A Review of Radar Sea Echo

Abstract

The radar echo from the sea limits the ability of radar to detect targets.A knowledge of the uea echo is necessary, therefore, for proper design of radars that must detect targets on or over the sea.This report briefly reviews the ocean eurface characteristics that affect radar echo and summarizes the present status of knowledge of the sea echo as a function of radar grazing angle, sea state and wind, polarization, frequency and other factors. A plot of ao (radar cross section per unit area) as a function of grazing angle and frequency obtained from an averaged comi posite of reported data shows that no simple law of frequency dependence should be expected.The attempts made in the past to 2 provide theoretical models describaing the sea echo are reviewed and lead up to the presently accepted models of scattering surfaces composed of the larger gravity wares on which are superimposed the smaller capillary waves. The influence of sea echo on radar design is discussed and is considerably different than the uaual design restraints imposed by thermal ncoae.The potential application of radar for oceanographic measuretrents such as sea state and wind is described.

The crystal and molecular structure of the five-membered-ring analogue of vitamin-A acid

“…This is reflected in the physlologtcal activities of the various analogues; the pentene analogue has a growth activity which is 50--60 % of that of vitamine A, but the other analogues do not show any appreciable activity (Huisman & Baas, 1969;Skolnik, 1969).…”

“…Various other analogues of vitamin A have been prepared such as des-methyl compounds, in which one or more methyl groups have been removed, ethyl-desmethyl compounds, in which a methyl group has been substituted by an ethyl group, and retro-compounds, in which the double bonds have been shifted (van de Tempel & Huisman, 1966;Skolnik, 1969;Huisman, Smit, van Leeuwen & van Rij, 1958). All these modifications involve small changes in the conformation and therefore in the geometry of the vitamin-A molecule, but the steric interaction of the substituents and the backbone is affected, which is not the case in the pen-…”

Polarization-Based Radar Detection in Sea Clutter

“…When the surface is not smooth [h-^ ^ /12), the amplitude of the specular field will be reduced. The loss may be approximated by e~^^^ where g = 4k^a^cos^e^ = 4Rj (21) Surfaces may be characterized by a height distribution function [relative to a reference surface] and a surface correlation function. Normally the reference is chosen so that the height distribution has zero mean.…”

Reconstruction and deterministic prediction of ocean waves from synthetic radar images

“…Since marine radar images are typically shaped like a disc with an area around the radar where the radar backscatter is too high due to specular scatter from the sea 42 Determination of the significant wave height from shadowing in synthetic radar images surface [Skolnik, 1969] and/or due to the interaction from the ship's hull, we remove all the elevations over a certain radius r in around the radar. At multiples of the radar rotation time, n · ∆t, a snapshot of a synthesized radar image is then given by I n (r, θ) = S sha n (r, θ)Θ(r − r in ) (3.6)…”

“…For details of the construction of the sea see [van Groesen et al, 2017]. In the second subsection (distorted) synthetic radar images are designed from the nonlinear sea states by adding the shadowing effects, and restricted to the radar observation domain to cover only a ring shaped area between 500 and 2000 m in the northern semicircle; the small semicircle with r < 500 is the blind area of the radar where the radar backscatter is too high to be useful due to specular scatter from the sea surface [Skolnik, 1969]. After that a sort description is given of the idea to improve the quality of the images by an averaging technique.…”