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Atmospheric Profilers

Atmospheric Profilers. Marc Sarazin (European Southern Observatory). 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

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Atmospheric Profilers

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  1. Atmospheric Profilers Marc Sarazin (European Southern Observatory) Zanjan, Iran

  2. List of ThemesHow 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 Zanjan, Iran

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

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

  5. Turbulence Profilers The various methods for generating atmospheric turbulence profiles • Full line: Mauna Kea Model (Olivier, 94) • Dots: SCIDAR, Paranal • Dashes: Baloon borne microthermal sensors Ref: PARCSA Campaign, Univ. of Nice, 1992-1993 Zanjan, Iran

  6. 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 Zanjan, Iran

  7. Doppler SODAR Profiler 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 Source: http://www.remtechinc.com/sodar.htm Zanjan, Iran

  8. 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: http://www.remtechinc.com/sodar.htm Zanjan, Iran

  9. The SCIDAR 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 Ref: tutorial at the Imperial College Site: http://op.ph.ic.ac.uk/scidar/scidar.html/ Zanjan, Iran

  10. The SCIDAR Practically, thousands of frames of <1ms exposure are combined to generate one profile every minute Ref: tutorial at the Imperial College Site: http://op.ph.ic.ac.uk/scidar/scidar.html/ Zanjan, Iran

  11. The SCIDAR 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 Source: A. Tokovinin, Study of the SCIDAR concept for Adaptive Optics Applications, ESO-VLT Report TRE-UNI-17416-0003 Zanjan, Iran

  12. The SCIDAR 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 Source: A. Tokovinin, Study of the SCIDAR concept for Adaptive Optics Applications, ESO-VLT Report TRE-UNI-17416-0003 Zanjan, Iran

  13. The SCIDAR Scidar Profile, seeing 1” Scidar Profile, seeing 2” Ref: tutorial at the Imperial College Site: http://op.ph.ic.ac.uk/scidar/scidar.html/ Zanjan, Iran

  14. The SCIDAR and the Models MM5, a mesoscale model is available as freeware. It is used at the Mauna Kea Weather Center(http://hokukea.soest.hawaii.edu/forecast/mko/) to produce vertical profiles of the turbulence. Comparison of MM5 profiles above Mauna Kea Observatory with in situ SCIDAR observations Zanjan, Iran

  15. 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 Zanjan, Iran

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