How does TNM handle terrain lines?
Insert terrain lines wherever you wish TNM to know the general height of the terrain between source and receiver. However, please note that small changes in terrain elevations have little effect on the final sound levels. TNM’s ground-smoothing algorithm will automatically “smooth” away minor elevation changes prior to sound level calculations to reduce computation time. TNM has shown some weaknesses in the diffraction algorithms, which would be invoked when computing the effects of terrain lines (This has been corrected in TNM version 2.5). Please refer to the previous terrain line FAQ, “Should I use terrain lines as often as possible?” for guidance on the use of terrain lines.
