RASS - Calculation of virtual temperature

• The RASS unit sends out an acoustic (sound) wave in the vertical direction.  

• The propagation speed of the acoustic wave depends on the temperature and moisture composition of the atmosphere.  The speed of the acoustic wave is related to the virtual temperature by C_a = 20.047(T_v^1/2)

• The profiler then sends out it's own pulse which backscatters off of the RASS acoustic wave.  It measures the Doppler shifted frequency of the acoustic wave, thus one can obtain C_a from the Doppler shifted frequency.  This is very similar to determining the radial velocity of precipitation targets with an 88-D by measuring the Doppler shifted frequency of the backscattered energy.  

• Once C_a is known, then T_v = (C_a/20.047)²