# Atmospheric Turbulence Study with Deep Machine Learning of Intensity Scintillation Patterns
## 2 Atmospheric Sensing Trials: Collection of ATM Datasets  
A schematic of the experimental setup used for the collection of \(C_{n}^{2}\) values and laser beam intensity scintillation images for the ATM datasets is shown in Figure 1. Both a laser beacon module and commercial scintillometer transmitter (Scintec BLS 2000 [15]) were located on the 40 m-high roof of the VA Medical Center (VAMC) in Dayton, Ohio. The laser beacon was positioned inside an instrument shed on the VAMC roof 3 m from the scintillometer transmitter. After propagating over 7 km, the beacon light entered an optical receiver positioned inside the University of Dayton (UD) Intelligent Optics Laboratory (IOL) located on the 5 th floor (\(\sim\)20 m height) of the UD Fitz Hall building. Both optical and the scintillometer receivers were placed right behind the IOL window (shown by arrow in Figure 1) approximately 1.5 m from each other. The propagation path in Figure 1 can be considered as nearly horizontal with a relatively small (\(\sim\)\(-\)1.15\({}^{\circ}\)) slant angle. As a light source we used a 1064 nm wavelength laser with \(\sim\)5 mW output power. The laser beam was coupled into a single-mode polarization maintaining fiber. The Gaussian-shape laser beam emitted through the fiber tip was expanded to a diameter of \(\sim\)25 mm and collimated by a lens with aperture diameter of 50 mm. The power losses due to laser beam truncation by the collimating lens aperture was of the order of 0.5%. For the laser beacon beam angular alignment, the end section (\(\sim\)3 cm) of the beam delivery fiber was installed inside a fiber-tip positioner module that provided piezo-actuator-based controllable fiber tip x- and y-displacements [16]. This angular alignment was performed remotely from the UD/IOL site through an RF communication link. The optical receiver of the beacon light was composed of lens \(L_{1}\) and \(L_{2}\) (see Figure 1). Lens \(L_{2}\) was used for re-imaging of the receiver (lens \(L_{1}\)) pupil of diameter \(D\) onto a CCD camera (12-bit SU320 sensor with \(320\times 256\) pixels resolution). To prevent the negative impact of ambient light, a narrow band interference filter was placed in front of the CCD camera. The camera was synchronized with a scintillometer that provided \(C_{n}^{2}\) values each \(\Delta T\) = 60 s (the shortest measurement rate available with the BLS 2000 scintillometer). Between two sequential \(C_{n}^{2}\) measurements the camera captured \(N_{\Delta T}\) short-exposure intensity scintillation images. Prior to being included into an ATM dataset, the scintillation images were digitally processed. Image processing included selection of a 256 \(\times\) 256 pixel central square area, followed by a reduction in the selected image section resolution to 128 \(\times\) 128 pixels by averaging 2 \(\times\) 2 square pixel areas, normalization on the maximum value and downscaling from 12- to 8-bit grey scale resolution. To obtain data that represent a wide range of atmospheric turbulence conditions several experimental trials were conducted at different times over several days between 9 March and 29 April 2020. The major details of the experimental trials are presented in Table 1.  
The first ATM dataset (ATM#1) was composed of the instances (scintillation images and \(C_{n}^{2}\) measurements) collected during three sensing trials performed on 9 March and 13 March (trials 1A, 1B and 1C). During these trials, an optical receiver with \(D\) = 11 cm aperture diameter was used. The CCD camera frame rate was set to 1.0 frame per second (f/s) which corresponds to \(N_{\Delta T}\) = 60 images captured between two sequential \(C_{n}^{2}\) measurements. The ATM#1 dataset included a total of  
Figure 1: Notional schematic of the experimental setting used for collection of short-exposure laser beam intensity scintillation images and the corresponding values of the refractive index structure parameter \(C_{n}^{2}\) (ATM data sets) under different atmospheric turbulence conditions.