  We perform a detailed 2-dimensional weak gravitational lensing analysis of
the nearby (z = 0.058) galaxy cluster Abell 3128 using deep ugrz imaging from
the Dark Energy Camera (DECam). We have designed a pipeline to remove
instrumental artifacts from DECam images and stack multiple dithered
observations without inducing a spurious ellipticity signal. We develop a new
technique to characterize the spatial variation of the PSF which enables us to
circularize the field to better than 0.5% and thereby extract the intrinsic
galaxy ellipticities. By fitting photometric redshifts to sources in the
observation, we are able to select a sample of background galaxies for weak
lensing analysis free from low-redshift contaminants. Photometric redshifts are
also used to select a high-redshift galaxy subsample with which we successfully
isolate the signal from an interloping z = 0.44 cluster. We estimate the total
mass of Abell 3128 by fitting the tangential ellipticity of background galaxies
with the weak lensing shear profile of an NFW halo, and also perform NFW fits
to substructures detected in the 2-D mass maps of the cluster. This study
yields one of the highest resolution mass maps of a low-z cluster to date, and
is the first step in a larger effort to characterize the redshift evolution of
mass substructures in clusters.
