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Backscattered Power

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Guy Cloutier – One of the best experts on this subject based on the ideXlab platform.

  • Frequency Dependence of Simulated Ultrasound Signals Backscattered by Aggregating Red Blood Cells
    Acoustical Imaging, 2020
    Co-Authors: Isabelle Fontaine, Guy Cloutier

    Abstract:

    The frequency dependence of the ultrasound signal Backscattered by blood was studied with a simulation model. The ultrasound Backscattered signal was simulated with a linear model that considers the characteristics of the ultrasound system and the tissue scattering properties. The tissue function was described by the position and the shape of the red blood cells (RBCs). The effect of the flow on the spatial organization of aggregating RBCs was simulated with a 2D model. It is an iterative model that considers the effect of the flow and the adhesive and repulsive forces acting on each RBC. RBC aggregation was simulated at 40 % hematocrit and shear rates of 0.05 s−1, 0.08 s−1, 0.1 s−1, 0.5 s−1, and 5 s−1. Ultrasound frequencies between 5 and 500 MHz were studied. Results suggest that in the presence of RBC aggregation, the frequency dependence may vary depending on the shear rate and the range of frequencies studied. The enhancement of the Backscattered Power with RBC aggregation may be more important at frequencies below 30 MHz. At higher frequencies, changes in the frequency dependence of the ultrasound Backscattered Power were noted in the presence of RBC aggregation. It is concluded that further studies may be necessary to understand the relationship between the ultrasound Backscattered Power and the spatial organization of aggregating RBCs.

  • Modeling and analysis of ultrasound backscattering by spherical aggregates and rouleaux of red blood cells
    IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2020
    Co-Authors: Guy Cloutier

    Abstract:

    The present study concerns the modeling and analysis of ultrasound backscattering by red blood cell (RBC) aggregates, which under pathological conditions play a significant role in the rheology of blood within human vessels. A theoretical model based on the convolution between a tissue matrix and a point spread function, representing, respectively, the RBC aggregates and the characteristics of the ultrasound system, was used to examine the influence of the scatterer shape and size on the Backscattered Power. Both scatterers in the form of clumps of RBC aggregates and rouleaux were modeled. For all simulations, the hematocrit was kept constant at 10%, the ultrasound frequency was 10 MHz, the insonification angle was varied from 0 to 90/spl deg/, and the scatterer size (diameter for clumps and length for rouleaux) ranged from 4 /spl mu/m to 120 /spl mu/m. Under Rayleigh scattering by assuming a Poisson distribution of scatterers in space, the ultrasound Backscattered Power increased linearly with the particle volume. For non-Rayleigh scatterers, the intensity of the echoes diminished as the scatterer volume increased, with the exception of rouleaux at an angle of 90/spl deg/. As expected, the Backscattered Power was angularly dependent for anisotropic particles (rouleaux). The ultrasound Backscattered Power did not always increase with the size of the aggregates, especially when they were no longer Rayleigh scatterers. In the case of rouleaux, the anisotropy of the Backscattered Power is emphasized in the non-Rayleigh region.

  • Simulation of ultrasound backscattering by red cell aggregates: effect of shear rate and anisotropy.
    Biophysical Journal, 2002
    Co-Authors: Isabelle Fontaine, David Savéry, Guy Cloutier

    Abstract:

    Abstract Tissue characterization using ultrasound (US) scattering allows extraction of relevant cellular biophysical information noninvasively. Characterization of the level of red blood cell (RBC) aggregation is one of the proposed application. In the current paper, it is hypothesized that the microstructure of the RBCs is a main determinant of the US Backscattered Power. A simulation model was developed to study the effect of various RBC configurations on the Backscattered Power. It is an iterative dynamical model that considers the effect of the adhesive and repulsive forces between RBCs, and the effect of the flow. The method is shown to be efficient to model polydispersity in size, shape, and orientation of the aggregates due to the flow, and to relate these variations to the US backscattering properties. Three levels of aggregability at shear rates varying between 0.05 and 10s −1 were modeled at 40% hematocrit. The simulated Backscattered Power increased with a decrease in the shear rate or an increase in the RBC aggregability. Angular dependence of the Backscattered Power was observed. It is the first attempt to model the US Power Backscattered by RBC aggregates polydisperse in size and shape due to the shearing of the flow.

Stefano Tebaldini – One of the best experts on this subject based on the ideXlab platform.

  • Comparison of tropical forest above ground biomass estimation techniques based on polarimetrie and tomographic SAR data acquired at P band
    2017 European Radar Conference (EURAD), 2017
    Co-Authors: Bassam El Hajj Chehade, Laurent Ferro-famil, Stefano Tebaldini, Dinh Ho Tong Minh, Thuy Le Toan

    Abstract:

    To understand and quantify the role of forests on carbon cycle and its impact on climate change, it is critical to accurately quantify and monitor changes in forest AboveGround-Biomass (AGB). New advances in radar technologies have enabled the development of methods to map forest structure in 3-D. These techniques are based on the use of Polarimetric SAR Tomography (PolTomSAR) that enables the estimation of vertical profiles through a tridimensional (3-D) mapping of the Backscattered Power. The estimated vertically-spaced slices of Backscattered Power may contain information relative to two uncorrelated layers: the ground defined as a surface backscat-terer and the canopy modeled with its volume vertical structure. Thus, an accurate AGB information may be extracted from the Power measured at a domain adapted to the canopy layer and less affected by the ground echo mainly due to the double bounce contribution. An algebraic synthesis of the forest allows a Sum of Kronecker Product (SKP2-) decomposition of the data covariance matrix which makes possible a polarimetric filtering of the ground echo. Moreover, the processing of a vertical domain adapted to the TomSAR vertical resolution and to the tree height allows a spatial filtering of the ground echo. The proposed tomographic biomass estimator is compared to the existing ones using P-band data acquired by the SETHI sensor over the Paracou data site in French Guiana in 2009.

  • Tropical forest biomass retrieval using P-band PolTomSAR data
    , 2016
    Co-Authors: Bassam El Hajj Chehade, Laurent Ferro-famil, Ho Tong Minh Dinh, Thuy Le Toan, Stefano Tebaldini

    Abstract:

    This paper investigates the ability of Polarimetric SAR Tomography (PolTomSAR), performed at P-band, to retrieve Above-Ground-Biomass (AGB) over dense tropical forests. PolTomSAR techniques allow an accurate estimation of the Backscattered Power distribution in the vertical direction. A first tomographic biomass estimator, relating AGB to the Backscattered Power in the higher part of the vegetation is analyzed through a Random-Volume-over-Ground (RVoG) analytical description of a forest profile. A PolTom-RVoG derivation of the Power Backscattered by the upper vegetation layer is performed as an integration of the reflectivity along the volume vertical structure. This integration is carried out over a domain fixed by TomSAR resolution and tree height, leading to a novel and accurate ABG estimator. The proposed techniques are applied to P-Band data acquired over the Paracou data site on French Guiana in 2009, in the frame of the European Space Agency (ESA) TropiSAR campaign.

  • Relating P-Band Synthetic Aperture Radar Tomography to Tropical Forest Biomass
    IEEE Transactions on Geoscience and Remote Sensing, 2014
    Co-Authors: Dinh Ho Tong Minh, Stefano Tebaldini, Thuy Le Toan, Fabio Rocca, Mauro Mariotti D'alessandro, Ludovic Villard

    Abstract:

    The retrieval of above-ground biomass (AGB) in dense tropical forests using synthetic aperture radar (SAR) images is widely recognized as a challenging task. The first difficulty arises from the decrease of sensitivity of the Backscattered intensity to biomass at high biomass values, often referred to as the backscatter saturation effect. At P-band, the decrease of sensitivity can occur at biomass values higher than about 300 t ha-1, e.g., those of many dense tropical forests. Another limiting factor is associated with the ground effects, as they can change significantly the magnitude of returns from vegetation-ground interactions. As a consequence, terrain topography or ground moisture status can determine the variations of the observed signal that are not due to forest biomass. A solution to reduce the ground effects is to have access to layers inside the forest canopy where the backscatter from vegetation-ground interactions is not significant. The study presented in this paper is an attempt to overcome the issues outlined above based on direct 3-D imaging of the forest volume, which is possible through multibaseline SAR tomography. In this way, forest biomass can be investigated by considering not only the Backscattered Power at each slant range and azimuth location but also its vertical distribution. The data analyzed in this paper are from the P-band airborne dataset acquired by Office National d’Études et de Recherches Aérospatiales (ONERA) over French Guiana in 2009, in the frame of the European Space Agency campaign TropiSAR. The dataset is characterized by a favorable baseline distribution, resulting in a vertical resolution less than half the forest height, which made it possible to decompose the vertical distribution of the Backscattered Power into a number of layers by coherent focusing, i.e., without assuming any prior knowledge about the forest vertical structure. For each layer, the relationship between the Backscattered Power and forest AGB was then analyzed. As expected, it was found that the Power from the bottom layer is very weakly correlated to AGB, whereas the Power from a layer at about 30 m above the ground yields the best correlation and sensitivity to AGB in all polarizations, for actual AGB values ranging from 250 to 450 t ha-1. An interpretation of this result is also provided, based on a forest growth model simulation. Finally, the relevance of tomographic technique in P-band spaceborne mission is discussed.

Ludovic Villard – One of the best experts on this subject based on the ideXlab platform.

  • Relating P-Band Synthetic Aperture Radar Tomography to Tropical Forest Biomass
    IEEE Transactions on Geoscience and Remote Sensing, 2014
    Co-Authors: Dinh Ho Tong Minh, Stefano Tebaldini, Thuy Le Toan, Fabio Rocca, Mauro Mariotti D'alessandro, Ludovic Villard

    Abstract:

    The retrieval of above-ground biomass (AGB) in dense tropical forests using synthetic aperture radar (SAR) images is widely recognized as a challenging task. The first difficulty arises from the decrease of sensitivity of the Backscattered intensity to biomass at high biomass values, often referred to as the backscatter saturation effect. At P-band, the decrease of sensitivity can occur at biomass values higher than about 300 t ha-1, e.g., those of many dense tropical forests. Another limiting factor is associated with the ground effects, as they can change significantly the magnitude of returns from vegetation-ground interactions. As a consequence, terrain topography or ground moisture status can determine the variations of the observed signal that are not due to forest biomass. A solution to reduce the ground effects is to have access to layers inside the forest canopy where the backscatter from vegetation-ground interactions is not significant. The study presented in this paper is an attempt to overcome the issues outlined above based on direct 3-D imaging of the forest volume, which is possible through multibaseline SAR tomography. In this way, forest biomass can be investigated by considering not only the Backscattered Power at each slant range and azimuth location but also its vertical distribution. The data analyzed in this paper are from the P-band airborne dataset acquired by Office National d’Études et de Recherches Aérospatiales (ONERA) over French Guiana in 2009, in the frame of the European Space Agency campaign TropiSAR. The dataset is characterized by a favorable baseline distribution, resulting in a vertical resolution less than half the forest height, which made it possible to decompose the vertical distribution of the Backscattered Power into a number of layers by coherent focusing, i.e., without assuming any prior knowledge about the forest vertical structure. For each layer, the relationship between the Backscattered Power and forest AGB was then analyzed. As expected, it was found that the Power from the bottom layer is very weakly correlated to AGB, whereas the Power from a layer at about 30 m above the ground yields the best correlation and sensitivity to AGB in all polarizations, for actual AGB values ranging from 250 to 450 t ha-1. An interpretation of this result is also provided, based on a forest growth model simulation. Finally, the relevance of tomographic technique in P-band spaceborne mission is discussed.