1,720,990 research outputs found
Modal Expansion Approach for Electromagnetic Propagation in Street Canyons
No full textWe present a simple and efficient model to compute
electromagnetic (EM) propagation in urban street canyons, when
transmitting and receiving antennas are located below the rooftop
level. A parallel-plate dielectric hollow waveguide model of the
street canyon is proposed, and propagation is analyzed by using
the modal expansion approach. Obtained results for the case
of line-of-sight (LoS) propagation are substantially equivalent to
those obtained with the ray-optics method, but, with respect to
the latter, our method presents important advantages: it is more
efficient from a computational viewpoint, it allows deriving a
very simple and reasonably accurate formulation of the average
received signal strength, and it provides a fairly simple way
to compute coupling at cross-junctions, exploited to obtain an
analogous formulation for the non-LoS case. Obtained results
are compared with simulations of a ray-tracing-based EM solver
and with experimental measurements available in the literature
Correlation of the Fields Scattered by a Fractal Surface at Two Closely Spaced Receivers
No full textNatural surfaces show scale invariance statistical properties over a wide range of scales, and exhibit power-law spectra over a wide range of spatial frequencies: these properties are well modelled by fractional Brownian motion (fBm) two-dimensional processes. We here present a closed form expression of the correlation coefficient of the fields scattered by a fBm surface and measured at two closely spaced positions. The obtained formulation shows that the correlation coefficient in the near-specular scattering case depends on a parameter that is related to the rms surface slope measured at the electromagnetic wavelength scale: when this parameter decreases, the correlation coefficient smoothly increases from the value obtained by the roughness-independent expression already available in literature to a value close to unity
Fractal-based local range slope estimation from single SAR image with applications to SAR despeckling and topographic mapping
No full textIn this paper, we propose a range slope estimation procedure from single synthetic aperture radar (SAR) images with both methodological and applicative innovations. The retrieval algorithm is based on an analytical linearized direct model, which relates the SAR intensity data to the range local slopes and encompasses both a surface model and an electromagnetic scattering model. Scene topography is described via fractal geometry, whereas the Small Perturbation Method is adopted to represent the scattering behavior of the surface. The range slope map is then used to estimate the surface topography and the local incidence angle map. For topographic mapping applications, also referred to as shape from shading, a regularization procedure is derived to recover the azimuth local slope and reduce distortions. Then we present a new intriguing application of the inversion procedure in the field of SAR despeckling. Proposed techniques and high-level products are tested in a wide series of experiments, where the algorithms are applied to both simulated (canonical) and actual SAR images. It is proved that the proposed range slope retrieval technique can (1) provide an estimate of the surface shape, with overall better performance w.r.t. typical models used in this field and (2) be useful in advanced despeckling techniques
Sensitivity analysis of a scattering-based nonlocal means despeckling algorithm
No full textSynthetic Aperture Radar (SAR) images are greatly affected by the speckle noise. In order to improve SAR data readability by human interpreters and information extraction performed by computer programs, a despeckling preprocessing step is mandatory. The authors recently presented a despeckling algorithm based on the a priori knowledge of the local topography. In this paper, an experimental sensitivity analysis of the aforementioned despeckling algorithm is conducted and the main results are discussed. In particular, the sensitivity of the filter against surface parameters and scattering behavior is analyzed. A comprehensive understanding of the role of the Digital Elevation Model resolution and the coregistration step is also provided
The Role of Skin in mm-Wave Exposure of Human Body
No full textThe advent of 5G/B5G wireless communications networks has stimulated research efforts in assessing health effects of human tissues exposure to electromagnetic fields (EMF). In this paper, we investigate the role of skin thickness in the exposure of human body to EMF at mm-Waves. Different skin models and dielectric characterizations, including layered skin, are studied using the equivalent multi-layer model framework. Simulation analyses show that as frequency increases the impact of changes in the dielectric and geometric characterization of the skin is less and less relevant due to the decreasing penetration depth. Additionally, the presence of stratum corneum determines an increased power absorption
Scattering Along the Specular Direction from the Sea Modeled as a Fractal Surface
No full textModels linking the electromagnetic field scattered from the sea surface along the specular direction to the speed of the wind blowing over the surface are of fundamental importance for wind speed retrieval via Global Navigation Satellite System Reflectometry (GNSS-R). In this work, by modelling the sea surface as a fractional Brownian motion (fBm) random process and using the Kirchhoff approximation (KA), we express the sea bistatic normalized radar cross section (NRCS) at specular direction directly in terms of sea surface spectrum parameters, and hence of wind speed. This avoids the need of intermediately computing the large-scale sea surface slope variance, which in turn would require the definition of a somewhat arbitrary cut-off surface wavenumber. We show that the obtained theoretical relationship between wind speed and σ0 is in reasonable agreement with the empirical ones available in literature
Baseline Decorrelation in Bistatic Interferometric SAR Systems Over Bare Soil Surfaces
No full textIn the context of bistatic synthetic aperture radar (SAR) imaging, SAR interferometry is an appealing application due to the capability of retrieving accurate topographic information or surface deformations at fractions of wavelength. Within this framework, we present a new physical-based approach to evaluate the correlation between a pair of bistatic SAR acquisitions over a bare soil surface and in a very general imaging geometry, which includes two transmitters and two receivers. Some specific configurations of practical interest for proposed bistatic spaceborne SAR missions, e. g., SESAME and PLATiNO-1, namely co-planar and along-track bistatic geometries, are analyzed as well. The proposed methodology makes use of electromagnetic scattering models suited to random rough surfaces, namely the Kirchhoff Approximation and the first-order Small-Slope Approximation, under which analytical formulations of the correlation between the received electromagnetic fields are derived. It is found that in the co-planar imaging geometry, a unitary correlation coefficient can be obtained with non-null orthogonal baselines. Closed-form expressions of the critical baseline are derived as well. The proposed approach can be applied to such scenarios where single surface scattering is the dominant mechanism, such as bare soil surfaces or scarcely-to-moderately vegetated areas
Scattering-Based SARBM3D
No full textInterpreting synthetic aperture radar (SAR) images may be a very challenging task, even for expert users. One of the main reasons is the multiplicative speckle noise typical of coherent acquisition systems. Therefore, despeckling can be expected to play a key role in the full exploitation of SAR imagery potential. However, even state-of-the-art despeckling algorithms neglect the physical phenomena hidden behind SAR imagery. Image acquisition depends on electromagnetic scattering, which is also at the basis of speckle noise. Taking into account scattering issues into more physical-based despeckling algorithms may only benefit the overall performance. In this paper, we propose a scattering-based (SB) version of the SAR block-matching 3D (BM3D) filter, named SB-SARBM3D. SARBM3D can be arguably considered as one of the most promising and accurate despeckling algorithms, providing a good compromise between speckle reduction and detail preservation. We modify the original algorithm so as to exploit the prior information available on the imaged scene, taken into account based on scattering concepts. The new algorithm is tested in a variety of different and complementary simulated scenarios, and its performance is assessed objectively by means of numerous synthetic parameters. Moreover, comparison with different state-of-the-art despeckling algorithms is performed on some actual SAR images, both inherent to natural and urbanized areas, for subjective evaluation. Thanks to the prior information, SB-SARBM3D outperforms the original algorithm in terms of both speckle reduction and detail preservation. Moreover, it reduces the annoying artifacts introduced sometimes by SARBM3D in homogeneous areas of the image
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