1,721,040 research outputs found
Space-borne GNSS-R signal over a complex topography. Modeling and validation
Full text linkA 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
Bistatic coherent scattering from rough soils with application to GNSS reflectometry
No full textWe present and discuss an electromagnetic model for the description of the coherent scattering from bare soils illuminated by a radar system under arbitrary bistatic geometries. The scattering problem is solved under the Kirchhoff approximation (KA) accounting for both the sphericity of the wavefront of the incident wave and the radiation pattern of the transmitting and receiving antennas. We propose here a general formulation and solution of the scattering problem applicable to an arbitrary bistatic geometry. We discuss and demonstrate the importance of our extension for the characterization of the coherent scattering generated in bistatic radar systems, both inside and outside the plane of incidence. The model is validated against the numerical solution of the Kirchhoff integral and, in the case of the perfect plane conductor, by comparison with the image theory. The work is intended to provide a simple methodology to characterize the coherent normalized radar cross section (NRCS) of a rough surface to be used within the radar equation for extended targets, similarly to what is done for the incoherent component. It aims at enabling a local characterization of the coherent scattering in realistic conditions (e.g., in the presence of inhomogeneous and mountainous surfaces), a feature that is particularly important for practical applications, such as the modeling and understanding of the bistatic scattering generated by sources of opportunity and specifically for Global Navigation Satellite System Reflectometry (GNSS-R) related applications
Expression of human alpha 1-acid glycoprotein genes in cultured cells and in transgenic mice.
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Molecular cloning and expression analysis of dystroglycan during Xenopus laevis embryogenesis.
No full textCommon and interchangeable elements in the promoters of genes transcribed by RNA polymerase III. Cell, 1983, 32, 725-733
No full textCommon and interchangeable elements in the promoters of genes transcribed by RNA polymerase III. Cell, 1983, 32, 725-733
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