Knife-edge diffraction ($\mathcal{T}(v)=\{[1/2-C(v){]}^2+[1/2-S(v){]}^2\}/2$)

For an opaque half-plane whose edge lies height $h$ above the direct source–receiver ray, the paraxial parameter is $v=h\sqrt{2(d_1+d_2)/(\lambda d_1{d}_2)}$. The unobstructed half-aperture supplies the Cornu spiral chord from $v$ to infinity. Division by the full-aperture chord gives the displayed intensity transmission. It is $1/4$ at grazing incidence, approaches one well into the illuminated region and tends to zero deep in shadow.^[ref]

A diffraction-loss ratio is normalized to the unobstructed intensity at the same receiver position. With a point source that unobstructed intensity changes as inverse source–receiver distance squared. Moving the receiver can therefore decrease the transmission ratio while increasing its absolute received intensity. The two curves require separate normalization; a Cornu-chord plot alone omits geometric spreading.