Characterization of optical turbulence at the solar observatory at the Mount Teide, Tenerife

Optical turbulence represented by the structure function parameter of the refractive index Cn2 is regarded as one of the chief causes of image degradation of ground-based astronomical telescopes operating in visible or infrared wavebands. Especially, it affects the attainable spatial resolution. Therefore since the middle of September 2012 the optical turbulence has been monitored between two German solar telescopes at the Observatory in Tenerife /Canary Islands /Spain. It comprises the solar telescope GREGOR and the vacuum tower telescope VTT mounted on two 30 m high towers. Between the two towers at the level of the telescopes, Cn2 was measured using a Laser-Scintillometer SLS40 (Scintec, Rottenburg, Germany). The horizontal distance of the measurement path was 75 m. The first results of the measurements starting from the 15th September 2012 up to the end of December 2012 are presented and analyzed using simultaneous measured meteorological data of wind, temperature and humidity. Daily and seasonal variations are shown and discussed

An Electro-Optical Detection and Recognition Trial in a Desert-Like Environment: First Results

We report on first findings of a field trial, which has been carried out in a desert-like shrub land environment in New Mexico (USA) to acquire data for the improvement of electrooptical tactical decisions aids

Investigation of the integrated optical turbulence over a horizontal path using different measurement techniques

Measurements of the integrated optical turbulence were effected the Baltic Sea at a distance of 8.2 km. A comparsion between different measurement techniques is presented. The conformity between two applied measurement systems was good

Inhomogeneity of optical turbulence over False Bay (South Africa)

Atmospheric turbulence impacts on the propagation of electro-optical radiation. Typical manifestations of optical turbulence are scintillation (intensity fluctuations), beam wander and (for laser systems) reduction of beam quality. For longer propagation channels, it is important to characterize the vertical and horizontal distribution (inhomogeneity) of the optical turbulence. In the framework of the First European South African Transmission ExpeRiment (FESTER) optical turbulence was measured between June 2015 and February 2016 on a 2 km over-water link over False Bay. The link ran from the Institute of Maritime Technology (IMT) in Simons Town to the lighthouse at Roman Rock Island. Three Boundary layer scintillometers (BLS900) allowed assessing the vertical distribution of optical turbulence at three different heights between 5 and 12 m above the water surface. The expected decrease of Cn2 with height is not always found. These results are analyzed in terms of the meteorological scenarios, and a comparison is made with a fourth optical link providing optical turbulence data over a 8.7 km path from IMT to Kalk Bay, roughly 36° to the north of the three 2 km paths. The results are related to the inhomogeneous meteorological conditions over the Bay as assessed with the numerical weather prediction tool, the Weather Forecast and Research model WRF

Characterization of optical turbulence at the GREGOR solar telescope: Temporal and local behavior and its influence on the solar observations

Local atmospheric turbulence at the telescope level is regarded as a major reason for affecting the performance of the adaptive optics systems using wavelengths in the visible and infrared for solar observations. During the day the air masses around the telescope dome are influenced by flow distortions. Additionally heating of the infrastructure close to telescope causes thermal turbulence. Thereby optical turbulence is produced and leads to quality changes in the local seeing throughout the day. Image degradation will be yielded affecting the performance of adaptive optical systems. The spatial resolution of the solar observations will be reduced. For this study measurements of the optical turbulence, represented by the structure function parameter of the refractive index Cn2 were performed on several locations at the GREGOR telescope at the Teide observatory at Tenerife at the Canary Islands / Spain. Since September 2012 measurements of Cn2 were carried out between the towers of the Vacuum Tower Telescope (VTT) and of GREGOR with a laser-scintillometer. The horizontal distance of the measurement path was about 75 m. Additional from May 2015 up to March 2016 the optical turbulence was determined at three additional locations close to the solar telescope GREGOR. The optical turbulence is derived from sonic anemometer measurements. Time series of the sonic temperature are analyzed and compared to the direct measurements of the laser scintillometer. Meteorological conditions are investigated, especially the influence of the wind direction. Turbulence of upper atmospheric layers is not regarded. The measured local turbulence is compared to the system performance of the GREGOR telescopes. It appears that the mountain ridge effects on turbulence are more relevant than any local causes of seeing close to the telescope. Results of these analyses and comparison of nearly one year of measurements are presented and discussed

Lidar for Wind and Optical Turbulence Profiling

A field campaign for the comparison investigation of systems to measure wind and optical turbulence profiles was conducted in northern Germany. The experimental effort was to compare the performance of the LIDAR, SODAR-RASS and ultrasonic anemometers for the measurement of the above mentioned atmospheric parameters. Soreq's LIDAR is a fiber laser based system demonstrator for the vertical profiling of the wind and turbulence, based on the correlation of aerosol density variations. It provides measurements up to 350m with 20m resolution

Investigation of optical turbulence from an unmanned aerial system

Wave propagation of electro-optical systems, lasers or imaging depends on the state of the atmosphere their beams are passing through. Fluctuations in the refractive index of air are responsible for signal attenuation and image degradation. This atmospheric effect is called optical turbulence and its strength is quantified by the structure function parameter of the refractive index \u1d4362\u1d45b . In the atmospheric surface layer it is highly variable. Usually \u1d4362\u1d45b decreases with height. In non-uniform terrain, big horizontal variations can arise. We developed a mobile airborne system for monitoring \u1d4362\u1d45b to investigate the three-dimensional character of optical turbulence. Therefore the dodecacopter system HORUS (Hovering Remote controlled Ultra-light Sensor-platform (AIRCLIP /Dresden/Germany)) was chosen as mobile platform. An ultrasonic anemometer was mounted on a boom for high-resolution measurements of temperature and wind speed. Analyzing the time series of temperature, \u1d4362\u1d45b values were derived from time averages of several minutes. The measurements took place in the surface layer over land in the vicinity of an 80 m high tower, equipped with ultrasonic anemometers at four discrete heights. Comparison measurements were performed. The minimum length of the boom outside the turbulent influence of the rotors was investigated. The comparison of the \u1d4362\u1d45b values shows a good agreement. A second, smaller quadrocopter system in combination with a new very small and light-weight ultrasonic anemometer was also tested for turbulence measurements. The system is introduced and the applicability shown. Results from first field trials are presented and discussed

Comparison of integrated optical turbulence over the sea in different coastal regions in the world

Electro-optical and laser systems are presently deployed in naval operations around the world. The performance of these systems is negatively affected by optical turbulence in the atmosphere, quantified by the parameter Cn2. The strength of the integrated optical turbulence Cn2 was investigated for several coastal locations in different climatic conditions: False Bay (South Africa), the Baltic Sea (Bay of Eckernförde, Germany), the Mediterranean Sea (Crete, Greece), the Gulf of Mexico (Dauphin Island, Alabama, US), and the Arabian Gulf. The over-water, near-surface turbulence was characterized along paths that typically spanned 1.5 - 8.7 km using large aperture scintillometers. The dependency of Cn2 on the air-sea surface temperature difference and wind speed is discussed, and the results for the five geographic regions are compared and discussed in terms of environmental conditions and climate

The dependence of optical turbulence on thermal and mechanical forces over the sea

Optical turbulence for over-water conditions was investigated in a long-term experiment over False Bay near Cape Town, South Africa. A sonic anemometer and two boundary-layer scintillometers were deployed to access in-situ turbulence as well as the integrated turbulence over two 1.8 and 8.7 km paths. Statistical analysis reveals spatial temporal variations of the turbulence conditions over False Bay, which might be related to differences in the atmospheric conditions and/or the surface (water) temperatures. An analysis in terms of mechanical and thermal forcing reveals that the latter factor is more dominant in determining the turbulence strength

Ultimate turbulence experiment: simultaneous measurements of C n

We have performed a series of experiments in order to simultaneously validate several devices and methods for measurement of the path-averaged refractive index structure constant ( \u1d436\u1d45b 2). The experiments were carried out along a horizontal urban path near the ground. Measuring turbulence in this layer is particularly important because of the prospect of using adaptive optics for free-space optical communications in an urban environment. On one hand, several commercial sensors were used: SLS20, a laser scintillometer from Scintec AG, BLS900, a largeaperture scintillometer, also from Scintec, and a 3D sonic anemometer from Thies GmbH. On the other hand, we measured turbulence strength with new approaches and devices developed in-house. Firstly, an LED array combined with a high-speed camera allowed for measurement of \u1d436\u1d45b 2 from raw- and differential image motion, and secondly a two-part system comprising a laser source, a Shack-Hartmann sensor and a PSF camera recoded turbulent modulation transfer functions, Zernike variances and angle-of-arrival structure functions, yielding three independent estimates of \u1d436\u1d45b 2. We compare the measured values yielded simultaneously by commercial and in-house developed devices and show very good agreement between \u1d436\u1d45b 2 values for all the methods. Limitations of each experimental method are also discussed