Jerry R. Smith

Electromagnetic forward-scattering measurements over a known, controlled sea surface at grazing

A series of low-angle radar measurements were conducted over a large wave pool capable of producing a wide range of scaled sea conditions. The X-band (8-12 GHz) measurements were performed for 1/spl deg/, 3/spl deg/, and 5/spl deg/ look down angles (LDAs) for the HH and VV polarizations. The roughened water simulated a one-dimensional 1/10th-scale Pierson-Moskowitz surface at sea states 0, 3, and 5. The wave profiles were detailed using both ultrasonic point detectors and a laser sheeting technique capable of measuring a cross section of the sea. The compiled data represent the first forward-scattering measurement 1) preformed under a variety of controlled conditions for low grazing angles and 2) with detail profiling of the wave structure syncronized with the radar. Presented are the experimental setup with calibration methodology, measurement conditions, and selected radio-frequency forward-scattering (HH polarization) results for the 5/spl deg/ LDA for sea state 0, 3, and 5 sea conditions.

Moments via Integral transform method for 2-D dielectric materials

This paper extends the moments via integral transform method (MITM) which analytically reduces the general method of moments (MoM) impedance equation from a double integral to a single integral thereby significantly reducing the matrix fill time. The MITM makes use of a specialized integral representation of the two dimensional Greens function (Hankel function) and represents the MoM impedance as a single integral in terms of integral transforms which are analytic for nearly arbitrary shape and weight functions.

Channeling phenomenon in electromagnetic forward scattering at low grazing

Channeling phenomenon is a type of forward scattering and multipath that occasionally occurs when a well-formed sea wave briefly reflects or focuses the out-of-plane energy toward the receiver, yielding a higher than expected, broadband power gain. A series of X-band, forward-scattering measurements in a large wave tank observed multiple channeling events at low grazing angles. The wave tank simulated a one-dimensional, 1/10th-scale Pierson-Moskowitz surface at sea states 0, 3, and 5. During the measurements, channeling events were observed under crosswind wave conditions when a properly constructed wave trough, coinciding with the radars line of sight, channeled or focused the out-of-plane, forward-scattered energy toward the receiver. Presented is a summary of the channeling events observed and a physical model of the channeling phenomenon based on experimental observations and numerical simulations.

Analytical simplification of the 2-D method of moments impedance integral

The elements of the two-dimensional (2-D), method of moments (MoM) impedance matrix are analytically reduced by way of an integral transform. The resulting impedance expression is a single integral with an analytic integrand for nearly arbitary shape and weight function sets. The reduced expression requires fewer computations, thereby reducing the matrix fill time. This moments via integral transform method (MITM) is based on an integral representation of the Greens function (Hankel function) and utilizes a special integral transform. The method is developed for 2-D perfectly electrically conducting bodies subjected to a transverse magnetic field. A comparison between brute force and MITM is presented for polynomial shape and weight functions.

Corrections to Moments via Integral Transform Method for 2-D Dielectric Materials [Jan 05 560-563]

In the above titled paper (ibid., vol 53, no. 1, pp. 560-563, Jan 05), there were two typographical errors. Corrections are presented here.

The forward scattering surface interaction region

This paper presents measured data from a low grazing, rough sea forward scattering measurement which shows that, while the forward scattering is generally restricted to the first few Fresnel zones for crosswind waves, measurable scattering frequently occurs many zones out for downwind waves.

Moments via integral transform method for 2-D curvilinear elements

The development of the 2D MITM to PEC curvilinear elements is a direct extension of Smith et al. (2004) and Smith et al. (2005) and the MITM integrals are expressed in terms of the quadratic R transformed shape and weight functions. The extension of MITM to PEC quadratic elements means that the impedance terms can be analytically reduced from a double integral to a single integral for any shape and weight function set whenever the equation is analytic for the shape and weight functions.

High frequency forward scattering models with shadowing correction

The Brown and Miller (1974) model for the coherent component of rough surface forward scattering is based on a flat surface, geometric optics argument and is unable to account for shadowing effects at low grazing or the weakened nulls observed in experiments. This paper develops modifications to the coherent component of rough ocean forward scattering to account for shadowing for downwind wave conditions.