The Sensitivity of Hybrid Differential Stereoscopy for Spectral Imaging

Abstract

Stereoscopic spectral imaging is an observing technique that affords rapid acquisition of limited spectral information over an entire image plane simultaneously. Light from a telescope is dispersed into multiple spectral orders, which are imaged separately, and two or more of the dispersed images are combined using an analogy between the (x,y,λ) spectral data space and conventional (x,y,z) three-space. Because no photons are deliberately destroyed during image acquisition, the technique is much more photon-efficient in some observing regimes than existing techniques such as scanned-filtergraph or scanned-slit spectral imaging. Hybrid differential stereoscopy, which uses a combination of conventional cross-correlation stereoscopy and linear approximation theory to extract the central wavelength of a spectral line, has been used to produce solar Stokes-V (line-of-sight) magnetograms in the 617.34 nm Fe I line, and more sophisticated inversion techniques are currently being used to derive Doppler and line separation data from EUV images of the solar corona collected in the neighboring lines of He-II and Si-XI at 30.4 nm. In this paper we develop an analytic a priori treatment of noise in the line shift signal derived from hybrid differential stereoscopy. We use the analysis to estimate the noise level and measurement precision in a high resolution solar magnetograph based on stereoscopic spectral imaging, compare those estimates to a test observation made in 2003, and discuss implications for future instruments.