Experimental validation and design feasibility of a compact interferometric refractive index structure constant measurement sensor for atmospheric turbulence characterization

Abstract

Measurement of atmospheric turbulence has long been carried out using differential temperature sensors, DTS. DTS measurements of small temperature fluctuation differences between two spatially separated thermocouples can be ensemble averaged to calculate the temperature structure constant which can be used to approximate the refractive index structure constant. This technique has been widely applied and used with reasonable success in spite of several important limitations. One of the primary limitations is that the temperature structure constant alone does not fully define the refractive index structure constant; because the water vapor structure and water vapor to temperature cross correlation terms, which are much more difficult to measure, are ignored. This paper presents an initial feasibility analysis and experimental validation for a new type of refractive index structure constant sensor that is based on a compact, low cost interferometric sensor. This method is being explored as a potential alternative to DTS, because it measures index of refraction directly and thus offers the possibility of significant improvement in measurement accuracy. The paper outlines the sensor concept, its key components, and an analytical and experimental validation of the refractive index structure measurement accuracy.