Bistatic Coherent Scattering From Rough Soils With Application to GNSS Reflectometry

Comite, Davide; Ticconi, Francesca; Dente, Laura; Guerriero, L.; Pierdicca, Nazzareno

doi:10.1109/tgrs.2019.2938442

Cited by 43 publications

(36 citation statements)

References 39 publications

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“…The simulation area A is set large enough to take into account the significant contributions to the received signal. The area mainly contributing to the coherent part of the bistatic scattering coefficient for a plane surface can be approximated by the first Fresnel zone [22], [23], but the area contributing to the incoherent component can expand either to the entire antenna footprint, or to the delay-Doppler discrimination cell, whichever is the smaller. As well known, the space-borne GNSS-R system is a pulse-limited system, which means that the area mainly contributing to the signal reaching the receiver first in time is defined by the intersection of the first iso-range zone and the first Doppler zone.…”

Section: A Savers General Structurementioning

confidence: 99%

Space-Borne GNSS-R Signal Over a Complex Topography: Modeling and Validation

Dente

Guerriero

Comite

et al. 2020

IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing

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A significant quantity of space-borne Global Navigation Satellite Systems-Reflectometry (GNSS-R) data over land was made available in the last decade, leading to an increasing interest in the assessment of the potentialities of this new remote sensing technique for land monitoring. In this frame, an electromagnetic simulator, such as the Soil And VEgetation Reflection Simulator (SAVERS), has the key role to support the understanding of the physical mechanism involved in the bistatic scattering and to identify the surface features mainly contributing to the observed signal. Originally developed for ground and airborne GNSS-R observations over homogeneous areas, in this study, SAVERS was upgraded to account for space-borne systems. The new version of SAVERS takes into account the inhomogeneity characterizing the large area observed from space altitudes, due to a variable surface elevation and land cover. Coherent and incoherent scattering and polarization rotation are computed taking into account the local slope and elevation of the surface. The simulator was validated against TechDemoSat-1 observations over a bare surface with a complex topography and over a forested surface with a gentle topography. The validation results show the capability of SAVERS to correctly estimate the effect of the topography, enhancing the understanding of the observations. Moreover, it was found that the sensitivity to soil moisture is independent of the topography (about 1.5 dB for a 10% variation of soil moisture). Whereas a saturation of the GNSS-R reflectivity over a variable topography is reached for lower values of biomass, earlier than in the flat case.

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Section: A Savers General Structurementioning

confidence: 99%

Space-Borne GNSS-R Signal Over a Complex Topography: Modeling and Validation

Dente

Guerriero

Comite

et al. 2020

IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing

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“…This is evident in case of liquid water (very high reflectivity), but also in frozen conditions, when the water bodies are expected to be much smoother than the soil. Assuming a relative permittivity equal to 3, variations of the order of 6-10 dB between the square module of the Fresnel reflection coefficient of mainly frozen flat surfaces can be straightforwardly calculated with respect to the one reduced by the surface roughness, as dictated by the geometric optics approach (see, e.g., [31]). This has been verified by analyzing the TDS-1 reflectivity (evaluated as given by (2)) achieved in February when crossing three different lakes at three different latitudes.…”

Section: Comparison With In-situ Datamentioning

confidence: 99%

“…As concerns the GNSS-R spatial resolution, signals over smooth land surfaces are generally assumed as mainly constituted by coherent reflections along the specular direction. At least for a flat profile, the signal mainly originates from the first Fresnel zone (FFZ) described by the transmitter-receiver configuration [23] (see also [29], [30], [31] for a discussion about these aspects). A contribution of the incoherent and diffuse scattering coming from the whole glistening zone does also exist [23], which is however less relevant for this investigation.…”

Section: Introductionmentioning

confidence: 99%

Monitoring Freeze-Thaw State by Means of GNSS Reflectometry: An Analysis of TechDemoSat-1 Data

Comite

Cenci

Colliander

et al. 2020

IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing

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The study of the freeze/thaw dynamic of highlatitude Earth surfaces is extremely important and informative for monitoring the carbon cycle, the climate change, and the security of infrastructures. Current methodologies mainly rely on the use of active and passive microwave sensors, whilst very few efforts have been devoted to the assessment of the potential of observations based on signals of opportunity. This work aims at assessing the performance of spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) for high-spatial and high-temporal resolution monitoring of the Earth-surface freeze/thaw state. To this aim, reflectivity values derived from the TechDemoSat-1 (TDS-1) data have been collected and elaborated, and thus compared against the Soil Moisture Active Passive (SMAP) freeze/thaw information. Shallow sub-surface soil temperature values recorded by a network of in situ stations have been considered as well. Even if an extensive and timeliness cross-availability of both types of experimental data is limited by the spatial coverage and density of TDS-1 observations, the proposed analysis clearly indicates a significant seasonal cycle in the calibrated reflectivity. This opens new perspectives for the bistatic L-band highresolution satellite monitoring of the freeze/thaw state, as well as to support the development of next-generation of GNSS-R satellite missions designed to provide enhanced performance and improved temporal and spatial coverage over high latitude areas.

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“…In assessing the observables to be used for inundation detection, two scattering models were considered, both assuming distributed targets (see [19] for a more refined scattering model): one where the signal is absorbed by the surface and retransmitted, and another where the surface is assumed flat and conducting. The first model follows the standard derivation of the radar equation [20], where the received surface-reflected power, P r , is given by…”

Section: Scattering Modelmentioning

confidence: 99%

An Aircraft Wetland Inundation Experiment Using GNSS Reflectometry

et al. 2020

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In early May of 2017, a flight campaign was conducted over Caddo Lake, Texas, to test the ability of Global Navigation Satellite System-Reflectometry (GNSS-R) to detect water underlying vegetation canopies. This paper presents data from that campaign and compares them to Sentinel-1 data collected during the same week. The low-altitude measurement allows for a more detailed assessment of the forward-scattering GNSS-R technique, and at a much higher spatial resolution, than is possible using currently available space-based GNSS-R data. Assumptions about the scattering model are verified, as is the assumption that the surface spot size is approximately the Fresnel zone. The results of this experiment indicate GNSS signals reflected from inundated short, thick vegetation, such as the giant Salvinia observed here, results in only a 2.15 dB loss compared to an open water reflection. GNSS reflections off inundated cypress forests show a 9.4 dB loss, but still 4.25 dB above that observed over dry regions. Sentinel-1 data show a 6-dB loss over the inundated giant Salvinia, relative to open water, and are insensitive to standing water beneath the cypress forests, as there is no difference between the signal over inundated cypress forests and that over dry land. These results indicate that, at aircraft altitudes, forward-scattered GNSS signals are able to map inundated regions even in the presence of dense overlying vegetation, whether that vegetation consists of short plants or tall trees.

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Bistatic Coherent Scattering From Rough Soils With Application to GNSS Reflectometry

Cited by 43 publications

References 39 publications

Space-Borne GNSS-R Signal Over a Complex Topography: Modeling and Validation

Space-Borne GNSS-R Signal Over a Complex Topography: Modeling and Validation

Monitoring Freeze-Thaw State by Means of GNSS Reflectometry: An Analysis of TechDemoSat-1 Data

An Aircraft Wetland Inundation Experiment Using GNSS Reflectometry

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