Over the last 25 years, ground-based remote profiling has found increasing applications in atmospheric studies where its high vertical and temporal resolution and extended vertical coverage are giving scientists a clearer understanding of atmospheric processes in the troposphere. The authors describe the current status of techniques for vertical profiling of mean wind speeds, temperature, and humidity, and discuss options for combining them. >

Ground-based remote profiling in atmospheric studies: an overview

Sodar has been used for about 20 years to determine mixing height. However, estimation of the height of a convective boundary layer (CBL) that exceeds the sodar-probing range is still an unsolved question. As one possible way, it is suggested that one adapt a simple mixed-layer model to sodar observations during the morning growth period of the CBL, when its top can be clearly detected. Results are compared with other methods for CBL-height estimation from sodar data that have been proposed in the literature. Finally, some prognostic aspects are discussed.

Mixing-height estimation in the convective boundary layer using sodar data

During the week 29 October–4 November 1988, a Ground-based Atmospheric Profiling Experiment (GAPEX) was conducted at Denver Stapleton International Airport. The objective of GAPEX was to acquire and analyze atomspheric-temperature and moisture-profile data from state-of-the-art remote sensors. The sensors included a six-spectral-channel, passive Microwave Profiler (MWP), a passive, infrared High-Resolution Interferometer Sounder (HIS) that provides more than 1500 spectral channels, and an active Radio Acoustic Sounding System (RASS). A Cross-Chain Loran Atmospheric Sounding System (CLASS) was used to provide research-quality in situ thermodynamic observations to verify the accuracy and resolution characteristics of each of the three remote sensors. The first results of the project are presented here to inform the meteorological community of the progress achieved during the GAPEX field phase. These results also serve to demonstrate the excellent prospects for an accurate, continuous thermodynamic ...

GAPEX: A Ground-Based Atmospheric Profiling Experiment.

The degradation of doppler sodar performance due to noise: a review

A simple expression for the expected average signal power of a radio acoustic sounding system (RASS) comprising a monostatic pulsed Doppler radar and a continuous-wave broadbeam acoustic source is developed. The effects of horizontal winds, atmospheric turbulence, and vertical temperature gradients are included. Under ideal conditions (i.e., in the absence of winds, turbulence, and gradients) the received signal power is a maximum and, for a broadband acoustic source, is predicted to be proportional to the radar range resolution and inversely proportional to the acoustic bandwidth and square of the range R. Turbulence-induced distortion of the acoustic wave fronts yields the expected R−26/5 range dependence, provided winds are light. This result is based on the assumption that the turbulence strength does not vary with range. For the more realistic case of turbulence concentrated primarily within the boundary layer (R ≲ 1 km) a much weaker range dependence at longer ranges is predicted. A flattening of the acoustic wave fronts by temperature gradients typical of unstable midday conditions results in an R−6 range dependence, provided winds are light. Turbulence effects are predicted to dominate at shorter ranges (R ≲ 8 km) and gradient effects at longer ranges. The expected compensation of power loss associated with the wind-induced lateral displacement of the acoustic wave fronts by the turbulence- and gradient-induced broadening of the displaced RASS focal spot is also predicted.

Signal power for radio acoustic sounding of temperature: The effects of horizontal winds, turbulence, and vertical temperature gradients

Results on planetary boundary layer sounding by automatic rass

The automatic metric RASS (Radio Acoustic Sounding System), operating at an acoustic wavelength ∼1 m, proved to be able to measure continuously the thermal vertical profiles as far as about 1 km in 50% of soundings with an accuracy generally within a few tenths ofK degrees and with an altitude resolution of (30÷40) m. A set of triennal data of the diurnal evolution of the convective boundary layer (CBL) during Summer, as monitored by a metric RASS operating in the Po Valley (Italy) is presented and discussed. Although atmospheric turbulence, pertinent to the considered unstable conditions, is one of the main factors limiting the radio-acoustic sounding range, by means of the metric RASS it is possible to follow the growth of the mixing layer and to estimate the multilayered structure of the CBL. In addition to the RASS data, the measurements of wind speed, temperature, radiation, humidity and so on, performed by conventional equipments near ground level, are considered.

Evolution of the atmospheric convective boundary layer monitored by the metric RASS

The sounding range of a RASS (Radio Acoustic Sounding System) for remote measurement of the atmospheric thermal profile is determined both by the structural peculiarities of the system (wavelength, size of antennas, acoustic and radar power, etc.) and by the properties of the atmosphere (turbulence, wind, temperature and humidity). In this report we experimentally investigate the effect of antenna size and the number of cycles in the acoustic pulse on the range of a metric RASS (acoustic wavelength ∼1 m). We find good agreement between theory and experiment.

On the Sounding Range of a 1-m Wavelength Radio Acoustic Sounder

A long-lasting and deep-fog episode, occurred in the western region of the Po Valley (Italy) during February 1992, has been studied by means of remote-sensing systems, coupled to more conventional meteorological instruments operating at ground level. The temperature profiles were monitored by a metric RASS and the three components of the wind profiles were measured by a Doppler Sodar. The typical altitude coverage of the metric RASS is 80–1000 m; therefore, it is suitable to measure fog-capping thermal inversions and temperature profiles above the fog layer, so that it makes it possible to follow with continuity the growth, the evolution and the end of the fog episode accompanied by subsidence conditions.

P. Trivero

Papers

Results on planetary boundary layer sounding by automatic rass

Evolution of the atmospheric convective boundary layer monitored by the metric RASS

On the Sounding Range of a 1-m Wavelength Radio Acoustic Sounder

Long-lasting fog episode monitored by radioacoustic systems