  We construct a model for the angular power spectrum of the instrumental noise
in interferometer networks mapping gravitational wave backgrounds (GWBs) as a
function of detector noise properties, network configuration and scan strategy.
We use the model to calculate the noise power spectrum for current and future
ground-based experiments, as well as for planned space missions. We present our
results in a language similar to that used in cosmic microwave background and
intensity mapping experiments, and connect the formalism with the sensitivity
curves that are common lore in GWB analyses. Our formalism is implemented in a
lightweight python module that we make publicly available at
https://github.com/damonge/schNell.
