DMTN-021: Implementation of Image Difference Decorrelation

Herein, we describe a method for decorrelating image differences produced by the Alard and Lupton (1998) method of PSF matching. Inspired by the recent work of Zackay et al. (2016) and the prior work of Kaiser [2004], this proposed method uses a single post-subtraction convolution of an image difference to remove the neighboring pixel covariances in the image difference that result from the convolution of the template image by the PSF matching kernel. We describe the method in detail, analyze its effects on image differences (both real and simulated) as well as on detections and photometry of detected sources in decorrelated image differences. We also compare the decorrelated image differences with those resulting from a basic implementation of Zackay et al. (2016). We describe the implementation of the new correction in the LSST image differencing pipeline, and discuss potential issues and areas of future research.