Optimal Cosmic-Ray Detection for Nondestructive Read Ramps

TL;DR

This paper evaluates three cosmic-ray correction methods for nondestructive readout ramps in space telescopes, finding the y-intercept method most effective in read-noise regimes and both y-intercept and two-point difference methods effective in photon-noise regimes.

Contribution

It introduces and compares three cosmic-ray correction techniques specifically for nondestructive readout schemes in space-based astronomy instruments.

Findings

Y-intercept method is optimal in read-noise-dominated regimes.

Both y-intercept and two-point difference methods are effective in photon-noise regimes.

Two-point difference method requires fewer computations.

Abstract

Cosmic rays are a known problem in astronomy, causing both loss of data and data inaccuracy. The problem becomes even more extreme when considering data from a high-radiation environment, such as in orbit around Earth or outside the Earth's magnetic field altogether, unprotected, as will be the case for the James Webb Space Telescope (JWST). For JWST, all the instruments employ nondestructive readout schemes. The most common of these will be "up the ramp" sampling, where the detector is read out regularly during the ramp. We study three methods to correct for cosmic rays in these ramps: a two-point difference method, a deviation from the fit method, and a y-intercept method. We apply these methods to simulated nondestructive read ramps with single-sample groups and varying combinations of flux, number of samples, number of cosmic rays, cosmic-ray location in the exposure, and cosmic-ray strength. We show that the y-intercept method is the optimal detection method in the read-noise-dominated regime, while both the y-intercept method and the two-point difference method are best in the photon-noise-dominated regime, with the latter requiring fewer computations.