An Investigation of non-Bragg Scattering from the Sea Surface

Abstract

The long-range objective of this work is to investigate non-Bragg sea surface scattering at intermediate angles of incidence. We seek to define the characteristics and statistical properties of these scatterers and to establish a link between radar observations and the underlying physical processes. OBJECTIVES Our objective is to investigate scattering from the sea surface that seemingly cannot be explained using composite surface models based on Bragg scattering theory. Models based on Bragg scattering adequately predict most backscatter observations, but several phenomena are not well predicted using this type of approach, suggesting the models exclude some relevant physical processes. This research examines scattering events that are apparently inconsistent with composite surface theory, and seeks to identify prospective mechanisms and to develop predictive models for these non-Bragg scatterers. APPROACH Our approach is to analyze data from the SAXON-FPN experiment conducted in 1990/1991 (described in detail by Plant and Alpers, 1994) to define the physical and statistical characteristics of non-Bragg sea surface scattering. This data set includes simultaneously acquired horizontally (HH) and vertically (VV) polarized radar cross-section observations at several frequencies, and detailed environmental measurements. The ratio of HH-to-VV cross sections is commonly used to separate Bragg and non-Bragg scattering. Since Bragg scattering predicts that on average VV cross sections should be larger than HH at moderate incidence angles, events for which the HH cross sections exceed the VV are often designated as non-Bragg scattering. We have investigated the ratio of HH-to-VV, previously used as a criterion for designating non-Bragg scattering events, by comparing the data with simulations based on composite surface theory, and through statistical analysis of the observations. We have found that the polarization ratio does not serve as a useful metric for identifying non-Bragg scattering. To explain events where HH cross-section exceeds VV, we have investigated physical mechanisms including bound waves and sea spray. In addition, we have analyzed the characteristics of extreme

Star polymers confined in a nanoslit: a simulation test of scaling and self-consistent field theories

“…For star polymers with higher functionality, f > 12, a larger core bead diameter σ core > σ has been taken so as to accommodate the f -grafting beads of the arms on the surface of the core bead. An initially random placement of these beads on the surface of the core bead has been subsequently rendered to produce a uniform separation between the grafting points (as if being subjected to repulsive Coulomb potential), using the 'diffuse.cpp' code, developed by J. D. Lettvin [57].…”