Effects of the acoustic and radar pulse length ratio on the accuracy of radio acoustic sounding system (RASS) temperature measurements with monochromatic acoustic pulses

Abstract

This paper is concerned with the accuracy of temperature measurements with radio acoustic sounding system (RASS) consisting of a pulsed Doppler radar and an acoustic source, where the latter excites short monochromatic pulses. Through the use of a numerical model and middle and upper atmosphere (MU) radar experiments, we found that the accuracy is significantly affected by the acoustic and radar pulse length ratio. When the Bragg condition is not strictly satisfied, a numerical model predicted that the mean frequency shift fm of a RASS echo spectrum is detected between the Doppler‐shifted frequency corresponding to the sound speed fs and the transmitted acoustic frequency fa. When the ratio is close to or larger than unity, fm becomes almost identical with fa, while fm approaches fs as the ratio decreases. RASS experiments involving the MU radar operating at 46.5 MHz (6.45‐m wavelength) and an acoustic transmitter with a frequency of about 100 Hz showed that the observed characteristics of RASS echoes for various acoustic pulse lengths agreed quite well with model predictions. Although the numerical model suggested that a small value of the ratio is preferable for accurate measurement of temperature with RASS, the minimum value of the ratio was determined to be about 0.2 by taking into account the system sensitivity of the MU radar, since the RASS echo intensity decreases as the acoustic pulse length becomes shorter. When the lengths of the acoustic and radar pulses were set equal to about 60 m (18 acoustic wave cycles) and 300 m (l μs in pulse duration), respectively, which gives a ratio of the acoustic pulse length to the radar pulse length of approximately 0.2, we were able to obtain temperature profiles at 5 to 9 km every 3 min with an accuracy of about 0.5°C.

A review of Mesosphere–Stratosphere–Troposphere (MST) radar developments and studies, circa 1997–2008

“…Increased maximum altitudes can be achieved by using multiple acoustic sources placed at various points around the radar, or by employing fast and flexible beam-steering. For example, Adachi et al (1993) demonstrated excellent agreement with radiosondes up to an altitude of 10 km when using the MU radar in fast beam-steering mode. Other useful work related to RASS includes publications by Peters et al (1985), May et al (1988May et al ( , 1990May et al ( , 1996, Angevine et al (1994), Tsuda et al (1994), and Yamamoto et al (1996).…”

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

“…This is the first active phased-array 1.3-GHz band wind profiler radar. It also enables observations of atmospheric temperature using the radio acoustic sounding system (RASS) technique with speaker horns (e.g., Adachi et al 1993;May et al 1996). The same radar system is adopted in the wind profiler network, the Wind Profiler Data Acquisition System (WINDAS), of the Japan Meteorological Agency (JMA) (Ishihara and Goda 2000;Kato et al 2004).…”

“…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.…”

Temperature retrieval with VHF radar using combined techniques

“…The Radio Acoustic Sounding System (RASS) capabilities to measure virtual temperature profiles using a wind profiler have already been widely attested (Adachi et al, 1993;Angevine et al, 1994;May et al, 1989;Peters, 2000;Klaus et al 1998). This technology, involving acoustic transmission in the atmosphere combined with an UHF or a VHF radar, is potentially one of the most promising tools for an automated continuous temperature profiling due to its accuCorrespondence to: V. Klaus (vladislav.klaus@meteo.fr) racy and efficiency in all weather conditions.…”