Influence of wind and temperature on the height limit of a radio acoustic sounding system

Abstract

Influences of the atmospheric wind and temperature profiles upon the maximum height in temperature measurement by using a radio acoustic sounding system (RASS) were studied. The RASS uses radar to receive echoes (RASS echoes) backscattered from periodic perturbations in the atmospheric refractive index produced by an incident acoustic pulse and to measure the atmospheric temperature from the local speed of sound which is derived from the Doppler frequency shift of the RASS echo signal. One of the important conditions for the RASS echo to be efficiently backscattered (for monostatic radar) is that the radar beam is incident normal to the wave surface of the perturbations in the refractive index, i.e., to the acoustic wave front. This paper gives the results from numerical calculations to simulate the portion of the acoustic wave front where the above condition is satisfied, under a fixed configuration of the radar and acoustic antennas, and under changing shapes of the propagating acoustic pulse wave front influenced by height‐varying background atmospheric wind and temperature. Comparisons between the calculations and RASS experiments were made by using the middle and upper atmosphere (MU) radar with steerable beam under different atmospheric conditions. The numerical estimations of the height range for effective reception of RASS echo agree quite well with actual RASS observations carried out by using the MU radar. RASS echoes were obtained at altitudes up to 8.4 km under strong wind conditions in January 1988 and up to 22 km under calm wind conditions in July 1986.

Retrieval of temperature profiles using radio acoustic sounding system (RASS) with the equatorial atmosphere radar (EAR) in West Sumatra, Indonesia

“…However, RASS with a 50-MHz WPR, such as the MU radar in Japan (Matuura et al 1986;Tsuda et al 1989Tsuda et al , 1994Adachi et al 1993) and the Gadanki MST radar in India (Sarma et al 2008(Sarma et al , 2010, used the sound at about 100 Hz, which made it possible to measure atmospheric temperatures up to about 23 km, exceeding the tropopause. Furthermore, the height coverage of RASS was significantly determined by the effects of the background wind velocity on the propagation of acoustic waves (Masuda 1988).…”

A Lower Troposphere Radar: 1.3-GHz Active Phased-Array Type Wind Profiler with RASS

“…Masuda (1988) employed ray-tracing in order to analyze the propagation characteristics of acoustic wavefronts, and showed that the normal condition depends largely on profiles of background temperature and horizontal wind velocity, as well as distance between radar and acoustic sources. In the case of LTR/ RASS observations, the LTR cannot always steer the beam in the windward direction, while the MU radar can.…”

“…If the wind flows from the direction to which the LTR cannot steer the beam, it is expected that the height coverage is severely reduced. Based on the discussions using ray-tracing of acoustic wavefronts for various wind conditions (Masuda 1988), we decided on the speaker positions as shown in Fig. 11.…”

“…Since we required the acoustic signal to include frequency components satisfying the Bragg condition in the measurement height range, we decided to sweep the frequency within the pulse length (e.g., Adachi et al 1993;Masuda et al 1992). It is expected that the maximum and minimum temperatures observed with LTR/RASS in Japan are about 30 C (which is the temperature near the ground in summer) and about À20 C (which is the temperature at the top of the ABL in winter), respectively.…”

Estimation of Humidity Profiles by Combining Co-Located VHF and UHF Wind-Profiling Radar Observation

“…For turbulence echo observations by the MU radar and LTR, the vertical beam and four oblique beams steered to north, south, east, and west direction were employed. The turbulence echo parameters for the MU radar and LTR were estimated every 162 seconds and 86 seconds, respectively, with a height resolution of 150 m. The beam directions for MU radar-RASS observations were determined from real-time ray-tracing of acoustic wave-fronts (Masuda 1988).…”