In this work we describe a new modular Multi-Tone Sodar system (PC-MTSodar) able to drive up to four antennas radiating acoustic bursts simultaneously, each at a different frequency, and based on and entirely controlled by a Personal Computer (PC). The system uses two synchronised commercial 1/0 cards and a specifically developed software to handle all system functions. It has capabilities of on-line processing of data, has a minimum of dedicated electronics and is sufficiently versatile to be used as a sodar or a minisodar. A decreasing of maintenance and of spurious electronic problems is expected with the reduction of electronics, especially when the system is used in adverse environment. As a test of the system, working at high frequency in a minisodar configuration, a comparison of measured average vertical wind velocity < W > and of its standard deviation a,, with the results obtained with another minisodar (Remtech PA1) and with two ultrasonic anemometers has been performed. The < W > and a, are parameters useful in pollution dispersion studies and in the analysis of boundary-layer properties. For example, a, can be used for an indirect estimation of turbulent heat and momentum fluxes and mixing-layer depth if the shear production of turbulent kinetic energy may be considered negligible. Our results indicate that the performances of the two sodar systems in measuring vertical wind are different and the results of the PC-MTSodar are in a better agreement with the ones of the ultrasonic anemometers. In particular there is only a fair agreement between measurements of < W > with the PC-MTSodar system and the ultrasonic anemometers. Both instruments however put in evidence the same long-time average pattern with a predominance of negative < W > during diurnal periods. Measurements of or, show an overestimation in nocturnal low turbulence conditions, due to system errors when vertical velocity fluctuations are too low, and a small underestimation of sigma(w), during diurnal convective conditions due to the incomplete coverage of the energy spectrum of turbulence. Our results indicate that there is a high correlation between or,, measurements with the PC-MTSodar and the ultrasonic anemometers (Pearson coefficient 0.97) with a good agreement between the measurements of the two instruments for (7,, greater than 0.2 m/s.
Performances of a modular PC-based Multi-Tone Sodar system in measuring vertical wind velocity
Contini D;F M Grasso;G Mastrantonio;A P Viola;P Martano
2007
Abstract
In this work we describe a new modular Multi-Tone Sodar system (PC-MTSodar) able to drive up to four antennas radiating acoustic bursts simultaneously, each at a different frequency, and based on and entirely controlled by a Personal Computer (PC). The system uses two synchronised commercial 1/0 cards and a specifically developed software to handle all system functions. It has capabilities of on-line processing of data, has a minimum of dedicated electronics and is sufficiently versatile to be used as a sodar or a minisodar. A decreasing of maintenance and of spurious electronic problems is expected with the reduction of electronics, especially when the system is used in adverse environment. As a test of the system, working at high frequency in a minisodar configuration, a comparison of measured average vertical wind velocity < W > and of its standard deviation a,, with the results obtained with another minisodar (Remtech PA1) and with two ultrasonic anemometers has been performed. The < W > and a, are parameters useful in pollution dispersion studies and in the analysis of boundary-layer properties. For example, a, can be used for an indirect estimation of turbulent heat and momentum fluxes and mixing-layer depth if the shear production of turbulent kinetic energy may be considered negligible. Our results indicate that the performances of the two sodar systems in measuring vertical wind are different and the results of the PC-MTSodar are in a better agreement with the ones of the ultrasonic anemometers. In particular there is only a fair agreement between measurements of < W > with the PC-MTSodar system and the ultrasonic anemometers. Both instruments however put in evidence the same long-time average pattern with a predominance of negative < W > during diurnal periods. Measurements of or, show an overestimation in nocturnal low turbulence conditions, due to system errors when vertical velocity fluctuations are too low, and a small underestimation of sigma(w), during diurnal convective conditions due to the incomplete coverage of the energy spectrum of turbulence. Our results indicate that there is a high correlation between or,, measurements with the PC-MTSodar and the ultrasonic anemometers (Pearson coefficient 0.97) with a good agreement between the measurements of the two instruments for (7,, greater than 0.2 m/s.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
