Observations of optical turbulence in the marine atmospheric surface layer during CASPER-West

Abstract

It is understood that atmospheric turbulence results in fluctuations in the received power of an electro-optical (EO) link, a phenomenon known as optical scintillation. The atmospheric variable relevant to optical scintillation is the structure function parameter (Cn2) which can be quantified through optical scintillation measurements or derived from measurements of high-rate sampled atmospheric turbulence, especially the temperature perturbations. In addition to this (Cn2) can be estimated using models, some of which are based on surface layer similarity theory. However, the near shore marine atmospheric surface layer (MASL) provides an optically heterogeneous and complex turbulent environment that can be difficult to model accurately. A better understanding of the characteristics of near shore surface layer scintillation will provide increased exploitation of the environment by current and future EO systems operating in littoral regions. In an effort to better determine the scintillation effects in the MASL, observations were taken during the 26-day Couple Air-Sea Processes and Electromagnetic ducting Research West coast (CASPER-West) field campaign in September - October 2017 off the coast of Pt Mugu, CA. In this paper, we introduce the CASPER-West EO component to include a description of the operating area, major platforms and major instruments relevant to EO measurements, and sampling strategy. We show comparisons of the derived (Cn2) from scalar perturbation measurements, bulk model parameterization, and from concurrent scintillation measurements between the R/V Sally Ride and R/P FLIP. Slant path optical links between a remotely piloted hexa-copter and the R/P FLIP were also available. Both stable and unstable thermal stratifications of the MASL were encountered throughout the campaign and we will discuss the observed differences between the experiment and those from current similarity theories in these different stability conditions.