Mixing height estimation from sodar data — A critical discussion☆

A complete description of urban diffusion and dispersion generally requires knowledge of emission sources, an appropriate dispersion model, atmospheric stability, mixing height and dispersion parameters, etc. To determine the air pollution related to meteorological parameters, a remote sensing acoustic sounding system has been found to be a useful tool. This paper describes the techniques developed at the National Physical Laboratory, New Delhi to determine Pasquill stability classification, mixing height and diffusion coefficients from monostatic sodar echograms. On the assumption that the Gaussian plume model holds good, concentrations of particulate matter with distances have been compared with actually observed values of particulate matter concentration to show the validity of approach

Application of sodar to air pollution meteorology

Sodar in air pollution meteorology

Estimating atmospheric stability from monostatic acoustic sounder records

Hazardous situations in air pollution can many a times be avoided in case short term local weather forecasting of the boundary layer meteorology becomes available. Amongst the various remote sensing techniques, it has been seen that acoustic remote sensing (SODAR) of the lower atmosphere can be employed to determine and predict the atmospheric boundary layer meteorological parameters. In specific, information can be obtained about thermal stratification, mixing height, low level disturbances, depth of the planetary boundary layer, stability classification, wind velocity, wind variances, turbulence parameters, and diffusion characteristics etc. when SODAR is used in conjunction with surface level measurements of the usual meteorological parameters. In the paper a brief description of the acoustic remote sensing technique and a review of the work done during the last two decades to determine the various air quality related meteorological parameters has been given. The methodology to determine mixing height, stability classification and diffusion and dispersion characteristics using mostly the information from the SODAR echograms has also been described. The SODAR echograms obtained at Delhi for the period May 1977 to April 1982 have been processed and analyzed using pattern recognition to determine these parameters. Doppler SODAR information of wind speed and direction have not been treated for the above purpose. Using the Gaussian dispersion model, pollution concentration downwind of a emission source (in the present case it is a cement factory at Nimbahera, Chittorgarh, India) has also been computed with the help of SODAR determined data. It has been found that measured values with the help of high volume sampler conform to the estimated pollution concentration. A peak in the value of the estimated pollution concentration during the fumigation period has also been seen.

D. Green

Papers

Convective dispersion modelling utilising acoustic sounder information