Index: /trunk/doc/release.2015/ps1.calibration/calibration.tex =================================================================== --- /trunk/doc/release.2015/ps1.calibration/calibration.tex (revision 39832) +++ /trunk/doc/release.2015/ps1.calibration/calibration.tex (revision 39833) @@ -88,51 +88,253 @@ \keywords{Surveys:\PSONE } +\section{Introduction}\label{sec:intro} + +\section{Pan-STARRS\,1} + +From May 2010 through March 2014, the Pan-STARRS Science Consortium +used the 1.8m \PSONE\ telescope to perform a set of wide-field science +surveys. These surveys are designed to address a range of science +goals included the search for hazardous asteroids, the study of the +formation and architecture of the Milky Way galaxy, and the search for +Type Ia supernovae to measure the history of the expansion of the +universe. + +The wide-field \PSONE\ telescope consists of a 1.8~meter diameter +$f$/4.4 primary mirror with an 0.9~m secondary, producing a 3.3 degree +field of view \citep{PS1.optics}. The optical design yields low +distortion and minimal vignetting even at the edges of the illuminated +region. The optics, in combination with the natural seeing, result in +generally good image quality: 75\% of the images have full-width +half-max values less than \note{(1.X, 1.X, 1.X, 1.X, 1.X), update} +arcseconds for (\grizy), with a floor of $\sim 0.7$ \note{update} +arcseconds. The \PSONE\ camera \citep{PS1.GPCA} is a mosaic of 60 +edge-abutted $4800\times4800$ pixel back-illuminated \note{name} CCDs +manufactured by Lincoln Laboratory. The CCDs have 10~$\mu$m pixels +subtending 0.258~arcsec and are \note{70um} thick. The detectors are +read out using a StarGrasp CCD controller, with a readout time of 7 +seconds for a full unbinned image \citep{PS1.GPCB}. The active, +usable pixels cover $\sim 80$\% of the FOV. + +Nightly observations are conducted remotely from the Advanced +Technology Research Center in Kula, the main facility of the +University of Hawaii's Institute for Astronomy operations on Maui. +During the \PSONE\ Science Survey, images obtained by the +\PSONE\ system were stored first on computers at the summit, then +copied with low latency via internet to the dedicated data analysis +cluster located at the Maui High Performance Computer Center in Kihei, +Maui. + +Images obtained by \PSONE\ are automatically processed in real time by +the \PSONE\ Image Processing Pipeline \citep[IPP,][]{PS1.IPP}. +Real-time analysis goals are aimed at feeding the discovery pipelines +of the asteroid search and supernova search teams. The data obtained +for the \PSONE\ Science Survey has also been used in three additional +complete re-processing of the data: Processing Versions 1, 2, and 3 +(PV1, PV2, and PV3). The real-time processing of the data is +considered ``PV0''. Except as otherwise noted, the PV3 analysis of +the data is used for the purpose of this article. + +The data processing steps are described in detail by Waters REF and +Magnier REF. In summary, individual images are detrended: +non-linearity and bias corrections are applied, a dark current model +is subtracted and flat-field corrections are applied. The \yps-band +images are also corrected for fringing: a master fringe pattern is +scaled to match the observed fringing and subtracted. Mask and +variance image arrays are generated with the \changed{detrend + analysis} and carried forward at each stage of the IPP processing. +Source detection and photometry are performed for each chip +independently. As discussed below, preliminary astrometric and +photometric calibrations are performed for all chips in a single +exposure in a single analysis. + +Chip images are geometrically transformed based on the astrometric +solution into a set of pre-defined pixel grids covering the sky, +called skycells. These transformed images are called the warp images. +Sets of warps for a given part of the sky and in the same filter may +be added together to generate deeper `stack' images. PSF-matched +difference images are generated from combinations of warps and stacks; +the details of the difference images and their calibration are outside +of the scope of this article. + +% Individual warp images are differenced during the nightly processing +% to detect the fast moving asteroids. Stacks are subtracted from +% individual warps, and deep stacks are subtracted from stack generated +% from images for a single night (nightly stacks). + +Astronomical objects are detected and characterized in the stacks +images. The details of the analysis of the sources in the stack +images are discussed in Magnier et al REF, but in brief these include +PSF photometry, along with a range of measurements driven by the goals +of understanding the galaxies in the images. Because of the +significant mask fraction of the GPC1 focal plane, and the varying +image quality both within and between exposures, the effective PSF of +the PS1 stack images is highly variable. The PSF varies significantly +on scales as small as a few to tens of pixels, making accurate PSF +modelling essentially infeasible. The PSF photometry of sources in +the stack images is thus degraded significantly compared to the +quality of the photometry measured for the individual chip images. + +To recover most of the photometric quality of the individual chip +images, while also exploiting the depth afforded by the stacks, the +PV3 analysis make use of forced photometry on the individual warp +images. PSF photometry is measured on the warp images for all sources +which are detected in the stack images images. The positions +determined in the stack images are used in the warp images, but the +PSF model is determined for each warp independently based on brighter +stars in the warp image. The only free parameter for each object is +the flux, which may be insignificant or even negative for sources +which are near the faint limit of the stack detections. When the +fluxes from the individual warp images are averaged, a reliable +measurement of the faint source flux is determined. The details of +this analysis are described in detail in Magnier et al REF. + +In this article, we discuss the photometric calibration of the +individual exposures, the stacks, and the warp imags. We also discuss +the astrometric calibration of the individual exposures and the stack +images. + +\section{Real-time Calibration} + +As images are processed by the data analysis system, every exposure is +calibrated individually with respect to a photometric and astrometric +database. The goal of this calibration step is to generate a preliminary +astrometric calibration, to be used by the warping analysis to determine +the geometric transformation of the pixels, and preliminary +photometric transformation, to be used by the stacking analysis to +ensure the warps are combined using consistent flux units. + +The program used for the real-time calibration, \code{psastro}, loads +the measurements of the chip detections from their individual +\code{cmf}-format files. It uses the header information populated at +the telescope to determine an initial astrometric calibration guess +based on the position of the telescope boresite right ascension, +declination and position angle as reported by the telescope \& camera +subsystems. Using the initial guess, \code{psastro} loads astrometric +and photometric data from the reference database. + +During the course of the PS1SC Survey, several reference databases +have been used. For the first 20 months of the survey, \code{psastro} +used a reference catalog with synthetic PS1 \grizy\ photometry +generated by the Pan-STARRS IPP team based on based combined +photometry from Tycho (B, V), USNO (red, blue, IR), and 2MASS $J, H, +K$. The astrometry in the database was from 2MASS. After 2012 May, a +reference catalog generated from internal re-calibration of the PV0 +analysis of PS1 photometry and astrometry was used for the reference +catalog. \note{discuss history of the different refcats?} + +{\bf Astrometric Model in PSASTRO} \code{pasastro} loads the +coordinates and calibrated magnitudes of stars from the reference +database. A model for the positions of the 60 chips in the focal +plane is used to determine the expected astrometry for each chip based +on the boresite coordinates and position angle reported by the header. +Reference stars are selected from the full field of view of the GPC1 +camera, padded by an additional \note{25\%} to ensure a match can be +determined even in the presence of substantial errors in the boresite +coordinates. It is important to choose an appropriate set of +reference stars: if too few are selected, the chance of finding a +match between the reference and observed stars is diminished. In +addition, since stars are loaded in brightness order, a selection +which is too small is likely to contain only stars which are saturated +in the GPC1 images. On the other hand, if too many reference stars +are chosen, there is a higher chance of a false-positive match, +especially as many of the reference stars may not be detected in the +GPC1 image. The seletion of the reference stars includes a limit on +the brightest and fainted magnitude of the stars selected. + +Three somewhat distinct astrometric models are employed within the IPP +at different stages. The simplest model is defined independently for +each chip: a simple TAN projection (Calabretta \& Griesen REF) is used +to relate sky coordinates to a cartesian tangent-plane coordinate +system. \note{include projection math?} A pair of low-order +polynomials are used to relate the chip pixel coordinates to this +tangent-plane coordinate system. The transforming polynomials are of +the form: +\begin{eqnarray} +P & = & \sum_{i,j} C^P_{i,j} X^i_{\rm chip} Y^j_{\rm chip} \\ +Q & = & \sum_{i,j} C^Q_{i,j} X^i_{\rm chip} Y^j_{\rm chip} +\end{eqnarray} +where $P,Q$ are the tangent plane coordinates, $X_{\rm chip}, Y_{\rm + chip}$ are the coordinates on the 60 GPC1 chips (\note{see + discussion somewhere on cell vs chip}), and $C^P_{i,j}, C^Q_{i,j}$ +are the polynomial coefficients for each order. In the \code{psastro} +analysis, $i + j <= N_{\rm order}$ where the order of the fit, $N_{\rm + order}$, may be 1 to 3, under the restriction that sufficient stars +are needed to constraint the order \note{describe a bit better: this + is automatically selected based on the number of stars}. + + +{\bf WCS Keywords} When this polynomial representation is written to +the output files, a set of WCS keywords are used to define the +astrometric transformation elements. It is necessary to +\begin{eqnarray} +P & = & \sum_{i,j} C^P_{i,j} (X_{\rm chip} - X_0)^i (Y_{\rm chip} - Y_0)^j \\ +Q & = & \sum_{i,j} C^Q_{i,j} (X_{\rm chip} - X_0)^i (Y_{\rm chip} - Y_0)^j +\end{eqnarray} +where $X_0, Y_0$ is the reference pixel, represented in the header as + + + are functions then related the The astrometric model u + +The astrometric analysis is necessarily performed first; after the +astrometry is determined, an automatic byproduct is a reliable match +between reference and observed stars, allowing a comparison of the +magnitudes to determine the photometric calibration. The astrometric +calibration is performed in two major stages: first, the chips are +fitted independently with a low-order model consisting + + + + +\code{smf} + +\section{DVO Description} + + + +\section{Photometry Calibration} + +\subsection{Ubercal Analysis} \begin{verbatim} -Intro - Pan-STARRS background - Scope: Source Detection \& Characterization, Galaxy modeling - Requirements / Goals - Comparable programs - PSPhot - -Figures which might be interesting: - -* kron vs psf star-galaxy separation -* lensing parameters for star-galaxy separation? -* color-color locus plots -* density of stars on the sky vs mag? -* density of galaxies on the sky -* good objects vs garbage? +* data loaded into LSD database (Juric REF) @ CFA (?). +* refer to Ubercal paper +* modifications for PV3 : 2x2 grid, no new flats +* result is a collection of zero points for photometric images + * discuss stats on the zero points and the airmass terms +\end{verbatim} + +\subsection{Relphot Analysis} +\begin{verbatim} +* ingest the ubercal zero points (setphot) +* first pass to determine initial zero points for the full set of exposurse +* measure the camera-static average correction (high-resolution flat-field residual) + * report the pixel scale + * discuss the structures +* second pass to determine final zero points and average photometry + * discuss in detail the averaging, clipping strategy, IRLS +\end{verbatim} + +\section{Astrometry Analysis} +\begin{verbatim} +* initial astrometry based on real-time calibration +* relative astrometry calibration of images + * bright objects, images +* first pass to deter +\end{verbatim} + +\section{Systematic Residuals} + +\subsection{Camera-Scale Trends} + +\section{Discussion} + +\section{Conclusion} + +\begin{verbatim} + Plots: * bright-end astrometry residuals * bright-end photometry residuals * photometry residuals vs camera -in patches, measure dlogN/dmag slope and roll-off (scale?) - -chip vs warp vs stack photometry across the sky - -color-color plots: g-r,r-i r-i,i-z (the stats from photladder paper) - -number of stars @ 20.5 - -** do these plots in parallel : - \end{verbatim} -\section{INTRODUCTION}\label{sec:intro} - -\section{Pan-STARRS1} - -\section{Photometry Analysis} - -\section{Astrometry Analysis} - -\section{Systematic Residuals} - -\subsection{Camera-Scale Trends} - -\section{Discussion} - -\section{Conclusion} - \end{document} Index: /trunk/doc/release.2015/systematics.20140411/systematics.tex =================================================================== --- /trunk/doc/release.2015/systematics.20140411/systematics.tex (revision 39832) +++ /trunk/doc/release.2015/systematics.20140411/systematics.tex (revision 39833) @@ -17,6 +17,6 @@ \def\plotext{ps} -\def\picdir{/home/eugene/chipresid.20140404} -%\def\picdir{/data/pikake.2/eugene/chipresid.20140404} +%\def\picdir{/home/eugene/chipresid.20140404} +\def\picdir{/data/kukui.2/eugene/chipresid.20140404} % Pick a terse version of the title here;