Wavelength and roughness dependence of backscattering
The variation of scattered light with surface roughness and illuminating wavelength is analyzed with a particular emphasis on remotely sensing the surface structure and height profile of the scattering object. The wavelength variation is used to determine the height distribution of the scattering surface and is compared to the stretched envelope of a pulse echo system. Remarkable consistency is found between the processes complex field amplitude and the stretched pulse envelope. The autocorrelation of the intensity scattered from a surface measured as a function of the illuminating frequency is shown to be proportional to the square of the first order characteristic function associated with the surface height distribution. Experiments, supported by computer simulations, are conducted for imaging and far-zone scattering systems in which roughnesses ranging from 1 {mu}m to 1 mm can be determined in a noncontact method. In studying the effects of surface roughness on the scattered intensity, a useful quantity to calculate is the scattering cross section. The cross section depends only on the characteristics of the surface and the incident and scattering angles. It is found by reducing the two point correlation of the field scattered from the surface or disc. The field correlation requires an intricate calculation of the ensemble average of several surface height and slope terms that become dominant for large roughnesses and for large incident angles. Two surface types are considered and the important effect of shadowing is included. In the backscatter direction, the Gaussian surface has a cross section which however, has a cross section that actually increases with incident angle for certain roughness conditions. Experimental measurements support these calculations. The backscattering cross section calculation for the titled disc is extended to curved or shaped objects, specifically a sphere.
- Research Organization:
- Rochester Univ., NY (United States)
- OSTI ID:
- 121186
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); PBD: 1993
- Country of Publication:
- United States
- Language:
- English
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