and there is excellent spatial resolution along the line-of-sight (since high spectral resolution is relatively easy to achieve), but poor angular resolution. In addition to addressing these geometric peculiarities, we also show how interferometric data can be analyzed with spherical Fourier-Bessel methods. Importantly, we find that the foregrounds again appear as a wedge in interferometric measurements of $S_\ell (k)$, which suggests that the $\ell$-$k$ plane is at least as powerful a diagnostic tool as the $k_\perp$-$k_\parallel$ plane, particularly given the signal-to-noise advantages discussed above.[^5]

The rest of this paper is organized as follows. In Section \[sec:Notation\] we establish notational conventions for this paper. Section \[sec:SphericalPspecFormalism\] introduces spherical Fourier-Bessel methods for power spectrum estimation, with the complication of finite surveys (in both the angular and spectral directions) the subject of Section \[sec:FiniteVolume\]. In Section \[sec:Foregrounds\] we compute the signature of smooth spectrum foregrounds on the $\ell$-$k$ plane. Interloper lines are explored in Section \[sec:Interlopers\]. A framework for interferometric power spectrum estimation using spherical Fourier-Bessel methods (which includes a derivation of the foreground wedge) is presented in Section \[sec:Interferometry\]. To build intuition, we develop a parallel series of flat-sky, narrow field-of-view expressions in a series of Appendices. Our conclusions are summarized in 