166 research outputs found
Remote sensing of earth terrain
In remote sensing, the encountered geophysical media such as agricultural canopy, forest, snow, or ice are inhomogeneous and contain scatters in a random manner. Furthermore, weather conditions such as fog, mist, or snow cover can intervene the electromagnetic observation of the remotely sensed media. In the modelling of such media accounting for the weather effects, a multi-layer random medium model has been developed. The scattering effects of the random media are described by three-dimensional correlation functions with variances and correlation lengths corresponding to the fluctuation strengths and the physical geometry of the inhomogeneities, respectively. With proper consideration of the dyadic Green's function and its singularities, the strong fluctuation theory is used to calculate the effective permittivities which account for the modification of the wave speed and attenuation in the presence of the scatters. The distorted Born approximation is then applied to obtain the correlations of the scattered fields. From the correlation of the scattered field, calculated is the complete set of scattering coefficients for polarimetric radar observation or brightness temperature in passive radiometer applications. In the remote sensing of terrestrial ecosystems, the development of microwave remote sensing technology and the potential of SAR to measure vegetation structure and biomass have increased effort to conduct experimental and theoretical researches on the interactions between microwave and vegetation canopies. The overall objective is to develop inversion algorithms to retrieve biophysical parameters from radar data. In this perspective, theoretical models and experimental data are methodically interconnected in the following manner: Due to the complexity of the interactions involved, all theoretical models have limited domains of validity; the proposed solution is to use theoretical models, which is validated by experiments, to establish the region in which the radar response is most sensitive to the parameters of interest; theoretically simulated data will be used to generate simple invertible models over the region. For applications to the remote sensing of sea ice, the developed theoretical models need to be tested with experimental measurements. With measured ground truth such as ice thickness, temperature, salinity, and structure, input parameters to the theoretical models can be obtained to calculate the polarimetric scattering coefficients for radars or brightness temperature for radiometers and then compare theoretical results with experimental data. Validated models will play an important role in the interpretation and classification of ice in monitoring global ice cover from space borne remote sensors in the future. We present an inversion algorithm based on a recently developed inversion method referred to as the Renormalized Source-Type Integral Equation approach. The objective of this method is to overcome some of the limitations and difficulties of the iterative Born technique. It recasts the inversion, which is nonlinear in nature, in terms of the solution of a set of linear equations; however, the final inversion equation is still nonlinear. The derived inversion equation is an exact equation which sums up the iterative Neuman (or Born) series in a closed form and, thus, is a valid representation even in the case when the Born series diverges; hence, the name Renormalized Source-Type Integral Equation Approach
Electrodynamics of Media
Contains reports on one research project.Joint Services Electronics Program (Contract DAAB07-71-C-0300
Electromagnetic Wave Theory and Remote Sensing
Contains reports on five research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Science Foundation (Grant ENG78-23145)National Aeronautics and Space Administration (Contract NAS5-24139)U.S. Air Force - Eglin (Contract F08635-78-C-0115)Schlumberger Doll Research Cente
Electrodynamics of Media
Contains reports on five research projects.Joint Services Electronics Program (Contract DAAG29-78-C-0020)National Science Foundation (Grant ENG76-01654)National Aeronautics and Space Administration (Contract NAS5-24139)U.S. Air Force- Eglin (Contract F08635-78-C-0115)Schlumberger Doll Research Cente
Extraordinary surface voltage effect in the invisibility cloak with an active device inside
The electromagnetic field solution for a spherical invisibility cloak with an
active device inside is established. Extraordinary electric and magnetic
surface voltages are induced at the inner boundary of a spherical cloak, which
prevent electromagnetic waves from going out. The phase and handness of
polarized waves obliquely incident on such boundaries is kept in the reflected
waves. The surface voltages due to an electric dipole inside the concealed
region are found equal to the auxiliary scalar potentials at the inner
boundary, which consequently gain physical counterparts in this case
Remote sensing of earth terrain
Abstracts from 46 refereed journal and conference papers are presented for research on remote sensing of earth terrain. The topics covered related to remote sensing include the following: mathematical models, vegetation cover, sea ice, finite difference theory, electromagnetic waves, polarimetry, neural networks, random media, synthetic aperture radar, electromagnetic bias, and others
Electrodynamics of Media
Contains reports on four research projects.Joint Services Electronics Program (Contract DAAB07-76-C-1400)California Institute of Technology (Contract 953524)National Science Foundation (Grant ENG76-01654)National Aeronautics and Space Administration (Contract NAS5-24139
Electrodynamics of Media
Contains research objectives and summary of research.Joint Services Electronics Program (Contract DAAB07-71-C-0300)California Institute of Technology (Contract 953524
Electrodynamics of Media
Contains reports on three research projects.Joint Services Electronics Program (Contract DAAB07-75-C-1346
Application of theoretical models to active and passive remote sensing of saline ice
The random medium model is used to interpret the polarimetric active and passive measurements of saline ice. The ice layer is described as a host ice medium embedded with randomly distributed inhomogeneities, and the underlying sea water is considered as a homogeneous half-space. The scatterers in the ice layer are modeled with an ellipsoidal correlation function. The orientation of the scatterers is vertically aligned and azimuthally random. The strong permittivity fluctuation theory is employed to calculate the effective permittivity and the distorted Born approximation is used to obtain the polarimetric scattering coefficients. We also calculate the thermal emissions based on the reciprocity and energy conservation principles. The effects of the random roughness at the air-ice, and ice-water interfaces are accounted for by adding the surface scattering to the volume scattering return incoherently. The above theoretical model, which has been successfully applied to analyze the radar backscatter data of the first-year sea ice near Point Barrow, AK, is used to interpret the measurements performed in the CRRELEX program
- …