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Snodar (Surface layer NOn-Doppler Acoustic Radar) A new instrument to measure the height of the Atmospheric boundary layer on the Antarctic plateau. Colin.

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Presentation on theme: "Snodar (Surface layer NOn-Doppler Acoustic Radar) A new instrument to measure the height of the Atmospheric boundary layer on the Antarctic plateau. Colin."— Presentation transcript:

1 Snodar (Surface layer NOn-Doppler Acoustic Radar) A new instrument to measure the height of the Atmospheric boundary layer on the Antarctic plateau. Colin S. Bonner Michael C.B. Ashley, Jon S. Lawrence, Daniel Luong-Van, John W.V. Storey

2 What is a SODAR? Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy) S. Bradley, et al Sodar calibration for wind energy applications, March 2005.

3 Why build a new SODAR? We needed it… The single purpose of Snodar is to measure the height of the boundary layer in Antarctica to ±1m. –Obtaining a calibrated C T 2 profile is a bonus. Snodar was not intended to measure C V 2 or wind profiles. –Snodar is truly monostatic and cannot measure C V 2, however it is possible to construct wind profiles. South Pole 2001… … Dome C 2003 …and Dome A 2008 ??? Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

4 System overview USB PC sound card, 96kHz 24bits. Custom 12-bit programmable gain preamplifier. Hardware loop back. 16bits Class-D power amplifier. Hardware triggered low noise solid state switch. Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

5 Hardware Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

6 Acoustics Operating frequency is a function of atmospheric absorption, scattering due to turbulence and background noise. - Background noise 1/f, but unknown at Dome A. Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

7 An Antisocial instrument? Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy) Snodar D.M. Howard, J. Angus, Acoustics and psychoacoustics. 2006

8 Acoustics We initially looked at a phased array with inertia-driven Piezoelectric speakers. Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

9 Acoustics Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

10 Acoustics Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

11 Acoustics Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

12 Acoustics Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

13 Acoustics Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

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15 Software The software is simple and runs in user space – not kernel space and does not require a real-time operating system. - Uses POSIX threads and ALSA API. - Hardware loop back allows software synchronization of signals and hardware relay triggering reduces timing constraints. - On site data reduction and compression (500x reduction, 2x comp.). Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

16 Performance - Noise Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

17 Performance - Example data Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

18 Calibration Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy) Calibrate Snodar using another instrument, but what?

19 Calibration Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

20 Calibration Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy) Calibrate Snodar using another instrument, but what? Direct in situ measurement of C T 2 with differential thermocouples: C T 2 = / r 2/3 K x2x2

21 Calibration Differential thermocouple Measurement BW 0.5 Hz to 300 Hz. Type E thermocouples with 13ms time constant (FW05). r = 0.75m H = 5.75m Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

22 Calibration Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

23 Noise equivalent C T 2 Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy)

24 Plans for the future Optical Turbulence Astronomy meets Meteorology, September 2008, Sardegna (Italy) - More calibration. - Dome A - again. - Dome C. - Possible collaboration with the British Antarctic Survey. Acknowledgments We would like to thank Elena Masciadri, Stuart Bradley, the entire Chinese PANDA traverse team.


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