Characterization of LSST CCDs Using Realistic Images, Before First Light

TL;DR

This paper characterizes LSST CCD systematics using realistic images and simulations to inform correction strategies, ensuring the camera meets the stringent requirements for weak lensing and precision cosmology before first light.

Contribution

It provides the first detailed laboratory measurements and physics-based models of LSST CCD systematics using realistic scenes, aiding in systematic bias correction.

Findings

Identified brightness-dependent image broadening effects.

Characterized charge transport anomalies and serial deferred charge.

Developed models for systematic bias correction.

Abstract

The 3.2 gigapixel LSST camera, an array of 189 thick fully-depleted CCDs, will repeatedly image the southern sky and accomplish a wide variety of science goals. However, its trove of tens of billions of object images implies stringent requirements on systematic biases imprinted during shift-and-stare CCD observation. In order to correct for these biases which, without correction, violate requirements on weak lensing precision, we investigate CCD systematics using both simulations of charge transport as well as with a unique bench-top optical system matched to the LSST's fast f/1.2 beam. By illuminating single CCDs with realistic scenes of stars and galaxies and then analyzing these images with the LSST data management pipelines, we can characterize the survey's imaging performance well before the camera's first light. We present measurements of several CCD systematics under varying conditions in the laboratory, including the brightness-dependent broadening of star and galaxy images, charge transport anomalies in the silicon bulk as well as the edges, and serial deferred charge. Alongside these measurements, we also present the development and testing of physics-based models which inform corrections or mitigation strategies for these systematics. Optimization of the CCD survey operation under a variety of realistic observational conditions, including systematic effects from the optics, clocking, sky brightness, and image analysis, will be critical to achieve the LSST's goals of precision astronomy and cosmology.