Experience in modeling applications using on-site tower and sodar data

ENSR Corporation has installed and operated meteorological data acquisition systems at several sites during the 1990s. The sites have been designed to provide profiles of meteorological data for use with CTDMPLUS, AERMOD, and/or CALPUFF.

This paper provides recommendations for merging the tower and sodar data for use in models that can accommodate meteorological profiles, such as CTDMPLUS, AERMOD, and CALPUFF. The use of coincident data at overlapping heights for data validation and quality assurance purposes is discussed. The paper also describes how the use of multiple backup levels can enhance the data capture statistics for on-site data programs when either the tower or sodar experiences a loss of data.

The dispersion models mentioned either require explicit measurements of turbulence (e.g., CTDMPLUS) or can parameterize these values (AERMOD, CALPUFF). The use of tower turbulence measurements at very low wind speeds can cause modeling problems due to an underestimation of the plume dispersion when wind speeds are below instrument thresholds. Sodar measurements are not as sensitive to low wind speed problems, but sigma-theta measurements from sodars are susceptible to errors for some applications due to contamination from side lobe echoes. These issues are discussed in this paper, since the use of measured turbulence from both tower and sodar data will be an important aspect of the models being proposed by EPA.