AERMOD Tech Guide

Gaussian Plume Air Dispersion Model

8.11 Using Profiles for Interpolating between Observations

When observations are available AERMOD uses the similarity profile functions to interpolate adjacent measurements. Figure 17 illustrates how AERMOD’s INTERFACE uses the expected shape of a meteorological profile to interpolate between observations..103

Figure 17

Figure 17: AERMOD’s construction of a continuous meteorological profiles by interpolating between observations.

For a gridded profile height between two observed profile heights, the observations are interpolated to the gridded height while maintaining the shape of the similarity profile. This is accomplished as follows:

1. The observations are linearly interpolated to the gridded profile height;

2. The similarity function is evaluated at the gridded profile height;

3. The similarity function is evaluated at the observed profile heights immediately above and below the grid height and linearly interpolated to the grid height;.104

4. The ratio of the value obtained in 2 to the value obtained in 3 is applied to the value obtained in 1.

For a gridded profile height above the highest observation, the procedure is modified slightly:

1. the observation at the highest observed profile height is extrapolated by persisting the value upward;

2. The similarity function is evaluated at the grid height;

3. The similarity function is evaluated at the highest height in the observed profile;

4. The ratio of the value obtained in 2 to the value obtained in 3 is applied to the value obtained in 1.

A similar procedure for extrapolating to heights above the observed profile is applied to heights below the lowest observed profile height.