1,320 research outputs found
Fundamental remote sensing science research program. Part 1: Scene radiation and atmospheric effects characterization project
Brief articles summarizing the status of research in the scene radiation and atmospheric effect characterization (SRAEC) project are presented. Research conducted within the SRAEC program is focused on the development of empirical characterizations and mathematical process models which relate the electromagnetic energy reflected or emitted from a scene to the biophysical parameters of interest
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
Polarimetric Signatures of Sea Ice
Physical, structural, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarimetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures
Toward RADSCAT measurements over the sea and their interpretation
Investigations into several areas which are essential to the execution and interpretation of suborbital observations by composite radiometer - scatterometer sensor (RADSCAT) are reported. Experiments and theory were developed to demonstrate the remote anemometric capability of the sensor over the sea through various weather conditions. It is shown that weather situations found in extra tropical cyclones are useful for demonstrating the all weather capability of the composite sensor. The large scale fluctuations of the wind over the sea dictate the observational coverage required to correlate measurements with the mean surface wind speed. Various theoretical investigations were performed to establish a premise for the joint interpretation of the experiment data. The effects of clouds and rains on downward radiometric observations over the sea were computed. A method of predicting atmospheric attenuation from joint observations is developed. In other theoretical efforts, the emission and scattering characteristics of the sea were derived. Composite surface theories with coherent and noncoherent assumptions were employed
Integer and Fractional Quantum Hall Effect in a Strip of Stripes
We study anisotropic stripe models of interacting electrons in the presence
of magnetic fields in the quantum Hall regime with integer and fractional
filling factors. The model consists of an infinite strip of finite width that
contains periodically arranged stripes (forming supercells) to which the
electrons are confined and between which they can hop with associated magnetic
phases. The interacting electron system within the one-dimensional stripes are
described by Luttinger liquids and shown to give rise to charge and spin
density waves that lead to periodic structures within the stripe with a
reciprocal wavevector 8k_F. This wavevector gives rise to Umklapp scattering
and resonant scattering that results in gaps and chiral edge states at all
known integer and fractional filling factors \nu. The integer and odd
denominator filling factors arise for a uniform distribution of stripes,
whereas the even denominator filling factors arise for a non-uniform stripe
distribution. We calculate the Hall conductance via the Streda formula and show
that it is given by \sigma_H=\nu e^2/h for all filling factors. We show that
the composite fermion picture follows directly from the condition of the
resonant Umklapp scattering
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