1,721,049 research outputs found
Monostatic and bistatic scattering modeling of the anisotropic rough soil
No full textThe electromagnetic scattering generated by agricultural tilled soils can be affected by a strong anisotropic component of the rough-surface profile. An accurate and reliable modeling of the normalized radar cross section, under both monostatic and bistatic geometries, is particularly important and desirable, especially for the correct estimation of the soil moisture content by means of satellite-based observations. In this paper, moving from the modeling so far proposed in the literature, we present and discuss a novel, more general (i.e., 2-D), spectral representation of an agricultural tilled soil, implementing a solution of the scattering based on the first-order small-slope approximation. Comparisons are given with a well-established model based on a 1-D representation of the soil correlation function, accounting for the radiation pattern of the illuminating antenna. The investigation gives new insight on the phenomenology of the bistatic scattering from the anisotropic soil, providing interesting information for the next generation of satellite missions, which foresees the possibility of launching companion satellites carrying aboard a passive receiver collecting the signal transmitted by active SAR-based platforms
Electromagnetic modeling of forward scatter radar
No full textThe forward scattering (FS) phenomenon is investigated in this work referring to a typical radar scenario where a metallic target crosses the baseline while is illuminated by a transmitting source. A straightforward electromagnetic (EM) analytical model is provided to predict the received signal both in near- and farfield conditions. The effect of different distances between target and receiving antenna are analyzed in terms of scattered and total EM fields. The results have been validated through an ad-hoc numerical implementation of a full-wave solution. Physical insight into the FS effect and restrictions on the applicability of the EM model are also discusse
First-order SSA modeling of the anisotropic rough-soil bistatic scattering
No full textIn this contribution, we analyze the bistatic scattering generated by agricultural soils, which can be characterized by a strong anisotropic component of the rough surface profile. A novel spectral representation is proposed in conjunction with a numerical solution of the scattering based on the well-known small-slope approximation. Comparisons are given with different modeling. The investigation provides interesting and novel information on the phenomenology of the bistatic scattering from the anisotropic soil. This is of great interest for the next generation of satellite missions, which foresees the possibility of launching companion satellites carrying aboard a passive receiver collecting the signal transmitted by an active SAR-based platform
Bistatic radar systems at large baselines for ocean observation
No full textThe capabilities of bistatic radar observations to estimate the wind field over the ocean are investigated in this paper. The work is based on the analysis of simulated data obtained through a well-established electromagnetic model, which accounts for the anisotropy of the ocean's spectrum and of second-order effects of the scattering phenomenon. Both co-polarized and cross-polarized C-band numerical data, obtained considering monostatic and bistatic configurations, are exploited to investigate on the existence of optimal configurations able to minimize the wind vector error estimation. To this aim, the sensitivities of the bistatic normalized radar cross section with respect to both wind speed and direction are accurately investigated and exploited to evaluate the minimum achievable error standard deviation of the estimation. Small and large baselines are analyzed, giving particular emphasis to bistatic geometries constituted by one or two passive receivers aligned along the track defined by the active system. This investigation, originally performed in the framework of the SAOCOM-CS scientific satellite mission, is conceived to accurately assess the potentiality of bistatic observations of the ocean over variable baselines and to gather valuable information for the design of future bistatic satellite missions
Electromagnetic modeling of scattered signals of opportunity: challenges and approaches
No full texthe possibility of exploiting signals of opportunity such as navigation signals for remote-sensing applications has been the object of extensive scientific research. Over the years, the potential of this technique has been mainly investigated for wind scatterometry and sea-surface altimetry, resulting in mission concepts and prototypes currently in orbit or under study. More recently, the potential of the Global Navigation Satellite System (GNSS) has attracted significant scientific and industrial interest, especially for land applications. The possibility of retrieving soil moisture and vegetation biomass by means of GNSS reflections, originally demonstrated through theoretical models and simulations, has been confirmed through the analysis of ground-based and airborne measurements. Even if these campaigns significantly contributed to consolidating the physics that is behind the interaction between navigation signals and some important geophysical parameters of the illuminated surface, a complete understanding of the experiments still needs further scientific efforts, especially for satellite observations. In this work, we review the main progress that has recently been made at two universities of Rome, Sapienza and Tor Vergata, as well as by some other research groups. Current challenges and modeling approaches are summarized, focusing the attention on the potential offered by GNSS reflectometry with respect to more established passive and active remote-sensing techniques. An electromagnetic model and the corresponding numerical simulator designed to characterize the field scattered under bistatic illumination and for the study of the signal at the receiver generated by sources of opportunity are reviewed and summarized
The role of the antenna radiation pattern in the performance of a microwave tomographic approach for GPR imaging
No full textMicrowave tomography has been exploited as a successful imaging technique for ground penetrating radar (GPR) surveys. However, an "ideal" antenna model (i.e., a filamentary current element) has usually been adopted so far to describe the involved scattering phenomena. In this study, such an assumption is removed, and the effects of a "realistic" antenna are taken into account by means of a customized numerical implementation. Specifically, we provide indications about the reconstruction capabilities expectable when the imaging is performed by using a "directional" wideband transceiver to gather GPR data. Moreover, we discuss to what extent the imaging performance is affected by a priori knowledge of the antenna model
Wire-medium loaded planar structures: modal analysis, near fields, and radiation features
No full textA novel transmission-line model is used for the analysis of planar structures, including wire-medium (WM) slabs with vertically aligned wires. The network formalism allows for an effective determination of the relevant spectral Green’s functions, of the modal dispersion equation via transverse resonance, as well as of the far-field radiation pattern produced by simple sources via reciprocity, as opposed to the more cumbersome field-matching approach. Numerical results, validated also against state-of-the-art simulation software, confirm the accuracy and effectiveness of the proposed approach. In particular, modal and radiation features are presented for a class of leaky-wave antennas based on planar WM loaded configurations covered by partially reflecting screens, for which leaky unimodal regimes are achieved by minimizing spurious radiation from the quasi-transverse electromagnetic (TEM) mode
Modeling of bistatic scattering from the anisotropic earth surfaces
No full textApproximate numerical modeling of microwave bistatic scattering (BS) from anisotropic rough surfaces, simulating large baselines radar bistatic system, is analyzed in this contribution. The investigation is performed in the framework of the SAOCOM-CS scientific satellite mission, a small satellite under design by the European Space Agency, to be associated with the Argentinian SAOCOM 1B satellite, aiming at collecting bistatic radar data at L-band. Similar bistatic concepts are being investigated at C-band as well. The main features of the normalized radar cross section (NRCS) of the sea surface in different operating conditions are discussed. This represents the first step to assess the potentiality of bistatic radar observations of natural surfaces with large baseline, and to gather valuable information on the bistatic scattering properties for the design of future spatial missions
Wire-medium loaded planar structures: A novel transmission-line model and relevant dispersion properties
No full textA transmission-line model is developed for the analysis of planar waveguides including wire-medium slabs with vertically aligned wires. The developed network formalism allows for an effective determination of the modal dispersion equation via transverse resonance, as opposed to the more cumbersome field-matching approach. Closed and open parallel-plate waveguides loaded with wire medium are considered. The suppression of undesired TEM-mode propagation and the possible achievement of a unimodal regime are investigated. Numerical results, validated also against state-of-the-art simulation software, confirm the accuracy and effectiveness of the proposed approach. Dispersion relations of complex modes are obtained for a class of leaky-wave antennas based on open wire-medium layered structures covered by partially reflecting screens
Relations between GPR early-time signal attributes and ground permittivity: A numerical investigation
No full textIn recent times, various theoretical and experimental studies have been carried out in order to address the relationship between amplitude attributes of the 'direct wave' propagating at the interface in bistatic ground-coupled radars (the so-called 'early-time signal') and the relevant shallow-soil permittivity. This issue is extensively analyzed here for the first time by means of an accurate and efficient numerical approach based on a CAD tool. The flexibility of the approach allows us to investigate in wider terms the role of the various physical parameters that affect the early-time signal features (type, location, and distance of the antennas, transmitted waveforms, etc.), in addition to the electromagnetic contrast between upper and lower media. Quantitative results are derived in order to clearly establish which are the more revealing signal attributes that enable for predictable correlation to the ground permittivity values and what kind of functional relations can be outlined. Novel and reliable information can thus be achieved on the actual potential of the 'early-time method' for efficient subsurface non-destructive testing
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