent experimental results of remote observation of micrometric vibration motion for bridge structural health monitoring. The presented approach offers cost reduction and applicability advantages compared to conventional techniques., Peer Reviewed, Postprint (published version)

This paper proposes a method to solve the absolute phase ambiguity introduced by an orbit determination interferometer system, suitable for GeoSAR missions. This method will be complemented with simulated results in order to validate its reliability., Peer Reviewed, Postprint (published version)

The paper analyzes the problem of achieving a coherent operation in Geostationary SAR (GEOSAR) missions intended for continuous monitoring of land surfaces. In contrast to LEOSAR missions, GEOSAR uses very long SAR integration times (from minutes to hours). Accordingly phase errors due to orbit perturbations, radar master oscillator drift, atmosphere propagation and other sources must be conveniently compensated during SAR processing to avoid image defocusing. A network of Active Radar Calibrators (ARC) distributed on the observed scene is proposed, providing echo envelope and phase observations before Synthetic Aperture Processing. In this way the radar antenna phase center trajectory and other phase error sources can be continuously tracked and compensated using a pyramidal sub-aperture processing approach., Peer Reviewed, Postprint (published version)

We discuss the effects of the clutter on geosynchronous SAR systems exploiting long integration times (from minutes to hours) to counteract for two-way propagation losses and increase azimuth resolution. Only stable targets will be correctly focused whereas unstable targets will spread their energy along azimuth direction. We derive here a generic model for the spreading of the clutter energy based on the power spectral density of the clutter itself. We then assume the Billingsley Intrinsic Clutter Motion model, representing the clutter power spectrum as an exponential decay, and derive the expected GEOSAR signal-to-clutter ratio. We also provide some results from a Ground Based RADAR experiment aimed at assessing the long-term clutter statistics for different scenarios to complement the Internal Clutter Motion model, mainly derived for windblown trees. Finally, we discuss the expected performances of two GEOSAR systems with different acquisition geometries., Peer Reviewed, Postprint (published version)

©2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., This paper presents a detailed characterization of sea/ocean clutter returns at X-band, imaged by TerraSAR-X (TSX) mission from the radiometric, statistical, and polarimetric standpoints. Different TSX data takes, covering the typical spaceborne incidence angle region (20 degrees-45 degrees), are analyzed: dual-polarized (dual-pol) and experimental quad-polarized (quad-pol) data have been used. The thermal noise of the receiver for quad-pol data turns out to be an important limitation in the sea characterization from TSX, particularly at high incidence angles (above 36 degrees), where low signal-to-noise ratios (SNRs) can impair the proper data distribution fitting and the polarimetric backscattering description. Statistical analysis shows large deviation from Gaussianity, indicating presence of texture, mainly in the small incidence region (20 degrees-36 degrees), with favorable SNR conditions. The different polarimetric features revealed contribution of nonpolarized scattering, related to the presence of breaking waves. This paper also proposes and evaluates an extension of the well-known X-Bragg model, named X2-Bragg (extended-extended Bragg), which properly accounts for the impact of thermal noise and sea clutter temporal decorrelation, due to the dual receive antenna (DRA) acquisition mode. Such additional decorrelation sources, if not properly analyzed and accounted for in the physical-based model description, could lead to an incorrect interpretation of the polarimetric properties and the related erroneous geophysical parametric inversion from the real data. In this sense, the X2-Bragg proves its fitting to the experimental data, quantifying accordingly the presence of nonpolarized scattering in terms of the roughness parameter beta(1)., Peer Reviewed, Postprint (author's final draft)

The Advanced Radar Geosynchronous Observation System is proposed to be a multiple-input–multiple-output synthetic aperture radar (SAR) system hosted on a swarm of minisatellites in quasi-geostationary orbits. The system is made of N iso-frequency sensors, each of them transmitting and receiving the signals. The system would combine the continuous imaging capabilities of a geostationary SAR, gaining a factor N^{2} in signal-to-noise ratio (SNR). The real aperture would be achievable in \sim 40 min, enabling applications so far unseen, such as monitoring fast deformations, landslides, and other applications for emergency and security. Still, the SNR of the long acquisition time would be conserved. The optimal design of the swarm is addressed, in order to trade resolution, coverage, and revisit time, Peer Reviewed, Postprint (author’s final draft)

“©2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., This paper proposes a new optimized multichannel synthetic aperture radar (SAR) configuration, based on receiving antennas with nonuniformly displaced phase centers, intended for ground moving target indication (GMTI) applications over maritime scenarios. This system is compared with current SAR missions, such as TerraSAR-X (TSX) or TanDEM-X (TDX). The GMTI capabilities of the different configurations are analyzed in a two-level performance approach. First, an intensive numerical simulation evaluation, based on Monte Carlo trials, is carried out in order to characterize the probabilities of detection under different system parameters and scenario conditions. Different GMTI techniques, i.e., displaced phase center antenna, along-track interferometry, and extended displaced phase center antenna, are assessed. In a second step, synthetic simulated SAR data, obtained in a study case scenario, is used to demonstrate the potential improvement of the proposed multichannel configuration compared with current SAR missions, providing subclutter visibility for maritime surveillance of small and slowly moving boats., Peer Reviewed, Postprint (author's final draft)

The paper presents a preliminary statistical evaluation of the sea clutter returns imaged by a spaceborne synthetic aperture radar (SAR) mission as TerraSAR-X. Two polarimetric data takes, Dual-polarized (Dual-Pol) and Quad-polarized (Quad-Pol), covering the range of incidence angles from 30 to 32 degrees, are considered for the stochastic characterization. The results show that the K-distribution, extendedly assumed statistics for high resolution radar sea clutter imaging, fits well the data's amplitude. This information jointly with the inverted sea spectrum are used to simulate SAR images of realistic scenarios that can be exploited for proper performance evaluation of ground moving target indication (GMTI) techniques and missions for maritime surveillance., Peer Reviewed, Postprint (published version)

In this paper, the impact of the internal clutter motion in GEOSAR acquisitions is analyzed. A nearly zero inclination with low eccentricity geosynchronous orbit is considered and, therefore, long integration, in order of 20-30 min (for 1-2 Km resolution) or even hours (for tenths of meters resolution), is required in order to reach the desired synthetic aperture length and the required along-track resolution. Moderate transmitted powers and antenna sizes are considered in the analysis. The power link budget of a long integration GEOSAR acquisition is presented and the limitations imposed by the clutter decorrelation are studied. The minimum target RCS to assure the correct performance of the system under clutter interference scenarios is evaluated. Finally, experimental data from Ground Based SAR X-band acquisitions will be used to validate the Billingsley model in long integration acquisitions, Peer Reviewed, Postprint (published version)

In this paper, the performance of a nearly zero inclination and low eccentricity geosynchronous synthetic aperture radar (GEOSAR) mission for midlatitude (30 degrees-60 degrees) Earth observation is analyzed. The slow motion of such satellites with respect to the Earth's surface makes it necessary to consider long coherent combination of pulses during hours to reach the desired along-track resolution. A system based on moderate transmitted powers and antenna sizes is considered. The necessary sensitivity in such GEOSAR system is obtained from the accumulated energy of the raw data using a pulse repetition frequency above the Doppler bandwidth and a long integration time. Several issues as a result of the long acquisition, such as target and atmospheric phase screen decorrelation, speckle noise impact on the received signal, and satellite station-keeping requirements, are analyzed. The feasibility of such systems to be placed on a broadcasting communication satellite makes nearly zero inclination GEOSAR a low-cost alternative of current SAR missions., Peer Reviewed, Postprint (published version)

The paper evaluates the effects of Atmospheric Phase Screen on focused Geosynchronous SAR data. We derive theoretical models for the resolution, the interferometric de-correlation and the induced clutter in presence of an APS, whose joint time and space power spectrum is modeled as an extension of the Kolmogorov power law. Finally we provide some statistics gathered from a GB RADAR experiment., Postprint (published version)

We propose an efficient method for the azimuth compression and Atmospheric Phase Screen estimation of Geosynchronous SAR data. The method is based on the iterative processing of sub-apertures of increasing size, allowing to gradually refine the quality of the focused data and of the estimated APS. The whole processing can be easily parallelized. Results over simulated data are shown. © 2013 IEEE., Peer Reviewed, Postprint (published version)

This paper presents a comparative study of the radiometric sensitivity and spatial resolution of three near-field (NF) passive screener systems: real aperture, 1-D synthetic aperture (SA), and 2-D SA radiometers are compared. The analytical expressions for the radiometric resolution, the number of required antennas, and the number of pixels in the image are derived taking into account the distortion produced by the NF geometry at nonboresight directions where the distortion is dominant. Based on the theoretical results, a performance comparison among the studied systems is carried out to show the advantages and drawbacks when using the radiometers in a close-range screening application. Moreover, the screener performance in a close-range environment is discussed from the results obtained in the aforementioned comparison., Peer Reviewed, Postprint (published version)

In this paper, a geosynchronous synthetic aperture radar (SAR) (GEOSAR) mission for atmospheric phase screen (APS) retrieval using a long coherent integration of pulses is analyzed. The nearly fixed position of the geosynchronous platforms makes GEOSAR systems suitable for continuous monitoring applications. However, using moderate transmitted powers and antenna sizes, very long integration times up to hours are required. In GEOSAR, the two-way propagation of radar signals can decorrelate significantly due to atmospheric changes during the long data take, resulting in an APS which can cause image defocusing and artifacts. In this paper, the APS effects are analyzed, and an APS correction algorithm from short-term periodic acquisitions (subapertures) of the whole long-term GEOSAR synthetic aperture is described. The results obtained from the APS retrieval algorithm in a simulated GEOSAR acquisition affected by atmospheric decorrelation are presented. Finally, an experimental test of the APS algorithm performance with a long-integration ground-based SAR acquisition is shown., Peer Reviewed, Postprint (published version)

In this paper we discuss a preliminary design for a constellation of geosynchronous (GEO) Synthetic Aperture Radars (SAR). The key design concept is to employ one or more pairs of closely-spaced twin receivers flown onboard GEO minisatellites moving with a velocity of few meters per second with respect to the Earth’s surface, so as to form a synthetic aperture on the order of few tenths of kilometers twice a day. The employement of closely-spaced receivers would enable the estimation of the temporal gradient of the tropospheric delay via along track Interferometry, resulting in the possibility to coherently integrate the signal over an aperture time on the order of hours. As a result an area as wide as one thousand kilometers could be imaged while providing: i) continuous temporal coverage at coarse resolution (hundreds of meters); ii) high resolution (few meters) imaging and interferometric capabilities two or more times a day by integrating the signal over few hours, thus ensuring high SNR performance (for stable targets) with a transmitted power com- parable to currently operated spaceborne SARs., Peer Reviewed, Postprint (published version)

In this paper, a high integration gain GEOSAR mission for Earth imaging is presented. The spatial-temporal atmospheric decorrelation issues of a long integration time GEOSAR mission must be carefully studied. The feasibility of a GEOSAR mission for Atmospheric Phase Screen retrieval purposes is studied. The raw data received from several hours of acquisition is divided into sub-acquisitions with integration time on the order of the APS decorrelation time. From each sub-matrix, a low-resolution but enough to sample the spatial variations of the atmospheric map is obtained. The simulated results of the APS retrieval from a GEOSAR acquisition are shown at the end of this paper., Peer Reviewed, Postprint (published version)

This paper presents an initial analysis of the possibilities for velocity and acceleration m easurement with the Bi- Directional SAR imaging mode (BiDi). It comprises single satellite single path acquisitions as well as a constellation of two satellites. The translati onal velocity components into azimuth and range directions are simulated. A BiDi ap- proach for measuring the azimuth velocity from one satellite with one receiving channel is proposed. Image examples acquired with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites show velocity and acceleration effects on ships and the proposed BiDi ve locity approach is verified. Interferometric fringes were observed on anchoring ships. A first approach into the understanding of rotational effects was achieved by simulation of rotational fringes., Peer Reviewed, Postprint (published version)

This paper presents an evaluation of a post-Doppler spacetime adaptive Processing (STAP) technique for non-uniformly displaced phase center receivers synthetic aperture radar (SAR). Both theoretical and simulation analysis are carried out in order to prove the ground moving target indication (GMTI) capabilities for specific non-uniformly spaced multichannel configurations on-board a single satellite platform. Simulated SAR data in the maritime scenario show improved performance, specially for small and slow targets, compared to current SAR missions, equipped with just two channels., Peer Reviewed, Postprint (published version)

The application of polarimetric radar interferometry to the estimation of vegetation height is studied. A comparison between different choices for the scattering mechanisms employed in the retrieval algorithm is presented. When applied to crops, the best results are derived from the height difference between interferograms generated at HH+VV and HH-VV polarizations, Peer Reviewed, Postprint (published version)

The usage of an airborne interferometric SAR to mass map production is strongly dependent on the capability of performing the data processing in a near automatic mode. One of the main limitations is related to both the accurate calibration of the system parameters, its stability from flight to flight and the correct in-flight recording of aircraft position and attitude. The unstable movements of an airborne SAR platform, if recorded in an accurate manner, can be corrected during the processing step. Measurement errors and time drifts lead to location errors in the final DEM. The system requirements in both accuracy and stability to fulfil a quality-mapping requirement can be resolved from the sensitivity equations. The same equations can be also used to calibrate the system parameters from the location errors on the imaging of well-known targets, usually corner reflectors, Peer Reviewed, Postprint (published version)

Presents different polarimetric and interferometric inversion radar approaches to extract the characteristics of vegetation and bare soil surfaces. The inversion techniques presented make use of multifrequency, radar interferometric and polarimetric data to increase the number of input data. The proposed techniques have been experimentally tested under laboratory conditions as well as in real outdoor scenarios, Peer Reviewed, Postprint (published version)

The authors present an improved technique for the generation of digital elevation models (DEM), capable of dealing with full scene images (100×100 km) coming from an interferogram obtained with ERS satellite data. Starting from an interferometric processor aimed to the geocoding of smaller areas, now the authors expound the new improvements based on the use of ground control points (GCP) in order to calibrate some imprecisions which appear in the case of very wide swaths. A generated DEM of the test zone of Tarragona (Spain) and its error assessment are presented, Peer Reviewed, Postprint (published version)

It is well known that by means of airborne interferometric SAR systems it is possible to generate high precision digital elevation models (DEM), although these platforms are seriously affected by motion instabilities. These deviations are recorded by navigation systems, such as GPS receivers and inertial units. The precision of these systems, and the subsequent off-line processing, determines the level of confidence in the generated heights. Errors in track knowledge lead to incorrect generation of the interferometric phase, which yields height errors in the final DEM. In this paper it is shown an analytical work which is useful to analyze the consequences of such factors onto the bias and the standard deviation of the height errors in digital elevation models, Peer Reviewed, Postprint (published version)

A coherence optimization method, which makes use of polarimetry to enhance the quality of the interferograms, has been experimentally tested under laboratory conditions in an anechoic chamber. The experiments have proved the remarkable contribution that this technique offers in two important applications: the improvement of digital elevation maps (DEM) generation and the estimation of the height of vegetation targets, Peer Reviewed, Postprint (published version)

Peer Reviewed, Postprint (published version)

In the following paper an analysis of the SAR impulse response signal from the interferometric point of view is expounded, with the intention of studying its phase behaviour in the presence of high squint values. The work will be focused on the development and verification of some methods for the generation of precise geocoded digital elevation models (DEM) in high squinted geometries, Peer Reviewed, Postprint (published version)

A SAR raw data simulator and a SAR processor are used as a tool for performance assessment of SAR interferometry algorithms like the multi-baseline and multifrequency. Traditional algorithms have also been tested with real ERS-1 data and validated with a high accuracy reference DEM., Peer Reviewed, Postprint (published version)

“TERESA” (Terrestrial Radar Equipment for Scattering Analysis) is a ground-based, fully polarimetric scatterometer operative in the S, C, X, and Ku bands. It has been designed to obtain the complete backscattering matrix of terrain and oceanographic surfaces with extensive information of its variation with frequency and incident angle. The system is able to measure the Doppler spectrum of the illuminated scene as well. The paper briefly describes the specifications and structure of the system and the first results obtained, Peer Reviewed, Postprint (published version)

The paper presents an algorithm which recovers a 3D reflectivity image of a target from near-field scattering measurements. Spherical wave nearfield illumination is used, in order to avoid a costly compact range installation to produce a plane wave illumination. The system is described and some simulated 3D reconstructions are included. The paper also presents a first experimental validation of this technique., Peer Reviewed, Postprint (published version)

The Born-iterative method (BIM) and the distorted-Born-iterative method (DBIM) have been proposed and verified as methods of solving the nonlinear inverse scattering problem for dielectric scatterers. The continuous-wave (CW) implementation of the DBIM was recently used to process microwave scattering data. Previously, diffraction tomography was used to process the data (a microwave image of human arm), resulting in an image with a small dynamic range due to the high contrasts present in the human body. Using the DBIM, the processed image was significantly improved. It is seen that upon iterating with DBIM, the contrast of the image is drastically enhanced., Peer Reviewed, Postprint (published version)

A bistatic radar system requires accurate synchronization between the transmitter and the remote receiver in order to achieve a correct coherent target detection and positioning. An unlinked receiver carrier phase/frequency synchronization method, from the radiated pulsed signal of a remote radar transmitter when its antenna beam illuminates the receiver, is presented. A modified discrete conception of the phase locked loop (PLL) technique is used, based on the special properties of the signal to be recovered, Peer Reviewed, Postprint (published version)

Pulse to pulse staggering in the pulse reference interval (PRI), usually used to increase the radar unambiguous range and MTI blind speeds, complicates notably the synchronization of the pulsed waveform. A free running open loop technique may be used for this purpose, adjusting a stable clock at the same frequency as the transmitted pulses, which is synchronized by the received sequence during direct illumination. When the received signal can be contaminated by interferences, noise, or multipath effects, a more robust closed loop approach is desirable. This paper presents a closed loop solution to the synchronism process, based on a delay-lock loop configuration, using the special properties of the pulse to pulse staggered signal, that can be considered as a digital pseudorandom code modulation with a period equal to the PRI, Peer Reviewed, Postprint (published version)

The authors present an imaging near-field spherical wave inverse synthetic aperture radar (SWISAR) algorithm based on a focusing operator of the scattered fields on the target surface. A spherical wave can be easily generated in an anechoic chamber using electrically small and low-cost horn antennas; no reflectors are used, avoiding surface tolerance problems, and diffraction can be minimized with an appropriate horn design. An additional advantage of this algorithm is its ability to account for bistatic measurement geometries and lateral tapers in the spherical wave illumination. A 2-D formulation has been used which is strictly valid for bodies which satisfy far-field conditions in the height dimension, as easily occurs with aircraft. The reconstruction of numerically simulated five point-like objects placed on a radial line for a frequency range of 18 to 26 GHz and an angular scan of 360 degrees is shown., Peer Reviewed, Postprint (published version)

Email Print Request Permissions The performance of a fusion data center for a network of N radar receivers is analyzed. The total probabilities of detection and false alarm are obtained using a rank fusion rule. A constant false alarm rate operation that has been analyzed for Rayleigh targets and interference is proposed. For a given probability of fused false alarm an iterative method to calculate the threshold of detection of each receiver and the best rank is presented. This method allows the maximization of the probability of detection., Peer Reviewed, Postprint (published version)

The authors present a novel approach to solving the problem of the reconstruction of arbitrary strong-scattering objects using optimization techniques. The algorithm is based on the minimization of the mean-squared error between the measured and calculated scattered fields from the reconstruction. The object is assumed to have cylindrical symmetry, and the radial profile of permittivity is to be determined. The validity of the proposed algorithm is investigated both numerically and experimentally. In the experimental part, a tomographic microwave system operating at 2.45 GHz was used to measure the scattered field produced by a dielectric cylinder. A comparison between the measured scattered field and the theoretical field corresponding to the optimized cylinder epsilon =61.62 tan delta =0.38 R=2.23 cm is shown, and the reconstruction error is negligible for the radius and below 10% for the dielectric constant and loss tangent, Peer Reviewed, Postprint (published version)

Peer Reviewed, Postprint (published version)

The Advanced Radar Geosynchronous Observation System is proposed to be a multiple-input–multiple-output synthetic aperture radar (SAR) system hosted on a swarm of minisatellites in quasi-geostationary orbits. The system is made of N iso-frequency sensors, each of them transmitting and receiving the signals. The system would combine the continuous imaging capabilities of a geostationary SAR, gaining a factor N^{2} in signal-to-noise ratio (SNR). The real aperture would be achievable in \sim 40 min, enabling applications so far unseen, such as monitoring fast deformations, landslides, and other applications for emergency and security. Still, the SNR of the long acquisition time would be conserved. The optimal design of the swarm is addressed, in order to trade resolution, coverage, and revisit time, Peer Reviewed, Postprint (author’s final draft)

In this paper, the performance of a nearly zero inclination and low eccentricity geosynchronous synthetic aperture radar (GEOSAR) mission for midlatitude (30 degrees-60 degrees) Earth observation is analyzed. The slow motion of such satellites with respect to the Earth's surface makes it necessary to consider long coherent combination of pulses during hours to reach the desired along-track resolution. A system based on moderate transmitted powers and antenna sizes is considered. The necessary sensitivity in such GEOSAR system is obtained from the accumulated energy of the raw data using a pulse repetition frequency above the Doppler bandwidth and a long integration time. Several issues as a result of the long acquisition, such as target and atmospheric phase screen decorrelation, speckle noise impact on the received signal, and satellite station-keeping requirements, are analyzed. The feasibility of such systems to be placed on a broadcasting communication satellite makes nearly zero inclination GEOSAR a low-cost alternative of current SAR missions., Peer Reviewed, Postprint (published version)

The paper evaluates the effects of Atmospheric Phase Screen on focused Geosynchronous SAR data. We derive theoretical models for the resolution, the interferometric de-correlation and the induced clutter in presence of an APS, whose joint time and space power spectrum is modeled as an extension of the Kolmogorov power law. Finally we provide some statistics gathered from a GB RADAR experiment., Postprint (published version)