Optimization of the multiple sampling and signal extraction in non-destructive exposures

TL;DR

This paper develops covariance matrix formulas for signal fitting in non-destructive exposures, showing significant improvements in signal-to-noise ratio when using all sampled frames, especially at higher flux levels.

Contribution

It introduces a comprehensive covariance matrix approach for better signal extraction and demonstrates optimal sampling strategies for different flux regimes.

Findings

Higher signal-to-noise ratio with covariance matrices at flux > 1 e/sec/pix

Using all frames during exposure maximizes signal-to-noise ratio

Coadding frames should be avoided at high flux levels

Abstract

We derive the full covariance matrix formulae are derived for proper treatment of correlations in signal fitting procedures, extending the results from previous publications. The straight line fits performed with these matrices demonstrate that a significantly higher signal to noise is obtained when the fluence exceeds 1 e/sec/pix in particular in long (several hundreds of seconds) spectroscopic exposures. The improvement arising from the covariance matrix is particularly strong for the initial intercept of the fit at t=0, a quantity which provides a useful redundancy to cross check the signal quality. We demonstrate that the mode that maximizes the signal to noise ratio in all ranges of fluxes studied in this paper is the one that uses all the frames sampled during the exposure. While at low flux there is no restriction on the organization of frames within groups for fluxes lower than 1 e/sec/pix, for fluxes exceeding this value the coadding of frames shell be avoided.