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2.3.3 High-resolution temperature measurement
Radio acoustic sounding system (RASS) is a radar remote sensing system for measuring profiles
of temperature 1 with high time and height resolutions (e.g., May et al., 1990; Tsuda et al., 1989).
RASS is also able to be used for monitoring humidity profiles (e.g., Furumoto et al., 2005; Tsuda
et al., 2001). Using the MU radar, Furumoto et al. (2011) applied RIM to RASS measurement
(RIM-RASS) in order to demonstrate that range resolution of temperature is improved down to
approximately 60 m compared with the nominal range gate width of 150 m determined by the
transmitted pulse width. Furumoto et al. (2011) pointed out that (1) sample time difference at an
arbitrary range among data on different operational frequencies and (2) the Doppler shift bias
due to the shape of range-gate weighting have to be corrected for RIM-RASS measurement, and
developed an iteration algorithm that corrects (1) and (2). By applying CRI to temperature
profiles measured by TEP with RASS, Dekker & Frasier (2004) retrieved virtual temperature
structure function from horizontal distribution of temperature. The study by Dekker & Frasier
(2004) indicates a usefulness of CRI to quantify turbulence intensity in the atmosphere.
Fig. 7. Time-altitude plot of (a) equivalent radar reflectivity factor, (b) reflectivity-weighted
particle fall velocity relative to the ground, (c) reflectivity-weighted particle fall velocity
relative to the air, and (d) vertical wind velocity (Yamamoto et al., 2008). Equivalent radar
reflectivity factor and reflectivity-weighted particle fall velocity relative to the ground were
measured by a millimeter-wave radar. Vertical wind velocity was measured by the EAR.
Horie et al. (2000) describe details of the millimeter-wave radar.
1 To be exact, RASS measures a virtual temperature expressed by T v= T (1+0.61 q ), where T v , T , and q are
virtual temperature in K, tempeature in K, and water vapor mixing ratio in kg kg-1, respectively.
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