Chin-Yuan Hsieh

A further study of the IEM surface scattering model

The IEM surface scattering model was developed based on an approximate solution of a pair of integral equations governing the surface current. Among the assumptions leading to the approximation is the use of a simplified expression for the Greens function in spectral form. In particular, it was argued that the absolute value of the difference in the surface heights at two surface points appearing in the phase of the Greens function can be ignored. This argument was arrived at by noting that (i) if the two points are close together, the difference in heights should be small and (ii) if the two surface points are far apart, there should be a negligible amount of correlation between the two points and hence will not contribute significantly to the scattered power. Mathematically, there is no reason to make this assumption and it is also questionable whether the contribution from two surface points that are neither near or far can always be ignored. In this paper the authors want to remove this assumption by keeping this phase term and examine the difference in scattering calculations with and without it. It is found that in all cases considered the existing IEM model gives satisfactory predictions in single scattering. However, in multiple scattering calculations it is not possible to ignore this phase especially for surfaces with large roughness. An application of this model to scattering from known rough dielectric surfaces acquired at the EMSL of the JRC at Ispra is shown and good agreements are realized. Further application to a large slope surface that causes backscattering enhancement also gives good agreement with data.

Incoherent bistatic scattering from the sea surface at L-band

A bistatic electromagnetic wave scattering model for the sea surface is developed to examine its wind dependence property over a wide range of incident angles along the specular direction. This is done by combining an existing scattering model with a sea spectrum recently reported in the literature. In general, electromagnetic wave scattering from a rough surface is dependent on the Fourier transform of the nth power of its height correlation function which can be computed numerically from the surface spectrum. This transform relation indicates that scattering is sensitive not only to the surface spectrum but also to its convoluted properties. Generally, surface scattering is sensitive only to a portion of the surface correlation measured from the origin. The size of this portion is a function of three variables (the incident angle, the surface height standard deviation, and the exploring wavelength) and the rate of decay of the correlation function. The decay rate near the origin of the sea surface correlation is very small, so much so that at L-band this portion is too wide for a two-term approximation of the correlation function. This is true in spite of the fact that the sea surface has a very large rms height. Thus, a scattering model based on geometric optics is generally not applicable at L-band especially at large angles of incidence. An additional finding is that in specular scattering wind dependence is stronger at larger angles of incidence for incident angles between 0 and 70/spl deg/ over the wind speed range of 4 m/s-20 m/s.

Application of an Extended Iem To Multiple Surface Scattering and Backscatter Enhancement

In the late 1980s backscattering enhancement and strong depolarization of waves scattered from randomly rough Gaussian surfaces with large rms slopes were observed in optical and millimeter wave measurements. It was noted that backscattering enhancement was most prominent, when the surface rms slope was of the order of unity, a condition under which multiple surface scattering may dominate. In this study an extended IEM model which includes surface multiple scattering called integral equation model with multiple scattering (IEMM) is applied to interpret this phenomenon. According to this model the conditions for significant multiple surface scatter to occur are (1) the normalized surface height kσ > 1 and (2) the surface rms slope > 0.5. In the analysis of multiple scattering from very rough surfaces it is found that there is a sharp but small peak in the specular direction also. This observation comes directly from the IEMM model and is partially confirmed by the data reported by Ishimaru. Further compa...

Depolarized Upward and Downward Multiple Scattering from a Very Rough Surface

From a very roughly random surface the backscattering enhancement is predicted due to the constructive interference of multiple surfaces scattering. For specialized surfaces involving roughness large compared with the incident wavelength, the backscattering enhancement takes place. The phenomenon of backscatter enhancement becomes evident for both larger normalized surface height and surface rms slope. In this paper we take further study to predict the backscattering enhancement mainly comes from upward multiple scattering. On the contrary the downward multiple scattering has no contributions to the scatter strength of backscattering enhancement. The model developed in this paper is based upon the integral equation method and able to predict this phenomenon of multiple scattering and backscattering enhancement. The depolarized multiple scattering makes much contribution along the plane of incidence from random rough surfaces, but depolarized single scattering makes little contributions. The total multiple scattering strength is the summation of upward and downward multiple scattering strength. In comparison of model prediction of total multiple scattering strength with measured data along the specular plane, excellent agreement is obtained.

Prediction of IEM Model for Backscattering Enhancement

Predictions for scattering from randomly very rough surfaces are developed and compared with experimental data. The integral equation method with multiple scattering is developed to predict this backscattering enhancement phenomenon. The backscattering enhancement can be predicted from the constructive interference of multiple surfaces scattering from a very roughly random surface. For specialized surfaces involving roughness large compared with the incident wavelength, the backscattering enhancement takes place. In this paper we show that the phenomenon of backscattering enhancement becomes evident for both the normalized surface height > 1.5 and the surface root mean square slope > 0.5. Further, we also show that the incident angle is a factor for the backscattering enhancement. The derivation of the basic surface scattering model is provided and a computer simulation is also provided to compare with measurement. The phenomenon of backscattering enhancement is observed in both the integral equation model (IEM) model prediction and experimental data. In comparing the IEM model with measured data over a wide range of frequency and angle, excellent agreement is found. The difference between the model prediction and data is less than a dB.

Application of an extended IEM to multiple surface scattering and backscatter enhancement

In the late 1980s backscattering enhancement and strong depolarization of waves scattered from randomly rough Gaussian surfaces with large rms slopes were observed in optical and millimeter measurements. It was noted that backscattering enhancement was most prominent, when the surface rms slope was of the order of unity, a condition under which multiple surface scattering may dominate. In this study an extended IEM model which includes surface multiple scattering called integral equation model with multiple scattering (IEMM) is applied to interpret this phenomenon. According to this model the conditions for significant multiple surface scattering to occur are (1) the normalized surface height k/spl sigma/>1 and (2) the surface rms slope >0.5. In the analysis of multiple scattering from very rough surfaces it is found that there is a sharp but small peak in the specular direction also. This observation comes directly from the IEMM model and is partially confirmed by the data reported by Ishimaru. Further comparisons of IEMM with experimental data acquired from very rough surfaces show excellent agreements in bistatic scattering including backscattering enhancement.

Effects of Bistatic Multiple Surface Scattering from Perfectly Conducting Rough Surfaces

This paper addresses the bistatic multiple surface scattering from perfectly conducting rough surfaces. A modified integral equation model for the bistatic surface scattering from a randomly rough surface is developed based upon an approximation of a pair of integral equations and a shadowing function for the tangential surface fields. Existing integral equation models without a shadowing function and the separation of upward and downward scattering cannot estimate correctly the scattering behavior of bistatic multiple surface scattering. In this paper the tangential surface fields, average scattered power, and bistatic-like and cross-polarized reflectivities from a randomly rough surface are formulated with the shadowing function. The effect of multiple surface scattering in the bistatic direction is analyzed. Further comparisons of this modified integral equation model with measurements show agreements to within a dB in bistatic scattering.

Dependence of backscattering enhancement from randomly very rough surfaces

The recent observations of surface backscattering enhancement phenomenon from randomly rough Gaussian surfaces with large slopes were reported experimentally and stimulated the critical discussions. In this paper the IEM model with multiple scattering and suitable shadowing function (IEMMS) is developed to be able to predict this phenomenon of backscattering enhancement. The backscattering enhancement may take place when the surface rms slope is of the order of unity and large rms height. Also, the backscattering enhancement can also be predicted from the multiple surface scattering from a very roughly random surface. To the best of the authors acknowledge, this is the first attempt to set up a fully integration equation model for fully theoretical polarized scattering. The derivation of basic surface. Scattering model is provided and a computer simulation is also provided to compare the experimental measurement.

Energy Transition for Depolarized Backscatter from Rough Surfaces

Abstract In this paper we study the depolarized backscatter enhancement phenomenon for electromagnetic wave scattering from rough surfaces. Some new experimental data on light scattering from rough metallic surfaces shows a phenomenon of backscattering enhancement existing in the antispecular direction under some conditions, such as the surface parameters, wave polarization and operating frequency. From a roughly random surface the backscattering enhancement is predicted due to the constructive interference of multiple surfaces scattering. The study is based upon the integral equation method modified to be able to predict the phenomenon of multiple scattering and backscattering enhancement. From the study we found the backscattering enhancement takes place on the specialized surface parameters large compared with the incident wavelength. Further we also conclude that the depolarized multiple scattering makes much contribution along the plane of incidence from random rough surfaces, but depolarized single scattering makes little contributions as our expectation. In comparison of model prediction of total multiple scattering strength with measured data along the specular plane, excellent agreement is obtained.

Depolarized Backscatter Phenomenon from Rough Surfaces

Abstract In this article, we study the depolarized backscatter enhancement phenomenon for electromagnetic wave scattering from rough surfaces. There is some new experimental data on light scattering from rough metallic surfaces that shows there is an enhancement of backscattering in the antispecular direction under certain conditions of surface parameters, wave polarization, and operating frequency. From a roughly random surface, the backscattering enhancement is predicted as the constructive interference of multiple surfaces scattering. The study is based upon the integral equation method modified to be able to predict the phenomenon of multiple scattering and backscattering enhancement. From the study, it was found that the backscattering enhancement takes place largely on the specialized surface parameters compared with the incident wavelength. Further, it is also concluded that the depolarized multiple scattering makes many contributions along the plane of incidence from random rough surfaces, but depolarized single scattering makes little contributions. In the comparison of model prediction of total multiple scattering strength with measured data along the specular plane, excellent agreement is obtained.