Derivation of Microwave Refractive Index Structure Constant $(C_{n}^{2})$ of the Atmosphere From K-Band Interferometric Phase Measurements

Differential phase data has been collected using a site test interferometer (STI) at K-band for several years at various NASA ground station sites, including the NASA Deep Space Network (DSN) in Goldstone, CA, and the NASA Space Network (SN) sites in White Sands, NM, and Guam. An objective of this work is to characterize the site-dependent atmospheric phase stability to determine the viability of that site for arraying applications. A useful figure of merit to quantify this effect is the determination of the microwave refractive index structure constant, C_n², which is highly dependent on variations in the water vapor concentration of the troposphere. In this paper, a method is proposed to derive C_n² from a two-element site test interferometer utilizing temporal phase structure function information. In this way, a path-averaged C_n² at each ground station site is determined which can be used in the design and expected system performance of future Ka-band communication systems in an arrayed architecture. Statistical characterization of microwave C_n² indicates that a mean value of 2.04 ×10^-14, 2.08×10^-14, and 9.8×10^-13 is expected for Goldstone, CA, White Sands, NM, and Guam, respectively.