Avoiding the Geometric Boundary Effect in Shear Measurement

TL;DR

This paper introduces a method to eliminate boundary-induced shear bias in astronomical image processing, improving the accuracy of shear measurements near image edges.

Contribution

A simple, effective approach to mitigate geometric boundary effects in shear measurement, validated with simulations and real survey data.

Findings

Significant reduction of shear bias near boundaries.

Validated method with simulations and DECam Legacy Survey data.

Enhanced accuracy in shear measurement near image edges.

Abstract

In image processing, source detections are inevitably affected by the presence of the geometric boundaries in the images, including the physical boundaries of the CCD, and the boundaries of masked regions due to column defects, bright diffraction spikes, etc.. These boundary conditions make the source detection process not statistically isotropic. It can lead to additive shear bias near the boundaries. We build a phenomenological model to understand the bias, and propose a simple method to effectively eliminate the influence of geometric boundaries on shear measurement. We demonstrate the accuracy and efficiency of this method using both simulations and the z-band imaging data from the third data release of the DECam Legacy Survey.