Jin Au Kong

Rice crop mapping and monitoring using ERS-1 data based on experiment and modeling results

Information on rice growing areas and on rice growth conditions are necessary in rice monitoring programs and in studies on the emission of methane from flooded rice fields. The objective of this paper is to assess the use of ERS-1 SAR data to map rice growing areas and to retrieve rice parameters. The approach includes first a synthesis of experimental results at two different test areas followed by a development of a theoretical model to interpret the observations. The synthesis of experimental data at two test areas, a tropical site with short cycle rice (Semarang, Indonesia) and a temperate site with long cycle rice (Akita, Japan), has shown that flooded rice fields have characteristic increasing temporal radar responses. When the radar backscattering coefficients are expressed as a function of the rice biomass, the effect of cultural practices and climate (long cycle versus short cycle) is reduced. The observations have been interpreted by a theoretical model, which relies on a realistic description of rice plants and which considers the backscattering enhancement and clustering effects of the scatterers. Good agreement has been obtained between experimental data and theoretical results. The strong temporal variation of the radar response of rice fields is due to the wave-vegetation-water interaction, which increases from the transplanting stage to reproductive stage. By simulations using the validated model, the length of the rice cycle or the rice varieties have shown minor effects on the temporal curve. A method for rice fields mapping has been developed, based on the temporal variation of the radar response between two acquisition dates. Inversion of SAR images into plant height and plant biomass has also been performed. The results appear promising for the use of ERS-1 and RADARSAT data for rice monitoring.

Scattering of Electromagnetic Waves: Advanced Topics

Preface. Two-Dimensional Random Rough Surface Scattering Based on Small Perturbation Method. Kirchhoff Approach and Related Methods for Rough Surface Scattering. Volume Scattering: Cascade of Layers. Analytic Wave Theory for a Medium with Permittivity Fluctuations. Multiple Scattering Theory for Discrete Scatterers. Quasi-Crystalline Approximation in Dense Media Scattering. Dense Media Scattering. Backscattering Enhancement. Index.

Effective permittivity of dielectric mixtures

General mixing formulas are derived for discrete scatterers immersed in a host medium. The inclusion particles are assumed to be ellipsoidal. The electric field inside the scatterers is determined by quasi-static analysis, assuming the diameter of the inclusion particles to be much smaller than one wavelength. The results are applicable to general multiphase mixtures, and the scattering ellipsoids of the different phases can have different sizes and arbitrary ellipticity distribution and axis orientation, i.e. the mixture may be isotropic or anisotropic. The resulting mixing formula is nonlinear and is suitable for iterative solutions. The formula contains a quantity called the apparent permittivity, and with different choices of this quantity, the result leads to the generalized Lorentz-Lorenz formula, the generalized Polder-van Santen formula, and the generalized coherent potential-quasicrystalline approximation formula. The results are applied to calculating the complex effective permittivity of dry and wet snow, and sea ice. >

A Study of Using Metamaterials as Antenna Substrate to Enhance Gain

Using a commercial software, simulations are done on the radiation of a dipole antenna embedded in metamaterial substrates. Metamaterials under consideration are composed of a periodic collection of rods, or of both rods and rings. The S-parameters of these metamaterials in a waveguide are analyzed and compared with their equivalent plasma or resonant structure. Farfield radiation is optimized by analytic method and is simulated numerically. The metamaterial is shown to improve the directivity.

Experimental confirmation of negative refractive index of a metamaterial composed of Ω-like metallic patterns

A one-dimensional metamaterial is realized using three connected Ω rings printed back-to-back and reversed on two sides of a dielectric substrate. Both transmission and prism experiments are reported, yielding concordant results of the presence of a left-handed frequency band. Experiments show reduced losses and an enlarged left-handed frequency band.

Guided modes with imaginary transverse wave number in a slab waveguide with negative permittivity and permeability

The guidance conditions of modes with both real and imaginary transverse wave numbers inside a dielectric slab with negative permittivity and permeability are solved. We show that for real transverse wave numbers, cutoffs exist for all modes, unlike in conventional media where the first even mode is always propagating. In addition, we also show that guided modes exist for imaginary transverse wave numbers, with the power concentrated at the interfaces instead of having maxima inside the slab. A graphical method of determining the imaginary transverse wave numbers of the guided modes is introduced which clearly identifies the different conditions of propagation depending on the properties of the slab. In particular, propagation of guided waves inside less dense negative media is shown to be possible.

Theorems of bianisotropic media

Theorems concerning electromagnetic fields in linear nonconducting bianisotropic media are investigated. After establishing their symmetry properties, the constitutive relations are examined under time reversal and spatial inversion transformations. Conditions under which the image method and the reciprocity relationships can be applied are discussed. Dyadic Greens functions and duality relations are also derived. With a postulated Lagrangian density, Maxwells equations are obtained from Hamiltons principle, and energy momentum tensors are obtained from Noethers theorem. Introducing a quantum postulate in addition to the Maxwells equations, electromagnetic fields in bianisotropic media are quantized.

K-Distribution and Polarimetric Terrain Radar Clutter

A multivariate K- distribution is proposed to model the statistics of fully polarimetric radar data from earth terrain with polarizations HH, HV, VH, and VV. In this approach, correlated polarizations of radar signals, as characterized by a covariance matrix, are treated as the sum of N n- dimensional random vectors; N obeys the negative binomial distribution with a parameter α and mean N. Subsequently, an n- dimensional K- distribution, with either zero or nonzero mean, is developed in the limit of infinite N or illuminated area. The probability density function (PDF) of the K- distributed vector normalized by its Euclidean norm is independent of the parameter α and is the same as that derived from a zero-mean Gaussian-distributed random vector. The above model is well supported by experimental data provided by MIT Lincoln Laboratory and the Jet Propulsion Laboratory in the form of polarimetric measurements.

ELECTROMAGNETIC FIELDS DUE TO DIPOLE ANTENNAS OVER STRATIFIED ANISOTROPIC MEDIA

Solutions to the problem of radiation of dipole antennas in the presence of a stratified anisotropic media are facilitated by decomposing a general wave field into transverse magnetic (TM) and transverse electric (TE) modes. Employing the propagation matrices, wave amplitudes in any region are related to those in any other regions. The reflection coefficients, which embed all the information about the geometrical configuration and the physical constituents of the medium, are obtained in closed form. In view of the general formulation, various special cases are discussed.

Input impedance and radiation pattern of cylindrical-rectangular and wraparound microstrip antennas

The radiation from a cylindrical microstrip antenna excited by a probe is analyzed. Both the cylindrical-rectangular and the wraparound elements are discussed. The current distribution on the patch is rigorously formulated using a cylindrically stratified medium approach. A set of vector integral equations is derived which governs the current distribution on the patch. The set of equations is then solved using a moment method. The input impedance and the radiation pattern are derived both exactly and in the small substrate thickness limit. >