snodar (surface layer non-doppler acoustic radar) a new instrument to measure the height of the...

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. [email protected]

Michael C.B. Ashley, Jon S. Lawrence, Daniel Luong-Van, John W.V. Storey

What is a SODAR?

Optical Turbulence Astronomy meets Meteorology, 15-18 September 2008, Sardegna (Italy)

S. Bradley, et al “Sodar calibration for wind energy applications,” March 2005.

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 CT2 profile is a bonus.

• Snodar was not intended to measure CV2 or wind

profiles.

– Snodar is truly monostatic and cannot measure CV2,

however it is possible to construct wind profiles.

South Pole 2001…

… Dome C 2003

…and Dome A 2008 ???Optical Turbulence Astronomy meets Meteorology, 15-18 September 2008, Sardegna (Italy)

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.


Hardware


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.


An Antisocial instrument?


Snodar

D.M. Howard, J. Angus, “Acoustics and psychoacoustics”. 2006

Acoustics

We initially looked at a phased array with inertia-driven Piezoelectric speakers.


Acoustics


SoftwareThe 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.).


Performance - Noise


Performance - Example data


Calibration


Calibrate Snodar using another instrument, but what?

Calibration


Calibration


Calibrate Snodar using another instrument, but what?

Direct in situ measurement of CT2 with differential

thermocouples:

CT2 = <[T(x) – T(x+r)]2> / r2/3

K <...>x2

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


Calibration

0 20 40 60 80 100 1200

0.2

0.4

0.6

0.8

1

1.2

Time [Seconds]

CT2 [

k2 m-2

/3]

SNODAR

Microthermal

0 0.2 0.4 0.6 0.8 1 1.20

0.2

0.4

0.6

0.8

1

1.2

SNODAR CT2 [k2 m-2/3]

Mic

roth

erm

al C

T2 [k2 m

-2/3

]


Noise equivalent CT2

10 20 30 40 50 60 70 80 90 10010

-10

10-9

10-8

10-7

10-6

10-5

10-4

CT2

Height [m]


Plans for the future


- More calibration.- Dome A - again.- Dome C.- Possible collaboration with the British Antarctic Survey.

AcknowledgmentsWe would like to thank Elena Masciadri, Stuart Bradley, the entire Chinese PANDA traverse team.

snodar (surface layer non-doppler acoustic radar) a new instrument to measure the height of the...

Documents

sardegna italy snodar

x2x2 slide

storey slide

dome c

sodar calibration

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calibrated c t

situ measurement of