Yoshihisa Masuda

Observations of Tropospheric Temperature Fluctuations with the MU Radar-RASS

Abstract Applying the RASS (radio acoustic sounding system) technique to the MU (middle and upper atmosphere) radar, profiles of both temperature and wind velocity were observed every 90 s in the height range of about 1.5–7.0 km, with a height resolution of 300 m, for about 40 h on 6–8 August 1990. The temperature profiles obtained with RASS agreed well with the virtual temperature derived from radiosonde sounding, where the mean difference between the temperature values was approximately 0.3°C. The observed frequency spectra above about 2.5-km altitude, having an asymptotic slope of −5/3 and approximately 0 for temperature and vertical wind velocity fluctuations, respectively, were reasonably consistent with a model spectrum of gravity waves. But, below 2.5 km, low-frequency components were conspicuously enhanced, especially for vertical wind velocity, presumably affected by convection. Wavelike temperature fluctuations with a dominant period of 6–8 h clearly showed downward phase progression and a π/2 p...

Analysis of acoustic wave fronts in the atmosphere to profile the temperature and wind with a radio acoustic sounding system

Differential equations were introduced to analyze the acoustic wave fronts in the atmosphere. The wave fronts were found to make an ellipsoid whose major principal axis tilts at an angle of about 45° to the leeward. Utilizing this result, a radio acoustic sounding system (RASS) was used to measure the temperature and wind profiles to heights of over 23 km even under strong wind conditions. The profiles agree with those obtained from a radiosonde and a Doppler radar. The discrepancies are only about 0.5 °C in the air temperature and 1 m/s in the wind speed. The experiments show that the analytical result of the acoustic wave fronts is effective not only in the troposphere but also in the stratosphere. The analysis also shows quantitatively that acoustic waves propagate over the horizon to leeward.

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

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.

Analysis of the radio acoustic sounding system using a chirped acoustic wave

We investigated radio acoustic sounding system (RASS) echoes backscattered from refractive index fluctuations produced by an acoustic pulse linearly modulated in frequency (a chirped acoustic pulse). We have numerically simulated errors of the Doppler frequency shift which are caused by the fact that the widths of the acoustic and radar pulse are finite. We analytically showed that a RASS with a chirped acoustic pulse can correctly measure a wide range of Doppler shifts. The error of the Doppler shift measurement is found to be a function of the radar range resolution, the rate at which acoustic frequency is swept, and the width of the acoustic pulse. The error is also shown to be almost independent of the radar frequency and the lapse rates of the atmospheric temperatures. We have also numerically showed that when the chirped acoustic wave frequency is 50 Hz/s, errors are within 0.018°C when the radar frequency is 1357.5 MHz and the range resolution is 75 m. At the chirped wave frequency, errors are within 0.055°C for a 46.5-MHz radar with a 150-m range resolution. We also propose a method for designing a chirped acoustic pulse to measure atmospheric temperature.

A real multi-parent tri-hybrid evolutionary optimization method and its application in wind velocity estimation from wind profiler data

Abstract A real-coded multi-parent tri-hybrid evolutionary algorithm (EA) for problem optimization is presented. The hybrid EA algorithm combines the features of Simplex, stochastic relaxation (SR) and multi-parent EA reproduction in a model that encourages competition among the best individual solutions from various operations. Its strength has been evaluated using standard test functions and shown to do better than other methods. The algorithm’s ability to handle noise is evident when applied to experiments involving resolution of overlapping wind profiler (WP) data. Results obtained using raw data closely matched those obtained with data preprocessed by a low-pass FFT filter. Resolution of low-speed wind and clutter signals in various degrees of overlap is made possible, thereby allowing the determination of wind velocity and variance to be executed with ease.