ABLE Doppler Minisodar
The ABLE minisodar : One of these instruments is placed alongside each of the RASS wind profilers.
The minisodar measures wind profiles from about 10 m to 200 m above the surface, thus filling in the gap left below the minimum height of the wind profilers.
The primary quantities measured the the system are the intensity and Doppler shift of backscattered acoustic energy from index of refraction fluctuations (created by temperature and wind fluctuations) embedded in the atmosphere.
List of Components
The minisodar has been developed and fabricated at Argonne National Laboratory (ANL). It consists of a 32 element array of piezoceramic tweeters mounted vertically within a protective enclosure roughly 1.5 m X 1.5 m X 1.5 m. The acoustic "in phase" transmission is reflected off a plate into a vertically propagating wave. This orientation enables the system to operate in all weather conditions.
The minisodars operate by transmitting in two different vertical planes and receiving backscattered energy from refractive index fluctuations moving with the mean wind. By sampling in the vertical direction and two tilted planes, the three components of motion can be determined. Click here to listen to a typical sodar transmit sound.
The system consists of a single phased array antenna that transmits alternately along three pointing directions: one vertical, one in the north-south vertical plane (to the north) and one in the east-west vertical plane (to the east). The non-vertical beams are tilted about 17 degrees from vertical.
Radial components of motion above each pointing direction are determined sequentially, separated by about 1.5 seconds. Thus the system repeats its sequence about every 5 seconds. The data from each transmit pulse are processed with a FFT centered about each range gate (e.g. every 5 m increment in the vertical) to determine the mean Doppler shift. The signal-to-noise ratio is used to determine if each estimate is acceptable. All the acceptable data within an averaging interval (e.g. 15 minutes) are averaged and combined to produce a wind profile if there are enough acceptable data points (25%, e.g.) within the interval.
The averaged data are output in files with format similar to radar wind profiler (".sod") format for consistency. High resolution radial moments data and spectra can be produced if desired.
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