Statistics – Methodology
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........58h&link_type=abstract
Thesis (PH.D.)--GEORGIA INSTITUTE OF TECHNOLOGY, 1993.Source: Dissertation Abstracts International, Volume: 54-12, Section: B, p
Statistics
Methodology
Doppler Shift, Absorption Spectra
Scientific paper
An algebraic adjustment to a narrow band model is developed which accounts for the effect of line Doppler shifting on apparent radiance. Line Doppler shifting is the phenomena which arises from relative velocity between layers in an emitting, absorbing medium which possesses a spectral line structure. Layers of stationary gas closest to the observer will have an absorption spectrum that is fixed at the nominal, unshifted frequency. Moving gas layers beyond those closest to the observer will have a frequency shifted emission spectrum (due to the Doppler effect) relative to the absorption spectrum of the stationary gas layers. The Doppler shift will cause more radiance to reach the observer than would occur without the shift by moving the maximum spectral emission away from the maximum spectral absorption. Current methodology used to account for line Doppler shifting is restricted to line by line modelling, and to a modified narrow band model which evaluates the equivalent width by numerical integration. Both methods suffer from excessive computing time. An alternative method is proposed in this thesis whereby the equivalent width is determined from an algebraic relation. This new method reduces the computing time to a level expected in standard narrow band model calculations, yet accounts for line Doppler shifting. The algebraic relation is a function of the emitting layer optical depth, the absorbing layer optical depth, the respective layers' line widths, and the line Doppler shift. The apparent radiance calculated by the new model is compared to theoretical calculations and standard narrow band model calculations. The new line Doppler shift model is shown to be an improvement on the existing narrow band model, but retains inaccuracies resulting from the standard narrow band model formulation. Without substantial improvement to the standard narrow band model, any further modification to the line Doppler shift model will bring only a marginal improvement (i.e., reduction in the error) in the apparent radiance.
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