(a) Profile of virtual temperature derived from a radiosonde sounding at 15:30 LT on 18 October 1997. RASS measurements made from 15:00 to 15:15 LT indicated by .
(b) as for (a), but for 17:50 LT on 19 October 1997 with the RASS measurements made from 17:32 to 18:05 LT.

The difference in the height ranges of RASS temperatures in the above examples is due to some of the fundamental principles of RASS.

The spherical sound wave as it propagates upward can be considered as a concave reflecting surface which focuses the scattered radiation to a spot on the ground. This spot moves depending on the displacement of the acoustic wave due to the background wind. Thus the speaker is placed upwind of the radar so that as the acoustic wave propagates upward it and the focussed spot are blown across the radar. However, when the horizontal winds are appreciable the length of time that the spot is "seen" by the radar can be quite short, hence the range of heights for which temperatures can be determined can be limited.

For the two cases shown above, different height ranges were obtained. For (a) the speaker was far enough upwind that by the time the acoustic wave was above the radar it had also propagated to at least 1.5km, however the lower height coverage was limited. For (b) the speaker was closer to the radar than for (a) (compared with background winds), thus giving lower height coverage. Background winds were stronger thus restricting the range of height which could be measured.