Near Ground Surface Turbulence Measurements And Validation: A Comparison Between Different Systems

Recently, the number of optical systems that operate along near horizontal paths within a few meters of the ground has increased rapidly. Examples are LIDAR or optical sensors imbedded in a vehicle, long range surveillance or optical communication systems, a LIFI network, new weather monitoring stations, as well as directed energy systems for defense purposes. Near ground turbulence distortion for optical waves used in those systems cannot be well described by conventional turbulence and beam propagation theory. Phenomena such as anisotropy, micro mirage effects, a temporal negative relation between diurnal dips and altitude, and condensation induced measurement errors are frequently involved. As a result, there is a high risk of defective designs or even failures in those optical systems if the near ground turbulence effects are not well considered. To illustrate such risk, we make C n2 measurements by different approaches and cross compare them with associated working principles. By demonstrating the reasons for mismatched C n2 results, we point out a few guidelines regarding how to use the general anisotropy theorem and the risk of ignoring it. Our conclusions can be further supported by an advanced plenoptic sensor that provides continuous wavefront data

A Multi-Aperture Laser Transmissometer For Detailed Characterization Of Laser Propagation Over Long Paths Through The Turbulent Atmosphere

We present an experimental evaluation of a multi-aperture laser transmissometer system which profiles long-term laser beam statistics over long paths. While the system was originally designed to measure the aerosol extinction rate, the beam profiling capabilities of the transmissometer system also allows experimental observations of Gaussian beam statistics in weak and strong turbulence. Additionally, measurement of long-term beam spread at the receiver allows the system to estimate a path-averaged C n2 , including in strong turbulence regimes where scintillometers experience saturation effects. Additionally, a phase-frequency correlation technique for synchronizing with transmitter ON/OFF modulation in the presence of background ambient light is presented. In application, our ruggedized and weather resistant laser transmissometer system has significant advantages for the measurement and study of aerosol concentration, absorption, scattering, and turbulence properties over multi-kilometer paths, which are crucial for directed energy systems, ground-level free-space optical communication systems, environmental monitoring, and weather forecasting

Comparing Measurements Of Rtd Probe Systems And Sonic Anemometers

Ground to air temperature gradients are the drivers of optical turbulence. Different systems can measure temperature fluctuations. C2T and C2n are derived from RTD probe systems and sonic anemometers mounted at several heights and compared

The FESTER field trial

An overview is given of the First European – South African Transmission ExpeRiment (FESTER), which took place in South Africa, over the False Bay area, centered around Simon’s Town. The experiment lasted from April 2015 through February 2016 and involved continuous observations as well as periodic observations that took place during four Intensive Observation Periods (IOPs) of 2 weeks each, which were spread over the year. The continuous observations aimed at a characterization of the electro-optical propagation environment, and included standard meteorology, aerosol, refraction and turbulence measurements. The periodic observations aimed at assessing the performance of electro-optical sensors in VIS / SWIR / MWIR and LWIR wavebands by following a boat sailing outbound and inbound tracks. In addition, dynamic aspects of electro-optical signatures, i.e., the changes induced by variations in the environment and/or target orientation, were studied. The present paper provides an overview of the trial, and presents a few first results