C. Chang, P. J. Marshall, J. G. Jernigan, J. R. Peterson, S. M. Kahn, S. F. Gull, Y. AlSayyad, Z. Ahmad, J. Bankert, D. Bard, A. Connolly, R. R. Gibson, K. Gilmore, E. Grace, M. Hannel, M. A. Hodge, L. Jones, S. Krughoff, S. Lorenz, S. Marshall, A. Meert, S. Nagarajan, E. Peng, A. P. Rasmussen, M. Shmakova, N. Sylvestre, N. Todd, M. Young
The synoptic imaging survey proposed for the Large Synoptic Survey Telescope (LSST) will generate large numbers of short exposure ($\simeq$15 seconds) images. A primary science driver for this project is to measure the cosmic shear signal from weak lensing to extreme accuracy. One difficulty, however, is that in these short exposure images, the spatial variation of the Point Spread Function (PSF) shapes may be dominated by the atmosphere, in addition to optics errors. In particular, the atmosphere generates stochastic structures on a wide range of angular scales. Since the PSF patterns in these images can only be inferred by interpolating the sparsely sampled stars in the field, these multi-scale, complex patterns from the atmosphere complicates the PSF interpolation problem. In this paper we present a new method, PSFent, for interpolating atmospheric PSF shape parameters, based on reconstructing underlying shape parameter maps with a multi-scale maximum entropy algorithm. We demonstrate, using images from the LSST Photon Simulator (PhoSim), the performance of our approach relative to a 5th-order polynomial fit (representing the current standard) and a simple boxcar filtering technique. Quantitatively, PSFent predicts more accurate PSF models in all scenarios and the residual PSF errors are less correlated spatially. This improvement in PSF interpolation leads to a factor of 3.5 lower systematic errors in the shear power spectrum on scales smaller than $\sim13'$, compared to standard polynomial fitting. We estimate that with PSFent and for stellar densities greater than $\simeq$ 1 $/{\rm arcmin}^{2}$, the spurious shear correlation from PSF interpolation, after combining a complete 10-year, dataset from LSST is lower than the corresponding statistical uncertainties on the cosmic shear power spectrum, even in a conservative scenario.
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http://arxiv.org/abs/1206.1383
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