Figure 7

Link losses for two different orbital scenarios: (a) The lower (black) curve for a passage directly over the OGS and the upper (blue) curve for a ground track that passes at a distance of 500 km from the OGS. The solid curves give the losses for atmospheric turbulence characterized by a Fried parameter \(r _{0}=20~\mbox{cm}\) at 808 nm, whereas the shaded bands correspond to the range of \(15~\mbox{cm} < r _{0} < 25~\mbox{cm}\). (b) The same as (a) for the solid curves, and in addition the corresponding curves for the link budget at 1550 nm (same atmospheric conditions, corresponding to \(r _{0}= 44~\mbox{cm}\) at 1550 nm). The horizontal dashed line indicates the link loss limit of 45 dB for which the experiment duration that QKD would be possible is calculated