| Popis: |
We have compared measured angle-of-arrival (AOA) fluctuations to the prediction of various models, for a laser beam propagating through a turbulent atmosphere at ground level. Three models have been investigated: a simple small perturbation model, a model which incorporates also inner and outer scale effects and a third model which takes into account the contribution of additional spatial scales and is able to predict a saturation regime. Data were collected in an approximately ten year time span. We have used near infra-red LIDAR systems to determine the AOA fluctuations by measuring the short term movement of a laser spot in the receiver plane, reflected from targets placed at various distances. In parallel, we have also measured the turbulence strength with a short-range scintilometer and recorded the average wind speed along the laser path. Our analysis indicates that the simple model predictions are quite good for weak turbulence and short distances, however on the majority of the scenarios the conditions (turbulence strength and distance) are such that the AOA fluctuations deviate from the simple model and even approach saturation. In these cases the fluctuations follows the general form of the third model. We also found some differences between the day and night behavior which wasn't considered by any of the models. |
