Should I model my berm as a wedge or with a flat top?
In all versions of TNM, it is recommended that TNM users only use wedge berms (a default berm top-width of 0.0), because TNM had shown some apparent anomalies in the diffraction algorithms for berms with a top width (flat top berms). These anomalies may also surface for other TNM geometries that produce terrain shapes similar to flat top berms (i.e. rising slope, leveling off, and then recessing slope). This problem does not manifest itself for geometries that come to a peak, and in many instances, flat top berm geometries can be effectively modeled with wedge berms. If modeling flat-top-berm-like geometries with terrain lines, it has been found that by rounding-off any sharp corner geometries in TNM with 2 terrain lines per corner instead of just 1, the anomalies in the diffraction algorithms associated with flattop-berm-like geometries can be minimized and even eliminated. This has been shown to improve results as long as the slope of the “rounded” corner is not too shallow (similar
