scholarly journals A MOMENT METHOD FOR MEASURING THE HIGHER-ORDER WEAK GRAVITATIONAL LENSING EFFECTS

2008 ◽  
Vol 23 (17n20) ◽  
pp. 1506-1513 ◽  
Author(s):  
KEIICHI UMETSU ◽  
YUKI OKURA ◽  
TOSHIFUMI FUTAMASE
Keyword(s):  
Gravitational Lensing ◽  
Galaxy Cluster ◽  
Higher Order ◽  
Local Concentration ◽  
Fourier Space ◽  
Cluster Galaxy ◽  
Point Spread ◽  
Image Characteristics ◽  
Spread Function ◽  
Massive Galaxy

We present a method for measuring higher-order weak lensing distortions of faint background galaxies, namely the weak gravitational flexion, by fully extending the Kaiser, Squires & Broadhurst method to include higher-order lensing image characteristics (HOLICs) introduced by Okura, Umetsu, & Futamase. Our HOLICs formalism allows accurate measurements of flexion from practical observational data in the presence of non-circular, anisotropic point spread function. We have applied our method to ground-based Subaru observations of the massive galaxy cluster A1689 at a redshift of z = 0.183. From the high-precision measurements of spin-1 first flexion, we obtain a high-resolution mass map in the central region of A1689. The reconstructed mass map shows a bimodal feature in the central 4′ × 4′ region of the cluster. The major, pronounced mass peak is associated with the brightest cluster galaxy and central cluster members, while the secondary peak is associated with a local concentration of bright galaxies. In Fourier space we separate the reconstructed mass distribution into cluster and subhalo components, from which we obtain projected subhalo masses associated with the primary and the secondary peaks to be M1 = (2.2 ± 0.4) × 1013M⊙/h, and M2 = (1.1 ± 0.3) × 1013M⊙/h, respectively.

scholarly journals Micro-pixel accuracy centroid displacement estimation and detector calibration

2011 ◽  
Vol 467 (2136) ◽  
pp. 3550-3569 ◽  
Author(s):  
Chengxing Zhai ◽  
Mike Shao ◽  
Renaud Goullioud ◽  
Bijan Nemati
Keyword(s):  
Fourier Transforms ◽  
Image Data ◽  
Estimation Algorithm ◽  
Fourier Space ◽  
Third Order ◽  
Displacement Estimation ◽  
Point Spread ◽  
Spread Function ◽  
Centroid Estimation ◽  
Laser Metrology

Conventional centroid estimation fits a template point spread function (PSF) to image data. Because the PSF is typically not known to high accuracy, systematic errors exist. Here, we present an accurate centroid displacement estimation algorithm by reconstructing the PSF from Nyquist-sampled images. In absence of inter-pixel response variations, this method can estimate centroid displacement between two 32×32 images to sub-micropixel accuracy. Inter-pixel response variations can be calibrated in Fourier space by using laser metrology. The inter-pixel variations of Fourier transforms of the pixel response functions can be conveniently expressed in terms of powers of spatial wavenumbers. Calibrating up to the third-order terms in the expansion, the displacement estimation is accurate to a few micro-pixels. This algorithm is applicable to a new mission concept of performing mirco-arcsecond level relative astrometry using a 1 m telescope for detecting terrestrial exoplanets and high-precision photometry missions.

scholarly journals Mitigating the effects of undersampling in weak lensing shear estimation with metacalibration

2021 ◽  
Vol 502 (3) ◽  
pp. 4048-4063
Author(s):  
Arun Kannawadi ◽  
Erik Rosenberg ◽  
Henk Hoekstra
Keyword(s):  
Point Spread Function ◽  
Gravitational Lensing ◽  
State Of The Art ◽  
Weak Lensing ◽  
Weight Functions ◽  
High Signal ◽  
Signal To Noise ◽  
Space Telescope ◽  
Point Spread ◽  
Spread Function

ABSTRACT metacalibration is a state-of-the-art technique for measuring weak gravitational lensing shear from well-sampled galaxy images. We investigate the accuracy of shear measured with metacalibration from fitting elliptical Gaussians to undersampled galaxy images. In this case, metacalibration introduces aliasing effects leading to an ensemble multiplicative shear bias about 0.01 for Euclid  and even larger for the Roman Space Telescope, well exceeding the missions’ requirements. We find that this aliasing bias can be mitigated by computing shapes from weighted moments with wider Gaussians as weight functions, thereby trading bias for a slight increase in variance of the measurements. We show that this approach is robust to the point-spread function in consideration and meets the stringent requirements of Euclid for galaxies with moderate to high signal-to-noise ratios. We therefore advocate metacalibration as a viable shear measurement option for weak lensing from upcoming space missions.

Imaging through Scattering Media with a Learning Based Prior

2020 ◽  
Vol 2020 (14) ◽  
pp. 306-1-306-6
Author(s):  
Florian Schiffers ◽  
Lionel Fiske ◽  
Pablo Ruiz ◽  
Aggelos K. Katsaggelos ◽  
Oliver Cossairt
Keyword(s):  
Optimization Problem ◽  
Autonomous Driving ◽  
Scattering Media ◽  
Photon Scattering ◽  
Point Spread ◽  
Spread Function ◽  
Radiative Transport Equation ◽  
Spatio Temporal ◽  
Transient Imaging

Imaging through scattering media finds applications in diverse fields from biomedicine to autonomous driving. However, interpreting the resulting images is difficult due to blur caused by the scattering of photons within the medium. Transient information, captured with fast temporal sensors, can be used to significantly improve the quality of images acquired in scattering conditions. Photon scattering, within a highly scattering media, is well modeled by the diffusion approximation of the Radiative Transport Equation (RTE). Its solution is easily derived which can be interpreted as a Spatio-Temporal Point Spread Function (STPSF). In this paper, we first discuss the properties of the ST-PSF and subsequently use this knowledge to simulate transient imaging through highly scattering media. We then propose a framework to invert the forward model, which assumes Poisson noise, to recover a noise-free, unblurred image by solving an optimization problem.

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