Table 2.

Typical values of P_BGL for a 1550 nm wavelength.

Scene	$L_{e,\Omega ,\lambda }$ in W/(m2 nm sr)	A in m2	ω in µrad	Δλ in nm	PBGL in nW
towards horizon	25 × 10−3	0.1	200	40	50
towards horizon	25 × 10−3	0.7	100	40	88
to zenith	1.2 × 10−3	0.1	200	40	2.4
to zenith	1.2 × 10−3	0.7	100	40	4.2

Where 0.1 m² refers approximately to a Cassegrain telescope with a 40 cm aperture diameter and 0.7 m² to a 1 m telescope. A 40 nm-wide filter covers the whole C-Band and thus supports the span of several DWDM channels.