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Special Issue "Synthetic Aperture Radar (SAR) Technology: New Perspectives Offered by New-Generation and Forthcoming SAR Sensors"

A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Remote Sensors".

Deadline for manuscript submissions: 31 August 2018

Special Issue Editor

Guest Editor
Dr. Antonio Pepe

National Research Council (CNR) of Italy—Institute for the Electromagnetic Sensing of the Environment (IREA), via Diocleziano 328, 80124 Napoli, Italy
Website | E-Mail
Interests: remote sensing; synthetic aperture radar (SAR); InSAR; phase unwrapping; combination/integration of multi-mode/multi-sensor data

Special Issue Information

Dear Colleagues,

A new generation of synthetic aperture radar (SAR) instruments mounted on-board to space and aerial vectors has been emerging over recent years, thus guaranteeing improved temporal sampling and spatial resolutions of remote-based investigations. In this framework, of particular relevance is the development of new approaches for the effective processing of long-term sequences of SAR images. Use of novel High Computing paradigms and the development of new methods for the integration of information derived from different sets of SAR images acquired at complementary frequency bands represent the new challenging frontiers of SAR technologies. SAR-driven cutting-edge technologies also concern: combination/fusion of SAR and optical data; development of new multi-temporal/multi-mode InSAR methods based on the use of mono/multi-static SAR configurations; advances of Polarimetric InSAR and Tomography SAR techniques with new-generation of high-resolution SAR images; computer science applications for high-speed computing.     

The Special Issue is open to all researchers. Papers are solicited on the following general themes:

- Exploitation of the existing and planned SAR missions

- Advances of Interferometric SAR techniques: development of new algorithms and methodologies for the estimation of the height topography, the deformation, the atmospheric phase screen as well as other contributions regarding the InSAR signal.

- Potential of new-generation SAR instruments onboard the principal spaceborne platforms: the Sentinel constellation of the European Union, the COSMO-SkyMed constellation of the Italian Space Agency, the ALOS-2 mission of the Japanese Space Agency, the TerraSAR-X constellation operated by DLR, other SAR instruments.

- Future perspectives in the use of SAR data for the development of new emerging cutting-edge
technologies for Earth's remote sensing.

- Synergic use of SAR and optical data (e.g., Sentinel-2, LANDSAT, etc) for agricultural applications and/or for the study of land-use, land-cover of imaged scenes.

- High Performance Computing (HPC) for SAR data processing.

- Geophysical Investigations of the deformation sources that are responsible for the detected movements of the Earth's crust retrieved by InSAR measurements, due to heterogeneous causes, such as earthquakes, volcanic eruption, ground-water extraction in urban areas, landslide movements, etc.

- Integration of information provided through space-, aerial- and terrestrial-based InSAR data systems.

Dr. Antonio Pepe
Guest Editor

Manuscript Submission Information

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Keywords

  • Synthetic Aperture Radar
  • InSAR
  • deformation
  • space
  • high performance computing
  • cutting-edge technologies
  • agricultural, optical data
  • geodesy
  • new challenges
  • LIDAR
  • ALOS
  • Sentinel
  • TerraSAR-X
  • COSMO-SkyMed
  • SRTM
  • aerial SAR
  • ground-based SAR

Published Papers (11 papers)

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Research

Open AccessArticle Monitoring Highway Stability in Permafrost Regions with X-band Temporary Scatterers Stacking InSAR
Sensors 2018, 18(6), 1876; https://doi.org/10.3390/s18061876
Received: 22 April 2018 / Revised: 29 May 2018 / Accepted: 5 June 2018 / Published: 8 June 2018
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Abstract
Interferograms with short wavelength (e.g., X-band) are usually prone to temporal decorrelation in permafrost regions, leading to the unavailability of sufficient high-coherence interferograms for performing conventional time series InSAR analysis. This paper proposes the utilization of temporary scatterers for the stacking InSAR method,
[...] Read more.
Interferograms with short wavelength (e.g., X-band) are usually prone to temporal decorrelation in permafrost regions, leading to the unavailability of sufficient high-coherence interferograms for performing conventional time series InSAR analysis. This paper proposes the utilization of temporary scatterers for the stacking InSAR method, thus enabling extraction of subsidence in a permafrost region with limited SAR images and limited high-coherence interferograms. Such method is termed as the temporary scatterers stacking InSAR (TSS-InSAR). Taking the Gonghe-Yushu highway (about 30 km), part of G214 National Highway in Qinghai province (in a permafrost region), as a case study, this TSS-InSAR approach was demonstrated in detail and implemented. With 10 TerraSAR-X images acquired during the period from May 2015 to August 2015, the subsidence along this highway was extracted. In this case the lack of a consistent number of SAR acquisitions limits the possibility to perform other conventional time series InSAR analysis. The results show that the middle part of this highway is in the thermokarst and seasonal frozen soil area, and its accumulated subsidence reach up to 10 cm in 110 days. The thawing phenomena is still the main reason for the instability of highway. The results demonstrate that the TSS-InSAR method can effectively extract the subsidence information in a challenging scenario with limited X-band SAR images and limited high-coherence interferograms, where other time series InSAR-based techniques cannot be applied in a simple way. Full article
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Open AccessArticle Parameter Estimation of SAR Signal Based on SVD for the Nyquist Folding Receiver
Sensors 2018, 18(6), 1768; https://doi.org/10.3390/s18061768
Received: 27 April 2018 / Revised: 20 May 2018 / Accepted: 27 May 2018 / Published: 1 June 2018
PDF Full-text (2110 KB) | HTML Full-text | XML Full-text
Abstract
The Nyquist Folding Receiver (NYFR) is a novel ultra-wideband (UWB) receiver structure that can realize wideband signal monitoring with fewer components. The NYFR induces a Nyquist zone (NZ)-dependent sinusoidal frequency modulation (SFM) by a modulated local oscillator (LOS), and the intercepted linear frequency
[...] Read more.
The Nyquist Folding Receiver (NYFR) is a novel ultra-wideband (UWB) receiver structure that can realize wideband signal monitoring with fewer components. The NYFR induces a Nyquist zone (NZ)-dependent sinusoidal frequency modulation (SFM) by a modulated local oscillator (LOS), and the intercepted linear frequency modulated (LFM) synthetic aperture radar (SAR) signal will be converted into an LFM/SFM hybrid modulated signal. In this paper, a parameter estimation algorithm is proposed for the complicated NYFR output signal. According to the NYFR prior information, a chirp singular value ratio (CSVR) spectrum method based on singular value decomposition (SVD) is proposed to estimate the chirp rate directly before estimating the NZ index. Then, a fast search algorithm based on golden section method for the CSVR spectrum is analyzed, which can obviously reduce the computational complexity. The simulation shows that the presented algorithm can accurately estimate the parameters of the LFM/SFM hybrid modulated output signal by the NYFR. Full article
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Open AccessArticle Transmitting Pulse Encoding for Beyond-PRT Retransmitting Deception Jamming Detection in Spaceborne Synthetic Aperture Radar (SAR)
Sensors 2018, 18(5), 1666; https://doi.org/10.3390/s18051666
Received: 12 April 2018 / Revised: 19 May 2018 / Accepted: 21 May 2018 / Published: 22 May 2018
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Abstract
Retransmitting deception jamming (RDJ) degrades and misleads the Synthetic Aperture Radar (SAR) image interpretation by forming false targets. The beyond-Pulse Repetition Time (PRT) RDJ enlarges the effective jamming area without constraining the jammer location to reduce the spaceborne SAR working effectiveness. In order
[...] Read more.
Retransmitting deception jamming (RDJ) degrades and misleads the Synthetic Aperture Radar (SAR) image interpretation by forming false targets. The beyond-Pulse Repetition Time (PRT) RDJ enlarges the effective jamming area without constraining the jammer location to reduce the spaceborne SAR working effectiveness. In order to detect the beyond-PRT RDJ and enhance the working efficiency in electronic countermeasure environment, the transmitting pulse encoding method for use in spaceborne SAR is proposed based on the geometry and signal models of beyond-PRT RDJ. Optimum binary codes with maximum number of detection windows are determined by the encoding procedure. The detected area is found to be proportional to the code length and the encoding efficiencies of even and odd codes are analyzed. The simulation results validate the effectiveness of the transmitting pulse encoding method for beyond-PRT RDJ detection in spaceborne SAR. Full article
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Open AccessArticle Performance Analysis of Satellite Missions for Multi-Temporal SAR Interferometry
Sensors 2018, 18(5), 1359; https://doi.org/10.3390/s18051359
Received: 12 March 2018 / Revised: 23 April 2018 / Accepted: 24 April 2018 / Published: 27 April 2018
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Abstract
Multi-temporal InSAR (MTI) applications pose challenges related to the availability of coherent scattering from the ground surface, the complexity of the ground deformations, atmospheric artifacts, and visibility problems related to ground elevation. Nowadays, several satellite missions are available providing interferometric SAR data at
[...] Read more.
Multi-temporal InSAR (MTI) applications pose challenges related to the availability of coherent scattering from the ground surface, the complexity of the ground deformations, atmospheric artifacts, and visibility problems related to ground elevation. Nowadays, several satellite missions are available providing interferometric SAR data at different wavelengths, spatial resolutions, and revisit time. A new and interesting opportunity is provided by Sentinel-1, which has a spatial resolution comparable to that of previous ESA C-band sensors, and revisit times improved by up to 6 days. According to these different SAR space-borne missions, the present work discusses current and future opportunities of MTI applications in terms of ground instability monitoring. Issues related to coherent target detection, mean velocity precision, and product geo-location are addressed through a simple theoretical model assuming backscattering mechanisms related to point scatterers. The paper also presents an example of a multi-sensor ground instability investigation over Lesina Marina, a village in Southern Italy lying over a gypsum diapir, where a hydration process, involving the underlying anhydride, causes a smooth uplift and the formation of scattered sinkholes. More than 20 years of MTI SAR data have been processed, coming from both legacy ERS and ENVISAT missions, and latest-generation RADARSAT-2, COSMO-SkyMed, and Sentinel-1A sensors. Results confirm the presence of a rather steady uplift process, with limited to null variations throughout the whole monitored time-period. Full article
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Open AccessArticle Raw Data-Based Motion Compensation for High-Resolution Sliding Spotlight Synthetic Aperture Radar
Sensors 2018, 18(3), 842; https://doi.org/10.3390/s18030842
Received: 20 January 2018 / Revised: 8 March 2018 / Accepted: 9 March 2018 / Published: 12 March 2018
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Abstract
For accurate motion compensation (MOCO) in airborne synthetic aperture radar (SAR) imaging, a high-precision inertial navigation system (INS) is required. However, an INS is not always precise enough or is sometimes not even included in airborne SAR systems. In this paper, a new,
[...] Read more.
For accurate motion compensation (MOCO) in airborne synthetic aperture radar (SAR) imaging, a high-precision inertial navigation system (INS) is required. However, an INS is not always precise enough or is sometimes not even included in airborne SAR systems. In this paper, a new, raw, data-based range-invariant motion compensation approach, which can effectively extract the displacements in the line-of-sight (LOS) direction, is proposed for high-resolution sliding spotlight SAR mode. In this approach, the sub-aperture radial accelerations of the airborne platform are estimated via a well-developed weighted total least square (WTLS) method considering the time-varying beam direction. The effectiveness of the proposed approach is validated by two airborne sliding spotlight C band SAR raw datasets containing different types of terrain, with a high spatial resolution of about 0.15 m in azimuth. Full article
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Open AccessArticle A Novel Sidelobe Reduction Algorithm Based on Two-Dimensional Sidelobe Correction Using D-SVA for Squint SAR Images
Sensors 2018, 18(3), 783; https://doi.org/10.3390/s18030783
Received: 30 January 2018 / Revised: 22 February 2018 / Accepted: 3 March 2018 / Published: 5 March 2018
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Abstract
Sidelobe reduction is a very primary task for synthetic aperture radar (SAR) images. Various methods have been proposed for broadside SAR, which can suppress the sidelobes effectively while maintaining high image resolution at the same time. Alternatively, squint SAR, especially highly squint SAR,
[...] Read more.
Sidelobe reduction is a very primary task for synthetic aperture radar (SAR) images. Various methods have been proposed for broadside SAR, which can suppress the sidelobes effectively while maintaining high image resolution at the same time. Alternatively, squint SAR, especially highly squint SAR, has emerged as an important tool that provides more mobility and flexibility and has become a focus of recent research studies. One of the research challenges for squint SAR is how to resolve the severe range-azimuth coupling of echo signals. Unlike broadside SAR images, the range and azimuth sidelobes of the squint SAR images no longer locate on the principal axes with high probability. Thus the spatially variant apodization (SVA) filters could hardly get all the sidelobe information, and hence the sidelobe reduction process is not optimal. In this paper, we present an improved algorithm called double spatially variant apodization (D-SVA) for better sidelobe suppression. Satisfactory sidelobe reduction results are achieved with the proposed algorithm by comparing the squint SAR images to the broadside SAR images. Simulation results also demonstrate the reliability and efficiency of the proposed method. Full article
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Open AccessArticle Multichannel High Resolution Wide Swath SAR Imaging for Hypersonic Air Vehicle with Curved Trajectory
Sensors 2018, 18(2), 411; https://doi.org/10.3390/s18020411
Received: 6 January 2018 / Revised: 28 January 2018 / Accepted: 29 January 2018 / Published: 31 January 2018
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Abstract
Synthetic aperture radar (SAR) equipped on the hypersonic air vehicle in near space has many advantages over the conventional airborne SAR. However, its high-speed maneuvering characteristics with curved trajectory result in serious range migration, and exacerbate the contradiction between the high resolution and
[...] Read more.
Synthetic aperture radar (SAR) equipped on the hypersonic air vehicle in near space has many advantages over the conventional airborne SAR. However, its high-speed maneuvering characteristics with curved trajectory result in serious range migration, and exacerbate the contradiction between the high resolution and wide swath. To solve this problem, this paper establishes the imaging geometrical model matched with the flight trajectory of the hypersonic platform and the multichannel azimuth sampling model based on the displaced phase center antenna (DPCA) technology. Furthermore, based on the multichannel signal reconstruction theory, a more efficient spectrum reconstruction model using discrete Fourier transform is proposed to obtain the azimuth uniform sampling data. Due to the high complexity of the slant range model, it is difficult to deduce the processing algorithm for SAR imaging. Thus, an approximate range model is derived based on the minimax criterion, and the optimal second-order approximate coefficients of cosine function are obtained using the two-population coevolutionary algorithm. On this basis, aiming at the problem that the traditional Omega-K algorithm cannot compensate the residual phase with the difficulty of Stolt mapping along the range frequency axis, this paper proposes an Exact Transfer Function (ETF) algorithm for SAR imaging, and presents a method of range division to achieve wide swath imaging. Simulation results verify the effectiveness of the ETF imaging algorithm. Full article
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Open AccessArticle Accurate Analysis of Target Characteristic in Bistatic SAR Images: A Dihedral Corner Reflectors Case
Sensors 2018, 18(1), 24; https://doi.org/10.3390/s18010024
Received: 10 October 2017 / Revised: 5 December 2017 / Accepted: 11 December 2017 / Published: 22 December 2017
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Abstract
The dihedral corner reflectors are the basic geometric structure of many targets and are the main contributions of radar cross section (RCS) in the synthetic aperture radar (SAR) images. In stealth technologies, the elaborate design of the dihedral corners with different opening angles
[...] Read more.
The dihedral corner reflectors are the basic geometric structure of many targets and are the main contributions of radar cross section (RCS) in the synthetic aperture radar (SAR) images. In stealth technologies, the elaborate design of the dihedral corners with different opening angles is a useful approach to reduce the high RCS generated by multiple reflections. As bistatic synthetic aperture sensors have flexible geometric configurations and are sensitive to the dihedral corners with different opening angles, they specially fit for the stealth target detections. In this paper, the scattering characteristic of dihedral corner reflectors is accurately analyzed in bistatic synthetic aperture images. The variation of RCS with the changing opening angle is formulated and the method to design a proper bistatic radar for maximizing the detection capability is provided. Both the results of the theoretical analysis and the experiments show the bistatic SAR could detect the dihedral corners, under a certain bistatic angle which is related to the geometry of target structures. Full article
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Open AccessArticle Investigation of Wavenumber Domain Imaging Algorithm for Ground-Based Arc Array SAR
Sensors 2017, 17(12), 2950; https://doi.org/10.3390/s17122950
Received: 23 October 2017 / Revised: 10 December 2017 / Accepted: 15 December 2017 / Published: 19 December 2017
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Abstract
Ground-based synthetic aperture radar (GB-SAR) has become an important technique for remote sensing deformation monitoring. However, most of the existing GB-SAR systems realize synthetic aperture by exploiting two closely spaced horn antennas to move along a linear rail. In order to obtain higher
[...] Read more.
Ground-based synthetic aperture radar (GB-SAR) has become an important technique for remote sensing deformation monitoring. However, most of the existing GB-SAR systems realize synthetic aperture by exploiting two closely spaced horn antennas to move along a linear rail. In order to obtain higher data acquisition efficiency and a wider view angle, we introduce arc antenna array technology into the GB-SAR system, which realizes a novel kind of system: ground-based arc array SAR (GB-AA-SAR). In this paper, we analyze arc observation geometry and derive analytic expressions of sampling criteria. Then, we propose a novel wavenumber domain imaging algorithm for GB-AA-SAR, which can achieve high image reconstruction precision through numerical solutions in the wavenumber domain. The proposed algorithm can be applied in wide azimuth view angle scenarios, and the problem of azimuth mismatch caused by distance approximation in arc geometric efficient omega-k imaging can be solved successfully. Finally, we analyze the two-dimensional (2D) spatial resolution of GB-AA-SAR, and verify the effectiveness of the proposed algorithm through numerical simulation experiments. Full article
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Open AccessArticle Precise Aperture-Dependent Motion Compensation with Frequency Domain Fast Back-Projection Algorithm
Sensors 2017, 17(11), 2454; https://doi.org/10.3390/s17112454
Received: 20 August 2017 / Revised: 12 October 2017 / Accepted: 24 October 2017 / Published: 26 October 2017
PDF Full-text (17979 KB) | HTML Full-text | XML Full-text
Abstract
Precise azimuth-variant motion compensation (MOCO) is an essential and difficult task for high-resolution synthetic aperture radar (SAR) imagery. In conventional post-filtering approaches, residual azimuth-variant motion errors are generally compensated through a set of spatial post-filters, where the coarse-focused image is segmented into overlapped
[...] Read more.
Precise azimuth-variant motion compensation (MOCO) is an essential and difficult task for high-resolution synthetic aperture radar (SAR) imagery. In conventional post-filtering approaches, residual azimuth-variant motion errors are generally compensated through a set of spatial post-filters, where the coarse-focused image is segmented into overlapped blocks concerning the azimuth-dependent residual errors. However, image domain post-filtering approaches, such as precise topography- and aperture-dependent motion compensation algorithm (PTA), have difficulty of robustness in declining, when strong motion errors are involved in the coarse-focused image. In this case, in order to capture the complete motion blurring function within each image block, both the block size and the overlapped part need necessary extension leading to degeneration of efficiency and robustness inevitably. Herein, a frequency domain fast back-projection algorithm (FDFBPA) is introduced to deal with strong azimuth-variant motion errors. FDFBPA disposes of the azimuth-variant motion errors based on a precise azimuth spectrum expression in the azimuth wavenumber domain. First, a wavenumber domain sub-aperture processing strategy is introduced to accelerate computation. After that, the azimuth wavenumber spectrum is partitioned into a set of wavenumber blocks, and each block is formed into a sub-aperture coarse resolution image via the back-projection integral. Then, the sub-aperture images are straightforwardly fused together in azimuth wavenumber domain to obtain a full resolution image. Moreover, chirp-Z transform (CZT) is also introduced to implement the sub-aperture back-projection integral, increasing the efficiency of the algorithm. By disusing the image domain post-filtering strategy, robustness of the proposed algorithm is improved. Both simulation and real-measured data experiments demonstrate the effectiveness and superiority of the proposal. Full article
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Open AccessArticle A Fast Terahertz Imaging Method Using Sparse Rotating Array
Sensors 2017, 17(10), 2209; https://doi.org/10.3390/s17102209
Received: 19 July 2017 / Revised: 21 September 2017 / Accepted: 24 September 2017 / Published: 26 September 2017
PDF Full-text (6393 KB) | HTML Full-text | XML Full-text
Abstract
For fast and standoff personal screening, a novel terahertz imaging scheme using a sparse rotating array is developed in this paper. A linearly sparse array is designed to move along a circular path with respect to an axis perpendicular to the imaging scenario.
[...] Read more.
For fast and standoff personal screening, a novel terahertz imaging scheme using a sparse rotating array is developed in this paper. A linearly sparse array is designed to move along a circular path with respect to an axis perpendicular to the imaging scenario. For this new scheme, a modified imaging algorithm is proposed based on the frequency-domain reconstruction method in circular synthetic aperture radar. To achieve better imaging performance, an optimization method of the sparse array is also proposed, according to the distribution of the spectral support. Theoretical and numerical analysis of the point spread function (PSF) is provided to demonstrate the high-resolution imaging ability of the proposed scheme. Comprehensive simulations are carried out to validate the feasibility and effectiveness of the array optimization method. Finally, the imaging results of a human-scattering model are also obtained to further demonstrate the good performance of this new imaging scheme and the effectiveness of the array optimization approach. This work can facilitate the design and practice of terahertz imaging systems for security inspection. Full article
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