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Title: Lossy compression of weak lensing data

Future orbiting observatories will survey large areas of sky in order to constrain the physics of dark matter and dark energy using weak gravitational lensing and other methods. Lossy compression of the resultant data will improve the cost and feasibility of transmitting the images through the space communication network. We evaluate the consequences of the lossy compression algorithm of Bernstein et al. (2010) for the high-precision measurement of weak-lensing galaxy ellipticities. This square-root algorithm compresses each pixel independently, and the information discarded is by construction less than the Poisson error from photon shot noise. For simulated space-based images (without cosmic rays) digitized to the typical 16 bits per pixel, application of the lossy compression followed by image-wise lossless compression yields images with only 2.4 bits per pixel, a factor of 6.7 compression. We demonstrate that this compression introduces no bias in the sky background. The compression introduces a small amount of additional digitization noise to the images, and we demonstrate a corresponding small increase in ellipticity measurement noise. The ellipticity measurement method is biased by the addition of noise, so the additional digitization noise is expected to induce a multiplicative bias on the galaxies measured ellipticities. After correcting for thismore » known noise-induced bias, we find a residual multiplicative ellipticity bias of m {approx} -4 x 10-4. This bias is small when compared to the many other issues that precision weak lensing surveys must confront, and furthermore we expect it to be reduced further with better calibration of ellipticity measurement methods.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [4]
  1. Univ. of Chicago, IL (United States). Enrico Fermi Inst.; California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  2. Univ. of Pennsylvania, Philadelphia, PA (United States)
  3. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  4. California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  5. Royal Observatory, Edinburgh (United Kingdom). Inst. for Astronomy
Publication Date:
OSTI Identifier:
1021501
Report Number(s):
FERMILAB-PUB--11-338-AE
Journal ID: ISSN 0004-6280; arXiv eprint number arXiv:1106.5805; TRN: US1104012
Grant/Contract Number:
AC02-07CH11359
Type:
Accepted Manuscript
Journal Name:
Publications of the Astronomical Society of the Pacific
Additional Journal Information:
Journal Volume: 123; Journal Issue: 906; Journal ID: ISSN 0004-6280
Publisher:
Astronomical Society of the Pacific
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Contributing Orgs:
SNAP Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 97 MATHEMATICS AND COMPUTING; ACCURACY; ALGORITHMS; CALIBRATION; COMMUNICATIONS; COMPRESSION; CONSTRUCTION; GALAXIES; NONLUMINOUS MATTER; PHOTONS; PHYSICS; SKY Astrophysics