Annex D[Clause 4.4.3.2.4 (2) (ii)] CHANGES IN TERRAIN CATEGORIES D-1 Low to High Terrain Category Number

In cases of transition from a low terrain category number (corresponding to a low terrain roughness) to a higher terrain category number (corresponding to a rougher terrain), the velocity profile over the rougher terrain shall be determined as follows:

a) Below height $h_x$, the velocities shall be determined in relation to the rougher terrain; and

b) Above height $h_{\mathrm{x}}$, the velocities shall be determined in relation to the less rough (more distant) terrain.

D-2 High to Low Terrain Category Number

In cases of transition from a more rough to a less rough terrain, the velocity profile shall be determined as follows:

a) Above height $h_{\mathrm{x}}$, the velocities shall be determined in accordance with the rougher (more distant) terrain; and

b) Below height $h_x$, the velocity shall be taken as the lesser of the following:

1. That determined in accordance with the less rough terrain, and

2. The velocity at height $h_{x}$ as determined in relation to the rougher terrain

D-3 More Than One Category

Terrain changes involving more than one category shall be treated in similar way to that described in D-1 and D-2.

NOTE — Examples involving three terrain categories are shown in Fig. 22B.

PROFILE FOR CATEGORY 4

- - - - - - PROFILE FOR CATEGORY 2

22A DETERMINATION OF VELOCITY PROFILE NEAR A CHANGE IN TERRAIN CATEGORY (Less rough to more rough)