7,733 research outputs found
Overviews of Optimization Techniques for Geometric Estimation
We summarize techniques for optimal geometric estimation from noisy observations for computer
vision applications. We first discuss the interpretation of optimality and point out that geometric
estimation is different from the standard statistical estimation. We also describe our noise
modeling and a theoretical accuracy limit called the KCR lower bound. Then, we formulate estimation
techniques based on minimization of a given cost function: least squares (LS), maximum
likelihood (ML), which includes reprojection error minimization as a special case, and Sampson
error minimization. We describe bundle adjustment and the FNS scheme for numerically solving
them and the hyperaccurate correction that improves the accuracy of ML. Next, we formulate
estimation techniques not based on minimization of any cost function: iterative reweight, renormalization,
and hyper-renormalization. Finally, we show numerical examples to demonstrate that
hyper-renormalization has higher accuracy than ML, which has widely been regarded as the most
accurate method of all. We conclude that hyper-renormalization is robust to noise and currently is
the best method
Imfit: A Fast, Flexible New Program for Astronomical Image Fitting
I describe a new, open-source astronomical image-fitting program called
Imfit, specialized for galaxies but potentially useful for other sources, which
is fast, flexible, and highly extensible. A key characteristic of the program
is an object-oriented design which allows new types of image components (2D
surface-brightness functions) to be easily written and added to the program.
Image functions provided with Imfit include the usual suspects for galaxy
decompositions (Sersic, exponential, Gaussian), along with Core-Sersic and
broken-exponential profiles, elliptical rings, and three components which
perform line-of-sight integration through 3D luminosity-density models of disks
and rings seen at arbitrary inclinations.
Available minimization algorithms include Levenberg-Marquardt, Nelder-Mead
simplex, and Differential Evolution, allowing trade-offs between speed and
decreased sensitivity to local minima in the fit landscape. Minimization can be
done using the standard chi^2 statistic (using either data or model values to
estimate per-pixel Gaussian errors, or else user-supplied error images) or
Poisson-based maximum-likelihood statistics; the latter approach is
particularly appropriate for cases of Poisson data in the low-count regime. I
show that fitting low-S/N galaxy images using chi^2 minimization and
individual-pixel Gaussian uncertainties can lead to significant biases in
fitted parameter values, which are avoided if a Poisson-based statistic is
used; this is true even when Gaussian read noise is present.Comment: pdflatex, 27 pages, 19 figures. Revised version, accepted by ApJ.
Programs, source code, and documentation available at:
http://www.mpe.mpg.de/~erwin/code/imfit
Systematic effects on dark energy from 3D weak shear
We present an investigation into the potential effect of systematics inherent
in multi-band wide field surveys on the dark energy equation of state
determination for two 3D weak lensing methods. The weak lensing methods are a
geometric shear-ratio method and 3D cosmic shear. The analysis here uses an
extension of the Fisher matrix framework to jointly include photometric
redshift systematics, shear distortion systematics and intrinsic alignments. We
present results for DUNE and Pan-STARRS surveys. We show that assuming
systematic parameters are fixed, but possibly biased, results in potentially
large biases in dark energy parameters. We quantify any potential bias by
defining a Bias Figure of Merit. We also show the effect on the dark energy
Figure of Merit of marginalising over each systematic parameter individually.
We find that the largest effect on the Figure of Merit comes from uncertainty
in the photometric redshift systematic parameters. These can reduce the Figure
of Merit by up to a factor of 2 to 4 in both 3D weak lensing methods, if no
informative prior on the systematic parameters is applied. Shear distortion
systematics have a smaller overall effect. Intrinsic alignment effects can
reduce the Figure of Merit by up to a further factor of 2. This, however, is a
worst case scenario. By including prior information on systematic parameters
the Figure of Merit can be recovered to a large extent. We conclude that, as a
rule of thumb, given a realistic current understanding of intrinsic alignments
and photometric redshifts, then including all three primary systematic effects
reduces the Figure of Merit by at most a factor of 2, but that in reality this
factor should be much less. [abridged]Comment: 20 pages, 11 figures, submitted to MNRA
The X-ray Cluster Normalization of the Matter Power Spectrum
The number density of galaxy clusters provides tight statistical constraints
on the matter fluctuation power spectrum normalization, traditionally phrased
in terms of sigma_8, the root mean square mass fluctuation in spheres with
radius 8 h^-1 Mpc. We present constraints on sigma_8 and the total matter
density Omega_m0 from local cluster counts as a function of X-ray temperature,
taking care to incorporate and minimize systematic errors that plagued previous
work with this method. In particular, we present new determinations of the
cluster luminosity - temperature and mass - temperature relations, including
their intrinsic scatter, and a determination of the Jenkins mass function
parameters for the same mass definition as the mass - temperature calibration.
Marginalizing over the 12 uninteresting parameters associated with this method,
we find that the local cluster temperature function implies sigma_8
(Omega_m0/0.32)^alpha = 0.86+/-0.04 with alpha = 0.30 (0.41) for Omega_m0 <
0.32 (Omega_mo > 0.32) (68% confidence for two parameters). This result agrees
with a wide range of recent independent determinations, and we find no evidence
of any additional sources of systematic error for the X-ray cluster temperature
function determination of the matter power spectrum normalization. The joint
WMAP5 + cluster constraints are: Omega_m0 = 0.30+0.03/-0.02 and sigma_8 =
0.85+0.04/-0.02 (68% confidence for two parameters).Comment: 31 pages, 16 figures, accept for publication in ApJ 609, Jan. 10,
200
Unbiased Cosmological Parameter Estimation from Emission Line Surveys with Interlopers
The galaxy catalogs generated from low-resolution emission line surveys often
contain both foreground and background interlopers due to line
misidentification, which can bias the cosmological parameter estimation. In
this paper, we present a method for correcting the interloper bias by using the
joint-analysis of auto- and cross-power spectra of the main and the interloper
samples. In particular, we can measure the interloper fractions from the
cross-correlation between the interlopers and survey galaxies, because the true
cross-correlation must be negligibly small. The estimated interloper fractions,
in turn, remove the interloper bias in the cosmological parameter estimation.
For example, in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX)
low-redshift () [O II] {\AA} emitters contaminate
high-redshift () Lyman- line emitters. We demonstrate that
the joint-analysis method yields a high signal-to-noise ratio measurement of
the interloper fractions while only marginally increasing the uncertainties in
the cosmological parameters relative to the case without interlopers. We also
show the same is true for the high-latitude spectroscopic survey of Wide-Field
Infrared Survey Telescope (WFIRST) mission where contamination occurs between
the Balmer- line emitters at lower redshifts () and Oxygen
([O III] {\AA}) line emitters at higher redshifts ().Comment: 36 pages, 26 figure
Photometric Supernova Cosmology with BEAMS and SDSS-II
Supernova cosmology without spectroscopic confirmation is an exciting new
frontier which we address here with the Bayesian Estimation Applied to Multiple
Species (BEAMS) algorithm and the full three years of data from the Sloan
Digital Sky Survey II Supernova Survey (SDSS-II SN). BEAMS is a Bayesian
framework for using data from multiple species in statistical inference when
one has the probability that each data point belongs to a given species,
corresponding in this context to different types of supernovae with their
probabilities derived from their multi-band lightcurves. We run the BEAMS
algorithm on both Gaussian and more realistic SNANA simulations with of order
10^4 supernovae, testing the algorithm against various pitfalls one might
expect in the new and somewhat uncharted territory of photometric supernova
cosmology. We compare the performance of BEAMS to that of both mock
spectroscopic surveys and photometric samples which have been cut using typical
selection criteria. The latter typically are either biased due to contamination
or have significantly larger contours in the cosmological parameters due to
small data-sets. We then apply BEAMS to the 792 SDSS-II photometric supernovae
with host spectroscopic redshifts. In this case, BEAMS reduces the area of the
(\Omega_m,\Omega_\Lambda) contours by a factor of three relative to the case
where only spectroscopically confirmed data are used (297 supernovae). In the
case of flatness, the constraints obtained on the matter density applying BEAMS
to the photometric SDSS-II data are \Omega_m(BEAMS)=0.194\pm0.07. This
illustrates the potential power of BEAMS for future large photometric supernova
surveys such as LSST.Comment: 25 pages, 15 figures, submitted to Ap
The Hyper Suprime-Cam Software Pipeline
In this paper, we describe the optical imaging data processing pipeline
developed for the Subaru Telescope's Hyper Suprime-Cam (HSC) instrument. The
HSC Pipeline builds on the prototype pipeline being developed by the Large
Synoptic Survey Telescope's Data Management system, adding customizations for
HSC, large-scale processing capabilities, and novel algorithms that have since
been reincorporated into the LSST codebase. While designed primarily to reduce
HSC Subaru Strategic Program (SSP) data, it is also the recommended pipeline
for reducing general-observer HSC data. The HSC pipeline includes high level
processing steps that generate coadded images and science-ready catalogs as
well as low-level detrending and image characterizations.Comment: 39 pages, 21 figures, 2 tables. Submitted to Publications of the
Astronomical Society of Japa
- ā¦