Abstract
We develop and study two approaches for the prediction of optical refraction effects in the lower atmosphere. Refraction can cause apparent displacement or distortion of targets when viewed by imaging systems or produce steering when propagating laser beams. Low-cost, time-lapse camera systems were deployed at two locations in New Mexico to measure image displacements of mountain ridge targets due to atmospheric refraction as a function of time. Measurements for selected days were compared with image displacement predictions provided by (1) a ray-tracing evaluation of numerical weather prediction data and (2) a machine learning algorithm with measured meteorological values as inputs. The model approaches are described and the target displacement prediction results for both were found to be consistent with the field imagery in overall amplitude and phase. However, short time variations in the experimental results were not captured by the predictions where sampling limitations and uncaptured localized events were factors.
Highlights
The Earth’s atmosphere includes several phenomena that affect the propagation of light
The goal of this paper is to develop and evaluate two different methods, numerical weather prediction (NWP) and machine learning (ML), for predicting image displacement due to atmospheric refraction
We found that NWP along with a ray-tracing technique can be used for prediction of image displacement effects due to atmospheric refraction
Summary
The Earth’s atmosphere includes several phenomena that affect the propagation of light. Atmospheric turbulence causes image shimmering and blurring and is stochastic in nature with fluctuations over short timescales (e.g., milliseconds). Another phenomenon is atmospheric refraction where refractive index gradients can steer or bend light rays. The index gradients are associated with changes in air density, which for optical wavelengths is primarily a function of air temperature gradients. Atmospheric refraction tends to cause more deterministic, larger-scale effects than turbulence and the effects can persist from minutes to hours.[1,2,3,4] The interest here is refraction in the lower atmosphere, which can cause apparent displacement or distortion of objects when viewed by imaging systems or produce steering when propagating laser beams
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