Methods for Determining The Refractive Index Structure Parameter in the Marine Atmospheric Boundary Layer

• Main Author: Laughlin, Daniel Joseph
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2022
• Subjects: Wood Island
• Online Access: https://scholars.unh.edu/thesis/1561; https://scholars.unh.edu/cgi/viewcontent.cgi?article=2600&context=thesis

An experimental study of the marine atmospheric boundary layer effects on the index of refraction was conducted off the coast of Portsmouth, NH between Battery Farnsworth and Wood Island. This study aimed to compare measured changes in the refractive index structure parameter (Cn2) to estimates using time series data of single point atmospheric variables, including temperature, pressure, and wind velocity. A scintillometer transmitter and receiver located at Battery Farnsworth and Wood Island, respectively, provided direct measurements of Cn2. Data from a weather tower containing a sonic anemometer was used to estimate Cn2. Three methods of analysis to estimate Cn2 from the time-series data from single point atmospheric variables were employed. The three methods were a two-point structure function method (most common method in practice owing to its simplicity), a spectral analysis method assuming Kolmogorov turbulence with r2/3 (k -5/3) scaling, and a spectral analysis not assumingKolmogorov scaling. Here r (or wavenumber k) refers to the turbulent length scales. The measurements of Cn2 acquired in the present study are consistent with Cn2 measurements from other studies in the literature. The data for all three methods to estimate Cn2 closely followed Cn2 measured from the scintillometer, with the spectral analysis methods showing the best agreement. The study lends credence to the use of structure functions obtained from time-series data from single point measurements of atmospheric variables to accurately estimate Cn2 within the marine atmospheric boundary layer.