Engineering topics

Humphreys, T. J.

Publications and source records attributed to Humphreys, T. J..

3 records

NASA NTRS1981

Inelastic scattering in planetary atmospheres. I - The Ring effect, without aerosols

The contribution of inelastic molecular scattering (Rayleigh-Brillouin and rotational Raman scattering) to the filling-in of Fraunhofer lines in the light of the blue sky is studied. Aerosol fluorescence is shown to be negligible, and aerosol scattering is ignored. The angular and polarization dependences of the filling-in detail for single scattering are discussed. An approximate treatment of multiple scattering, using a backward Monte Carlo technique, makes it possible to investigate the effects of the ground albedo. As the molecular scatterings alone produce more line-filling than is observed, it seems likely that aerosols dilute the effect by contributing unaltered sunlight to the observed spectra.

Kattawar, G. W.↗

NASA NTRS1980

Electromagnetic scattering from two identical pseudospheres

In an attempt to gain some insight into the problem of how close particles have to be on the average before phase effects become important, the cross section and phase matrices for two identical particles as a function of the distance between their centers for both broadside and end-on illumination have been calculated. The point dipole approximation is employed to build two pseudospherical particles each consisting of 32 dipoles with an effective size parameter of 0.9283 and refractive index of 1.54-0.0i. In regard to cross sections, it is found that in certain cases several percent deviation from the converged value, which is twice the single particle cross section, could be found up to distances of separation of 25 single particle diameters. The maxima and minima in the cross section curves can be explained in terms of simple interference effects. Also the element P11 of the phase matrix showed a great deal of structure, and the position of maxima and minima could be explained by phase shift analysis.

Kattawar, G. W.↗

NASA NTRS1976

Remote sensing of chlorophyll in an atmosphere-ocean environment - A theoretical study

A Monte Carlo program was written to compute the effect of chlorophyll on the ratio of upwelling to downwelling radiance and irradiance as a function of wavelength, height above the ocean, and depth within the ocean. This program simulates the actual physical situation, since a real atmospheric model was used, i.e., one that contained both aerosol and Rayleigh scattering as well as ozone absorption. The complete interaction of the radiation field with the ocean was also taken into account. The chlorophyll was assumed to be uniformly mixed in the ocean and was also assumed to act only as an absorbing agent. For the ocean model both scattering and absorption by hydrosols was included. Results have been obtained for both a very clear ocean and a medium turbid ocean. Recommendations are made for optimum techniques for remotely sensing chlorophyll both in situ and in vitro.

Kattawar, G. W.↗