Radio Acoustic Sounding Research Articles

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.

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

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.

Radio acoustic sounding of the atmosphere using a FM CW radar

The use of a FM CW radar for the measurement of atmospheric sound velocity profiles is investigated. In contrast to particulate scatterers or clear air turbulence the sound waves represent a coherent scattering structure, and the consequences are examined. We derive the theoretical shape of the signal spectrum and present examples of velocity profiles of vertically propagating sound waves. As the sound and clear air echoes are separable by frequency, simultaneous measurements of atmospheric wind and temperature profiles should be feasible. Because of the excellent spatial and temporal resolution of the FM CW technique, these measurements perhaps offer a possibility of future remote heat flux measurements.

Results on planetary boundary layer sounding by automatic rass

A radio acoustic sounding system (RASS), operating at an acoustic frequency ƒ ∼ 360 Hz, proved to be capable of measuring the vertical temperature profile in the planetary boundary layer (PBL) with an accuracy and vertical resolution comparable to those of traditional apparatus (radiothermosondes borne by tethered or disposable balloons, thermosondes borne by aircraft and so on, yet combined with the advantages typical of remote sensing techniques. Since summer 1983 the system has been running in a completely automatic way by means of a microprocessor and can provide the average thermal profile at preset time intervals (typically 0.5 h). (Previously, the acoustic sounding frequency affording the fundamental condition of Bragg resonance between acoustic and radio wavelengths had to be identified by an operator). The maximum range of measurement has been ∼ 1000 m in 50% of cases. Temperature measurements are reliable from an altitude of a few tens of meters. Results for different thermodynamic stability conditions, together with good performances achieved in adverse atmospheric conditions such as strong wind, snow, rain, etc., are presented here. Such results indicate the usefulness of the automatic RASS as a tool for meteorological purposes and for the application of air pollution control strategies. Maximum sounding range attained for different areas of the acoustic antenna is also analysed in order to evaluate the performance of an automatic mobile RASS.

Radio acoustic measurement of temperature profile in the troposphere and stratosphere

The radio acoustic sounding system (RASS) uses radar to measure the temperature profile in the atmosphere. In the standard technique of atmospheric radar, the radar backscatter results from electrical permittivity variations due to natural phenomena such as turbulence and precipitation. In the RASS technique, the radar backscatter results from periodical permittivity variations due to density/temperature variations imposed on the atmosphere by an acoustic wave artificially generated in such a way that the acoustic wavelength is half the radar (electromagnetic) wavelength. This ‘Bragg condition’ is necessary for efficient backscattering. The backscatter echo of the RASS is affected by the Doppler frequency shift arising both from the speed at which the longitudinal acoustic perturbations propagate (the sound speed), and from the radial bulk velocity in the common volume of the atmosphere—the latter can be measured by the standard technique of turbulence scatter. The observed sound speed is reduced to give the local atmospheric temperature. Here we report an experiment using the RASS, carried out on 1–3 August 1985, which consisted of a high-power, very-high-frequency (VHF) Doppler radar at Shigaraki, Shiga, Japan and a movable high-power acoustic transmitter, and which gave the first experimental proof of the possibility of temperature profiling in the troposphere and stratosphere up to an altitude of ∼20 km.

Measurements of heat flux in the atmospheric boundary layer by sodar and RASS: A first attempt

By combined measurements with two ground‐based remote sensing techniques, sodar and radioacoustic sounding system (RASS), the covariance of vertical wind and temperature perturbations can be determined. The estimation of errors indicates that this method is probably so accurate that profiles of the atmospheric turbulent heat flux can be determined. This is supported by experimental results.

Automatic tuning of Bragg condition in a Radio-Acoustic System for PBL temperature profile measurement

A Radio-Acoustic Sounding System (RASS) with acoustic wavelength λ a ~ 1 m was designed and successfully tested. The system proved to be capable of measuring the vertical temperature profile in the Planetary Boundary Layer (PBL) with an accuracy and vertical resolution comparable to that of traditional apparatus (radiothermosondes borne by tethered or disposable balloons, thermosondes borne by aircraft and so on), yet combined with the advantages typical of remote sensing techniques. Up to the summer of 1983 the system needed attendance by an operator who had to identify the acoustic sounding frequency affording the fundamental condition of Bragg resonance between acoustic and radio wavelengths. Features and performance of the new completely automatic RASS arrangement are presented. These include the possibility of obtaining average thermal vertical profiles at preset time intervals. Maximum range of measurements obtained in about 1000 1 2 -h averages was: in 90% of cases ⩾ 600m; in 50% of cases ⩾ 1100m. Such results indicate the usefulness of automatic RASS as a tool for meteorological purposes and for the application of air pollution control strategies.

A bistatic scheme for radioacoustic sounding of the atmosphere

Abstract The problem of radioacoustic sounding of the atmosphere is considered with diffraction effects taken into account for the bistatic scheme of sounding. Formulae are obtained for the power and frequency of the scattered signal. The influence of wind displacement, sound extinction and the finite dimensions of wave packets upon the scattered signal frequency is proved to be significant and should be taken into account mainly for the calculation of power characteristics

Radio acoustic measurement of fog-capping thermal inversions

The radio acoustic sounding system (RASS) is a remote technique for measuring temperature profiles in the lower troposphere1,2. In essence, it consists of a powerful acoustic source beaming a short burst of sinusoidal waves towards the zenith. The speed of this pulse in its upwards path is proportional at every height to the square root of the local temperature. This speed is continuously measured from the ground by means of a Doppler radar. The radar echo is due to the change in refractive index of air compressed by the acoustic wave. The faint echo is enhanced by choosing an acoustic wave in Bragg resonance with the radio wave. The record of the measured sound speed displayed as a function of delay from the start of the acoustic beam leads to the acquisition of the temperature vertical profile. We now describe the use of such a system at metre-wavelengths in the study of fog-capping thermal inversions at a site in the Po Valley.

Comparison of RASS temperature profiles with other tropospheric soundings

The vertical temperature profile of the lower troposphere can be measured with a radio-acoustic sounding system (RASS). A comparison of the thermal profiles measured with the RASS and with traditional methods showsa) RASS ability to produce vertical thermal profiles at an altitude range of 170 to 1000 m with temperature accuracy and height discrimination comparable with conventional soundings,b) advantages of remote sensing as offered by new sounder,c) applicability of RASS both in assessing evolution of thermodynamic conditions in PBL and in sensing conditions conducive to high concentrations of air pollutants at the ground level.

A Metric Wave Radio-Acoustic Tropospheric Sounder

A metric wavelength version of the radio-acoustic sounding system (RASS) at Trino Vercellese, near Turin, Italy, is presented. Evidence is shown of satisfactory soundings in conditions of calm or light winds.

Interaction of electromagnetic and acoustic waves in a stochastic atmosphere

In the Stanford radio acoustic sounding system (RASS) an electromagnetic signal is made to scatter from a moving acoustic pulse train. Under a Bragg-scatter condition maximum electromagnetic scattering occurs. The scattered radio signal contains temperature and wind information as a function of the acoustic-pulse position. In this investigation RASS performance is assessed in an atmosphere characterized by the presence of turbulence and mean atmospheric parameters. The only assumption made is that the electromagnetic wave is not affected by stochastic perturbations in the atmosphere. It is concluded that the received radio signal depends strongly on the intensity of turbulence for altitudes of the acoustic pulse greater than the coherence length of propagation. The effect of mean vertical wind and mean temperature on the strength of the received signal is also demonstrated to be insignificant. Mean horizontal winds, however, shift the focus of the reflected electromagnetic energy from its origin, resulting in a decrease in received signal level when a monostatic radio-frequency (RF) system is used. For a bistatic radar configuration with space-diversified receiving antennas, the shifting of the acoustic pulse makes possible the remote measurement of the horizontal wind component.

A High-Frequency Radio Acoustic Sounder for Remote Measurement of Atmospheric Winds and Temperature

Abstract The Radio Acoustic Sounding System (RASS) is used to remotely measure atmospheric temperature profiles. The technique used for these measurements is Doppler tracking of a short, high-intensity acoustic pulse with an RF (electro-magnetic) radar. By measurement of the acoustic pulse propagation speed, temperature can be calculated as a function of altitude. The Stanford University RASS operates at an acoustic frequency of 85Hz. Because of this low frequency and the necessity of high system gain, the unit is too large for mobile applications. Our theoretical analyses show, however, that the RASS could operate at much higher acoustic frequencies and still provide data to altitudes of ∼1 km even during periods of moderate to strong atmospheric turbulence. These theoretical analyses have now been supported experimentally. A RASS operating with an acoustic frequency of 1 kHz not only provided Doppler data to altitudes of 1 km, but it also was able to provide a measure of horizontal winds over the same r...

RASS, a Remote Sensing System for Measuring Low-Level Temperature Profiles

Abstract A new technique for remote measurement of temperature in the lower atmosphere has been developed and successfully tested. The equipment used is called a Radio Acoustic Sounding System because a burst of sound propagating upward in the air is tracked by a Doppler radar. Air temperature at each height is determined from the instantaneous speed of the sound pulse and a complete profile can be obtained in only a few seconds. In order to improve accuracy, the measurements are normally averaged for several minutes, but even so the sampling rate is high enough to continuously monitor the temperature profile. Although earlier efforts showed that sound could indeed be tracked by radar, the work described here is the first successful attempt to use the technique to measure temperature profiles.