ISSN:0143-1161    

DOI:10.1080/01431168708954799

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The standard integral equation for the surface current is solved iterativcly to obtain an estimate of the surface current on a perfectly conducting randomly rough surface. The far-zone scattered fields and the backscattering coefficients for vertical, horizontal and cross-polarizations are then computed using this current estimate. The polarized backscattering coefficients are explicit functions of the surface parameters and reduce to the Kirchhoff solution in the high-frequency region and to the first-order perturbation solution in the low-frequency region. The cross-polarized scattering coefficient reduces to the second-order perturbation result in the low-frequency region and to zero in the high-frequency limit. A comparison is made with scattering measurements taken under laboratory conditions on a random surface with ka equal to 0-44 and kl equal to 3-25 ( l is the correlation length) It is found that better agreement is obtained with the current model than with the first-order perturbation model in predicting polarized scattering. It is also shown that the separation between VV and HH polarizations decreases gradually with frequency and approaches zero in the high-frequency limit

ISSN:0143-1161    

DOI:10.1080/01431168708954800

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A recent st udy of the range of validity of the surface scattering model by Eftimiu using a two-dimensional surface is re-examined with a more realistic surface correlation function that is everywhere-differentiable and vanishes gradually at infinity. Ii is shown that a sufficient condition on the range of validity is that cos2θ [(kσ)2/(kc)1/2]exp{−[2kc(1−sinθ)]1/2} ≪1where k is the electrical wave-number, 0 is the angle of incidence and a and c are the surface standard deviation and the surface correlation parameter respectively.

ISSN:0143-1161    

DOI:10.1080/01431168708954801

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A modified two-scale model is proposed for scattering and emissivity calculations for certain classes of random rough surfaces. It is based on an approach by Burrows and by Brown, but it has been extended to bistatic scattering by lossy dielectric surfaces, and it incorporates modified Fresnel reflection coefficients and a simple correction for multiple-scattering effects. The method is shown to be applicable to the ocean surface for light and moderate winds. A contracted form of the radiative-transfer equation is proposed and the included Wentz correction for surface scattering is discussed. This could lead to a method that could be both simple and accurate enough for real-time inversion algorithms in microwave remote sensing.

ISSN:0143-1161    

DOI:10.1080/01431168708954802

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

First, a general review is presented of wave-current interaction processes ( for horizontal shears) and their effect on radar backscatter and radar imagery ( SAR/ RAR ) Then numerical results on the refraction of wave energy trajectories by complex bottom topography (finite depth) and a linear shear current are presented. For deep water, the wave-energy trajectories are given for mesoscale currents ( e.g. eddies and double-vortex configurations). The focusing of wave energy by variable currents found here should have important influence on the spatial scale of wind stress over the ocean, and on optical and acoustic properties of the upper layer of the ocean.

ISSN:0143-1161    

DOI:10.1080/01431168708954803

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

This work is focused on the effects of large-scale wind-generated gravity waves on scatterometer wind-measurement accuracy. We present theoretical and experimental evidence of the important role played by the degree of wind-wave coupling in surface geometry and therefore in microwave signatures. Seasat scatterometer wind-measurement errors are analysed, and an error bias is found to be related to the degree of wind-wave development. Attention is focused on a dynamic measure of wind-wave development that characterizes the rate of energy transfer from the mean wind to the energy-carrying portion of the wave spectrum. An explanation of the bias is suggested based on the consideration of an additional component of surface scattering caused by electromagnetic-wave diffraction at the crests of individual, sufficiently steep wavelets.

ISSN:0143-1161    

DOI:10.1080/01431168708954804

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The particle-size dependence of microwave scattering from snow is investigated. Frozen crusts have been analysed, and the microslruclure is described by correlation functions. Relations between the correlation length and various quantities such as ice-intercept lengths or volume-to-surface ratios are checked. The scattering is calculated using the Bom approximation and is linked to the emissivity through the albedo. The model yields good agreement with the microwave data from C to K bands, and the predicted particle-size dependence is verified. The claims that the variance and the correlation length of the permittivity fluctuations are the characteristic parameters are confirmed. Initial uncertainties with respect to the validity of the Born approximation for an air-ice mixture are clarified.

ISSN:0143-1161    

DOI:10.1080/01431168708954805

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Radar backscattering from a snow-free ice surface characterized by an exponential correlation function is studied for conditions typical in the Baltic Sea. The C-band backscattering coefficient from first-year ice is normally found to be characterized primarily by the air-ice surface roughness. However, if the salinity and temperature are low, as in the Baltic Sea, both volume scattering and ice-water surface scattering might contribute. Even more important than scattering from the level ice is scattering from the ice ridges, and a simple approach is taken to characterize the properties of ice ridges and the corresponding scattering.

ISSN:0143-1161    

DOI:10.1080/01431168708954806

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The backscatter properties of Seasat altimeter data in the Beaufort Sea on the 3 October 1978 show distinct zones, which arc interpreted in terms of geophysical characteristics. An overlapping and near-simultaneous synthetic-aperture radar image shows regions of open water, new ice and multi-year sea ice, which correspond to the different zones. It is found that the altimeter signal is sensitive to the ocean-ice boundary and that it indicates the ice type. The pulse-echo waveforms also suggest that several scattering components are present in the returned power over sea ice.

ISSN:0143-1161    

DOI:10.1080/01431168708954807

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

This paper describes the microwave backscattering characteristics of three kinds of conifers, Matsu ( Japanese pine), Sugi (Japanese cedar) and Sawara (Japanese cypress), in the C and X bands for polarization combinations HH, VV, HV and VH. The measurements were made indoors using rotating-tree targets. ( i) Differences between HH and VV, (ii)the levels of the like backscatters of three conifers, and ( in) depolarization are discussed in relation to the features of canopy structure and leaf shapes. The method employed in this study will be ofuse in radar-signature studies of a wide variety of trees.

ISSN:0143-1161    

DOI:10.1080/01431168708954808

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor