$\nu$ to unit perturbation of spherical harmonic mode $Y_{\ell m}$   Eq.
  $g_{\ell m} (\mathbf{b}, \tau)$                   Response of baseline $\mathbf{b}$ at delay $\tau$ to unit perturbation of spherical harmonic mode $Y_{\ell m}$      Eq.
  $W_\ell (k; \mathbf{b}, \tau)$                    Spherical harmonic power spectrum window function for a single baseline delay-based                                 Eq.
                                                    power spectrum estimate                                                                                             
  $\Theta(\nu)$                                     Re-centered frequency profile of the foregrounds as seen in the data, with finite bandwidth                         Section \[sec:CurvedSkyWedge\]
                                                    and tapering effects                                                                                                
  $D(\mathbf{r})$                                   Survey volume selection function including primary beam, bandwidth, and data analysis                               Appendix \[sec:RectilinearInterferometerPspecNorm\]
                                                    tapering effects                                                                                                    

Notational preliminaries {#sec:Notation}
========================

Suppose an intensity mapping survey has surveyed the brightness temperature field $T({\hat{\mathbf{r}}}, \nu)$ of a particular spectral line as a function of angle (specified here in terms of unit vector ${\hat{\mathbf{r}}}$) and frequency $\nu$. Such a quantity represents a three-dimensional survey of our Universe, since different frequencies of a spectral line map to different redshifts, and thus different radial distances from the observer. Explicitly, the comoving radial distance $r$ is given by $$\label{eq:ComovingDistDef}
r (\nu) = \frac{c}{H_0} \int_0^{z(\nu)} \frac{dz^\prime}{E(z^\prime)},$$ where $c$ is the speed of light, $H_0$ is the present day Hubble parameter, with $$1 + z \equiv \frac{\nu_\textrm{rest}}{\nu}\quad \textrm{and} \quad E(z) \equiv \sqrt{\Omega_\Lambda + \Omega_m (1+z)^3},$$ where $\nu_\textrm{rest}$ 