Characteristic length earth surface

The characteristic length of the earth surface is the ratio of the surface area to the perimeter. For an infinite earth surface $L_{ch} = 0.5$.

Symbol
$L_{char}$
Formulae
 $0.5$ infinite surface $\frac{l w}{2 l + 2 w}$ rectangular surface with length l and width w
Used in
$h_{tr}$