# Lden calculation

For sake of simplification, the Lden calculation in the DEUFRABASE is carried out assuming the same sound velocity gradient for the whole periods (day, evening and night) and whatever the propagation distances.

If the user wants to consider the variations in the meteorological conditions during the day, evening and night periods, **for propagation distances greater than 100 m**, it is possible to carry out a more accurate calculation through the following procedure:

- Perform a first calculation for a given geometry without gradient celerity (for example, the geometry '1c dense surface'), which corresponds to the day and evening periods;
- From the DEUFRABASE results, export the resulting calculation of the LA,eq time distribution to an Excel or CSV file (use the Menu option on the corresponding chart);
- Perform a second calculation for the same geometry with gradient celerity (using the same example, the geometry '1c dense surface with gradient'), which corresponds to the night period;
- Export the resulting calculation of the LA,eq time distribution to an Excel or CSV file;
- In a new spreadsheet, open both files and create a new table using, as the first value series, the data from the first file that corresponds to the day-evening period [6:00-22:00] (for Ld and Le), and, as a second value series, the data from the second file that corresponds to the night period [22:00-6:00] (for Ln);
- Perform the Lden calculation using the following relation:

L_\text{den}=10\log_{10} \left( \frac{12}{24} 10^{0.1\times L_\text{d}} + \frac{4}{24} 10^{0.1\times \left(L_\text{e}+5\right)} + \frac{8}{24} 10^{0.1\times \left(L_\text{n}+10\right)} \right)