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.
Electro-optical (EO) and infrared (IR) signals propagating through the atmosphere exhibit intensity fluctuations caused by atmospheric turbulence, a phenomenon known as scintillation. Scintillation is directly related to the refractive index structure parameter Cn2 defined as the refractive index structure function scaled to for the turbulence inertial subrange. Quantifying Cn2 is essential to evaluate and predict scintillation effects on EO/IR systems. Meanwhile, aerosols in the lower atmosphere absorb and scatter EO/IR energy, resulting in attenuation, aliasing, and blurring.
We will present initial results on Cn2 and aerosol variability in the coastal zone using simultaneous measurements from a Twin Otter research aircraft, two instrumented ocean vessels [R/V John Martin and a rigid hull inflatable boat (RHIB)] , and a coastal land site. All measurements were taken as part of the Coastal Electro-Optical PropagaTion eXperiment (CEOPTeX) conducted in April/May 2016 offshore of Moss Landing, CA. Aerosol concentration, scattering, and absorption were obtained from the research aircraft in the atmospheric boundary layer. Cn2 was derived from measurements of temperature and humidity sampled at 20 Hz from all platforms/site. Two level Cn2 measurements were also taken when the R/V John Martin and the RHIB were co-located. We will discuss the spatial/temporal variability of the measured quantities, and the difference between the Cn2 at the coastal region and those predicted by surface layer similarity theory and the measured bulk quantities.