Radio Acoustic Sounding System Research Articles

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.

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.

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.

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

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.

Description of atmospheric variables measured with a RASS sodar: Cycles and distribution functions

A vertical description of low atmosphere is essential for air pollution analysis, structural design or wind resource assessment. Measurements of horizontal and vertical wind speed and virtual temperature obtained from a Radio Acoustic Sounding System (RASS) sodar below 200 m during 2 years have been considered in this paper with two objectives: the analysis of their yearly and daily cycles and the description of suitable expressions for their distribution functions in the height domain measured. Two prevailing directions have been observed and delimited, East North East (ENE) and West South West (WSW). The first has a yearly evolution and both show a daily cycle in the low atmosphere, where ENE prevails during the night and WSW during the day, resulting in a weak clockwise rotation of median wind vector. Distribution functions for the three variables measured have been proposed using the Chi-square and root mean square errors as goodness of fit estimators. For horizontal wind, the Weibull distribution has been considered during the day and an addition of Weibull and Gaussian distributions during the night. In this period the Weibull distribution has been fitted for the non-prevailing directions. Both functions have been parameterised in height. Two exponential functions have been proposed for vertical wind and triangular functions for virtual temperature.

The Variational Assimilation Method for the Retrieval of Humidity Profiles with the Wind-Profiling Radar

Abstract Recently, a humidity estimation technique was developed by using the turbulence echo characteristics detected with a wind-profiling radar. This study is concerned with improvement of the retrieval algorithm for delineating a humidity profile from the refractive index gradient (M) inferred from the echo power. To achieve a more precise estimate of humidity, a one-dimensional variational method is adopted. Because the radar data provide only the absolute value of M, its sign must be determined in the retrieval. A statistical probability for the sign of M [Pr(z)] is introduced to the cost function of the variational method to determine the optimum result with reduced calculation cost. GPS-derived integrated water vapor (IWV) was assimilated together with the radar-derived |M| for constraining the signs of |M| to agree with the radar-derived IWV and the GPS-derived IWV. Humidity profiles were retrieved from the Middle and Upper Atmosphere (MU) radar–Radio Acoustic Sounding System (RASS) data for July–August 1999 using the first guess calculated from the time interpolation of radiosonde results. The |M| profiles from the MU radar–RASS were assimilated at 21 height layers between 1.5 and 7.5 km. A genetic algorithm is employed to find the global optimum. The humidity profiles are retrieved with the same vertical resolution as that of the observation values. The precision of the retrieval result using the new method is superior to that of the conventional method. The difference between the analysis and simultaneous radiosonde results was related to a large error in the first guess. The sensitivity of the analysis result to the shape of the Pr(z) profile was investigated, and the result appears to be insensitive to the profile of Pr(z). The improvement over the conventional method is especially evident for the case of a large error in the first guess.

Effects of Atmospheric Stability on Wave and Energy Propagation in the Troposphere

Abstract The very high frequency (VHF) middle and upper atmosphere radar radio acoustic sounding system (MU-RASS) in Shigaraki, Japan, is able to provide tropospheric virtual temperature data with high temporal resolution on the order of a few minutes. The objective of this paper is to test the usefulness of MU-RASS as a tool for examining high-frequency changes in atmospheric stability and its effects on wave and energy propagation. For this study, temperature and wind data below 8-km altitude during a 2-day campaign period in October 2001 were used. A long-lasting inversion layer at 3.5-km altitude dominated the observation period. Large vertical wind perturbations with periods of less than 30 min were observed inside this inversion layer. Wavelet analysis was used to identify the dominant wave period for calculating the wind and temperature variances. The temperature variance characteristics exhibited a combination of the horizontal and vertical wind variance characteristics. In conclusion, the high temporal resolution of the MU-RASS enabled the study of short time-scale wind and temperature perturbations. These perturbations were related to the atmospheric stability, wave propagation, and energy in the troposphere, demonstrating the usefulness of the MU-RASS for this kind of study.

Boundary layer effects above a Himalayan valley near Mount Everest

Periodical Wind Profiler and Radio Acoustic Sounding System observations have been commenced at the Himalayas' northern slope nearby Mount Everest in September 2005. Primarily data sets obtained 25 km remote from the glacier edge are utilized for a preliminary discussion of planetary boundary layer circulation resembling high alpine mountainous regions. Substantial findings include the detection of two wind shears and the phenomenon of glacier wind at a distance of 25 km from the glaciers. The latter lead to a reversed compensatory flow in a vertical scale of up to 2000 m above ground level, pointing at supra regional impact.