July 2001Zanjan, Iran1 Atmospheric Profilers Marc Sarazin (European Southern Observatory)

July 2001Zanjan, Iran2 List of Themes How to find the ideal site...and keep it good? Optical Propagation through Turbulence –Mechanical and Thermal –Index of Refraction –Signature on ground based observations –Correction methods Integral Monitoring Techniques –Seeing Monitoring –Scintillation Monitoring Profiling Techniques –Microthermal Sensors –Scintillation Ranging Modelling Techniques

Outline Why do we need turbulence profiles? Microthermal sensing Sound back scattering Scintillation Mesoscale modeling

July 2001Zanjan, Iran4 Index of refraction of air Assuming constant pressure and humidity, n varies only due to temperature fluctuations, with the same structure function Atmospheric Turbulence P,e (water vapor pressure) in mB, T in K, Cn2 in m-2/3

July 2001Zanjan, Iran5 Turbulence Profilers Ref: PARCSA Campaign, Univ. of Nice, The various methods for generating atmospheric turbulence profiles Full line: Mauna Kea Model (Olivier, 94) Dots: SCIDAR, Paranal Dashes: Baloon borne microthermal sensors

July 2001Zanjan, Iran6 Balloon Borne Profilers Two Microthermal sensors, 1m apart are attached far below the load of a standard meteorological radiosondes Pros: Provide Temperature, Humidity and Wind High vertical resolution (5m) Cons: An ascent last one hour or more The balloon drifts horizontally (30 to 100 km) Expensive technique (1kUS$/flight) The rms of the differential temperature fluctuations over a few seconds is computed onboard and transmitted to the ground

July 2001Zanjan, Iran7 Doppler SODAR Profiler Source: Sound Detection And Ranging Monitoring the backscattered acoustic energy from the atmospheric layers The acoustic backscattering cross-section is a function of acoustic wavelength, absolute temperature and temperature structure coefficient

July 2001Zanjan, Iran8 Doppler SODAR Profiler Pros: Provides Wind profile (design goal) Good vertical resolution (30m) Fully automated Cons: Only relative Cn2 measurements: no absolute calibration (the sound absorption by air depends on T,Rh profiles which are unknown) Limited altitude range (<1km) when there is little turbulence Source:

July 2001Zanjan, Iran9 The SCIDAR Ref: tutorial at the Imperial College Site: SCIntillation Detection And Ranging (J. Vernin, 1979) Analysis of the interference pattern produced at the ground by the light of two closeby sources diffracted by a turbulence layer The aurocorrelation of the pupil scintillation pattern shows a peak for the distance BC. The separation of the double star scales the altitude of the turbulence layer

July 2001Zanjan, Iran10 The SCIDAR Practically, thousands of frames of <1ms exposure are combined to generate one profile every minute Ref: tutorial at the Imperial College Site:

July 2001Zanjan, Iran11 The SCIDAR Source: A. Tokovinin, Study of the SCIDAR concept for Adaptive Optics Applications, ESO-VLT Report TRE-UNI Optical Setup: 2: focal plane with field stop 3: collimator 4: chromatic filter 5: conjugate pupil plane 6: detector Detector and pupil plane conjugate are collocated in non generalized mode

July 2001Zanjan, Iran12 The SCIDAR Source: A. Tokovinin, Study of the SCIDAR concept for Adaptive Optics Applications, ESO-VLT Report TRE-UNI The double star separation, and the telescope diameter set the altitude range Fig: auto correlation shift X in generalized mode, with the detector conjugated at a plane 5km below ground, as a function of turbulence altitude. The minimum characteristic size of the scintillation patterns is 3.5cm. Telescope diameter=1.2m Pixel size=2cm

July 2001Zanjan, Iran13 The SCIDAR Ref: tutorial at the Imperial College Site: Scidar Profile, seeing 1” Scidar Profile, seeing 2”

July 2001Zanjan, Iran14 The SCIDAR and the Models MM5, a mesoscale model is available as freeware. It is used at the Mauna Kea Weather Center ( to produce vertical profiles of the turbulence. Comparison of MM5 profiles above Mauna Kea Observatory with in situ SCIDAR observations

July 2001Zanjan, Iran15 The SCIDAR and the MASS A single star profiler: the MASS: Multi Aperture Scintillation Sensor A portable instrument for site surveys with a reduced altitude resolution (1km instead of 200m) A. Tokovinin, V. Kornilov; Measuring turbulence profiles from scintillation of single stars, IAU Site 2000 Workshop, Marrakech, Nov. 2000