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The SODAR/RASS system, also simply referred to as the RASS system, a device that measures temperature and wind conditions in the lower atmosphere up to altitudes of 4 to 5 km. It consists of an acoustic based sounding radar, the SODAR, coupled with a Doppler radar, the RASS system. The RASS system senses (by means of Bragg reflections) the trajectory and radar signature of a sound pulse emitted by the SODAR as it travels upward into the atmosphere. The system reveals atmospheric conditions, including temperature inversions and wind speed and direction with altitude. The measurements are accomplished without the need for balloons or other devices to be sent aloft. The specific system components and pricing are detailed later.
The RASS temperature system is based on a few simple principles of physics: one being the relationship of the speed of sound and air temperature. Sound speed is proportional to the square root of absolute temperature. Sound pulses are transmitted into the air with a vertical trajectory, and their motion monitored using acoustic backscattering in the SODAR system and radar in the RASS system. Instruments intended for extended range into the atmosphere rely more on the radar and less on the acoustic responses. As the sound pulse travels upward, its velocity will change as it travels through layers having differing temperatures in the atmosphere. Software analysis of the changing velocity produces temperature and lapse rate data.
Doppler processing of the signal received by a second radar antenna measures the lateral wind drift of the sound pulse as it travels upward. This makes it possible to measure the wind speed and direction versus altitude. For risk assessment data, the system can easily measure temperature inversion phenomena. (A temperature inversion results from the air at altitudes being warmer than at ground level, a reversal of the neutral condition of temperature decreasing with altitude.)
The SODAR/RASS is becoming a widely used system where lower atmospheric sounding is important to operations. Users include manufactures in industry who need to monitor byproducts and plume dispersion, airports to determine wind shear, utility companies, research universities, meteorological offices, environmental consultants, private research facilities, military installations and national laboratories such as Los Alamos National Labs, Battelle Pacific Northwest Labs, Aberdeen Proving Ground, and White Sands Missile Range.
|CT||echo strength||no unit|
|SPEED||horizontal wind speed||cm/s|
|S DIR||standard deviation of the wind direction||degrees|
|W||vertical wind speed||cm/s|
|SW||standard deviation of the verical wind speed||cm/s|
|SU||standard deviation of the horizontal wind (along wind)||cm/s|
|SV||standard deviation of the horizontal wind (cross wind)||cm/s|
|INVMI||inersion and/or mixing height||meters|
|STAB||stability class||1 (F) stable
2 (E) slight stable
3 (D) neutral
4 (C) slightly unstable
5 (B) unstable
|ETAM||turbulent mechanical dissipation rate coefficient||cm2s-5|
|KZ||vertical turbulent eddy diffusion coefficient||m2s-3|
|DT/DZ||Lapse rate estimation||degrees Centigrade/km|
|ECHT||RASS echo||no unit|
|T||RASS temperature||°C x 10|
|ST||standard deviation of the RASS temperature||°C x 100|
|-9999||This value indicates that no measurement is
available for that altitude.