Arthur K. Jordan

Profile inversion of simple plasmas and nonuniform regions: Three-pole reflection coefficient

A mathematical method for the reconstruction of the electron density profile N(x) for an inhomogeneous, stratified, simple plasma is presented. If the reflection coefficient r(k) of the incident probing electromagnetic wave is approximated by a third-order rational approximation, then profiles can be obtained which are similar to profiles obtained from simulated VHF satellite tracking data. The method is based upon the solution of the fundamental integral equation of inverse scattering (Gelfand-Levitan) theory. Using this theory it is possible to obtain an analytical expression for N(x) as a function of distance x in the plasma if r(k) is a rational function of the wave number k . The integral equation is solved by the Laplace transform technique and checked by the differential operator technique. The method is exact once the functional form of r(k) is determined. Thus this analysis can supplement information about profiles which are obtained from calculations based on the WKB approximation (which approximation can also be applied to calculate the local wave impedance W(x) for propagation in nonuniform regions). The functional characteristics of N(x) depend on the pole positions of r(k) in the complex k plane. By calculating the variations in N(x) due to variations in these pole positions, it is possible to set a finite error bound on the profile of the electron density if the error bound in the rational approximation to the reflection coefficient is known.

Inverse scattering theory for optical waveguides and devices: Synthesis from rational and nonrational reflection coefficients

Electromagnetic inverse scattering theory is applied to the synthesis of optical waveguides and devices from specified reflection and transmission characteristics. The permittivity profiles in the inhomogeneous core regions of the devices are reconstructed from their transverse reflection coefficients. Two applications of this theory are demonstrated with examples using specified reflection coefficients: design of a single-mode inhomogeneous optical waveguide and design of an optical logic gate. The previous inverse scattering theory which used reflection coefficients that are rational functions of the transverse wavenumber has been supplemented with an inverse scattering theory that uses nonrational reflection coefficients. This inverse scattering theory uses an iterative discretized space-time finite-difference method with the “leapfrog” algorithm. The initial values for the iterative method are obtained from the inverse theory that uses rational function reflection coefficients. The inverse scattering calculations have been verified by finite-difference frequency domain direct scattering techniques.

Synthesis of Optical Interconnects and Logic Gates

The first part of this paper presents a method for designing guided wave optical interconnects with reduced clock skew, applicable in a chip-to-chip or intra chip situation. The interconnect consists of a multimode trunk waveguide and a set of single mode branch waveguides each of which couples one mode out of the trunk waveguide (see Fig.1). The graded-index guided wave interconnects can effectively reduce clock skew by suitable design of the refractive index profiles [1],[2]. This design is accomplished by properly tailoring the propagation constants of the guided modes to provide equal propagation times to a set of detectors. The scheme presented in this paper employs several optical channels, each having a different refractive index profile. This includes a main multimode channel and several single-mode waveguides coupled to the main line. Total system design takes into account the problem of clock skew as well as efficient coupling between the trunk and branch waveguides. An inverse scattering technique that provides the design parameters of an optoelectronic guided-wave structure from the prescribed transmission characteristics has been used to design the interconnect. This technique is contrary to the traditional techniques which require iterative adjustments of the design parameters to achieve the required transmission characteristics.

Inverse-scattering theory applied to the synthesis of gradient-index optical waveguides

Abstract not available.

An Analysis of Skylab II S193 Scatterometer Data

SKYLAB II S193 Scatterometer data for the passes of June 5, 1973, over the Gulf of Mexico and June 6, 1973, over Pacific Hurricane AVA were analyzed. These two passes were chosen since it was possible to correlate the scattering data with simultaneous measurements of the local ocean wind conditions. The S193 scatterometer measured the radar cross section of the ocean at 13.9 GHz (Ku-band) as a function of incidence angle. The S193 data of June 5, 1973, when a practically uniform wind field was present, show reasonable agreement with the Naval Research Laboratory (NRL) empirical and theoretical models. The data of June 6, 1973, are more complex, due to rapid variations in wind speeds and directions around Hurricane AVA. The NRL empirical model was interpolated to account for variation in wind heading relative to the S193 antenna pointing direction; a reasonable comparison could then be made with the corresponding S193 data of June 6, 1973.

Introduction To The Special Section On The Electromagnetic Properties Of Sea Ice

PPROXIMATELY 13% of the world’s oceans is covered by sea ice during some portion of the year. This volume of ice has significant effects on the world’s climate, ocean currents, and biological ecosystems. Furthermore, the extent of sea ice cover is used as an input parameter in many meteorological forecasting models. It is difficult to obtain ground-based measurements over large regions of the Arctic, where the distances are vast, the climate is hostile, and the operations are expensive. The material composition of sea ice varies with temperature and winds. Thus, remote sensing of sea ice may be the preferred method to obtain quantitative information about sea ice. This Special Section of the IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING presents results obtained by the Accelerated Research Initiative (ARI) on the Electromagnetic Properties of Sea Ice (EMPOSI) that was sponsored by the Office of Naval Research (ONR), Washington, DC. Briefly stated, the ARI had three broad objectives, as follows. To better understand the mechanisms and processes that link the morphological characteristics with its electromagnetic properties. To further develop and verify predictive models for the interactions of visible and microwave radiation with sea ice. To develop and verify the techniques in the mathematical theory of inverse scattering theory that are applicable

Final Report of Working Discussion Group W-C on Polarization Utilization in High Resolution Imaging

There is good evidence from particular problem areas that target detection and classification can be considerably improved by use of polarization information. However, the general usefulness of this technique in target detection and classification still involves many unresolved issues. Many of these issues have been identified at this ARW and initial recommendations were made for futher research.

Final Report of Working Discussion Groups

The working discussion groups are to work on isolating unresolved problems and providing recommendations for potential future research projects which will require active interaction of engineering scientists of all NATO-member countries. The five questions (W-A to W-E) chosen define issues for which immediate answers are required. The composition of the chosen speakers, senior research scientists/engineers is well suited to tackle these problems and we do expect clear-cut resolutions and recommendations for additional near-future NATO Advanced Study Institutes and/or NATO Advanced Research Workshops.

Final Report of Working Discussion Group W-F on Enhancement of Interaction Between Active R & D Labs Within Nato-Member Countries on the Subject of Electromagnetic Imaging

The present ARW-IMEI has successfully brought together key experts and observers from a majority of NATO-mem- ber countries allowing them to judge the current level of interaction. In this report we attempt to summarize the existing interaction paths, Substantiate why enhancement of interaction is desireable and to suggest mechanisms for achieving these goals.

Final Report of Working Discussion Group W-E on Holographic and Tomographic Imaging and Related Phase Problems

The phase retrieval problem occurs in electromagnetic inverse scattering, optical and x-ray applications. The phase unwrapping problem is of importance in signal processing applications, ultrasound, and geophysical diffraction tomography. This working group identified problem areas and made general recommendations.