On the Deduction of the Refractive Index Profile of a Stratified Atmosphere from Radio Field-Strength Measurements

A method developed by Macfarlane for the theoretical deduction of the refractive index profile of a horizontally stratified atmosphere from radio field-strength measurements was applied to several sets of radio field-strength data for which complementary measured refractive index profiles were available, for both standard and nonstandard meteorological conditions. The formal theoretical validity of Macfarlane´s method was affirmed for the case of a linear M curve, dM/dH=3.6 units/100 feet, by application of the method to several theoretical radio field-strength profiles given by Standard Diffraction Theory. M curves were derived which were linear and possessed slopes within 3 per cent of the control slope of 3.6 M units/100 feet However, application of the method to the theoretical radio field-strength profiles of Standard Diffraction Theory revealed that in order to yield satisfactory refractive index data, a higher degree of accuracy was required of the radio field-strength data than one could expect to realize experimentally. The inherent sensitivity of the method to small, inevitable inaccuracies in the radio field-strength data makes it impossible to apply the method directly to experimental data. It is often possible, however, to approximate a radio field-strength profile, within the limits of experimental error, by an analytical curve or a combination of curves appropriately joined together.