Radio Acoustic Sounding Research Articles

Characteristics of atmospheric waves in the upper troposphere observed with the Gadanki MST Radar—RASS

Indian MST Radar at Gadanki (13.46ºN, 79.17ºE) working at 53 MHz was operated continuously in Radio Acoustic Sounding System (RASS) mode with six distributed acoustic exciters during 22–25 August 2007 for about 69 h in RASS and turbulence echo modes alternately, with one cycle spanning about 20 min. Temperature and wind velocity were observed in the altitude range 3.6–12 km most of the time and 3.6–20 km, respectively, with a range resolution of 150 m. Presence of an inertia–gravity wave in the lower stratosphere was identified. Perturbations in the wind and temperature fields in the troposphere, however, indicated a mixture of waves with a wide frequency range, within which a dominant periodicity of ∼8 h with a vertical wavelength of ∼4 km was revealed by two-dimensional spectral analysis. Further, signatures of diurnal tide were also observed and the temperature phase profile was found to exhibit a close match with the Global Scale Wave Model (GSWM02). From the RASS virtual temperature profiles, time–height section of Brunt-Väisälä frequency squared was computed to deduce the background atmospheric stability, which showed stable layered structures with slow downward phase progression. Outgoing Longwave Radiation (OLR) over Gadanki and TRMM precipitation data over peninsular India was used as an indicator of convective activity. During the beginning of the observation period, even though lower OLR was seen, corresponding convective activity or precipitation was not seen in the TRMM data. On 24 August, enhanced temperature perturbations could be related to widespread precipitation shown by TRMM.

Meso-γ-scale convective systems observed by a 443-MHz wind-profiling radar with RASS in the Okinawa subtropical region

We observed a meso-γ-scale convective system in July 2007 using a 443-MHz wind profiler radar (WPR) with a radio acoustic sounding system (RASS) at the NICT Ogimi observatory in Okinawa, Japan. We analyzed the virtual temperature, T v, the Brunt–Vaisala frequency squared, N 2, and three components of wind velocity profiles from the WPR-RASS data. We also employed a non-hydrostatic meso-scale (NHM) numerical model. Although the island of Okinawa was covered with a Pacific high-pressure system from 21–26 July, the atmospheric condition was convectively unstable below about 5 km. A number of convective clouds generally appeared from 11:00–18:00 in local time (i.e., Japan Standard Time; JST) with a typical horizontal scale of 10 km and temporal scale of 40–60 min. We focused on the convective system that passed over the Ogimi radar site on 23rd and 25th July. Just before rain occurred on these days, a low N 2 region extended upward to 2.0 km, and this characteristics is also commonly seen around a convective cloud in the NHM model. The cloud water content from the NHM model indicated that the cloud top height correlates with the low N 2 structure. Before the convective system was generated, N 2 decreased below an altitude of about 1 km, because air with low T v intruded at 1–3 km, and the surface temperature increased due to solar radiation. The sea-breeze from both the east and west coasts of Okinawa collided to force the convergence below 1 km. Thus, the synergetic effects of the low static stability and convergence seemed to trigger the generation of a convective system, which eventually grew to 11 km over the radar site.

Comparison of Boundary-Layer Profiles and Layer Detection by AMDAR and WTR/RASS at Frankfurt Airport

At Frankfurt airport (EDDF) vertical soundings of the lower atmosphere from two independent sources are available. One of them is a wind and temperature profiler (wind temperature radar and radio acoustic sounding system, WTR/RASS) located at the western end of the main pair of runways. The second source is aircraft meteorological data relay (AMDAR), i.e. measurements operationally collected by approaching and departing aircraft. Together, both offer a rare opportunity to compare the performance of these widely used systems. We use 1 year of continuous data to calculate systematic temperature and wind vector differences between both measurement systems. The differences show a clear season-dependent structure in conjunction with typical inversion heights. Possible causes for this behaviour are discussed. Second, we compare the ability of both systems to identify inversion and wind-shear layers above the airport. AMDAR-detected layers are typically higher than wind profiler detections. The layer base is usually detected with more agreement than the top. The mutual probability of detection of inversions is found to be mostly between 40 and 60%.

Status of Development of Radio Acoustic Sounding System (RASS)

Status of Development of Radio Acoustic Sounding System (RASS)

Development and Research on Radio Acoustic Sounding System (RASS)

Development and Research on Radio Acoustic Sounding System (RASS)

Atmospheric Temperature Profiling with a Radio Acoustic Sounding System (RASS)

Atmospheric Temperature Profiling with a Radio Acoustic Sounding System (RASS)

Observation of the structure of the urban boundary layer with different ceilometers and validation by RASS data

U rban air quality assessment requires the knowledge of the temporal and spatial structure of the mixing layer, because this structure controls the vertical dilution of near-surface pollutants. The behaviour of the mixing layer is a consequence of vertical temperature and moisture profiles in the lower atmosphere so that remote sensing can be a suitable tool to monitor it. Three ceilometers, a Vaisala LD40 and two Vaisala CL31, have been operated for many months in the German city of Augsburg in order to observe the vertical aerosol distribution. Wind and temperature profile information have been obtained for a part of the period from radioacoustic sounding system (RASS) observations. This paper investigates the abilities of the instruments and compares the information received by the ceilometers among each other and with temperature profiles from the RASS data. Zusammenfassung

Early Forest Fire Detection Using Radio-Acoustic Sounding System

Automated early fire detection systems have recently received a significant amount of attention due to their importance in protecting the global environment. Some emergent technologies such as ground-based, satellite-based remote sensing and distributed sensor networks systems have been used to detect forest fires in the early stages. In this study, a radio-acoustic sounding system with fine space and time resolution capabilities for continuous monitoring and early detection of forest fires is proposed. Simulations show that remote thermal mapping of a particular forest region by the proposed system could be a potential solution to the problem of early detection of forest fires.

Daily and annual cycle of CO2 concentration near the surface depending on boundary layer structure at a rural site in Spain

CO2 in the rural atmosphere is related to respiration–photosynthesis processes, although the evolution of the low atmosphere is also a determinant factor. CO2 concentrations were measured at surface and meteorological variables obtained from a radio acoustic sounding system sodar at a flat rural site during a 3-year campaign. Yearly and daily cycles of CO2 were described. Maxima were observed in spring and autumn during the night. Wind speed and thermal structure of the lower atmosphere were analysed. Low level jets were observed during the night, their core proving lower in summer. Surface inversions observed with low winds reached up to 100 m. The turbulence layer which developed during the day extended up to 300–400 m and was capped by a stable layer. Median vertical wind speed reached 1 m s−1 in super-adiabatic conditions in summer. Determination of decoupled low level jets proved difficult with the device used and corresponding concentrations were slightly higher than medians calculated with all the observations. The bulk Richardson number was calculated in the lower atmosphere and four intervals were considered: drainage, transitional, shear flows and unstable conditions. Median CO2 concentrations were split according to these intervals. Higher values corresponded to drainage flow, which was associated to more stable conditions being less frequent and lower values to shear flow and unstable conditions, revealing a satisfactory link between the bulk Richardson number as a turbulence indicator in the low atmosphere and CO2 surface concentrations.

Radio-acoustic sounding of the ionosphere

We present the results of first experiments on radio-acoustic sounding of ionosphere at the altitudes from 70 to 85 km. The sounding was performed in autumn 2006, using a horn acoustic emitter and a radar on the basis of the “Sura” facility. The emitter had an acoustic power of about 1 kW and operated in the chirp-modulation regime with frequency variation from 15.9 to 18.4 Hz. The radar transmitter operated in the pulse regime at a frequency of 9 MHz and had an average power of 30 kW. The power of the radio signal scattered from a sound wave in the ionosphere did not exceed 10−16 W, and the measured values of the temperature in the scattering region ranged from 190 to 225 K.

Boundary layer structure and stability classification validated with CO<sub>2</sub> concentrations over the Northern Spanish Plateau

Abstract. A description of the lower boundary layer is vital to enhance our understanding of dispersion processes. In this paper, Radio Acoustic Sounding System sodar measurements obtained over three years were used to calculate the Brunt-Väisälä frequency and the Monin-Obukhov length. The Brunt-Väisälä frequency enabled investigation of the structure of this layer. At night, several layers were noticeable and the maximum was observed at the first level, 40 m, whereas during the day, it was present at about 320 m. The Monin-Obukhov length was calculated with the four first levels measured, 40–100 m, by an original iterative method and used to establish four stability classes: drainage, extremely stable, stable and unstable. Wind speed and temperature median profiles linked to these classes were also presented. Wind speeds were the lowest, but temperatures were the highest and inversions were intense at night in drainage situations. However, unstable situations were linked to high wind speeds and superadiabatic temperature profiles. Detrended CO2 concentrations were used to determine the goodness of the classification proposed evidencing values which under drainage at night in spring were nearly 28 ppm higher than those corresponding to unstable situations. Finally, atmosphere structure was presented for the proposed stability classes and related with wind speed profiles. Under extremely stable situations, low level jets were coupled to the surface, with median wind speeds below 8 m s−1 and cores occasionally at 120 m. However, jets were uncoupled in stable situations, wind speed medians were higher than 11 m s−1 and their core heights were around 200 m.

Temperature retrieval with VHF radar using combined techniques

Abstract. The purpose of this study is to evaluate the practical contribution of a VHF radar to high time resolution automatic temperature profiling both for research and operational applications in the frame of an integrated system of ground-based remote-sensing instruments. Based on the most prominent results already mentioned about this instrumentation, different techniques, related to the temperature data retrieval, are experimentally tested and documented using the INSU/Meteo 45 MHz wind profiler operating at CNRM/Toulouse or during cooperative campaigns. In parallel to the self-sufficient Radio Acoustic Sounding System (RASS), other approaches, using the Brunt-Vaisala frequency measurements, allow an extension of height coverage up to the higher troposphere and the tropopause. As only temperature gradients can be measured by this way, complementary data from other instruments are desirable. This makes it particularly fitted to an integrated remote-sensing system operating from the ground combining wind profilers with GPS, radiometers, lidar ceilometers and sodars.

Development of radio acoustic sounding system (RASS) with Gadanki MST radar – first results

Abstract. A high-power acoustic exciter was designed and developed for the Gadanki MST Radar to facilitate observations in the Radio Acoustic Sounding System (RASS) mode. Sweep range of acoustic signal frequencies was set to 94–125 Hz so as to satisfy Bragg matching condition for temperature range of −90°–40°C between surface and the tropopause (about 17 km). Raytracing of acoustic wave propagation was used to predict the antenna beam directions along which optimum RASS echoes could be obtained. During the RASS observation period of about 18 h on 23–24 July 2006 height profiles of atmospheric virtual temperature were obtained between 1.5 km and 10 km and occasionally up to 14 km. In comparison with the three simultaneous radiosonde launches, RASS derived temperature profiles had the r.m.s. discrepancy of about 1 K, although deviation of the RASS results sometimes appeared when the radial wind velocity was not fully available for the correction of apparent sound speed. This study has successfully demonstrated capability of the RASS application with the Gadanki MST radar, which will be used for continuous monitoring of the temperature profiles in the troposphere and lower stratosphere region in the tropics.

Direct observation of the break‐up of a nocturnal inversion layer using elemental mercury as a tracer

Concentrations of atmospheric mercury observed during July and August of 2005 in Riverside, CA and during August of 2006 at sites throughout the Los Angeles Basin indicate that a diurnal pattern of elemental mercury frequently exists within the basin during summer months. During these diurnal cycles, elemental mercury is observed to abruptly spike well above global background levels during the morning hours. These peak events were observed to be coincident across several monitoring sites throughout the Basin suggesting that mercury spikes were not a result of source plumes unique to each site but rather the impact of a basin‐wide phenomenon. Atmospheric temperature profiles measured by a Radio Acoustic Sounding System (RASS) located in Moreno Valley, CA indicate that peak events coincided with the shift in surface temperature profile from stable to neutral indicating the presence of fumigation episodes, the occurrence of which is supported by a generic model of basin dispersion. The presence of mercury in the stable layer aloft is a function of point sources within the basin, and in particular a single, elevated point source located in the Port of Long Beach. The unique dynamics of atmospheric mercury observed throughout the Los Angeles Basin combined with the location of this major point source upwind of the Basin provide a novel method of directly observing atmospheric mixing associated with the break‐up of the nocturnal inversion layer.

High-Resolution Radio Acoustic Sounding System Observations and Analysis up to 20 km

Abstract The first campaign-based measurements of virtual temperature in the upper-troposphere and lower-stratosphere (UTLS) region were made with the middle- and upper-atmosphere (MU) radar radio acoustic sounding system (RASS) during 4 days in August 1995. This dataset was examined in order to study high-frequency changes in the stability below 20 km, but especially in the UTLS region. Calculations of the WMO tropopause and cold-point tropopause heights showed the latter to be (1.0 ± 0.6) km higher, where 0.6 km is the standard deviation. A diurnal cycle of temperature and wind dominated the spectra, which was identified as the diurnal solar tide. Its phase maximum occurred in the afternoon between 5 and 15 km and showed upward energy propagation above this height. Changes in the UTLS kinetic energy dissipation rate ε showed significant high-frequency fluctuations embedded within layers that persisted for at least 1 day. Relative to the WMO tropopause height, the median ε increased from (0.5 ± 0.1) × 10−3 m2 s−3 in the upper troposphere to (0.7 ± 0.1) × 10−3 m2 s−3 in the lower stratosphere.

Development of radio acoustic sounding method in Kharkov National University of Radio Electronics

The analysis of the role of Kharkov National University of Radio Electronics in developing the atmosphere radio acoustic sounding (RAS) method within the period from 1968 to 2008 was carried out. As a part of the investigation program six experimental models of the sounding radio equipment were developed and manufactured. The atmosphere sounding methods were developed for measuring the base meteorological values. For the first time in the world practice, relevant comparative measurements of air temperature, wind velocity and direction were performed on a short base (about 150 m) using the centimetre RAS equipment and standard sensors of a high (300 m) meteorological mast. The RAS equipment was used for the purpose of meteorological support to investigations in the field of the atmosphere physics and applied problems. All instrumental, atmosphere and social factors, affecting operation the RAS systems, were generalized. It is shown that compact and mobile systems for remote monitoring of the atmospheric boundary layer with possible prompt obtaining of relevant information about base meteorological values in large volumes can be based on the RAS equipment.

Development of radio acoustic sounding method in Kharkov National University of Radio Electronics

The analysis of the role of Kharkov National University of Radio Electronics in developing the atmosphere radio acoustic sounding (RAS) method within the period from 1968 to 2008 was carried out. As a part of the investigation program six experimental models of the sounding radio equipment were developed and manufactured. The atmosphere sounding methods were developed for measuring the base meteorological values. For the first time in the world practice, relevant comparative measurements of air temperature, wind velocity and direction were performed on a short base (about 150 m) using the centimetre RAS equipment and standard sensors of a high (300 m) meteorological mast. The RAS equipment was used for the purpose of meteorological support to investigations in the field of the atmosphere physics and applied problems. All instrumental, atmosphere and social factors, affecting operation the RAS systems, were generalized. It is shown that compact and mobile systems for remote monitoring of the atmospheric boundary layer with possible prompt obtaining of relevant information about base meteorological values in large volumes can be based on the RAS equipment.

Analysis of current status of theory and practice of radio-acoustic sounding systems

Analysis of current status of theory and practice of radio-acoustic sounding systems

Analysis of current status of theory and practice of radio-acoustic sounding systems

The analysis of a current status of theory and practice of radio-acoustic sounding systems (RASS), which have been under development since 1961 for remote sensing the profiles of vertical air temperature and humidity and wind velocity and direction, is made. A traditional construction scheme of the RASS, as implemented in practically all known systems, is singled out. Methods used for radio-acoustic atmosphere sounding for the purpose of collecting relevant meteorological information are examined. It's pointed out that all problems of system, technical nature, arising in the course of development of the RASS, were resolved before 2000 by engineering, experimental way. Later on creation of the RASS theory started, and problems of synthesis and optimization of systems, devices, signals were formulated. In this connection an adequate constructive model of a radio-acoustic location channel and synthesized signal processing algorithms are under examination. For determining the form of base oscillations of a multi-channel processing unit the scattering function should be used.

Temperature profiles by ground-based remote sensing and in situ measurements

This study focuses on the accuracy of the temperature profiles measured with a Doppler Radio-Acoustic Sounding System and a Microwave Temperature Profiler during a period of about 3 months in winter 2007-2008. The experiment was carried on at the experimental facility of the Institute of Atmospheric Sciences and Climate (ISAC) of the Italian National Research Council (CNR). The temperature data measured with remote sensors were verified with in situ measurements on a mast as well as with tethered balloon data. The facsimile echograms obtained with the ISAC Doppler SODAR were analysed to understand to which extent the RASS and Radiometer temperature profiles behaviour can represent the real thermal structure of the atmosphere.