IPP Software Navigation Tools IPP Links Communication Pan-STARRS Links

Ignore:
Timestamp:
Jun 30, 2016, 5:31:41 PM (10 years ago)
Author:
watersc1
Message:

Merge of updated version with figures.

File:
1 edited

Legend:

Unmodified
Added
Removed

  • trunk/doc/release.2015/ps1.detrend/detrend.tex

    r39601 r39618  
    1111\RequirePackage{color}
    1212\input{astro.sty}
     13%\usepackage{subcaption}
    1314
    1415% online version may use color, but print version needs b/w
    … …  
    110111\keywords{Surveys:\PSONE }
    111112
    112 \section{OUTLINE}
    113 \begin{verbatim}
    114 * Introduction
    115 * Raw Data Description
    116 * Basic Detrending Steps
    117   * Overscan
    118   * Dark
    119   * Flats
    120   * Fringes
    121 * Non-traditional / Non-linear issues
    122   * Persistence & Burntool
    123   * faint-end non-linearity
    124   * regions of bad CTE
    125 * Variance Maps
    126 * Static Masks
    127 * Dynamic Masks
    128   * Ghosts
    129   * Glints
    130   * Diffraction Spikes
    131 * Magic
    132 * Warping
    133   * warping kernel
    134   * linear-by-pieces
    135   * Covariance
    136   * def of skycells?
    137 * Stacking
    138   * pixel combination rules
    139   * pixel rejections
    140   * convolution for matching (success and failure)
    141 * Difference Image analysis
    142 \end{verbatim}
    143 
    144 \section{INTRODUCTION}\label{sec:intro}
    145113%% http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2007ASPC..364..153M&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf
    146114\section{Introduction and Survey Description}
    147115
    148116
    149 The Pan-STARRS 1 Science Survey uses the 1.4 giga-pixel GPC1 camera with the PS1 telescope on Haleakala Maui to image the sky north of $-30^\circ$ declination.  The GPC1 camera is composed of 60 orthogonal transfer array (OTA) devices, each of with is an $8\times{}8$ grid of readout cells.  This parallelizes the readout process, reducing the overhead in each exposure.  However, as a consequence of this large number of individual detector readouts, there are a number of calibrations that need to be included to ensure the response is consistent across the entire field of view.
    150 
    151 The PV3 reduction represents the third full processing version of the Pan-STARRS archival data.  The first two reductions were used internally for pipeline optimization and the development of the initial photometric and astrometric reference catalog.  The products from these reductions were not publicly released, but have been used to produce a wide range of scientific papers from the Pan-STARRS 1 Science Consortium members. 
    152 
    153 The Pan-STARRS image processing pipeline (IPP) is described elsewhere \citep{MagnierKaiserChambers2006}, but a short summary follows.  The archive of raw exposures is stored on disk, with a database storing the metadata of exposure parameters.  For the PV3 processing, large contiguous regions were defined, and the images for all exposures within that region lauched for the \ippstage{chip} stage processing.  This stage performs the image detrending (described below in section \ref{sec:detrending}), as well as the single epoch photometry \citep{MagnierXXY}, in parallel on the individual OTA device data.  Following the \ippstage{chip} stage is the \ippstage{camera} stage, in which the astrometry and photometry for the entire exposure is calibrated against the reference catalog.  This stage also performs masking updates based on the now-known positions and brightnesses of stars that create dynamic features (see Section \ref{sec:dynamic_masks} below).  The \ippstage{warp} stage is the next to operate on the data, transforming the detector oriented \ippstage{chip} stage images into sky oriented images that have common tesselations and sky projections (Section \ref{sec:warping}).  When all \ippstage{warp} stage processing is done for the region of the sky, \ippstage{stack} processing is performed (Section \ref{sec:stacking}) to construct deeper, fully populated images from the set of \ippstage{warp} images that cover that region of the sky.  Beyond the \ippstage{stack} stage, a series of additional stages are done that are more fully  described in other papers.  Transient features are identified in the \ippstage{diff} stage, which takes input \ippstage{warp} and/or \ippstage{stack} data and performs image differencing \citep{HuberXXX}.  Further photometry is performed in the \ippstage{staticsky} and \ippstage{skycal} stages, which add extended source fitting to the point source photometry of objects detected in the \ippstage{stack} images, and calibrate the results against the reference catalog.  The \ippstage{fullforce} stage takes the catalog output of the \ippstage{skycal} stage, and uses the objects detected in that to perform forced photometry on the individual \ippstage{warp} stage images.  The details of these stages  are provided in \citet{MagnierXXY}.
    154 
    155 The same reduction procedure described above is also performed in real time on new exposures as they are observed by the telescope.  This process is largely automatic, with new exposures being downloaded from the summit to the main IPP processing cluster at the Maui Research and Technology Center in Kihei, and registered into the processing database.  This triggers a new \ippstage{chip} stage reduction for science exposures, advancing processing upon completion through to the \ippstage{diff} stage.  This allows the ongoing solar system moving object search to identify candidates for follow up observations within 24 hours of the initial set of observations \citep{WainscoatXXX}.
     117The Pan-STARRS 1 Science Survey uses the 1.4 giga-pixel GPC1 camera
     118with the PS1 telescope on Haleakala Maui to image the sky north of
     119$-30^\circ$ declination.  The GPC1 camera is composed of 60 orthogonal
     120transfer array (OTA) devices, each of with is an $8\times{}8$ grid of
     121readout cells.  This parallelizes the readout process, reducing the
     122overhead in each exposure.  However, as a consequence of this large
     123number of individual detector readouts, there are a number of
     124calibrations that need to be included to ensure the response is
     125consistent across the entire field of view.
     126
     127The PV3 reduction represents the third full processing version of the
     128Pan-STARRS archival data.  The first two reductions were used
     129internally for pipeline optimization and the development of the
     130initial photometric and astrometric reference catalog.  The products
     131from these reductions were not publicly released, but have been used
     132to produce a wide range of scientific papers from the Pan-STARRS 1
     133Science Consortium members.
     134
     135The Pan-STARRS image processing pipeline (IPP) is described elsewhere
     136\citep{MagnierKaiserChambers2006}, but a short summary follows.  The
     137archive of raw exposures is stored on disk, with a database storing
     138the metadata of exposure parameters.  For the PV3 processing, large
     139contiguous regions were defined, and the images for all exposures
     140within that region launched for the \ippstage{chip} stage processing.
     141This stage performs the image detrending (described below in section
     142\ref{sec:detrending}), as well as the single epoch photometry
     143\citep{MagnierXXY}, in parallel on the individual OTA device data.
     144Following the \ippstage{chip} stage is the \ippstage{camera} stage, in
     145which the astrometry and photometry for the entire exposure is
     146calibrated against the reference catalog.  This stage also performs
     147masking updates based on the now-known positions and brightnesses of
     148stars that create dynamic features (see Section
     149\ref{sec:dynamic_masks} below).  The \ippstage{warp} stage is the next
     150to operate on the data, transforming the detector oriented
     151\ippstage{chip} stage images into sky oriented images that have common
     152tessellations and sky projections (Section \ref{sec:warping}).  When
     153all \ippstage{warp} stage processing is done for the region of the
     154sky, \ippstage{stack} processing is performed (Section
     155\ref{sec:stacking}) to construct deeper, fully populated images from
     156the set of \ippstage{warp} images that cover that region of the sky.
     157Beyond the \ippstage{stack} stage, a series of additional stages are
     158done that are more fully described in other papers.  Transient
     159features are identified in the \ippstage{diff} stage, which takes
     160input \ippstage{warp} and/or \ippstage{stack} data and performs image
     161differencing \citep{HuberXXX}.  Further photometry is performed in the
     162\ippstage{staticsky} and \ippstage{skycal} stages, which add extended
     163source fitting to the point source photometry of objects detected in
     164the \ippstage{stack} images, and calibrate the results against the
     165reference catalog.  The \ippstage{fullforce} stage takes the catalog
     166output of the \ippstage{skycal} stage, and uses the objects detected
     167in that to perform forced photometry on the individual \ippstage{warp}
     168stage images.  The details of these stages are provided in
     169\citet{MagnierXXY}.
     170
     171The same reduction procedure described above is also performed in real
     172time on new exposures as they are observed by the telescope.  This
     173process is largely automatic, with new exposures being downloaded from
     174the summit to the main IPP processing cluster at the Maui Research and
     175Technology Center in Kihei, and registered into the processing
     176database.  This triggers a new \ippstage{chip} stage reduction for
     177science exposures, advancing processing upon completion through to the
     178\ippstage{diff} stage.  This allows the ongoing solar system moving
     179object search to identify candidates for follow up observations within
     18024 hours of the initial set of observations \citep{WainscoatXXX}.
    156181
    157182\czwdraft{Should there be a discussion of any header keywords/OTA file formats?}
    158183
    159 Section \ref{sec:detrend construction} provides an overview of the detrend creation process for GPC1, with details of the application of those detrends to correct particular issues in Section \ref{sec:detrending}.  The further image processing steps for \ippstage{warp} and \ippstage{stack} are given in Sections \ref{sec:warping} and \ref{sec:stacking} respectively. 
    160 
    161 \czwdraft{An analysis of the algorithms used to complete the \ippstage{warp} (section \ref{sec:warping}) and \ippstage{stack} (section \ref{sec:stacking}) stage transformations of the image data to from the detector frame to a common sky frame, and the co-adding of those common sky frame images continues after the list of detrend steps.  Finally, a discussion of the remaining issues and possible future development is presented in section \ref{sec:discussion}.}
    162 
     184Section \ref{sec:detrend construction} provides an overview of the
     185detrend creation process for GPC1, with details of the application of
     186those detrends to correct particular issues in Section
     187\ref{sec:detrending}.  An analysis of the algorithms used to complete
     188the \ippstage{warp} (section \ref{sec:warping}) and \ippstage{stack}
     189(section \ref{sec:stacking}) stage transformations of the image data
     190to from the detector frame to a common sky frame, and the co-adding of
     191those common sky frame images continues after the list of detrend
     192steps.  Finally, a discussion of the remaining issues and possible
     193future improvements is presented in section \ref{sec:discussion}.
     194
     195
     196\czwdraft{Is this a sufficient explanation?  Also, is this the right
     197  place for it?}  Image products presented in figures have been
     198mosaicked to arrange pixels in the following way.  Single cell images
     199are arranged such that pixel $(1,1)$ is at the lower left corner.
     200Images mosaicked to the OTA level have cell xy00 in the lower left
     201corner, with cells xy10, xy20, etc. sequentially to the right, and
     202cells xy01, xy02, etc. sequentially to the top of this cell.  Again,
     203pixel $(1,1)$ of cell xy00 is located in the lower left corner of the
     204image.  For mosaics of the full field of view, the OTAs are arranged
     205as they see the sky.  The lower left corner is the empty location
     206where OTA70 would exist.  Toward the right, the OTA labels decrease in
     207$X$ label, with the empty OTA00 located in the lower right.  The OTA
     208$Y$ labels increase upward in the mosaic.  The OTAs to the left of the
     209midplane (OTA4Y-OTA7Y) are oriented with cell xy00 and pixel $(1,1)$
     210to the lower left of their position.  Due to the electronic
     211connections of the OTAs in the focal plane, the OTAs to the right of
     212the midplane (OTA0Y-OTA3Y) oriented with cell xy00 and pixel $(1,1)$
     213to the top right of their position, and have a negative parity to the
     214mosaic in both x and y.
    163215
    164216% Discuss 2-phase/3-phase device differnces
    … …  
    170222\label{sec:detrend construction}
    171223
    172 The detrends for GPC1 are all constructed in similar ways.  A series of appropriate exposures is selected from the database, and processed with the \ippprog{ppImage} program.  The extent of this processing is dependent on the order in which the detrend is applied to science data.  In general, the input exposures to the detrend have all stages of detrend processing applied.  Table \ref{tab:detrend ppImage} summarizes stages applied the detrends we construct.
    173 
    174 Once the input data has been prepared, the \ippprog{ppMerge} program is used to construct some sort of ``average'' of the inputs.  This step need not be a mathematical average, but is used to combine the signal from the individual exposures into a single output product.  Table \ref{tab:detrend ppMerge} lists some of the properties of the process for the detrends, including how discrepant values are removed and the combination method used.  The outputs from this step have the format of the detrend under construction, and after construction, are applied to the processed input data.  This creates a set of residual files that can be checked to determine if the newly created detrend works correctly.
    175 
    176 The process of detrend construction and testing can be iterated, with individual exposures excluded if they are found to be contaminating the output.  If the final detrend is considered sufficient, then the iterations are stopped and the detrend is finalized by selecting the date range to which it applies.  This allows subsequent science processing to select the detrends needed based on the observation date.  Table \ref{tab:detrend list} lists the set of detrends used in the PV3 processing.
     224The detrends for GPC1 are all constructed in similar ways.  A series
     225of appropriate exposures is selected from the database, and processed
     226with the \ippprog{ppImage} program.  This program is used for the
     227\ippstage{chip} stage processing as well, and is designed to do image
     228processing.  The extent of this processing is dependent on the order
     229in which the detrend is applied to science data.  In general, the
     230input exposures to the detrend have all prior stages of detrend
     231processing applied.  Table \ref{tab:detrend ppImage} summarizes stages
     232applied for the detrends we construct.
     233
     234Once the input data has been prepared, the \ippprog{ppMerge} program
     235is used to construct some sort of ``average'' of the inputs.  This
     236step need not be a mathematical average, but is used to combine the
     237signal from the individual exposures into a single output product.
     238Table \ref{tab:detrend ppMerge} lists some of the properties of the
     239process for the detrends, including how discrepant values are removed
     240and the combination method used.  The outputs from this step have the
     241format of the detrend under construction, and after construction, are
     242applied to the processed input data.  This creates a set of residual
     243files that can be checked to determine if the newly created detrend
     244works correctly.
     245
     246The process of detrend construction and testing can be iterated, with
     247individual exposures excluded if they are found to be contaminating
     248the output.  If the final detrend is considered sufficient, then the
     249iterations are stopped and the detrend is finalized by selecting the
     250date range to which it applies.  This allows subsequent science
     251processing to select the detrends needed based on the observation
     252date.  Table \ref{tab:detrend list} lists the set of detrends used in
     253the PV3 processing.
    177254
    178255\begin{deluxetable}{lcccc}
    … …  
    194271\end{deluxetable}
    195272
     273
    196274\begin{deluxetable}{lcccc}
    197275  \tablecolumns{5}
    198276  \tablewidth{0pc}
    199277  \tablecaption{Detrend Merge Options}
    200   \tablehead{\colhead{Detrend Type} & \colhead{Iterations} & \colhead{Rejection Threshold} & \colhead{Additional Clipping} & \colhead{Combination Method} }
     278  \tablehead{\colhead{Detrend Type} & \colhead{Iterations} & \colhead{Threshold} & \colhead{Additional Clipping} & \colhead{Combination Method} }
    201279  \startdata
    202   DARKMASK  & 3 & $8\sigma$ & & Mask pixel if $>10\%$ rejected \\
    203   FLATMASK  & 3 & $3\sigma$ & & Mask pixel if $>10\%$ rejected \\
    204   CTEMASK   & 2 & $2\sigma$ & & Clipped mean; mask pixel if $\sigma^2/\langle I\rangle < 0.5$ \\
     280  DARKMASK  & 3 & $8\sigma$ & & Mask if $>10\%$ rejected \\
     281  FLATMASK  & 3 & $3\sigma$ & & Mask if $>10\%$ rejected \\
     282  CTEMASK   & 2 & $2\sigma$ & & Clipped mean; mask if $\sigma^2/\langle I\rangle < 0.5$ \\
    205283  DARK      & 2 & $3\sigma$ & & Clipped mean \\
    206284  NOISEMAP  & 2 & $3\sigma$ & & Mean \\
    207   FLAT      & 1 & $3\sigma$ & Exclude top $30\%$ and bottom $10\%$ & Mean \\
     285  FLAT      & 1 & $3\sigma$ & Top $30\%$; Bottom $10\%$ & Mean \\
    208286  FRINGE    & 2 & $3\sigma$ & & Clipped mean \\
    209287  \enddata
    … …  
    217295  \tablehead{\colhead{Detrend Type} & \colhead{Detrend ID} & \colhead{Start Date} & \colhead{End Date} & \colhead{Note} }
    218296  \startdata
    219   LINEARITY & 421  & & & \\
     297  LINEARITY & 421  & 2009-01-01 00:00:00 & & \\
    220298  MASK      & 945  & 2009-01-01 00:00:00 & & \\
    221299            & 946  & 2009-12-09 00:00:00 & & \\
    … …  
    231309            & 865  & 2011-08-01 00:00:00 & 2011-11-01 00:00:00 & \\
    232310            & 866  & 2011-11-01 00:00:00 & 2019-04-01 00:00:00 & \\
    233             & 869-935 & 2010-01-25 00:00:00* & 2011-04-25 23:59:59* & B-mode \\
     311            & 869-935 & 2010-01-25 00:00:00\tablenotemark{a} & 2011-04-25 23:59:59\tablenotemark{a} & B-mode \\
    234312  VIDEODARK & 976  & 2009-01-01 00:00:00 & 2009-12-09 00:00:00 & \\
    235313            & 977  & 2009-12-09 00:00:00 & 2010-01-23 00:00:00 & \\
    … …  
    238316            & 980  & 2011-08-01 00:00:00 & 2011-11-01 00:00:00 & \\
    239317            & 981  & 2011-11-01 00:00:00 & 2019-04-01 00:00:00 & \\
    240             & 982-1048 & 2010-01-25 00:00:00* & 2011-04-25 23:59:59* & B-mode \\
     318            & 982-1048 & 2010-01-25 00:00:00\tablenotemark{a} & 2011-04-25 23:59:59\tablenotemark{a} & B-mode \\
    241319            & 1049 & 2010-09-12 00:00:00 & 2011-05-01 00:00:00 & A-mode with OTA47fix \\
    242320  NOISEMAP  & 963  & 2008-01-01 00:00:00 & 2010-09-01 00:00:00 & \\
    … …  
    251329  ASTROM    & 1064 & 2008-05-06 00:00:00 & & \\
    252330  \enddata
     331  \tablenotetext{a}{These dates mark the beginning and ending of the two-mode dark models, between which multiple dates use the B-mode dark.}
    253332  \label{tab:detrend list}
    254333\end{deluxetable}
    … …  
    257336\label{sec:detrending}
    258337
    259 Ensuring a consistent and uniform detector response across the three-degree diameter field of view of the GPC1 camera is essential to a well calibrated survey.  Many standard image detrending steps are done for GPC1, with overscan subtraction removing the detector bias level, dark frame subtraction to remove temperature and exposure time dependent detector glows, and flat field correction to remove pixel to pixel response functions.  We also construct fringe correction for the reddest data in the y filter, to remove the interference patterns that arise in that filter due to the variations in the thickness of the detector surface.
    260 
    261 These corrections, however, assume that the detector response is linear across the full range of values.  This is not universally the case with GPC1, and this requires an additional set of detrending steps to remove these non-linear responses.  The first of these is the \ippprog{burntool} correction, which removes the persistence trails caused by the incomplete transfer of charge along the readout columns.  This bright-end nonlinearity is generally only evident for the brightest stars, as only pixels that are at or beyond the saturation point of the detector have this issue.  More widespread is the non-linearity at the faint end of the pixel range.  Some readout cells and some readout cell edge pixels experience a sag relative to linear at low illumination, such that faint pixels appear fainter than expected.  The correction to this requires amplifying the pixel values in these regions to match the expected model.
    262 
    263 The final non-linear response issue has no good option for correction.  Large regions of some OTA cells experience charge transfer issues, making them unusable to be used for science observations.  These regions are therefore masked in processing, with these CTE regions making up the largest fraction of masked pixels on the detector.  Other regions are masked for other regions, such as static bad pixel features or temporary readout masking caused by issues in the camera electronics that make these regions unreliable.  These all contribute to the detector mask, which is augmented in each exposure for dynamic features that are masked based on the astronomical features within the field of view.
    264 
    265 For the PV3 processing, all detrending is done by the \ippprog{ppImage} program.  This program applies the detrends to the individual cells, and then an OTA level mosaic is constructed for the science image, the mask image, and the variance map image.  The single epoch photometry is done at this stage as well.  The following  subsections (\ref{sec:burntool} - \ref{sec:background}) detail these detrending steps, presented in the order in which they are applied to the individual OTA image data.
     338Ensuring a consistent and uniform detector response across the
     339three-degree diameter field of view of the GPC1 camera is essential to
     340a well calibrated survey.  Many standard image detrending steps are
     341done for GPC1, with overscan subtraction removing the detector bias
     342level, dark frame subtraction to remove temperature and exposure time
     343dependent detector glows, and flat field correction to remove pixel to
     344pixel response functions.  We also construct fringe correction for the
     345reddest data in the y filter, to remove the interference patterns that
     346arise in that filter due to the variations in the thickness of the
     347detector surface.
     348
     349These corrections, however, assume that the detector response is
     350linear across the full range of values.  This is not universally the
     351case with GPC1, and this requires an additional set of detrending
     352steps to remove these non-linear responses.  The first of these is the
     353\ippprog{burntool} correction, which removes the persistence trails
     354caused by the incomplete transfer of charge along the readout columns.
     355This bright-end nonlinearity is generally only evident for the
     356brightest stars, as only pixels that are at or beyond the saturation
     357point of the detector have this issue.  More widespread is the
     358non-linearity at the faint end of the pixel range.  Some readout cells
     359and some readout cell edge pixels experience a sag relative to linear
     360at low illumination, such that faint pixels appear fainter than
     361expected.  The correction to this requires amplifying the pixel values
     362in these regions to match the expected model.
     363
     364The final non-linear response issue has no good option for correction.
     365Large regions of some OTA cells experience charge transfer issues,
     366making them unusable to be used for science observations.  These
     367regions are therefore masked in processing, with these CTE regions
     368making up the largest fraction of masked pixels on the detector.
     369Other regions are masked for other regions, such as static bad pixel
     370features or temporary readout masking caused by issues in the camera
     371electronics that make these regions unreliable.  These all contribute
     372to the detector mask, which is augmented in each exposure for dynamic
     373features that are masked based on the astronomical features within the
     374field of view.
     375
     376For the PV3 processing, all detrending is done by the
     377\ippprog{ppImage} program.  This program applies the detrends to the
     378individual cells, and then an OTA level mosaic is constructed for the
     379science image, the mask image, and the variance map image.  The single
     380epoch photometry is done at this stage as well.  The following
     381subsections (\ref{sec:burntool} - \ref{sec:background}) detail these
     382detrending steps, presented in the order in which they are applied to
     383the individual OTA image data.
    266384
    267385\subsection{Burntool / Persistence effect}
    … …  
    269387
    270388Pixels that approach the saturation point on GPC1, which varies by
    271 readout with common values around 60000 DN, cause persistance problems
    272 on that and subsequent images.  During the read out process of an image with such a
    273 bright pixel, some of the charge associated with
    274 it is not fully shifted down the detector column toward the
    275 amplifier.  As a result, this charge remains in the starting cell, and
    276 is partially collected in subsequent shifts, resulting in a ``burn
     389readout with common values around 60000 DN, cause persistence problems
     390on that and subsequent images.  During the read out process of an
     391image with such a bright pixel, some of the charge associated with it
     392is not fully shifted down the detector column toward the amplifier.
     393As a result, this charge remains in the starting cell, and is
     394partially collected in subsequent shifts, resulting in a ``burn
    277395trail'' that extends from the center of the bright source away from
    278396the amplifier (vertically along the pixel columns toward the top of
    … …  
    280398
    281399This incomplete charge shifting in nearly full wells continues as each
    282 row is read out.  This results in a remnant charge being deposited in the pixels that
    283 the full well was shifted through.  In following exposures, this
    284 remnant charge leaks out, resulting in a trail that extends from the
    285 initial location of the bright source on the previous image towards
    286 the amplifier (vertically down along the pixel column).  This remnant charge
    287 can remain on the detector for up to thirty minutes, requiring the
    288 locations of these ``burns'' be retained between exposures.
    289 
    290 Both of these types of persistance trails are detected and optionally repaired via the
    291 \ippprog{burntool} program.  This program does an initial scan of the images,
    292 and identifies objects with pixel values brighter than a threshold of
    293 30000 DN.  The trail from that star is fit with a one-dimensional
    294 power law in each pixel column above that threshold, based on
    295 empirical evidence that this is the functional form of this
    296 persistence effect.  This also matches the expectation that
    297   a constant fraction of charge is incompletely transfered at each
    298   shift beyond the persistence threshold.  Once this fit is done, the
     400row is read out.  This results in a remnant charge being deposited in
     401the pixels that the full well was shifted through.  In following
     402exposures, this remnant charge leaks out, resulting in a trail that
     403extends from the initial location of the bright source on the previous
     404image towards the amplifier (vertically down along the pixel column).
     405This remnant charge can remain on the detector for up to thirty
     406minutes, requiring the locations of these ``burns'' be retained
     407between exposures.
     408
     409Both of these types of persistence trails are detected and optionally
     410repaired via the \ippprog{burntool} program.  This program does an
     411initial scan of the images, and identifies objects with pixel values
     412brighter than a threshold of 30000 DN.  The trail from that star is
     413fit with a one-dimensional power law in each pixel column above that
     414threshold, based on empirical evidence that this is the functional
     415form of this persistence effect.  This also matches the expectation
     416that a constant fraction of charge is incompletely transferred at each
     417shift beyond the persistence threshold.  Once this fit is done, the
    299418model can subtracted from the image, and the location of the star is
    300419stored in a table along with the exposure PONTIME, which denotes the
    … …  
    311430is allowed to expire.
    312431
    313 An issue with this method of correcting the persistance trails is that
     432An issue with this method of correcting the persistence trails is that
    314433it is based on fits to the raw image data, which may have other signal
    315434sources not determined by the persistence effect.  The presence of
    316435other stars or artifacts along the path of the burn can result in a
    317436poor model to be determined, resulting in either an over- or
    318 under-subtraction of the persistance burn.  For this reason, the image
     437under-subtraction of the persistence burn.  For this reason, the image
    319438mask is marked with a value indicating that this correction has been
    320439applied.  These pixels are not fully excluded, but they are marked as
    … …  
    324443Another concern is that the cores of very bright stars are deformed by
    325444this process, as the burntool fitting subtracts flux
    326 from onlyl one side of the star.  As most stars that result in burns already
     445from only one side of the star.  As most stars that result in burns already
    327446have saturated cores, they are already ignored for the purpose of
    328447PSF determination and are flagged as saturated by the photometry
    … …  
    330449
    331450\begin{figure}
    332   \caption{Panel 1: Example image of burn trail.  Panel 2: example image of subsequent image persistence trail.  Panel 3: Repair of panel 1.  Panel 4: Repair of panel 2}
     451  \centering
     452  \begin{minipage}{0.45\hsize}
     453    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0123o_XY11_bt_trail.png}
     454%    \caption{(a)}
     455%  \end{subfigure}%
     456%  \begin{subfigure}[]{.45\hsize}
     457  \end{minipage}%
     458  \begin{minipage}{0.45\hsize}
     459    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0124o_XY11_bt_trail.png}
     460%    \caption{(b)}
     461%  \end{subfigure}
     462  \end{minipage}
     463
     464  \caption{Example of a profile cut along the y-axis through a bright star on exposure o5677g0123o OTA11 in cell xy60 (left panel) and on the subsequent exposure o5677g0124o (right panel).  In both figures, the green points show the image corrected with all appropriate detrending steps, but without burntool applied, illustrating the amplitude of the persistence trails.  The red points show the same data after the burntool correction, which reduce the impact of these features.  Both exposures are in the g-filter with exposure times of 43s}
    333465\end{figure}
    334466
    335467\begin{figure}
    336   \caption{example trail data and fit.}
     468  \centering
     469  \begin{minipage}{0.45\hsize}
     470    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0123o_XY11_nobt.png}
     471%    \caption{(a)}
     472%  \end{subfigure}%
     473%  \begin{subfigure}[]{.45\hsize}
     474  \end{minipage}%
     475  \begin{minipage}{0.45\hsize}
     476    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0124o_XY11_nobt.png}
     477%    \caption{(b)}
     478%  \end{subfigure}
     479  \end{minipage}
     480  \begin{minipage}{0.45\hsize}
     481    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0123o_XY11_bt.png}
     482%    \caption{(a)}
     483%  \end{subfigure}%
     484%  \begin{subfigure}[]{.45\hsize}
     485  \end{minipage}%
     486  \begin{minipage}{0.45\hsize}
     487    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0124o_XY11_bt.png}
     488%    \caption{(b)}
     489%  \end{subfigure}
     490  \end{minipage}
     491  \caption{Example of OTA11 cell xy60 on exposures o5677g0123o (left) and o5677g0124o (right).  The top panels show the image with all appropriate detrending steps, but with burntool, and the bottom show the same with burntool applied.  There is some slight over subtraction in fitting the initial trail, but the impact of the trail is greatly reduced in both exposures.}
    337492\end{figure}
    338493
    … …  
    382537bright columns and other static pixel issues.  This is first done by
    383538processing a set of 100 i filter science images in the same fashion as
    384 for the darktest.  A median image is constructed from these inputs
     539for the DARKMASK.  A median image is constructed from these inputs
    385540along with the per-pixel variance.  These images are used to identify
    386541pixels that have unexpectedly low variation between all inputs, as
    … …  
    394549vignetted regions around the edge of the detector. 
    395550
    396 Figure \ref{fig:static mask} shows an example of the static mask for the full GPC1 field of view.  Table \ref{tab:mask_values} lists the bitmask values used for the different sources of masking.
     551Figure \ref{fig:static mask} shows an example of the static mask for
     552the full GPC1 field of view.  Table \ref{tab:mask_values} lists the
     553bit mask values used for the different sources of masking.
    397554
    398555\begin{figure}
    399   \begin{center}
    400     \includegraphics[width=0.9\hsize,angle=0,clip]{images/gpc1_mask_indexed.png}
    401     \label{fig:static mask}
    402   \end{center}
    403 
     556  \centering
     557  \includegraphics[width=0.9\hsize,angle=0,clip]{images/gpc1_mask_indexed.png}
     558  \label{fig:static mask}
     559 
    404560  \caption{Image map of static mask. color coded based on mask reason?  It won't be visible at true pixel scale.}
    405561\end{figure}
    … …  
    435591\label{sec:dynamic_masks}
    436592
    437 In addition to the static mask that removes the constant detector level
    438 defects, we also generate a set of dynamic masks that change with the
    439 astronomical features in the image.  These masks are advisory in
    440 nature, and do not completely exclude the pixel from further
    441 processing consideration.  The first of these dynamic masks is the burntool advisory mask mentioned above.  These pixels are included
    442 for photometry, but are rejected more readily in the stacking and
     593In addition to the static mask that removes the constant detector
     594level defects, we also generate a set of dynamic masks that change
     595with the astronomical features in the image.  These masks are advisory
     596in nature, and do not completely exclude the pixel from further
     597processing consideration.  The first of these dynamic masks is the
     598burntool advisory mask mentioned above.  These pixels are included for
     599photometry, but are rejected more readily in the stacking and
    443600difference image construction, as they are more likely to have small
    444601deviations due to imperfections in the burntool correction.
    … …  
    509666\end{deluxetable}
    510667 
    511 \begin{figure}
    512   \caption{Figure of crosstalk ghost and bright star source.  Plot of cut across ghost to illustrate the flat-top shape.}
    513 \end{figure}
     668%% \begin{figure}
     669%%   \centering
     670%%   \caption{Figure of crosstalk ghost and bright star source.  Plot of cut across ghost to illustrate the flat-top shape.}
     671%% \end{figure}
    514672
    515673\subsubsection{Optical ghosts}
    … …  
    589747
    590748\begin{figure}
    591   \caption{Figure of full FOV showing optical ghosts.  Possibly only a few OTAs to illustrate shape deformation.}
     749  \centering
     750  \includegraphics[width=0.9\hsize,angle=0,clip]{images/full_fpa_ghosts.jpg}
     751  \caption{Example of the full GPC1 field of view illustrating the sources and destinations of optical ghosts on exposure o5677g0123o (2011-04-26, 43s g-filter).  The bright stars on OTA33 and OTA44 result in nearly circular ghosts on the opposite OTA.  In contrast, the trio of stars on OTA11 result in very elongated ghosts on OTA66.}
    592752\end{figure}
    593753
    … …  
    599759reflective surface resulted in light being scattered across the
    600760detector surface in a long narrow glint.  This surface was physically
    601 masked on \czwdraft{DATE}, removing the possiblility of glints in
     761masked on \czwdraft{DATE}, removing the possibility of glints in
    602762subsequent data, but that taken prior have a dynamic mask constructed
    603763when a reference source falls on the focal plane within one degree of
    … …  
    631791
    632792\begin{figure}
    633   \caption{Example of glint.}
     793  \centering
     794  \includegraphics[width=0.9\hsize,angle=0,clip]{images/glint_example_o5379g0103o.jpg}
     795  \caption{Example of a glint on exposure o5379g0103o (2010-07-02, 45s i-filter).  The source star out of the field of view creates a long reflection that extends through OTA73 and OTA63.}
    634796\end{figure}
    635797
    … …  
    638800
    639801Bright sources also form diffraction spikes that are dynamically
    640 masked.  These are filter independent, and are modelled as rectangles
     802masked.  These are filter independent, and are modeled as rectangles
    641803with length $L = 10^{0.096 * (7.35 - m_{instrumental})} - 200$ and
    642804width $W = 8 + (L - 200) * 0.01$, with negative values indicating no
    … …  
    650812
    651813The cores of stars that are saturated are masked as well, with a
    652 circular maskradius $r = 10.15 * (-15 - m_{instrumental})$.  An
     814circular mask radius $r = 10.15 * (-15 - m_{instrumental})$.  An
    653815example of a saturated star, with the masked regions for the
    654816diffraction spikes and core saturation highlighted, is shown in Figure
    … …  
    656818
    657819\begin{figure}
    658   \caption{Example of saturated star, which will also nicely show the diffraction spikes.}
     820  \centering
     821  \includegraphics[width=0.9\hsize,angle=0,clip]{images/o6802g0338o_XY51_b1.jpg}
     822  \caption{Example of saturated star, with diffraction spikes extending from the core on exposure o6802g0338o, OTA51 (2014-05-25, 45s g-filter).}
    659823  \label{fig:saturated star}
    660824\end{figure}
    … …  
    692856\label{sec:masking_fraction}
    693857
    694 For the full field of view that falls on the sixty OTAs, 14.7\%
    695 \czwdraft{check this} of all pixels are masked.  The large fraction of
    696 this masking is due to regions that fall within the vignetted region.
    697 Defining the diameter of the unvignetted region to be 3 degrees, and
    698 excluding pixels that fall beyond this point reduces the static
    699 masking fraction to 9.7\%.
     858For the full field of view that falls on the sixty OTAs, 14.7\% of all
     859pixels are masked.  The large fraction of this masking is due to
     860regions that fall within the vignetted region.  Defining the diameter
     861of the unvignetted region to be 3 degrees, and excluding pixels that
     862fall beyond this point reduces the static masking fraction to 9.7\%.
    700863
    701864Unfortunately, due to the design of the OTAs and readout cells, a
    … …  
    704867$4846\times{}4868$ pixel image, the 64 $590\times{}598$ pixel readout
    705868cells cover 95.7\% of the OTA area, providing an additional 4.3\%
    706 masking in the unvignetted field of view due to the absense of a
     869masking in the unvignetted field of view due to the absence of a
    707870detector pixel.
    708871
    … …  
    764927value, we can construct the expected trend by fitting a linear model,
    765928$f_{region} = G * t_{exp} + B$, to determine the gain, $G$, and the
    766 bias, $B$ for the region considered.  This fitting was limited to only
     929bias, $B$, for the region considered.  This fitting was limited to only
    767930the range of fluxes between 12000 and 38000 counts, as these ranges
    768931were found to match the linear model well.  This range avoids the
    … …  
    824987
    825988\begin{figure}
    826   \caption{Example plot of linearity as a function of incident brightness/exposure time.}
     989  \centering
     990  \includegraphics[width=0.9\hsize,angle=0,clip]{images/linearity_XY27_xy16.png}
     991  \caption{Example plot of the linearity correction as a fraction of observed flux for OTA27, cell xy16.}
    827992\end{figure}
    828993
    … …  
    8771042over corrects the positive-gradient mode, and under corrects the
    8781043negative-gradient mode.  Upon identifying this two-mode behavior, and
    879 determining the dates each mode was dominant, two separate darks
     1044determining the dates each mode was dominant, two separate dark
    8801045models were constructed from appropriate ``A'' and ``B'' mode dark
    8811046frames.  Using the appropriate dark minimizes the effect of this bias
    … …  
    8951060replaced with a slow observation date dependent drift in the magnitude
    8961061of the gradient.  This drift is sufficiently slow that we have modeled
    897 it using three dateobs-independent dark model for different date
    898 ranges.  These darks cover the range from 2011-05-01 to 2011-08-01,
    899 2011-08-01 to 2011-11-01, and 2011-11-01 and on.  The reason for this
    900 time evolution is unknown, but as it is correctable with a small
    901 number of dark models, this does not significantly impact detrending.
     1062it using three observation date independent dark model for different
     1063date ranges.  These darks cover the range from 2011-05-01 to
     10642011-08-01, 2011-08-01 to 2011-11-01, and 2011-11-01 and on.  The
     1065reason for this time evolution is unknown, but as it is correctable
     1066with a small number of dark models, this does not significantly impact
     1067detrending.
    9021068
    9031069\begin{figure}
    904   \caption{Example of raw and dark calibrated exposure.  Plots of horizontal cuts for A/B/average corrections.}
     1070  \centering
     1071%  \begin{subfigure}[]{.45\hsize}
     1072  \begin{minipage}{0.45\hsize}
     1073    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0123o_M_OS_NL_XY23_b1.jpg}
     1074%    \caption{(a)}
     1075%  \end{subfigure}%
     1076%  \begin{subfigure}[]{.45\hsize}
     1077  \end{minipage}%
     1078  \begin{minipage}{0.45\hsize}
     1079    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0123o_to_DARK_XY23_b1.jpg}
     1080%    \caption{(b)}
     1081%  \end{subfigure}
     1082  \end{minipage}
     1083  \caption{An example of the dark model application to exposure o5677g0123o, OTA23 (2011-04-26, 43s g-filter).  The left panel shows the image data mosaicked to the OTA level, and has had the static mask applied, the overscan subtracted, and the detector non-linearity corrected.  The right panel, shows the same exposure with the dark applied in addition to the processing shown on the left.}
    9051084\end{figure}
    9061085
    9071086\begin{figure}
    908   \caption{Example of the dark switching gradients}
     1087  \centering
     1088  \includegraphics[width=0.9\hsize,angle=0,clip]{images/B_profile_ex.png}
     1089  \caption{Example showing a profile cut across exposure o5676g0195, OTA67 (2011-04-25, 43s g-filter).  The entire first row of cells (xy00-xy07) have had a median calculated along each pixel column on the OTA mosaicked image.  Arbitrary offsets have been applied to shift the curves to not overlap.  The top curve (in purple) shows the initial raw profile, without no dark model applied.  The next curve (in green) shows the smoother profile after applying the correct B-mode dark model.  Applying the incorrect A-mode dark results in the blue curve, which shows a significant increase in gradients across the cells.  The orange curve shows the result of the PATTERN.CONTINUITY correction.  Although this creates a larger gradient across the mosaicked images, it decreases the cell-to-cell level changes.  The final yellow curve shows the final image profile after all detrending and background subtraction, and has not had an offset applied.  The bright source at the cell xy00 to xy01 transition is a result of a large optical ghost, which due to the area covered, increases the median level more than the field stars.}
    9091090  \label{fig:dark switching}
    9101091\end{figure}
    … …  
    9451126+ VD_{Modern}$ produces a satisfactory result that does not
    9461127oversubtract the amplifier glow.  This is shown in figure
    947 \ref{fig:video_darks}, which shows video cells from before and after
    948 2012-05-16, corrected with both the standard and video darks, with the
    949 early video dark constructed in such a manner.
     1128\ref{fig:video_darks}, which shows video cells from before 2012-05-16,
     1129corrected with both the standard and video darks, with the early video
     1130dark constructed in such a manner.
    9501131
    9511132\begin{figure}
    952   \caption{Example of dark/video dark application}
     1133  \centering
     1134%  \begin{subfigure}[]{.45\hsize}
     1135  \begin{minipage}{0.45\hsize}
     1136    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0123o_VIDEODARK_VDim_Rdark_XY22_b1.jpg}
     1137%    \caption{(a)}
     1138%  \end{subfigure}%
     1139%  \begin{subfigure}[]{.45\hsize}
     1140  \end{minipage}%
     1141  \begin{minipage}{0.45\hsize}
     1142    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5677g0123o_VIDEODARK_VDim_VDdark_XY22_b1.jpg}
     1143%    \caption{(b)}
     1144%  \end{subfigure}
     1145  \end{minipage}
     1146  \caption{An example of the video dark model application to exposure o5677g0123o, OTA22 (2011-04-26, 43s g-filter), which has a video cell located in cell xy16.  The left panel shows the image data mosaicked to the OTA level, and has had the static mask applied, the overscan subtracted, the detector non-linearity corrected, and a regular dark applied.  The right panel, shows the same exposure with a video dark applied instead of the standard dark.  The main impact of this change is the improved correction of the corner glows, which are oversubtracted with the standard dark.}
    9531147  \label{fig:video_darks}
    9541148\end{figure}
    … …  
    9861180level are used, to match that used in the photometry on science data.
    9871181This probability can be converted into a number of false number by
    988 considereing a given area.  As the detections must be isolated to not
     1182considering a given area.  As the detections must be isolated to not
    9891183be detected as an extended object, this area must be reduced by the
    990 area a given PSF occupies.  Combining this, we find that we expecte a
     1184area a given PSF occupies.  Combining this, we find that we expect a
    9911185probability $P = 1 - \Phi_{normal}(5) = \frac{1}{2}
    9921186\erfcinv\left(\frac{5}{\sqrt{2}}\right)$, and an area given $N$
    … …  
    10091203A/B modes visible in the dark, and so we do not generate different
    10101204models for each individual dark model.  The additional pixel-to-pixel
    1011 variance from this noisemap is added to the Poissionian variance to
     1205variance from this noisemap is added to the Poissonian variance to
    10121206form the science variance image generated by the \ippstage{chip}
    10131207processing.
    … …  
    10181212endeavor, as the wide field of view makes it difficult to construct a
    10191213uniformly illuminated image.  Using a dome screen is not possible, as
    1020 the variations in illumination and screen rigidity create unusably
    1021 large scatter between different images that are not caused by the
    1022 detector response function.  Because of this, we use sky flat images
    1023 taken at twilight, which are more consistently illuminated than screen
    1024 flats.  We calculate the mean of these images to determine the
    1025 initial flat model.
     1214the variations in illumination and screen rigidity create large
     1215scatter between different images that are not caused by the detector
     1216response function.  Because of this, we use sky flat images taken at
     1217twilight, which are more consistently illuminated than screen flats.
     1218We calculate the mean of these images to determine the initial flat
     1219model.
    10261220
    10271221From this starting model, we construct a correction to remove the
    … …  
    10761270to mitigate the offsets and correct the image values.  To force the
    10771271rows to agree, a second order clipped polynomial is fit to each row in
    1078 the cell.  Four fit iterations are run, and pixels $2.5\sigma$ deiant
     1272the cell.  Four fit iterations are run, and pixels $2.5\sigma$ deviant
    10791273are excluded from subsequent fits, to minimize the effect stars and
    10801274other astronomical signals have.  The final trend is then subtracted
    … …  
    10961290
    10971291Although this correction does largely resolve the row-by-row offset
    1098 issue in a satifactory way, large and bright astronomical objects can
     1292issue in a satisfactory way, large and bright astronomical objects can
    10991293bias the fit significantly.  This results in an oversubtraction of the
    11001294offset near these objects.  As the offsets are calculated on the pixel
    … …  
    11371331
    11381332\begin{figure}
    1139   \caption{Diagram illustrating which cells on GPC1 still require the PATTERN.ROW correction to be applied.}
     1333  \centering
     1334  \includegraphics[width=0.9\hsize,angle=0,clip]{images/pattern_row_edit.png}
     1335  \caption{Diagram illustrating in red which cells on GPC1 require the PATTERN.ROW correction to be applied.  The footprint of each OTA is outlined, and cell xy00 is marked with either a filled box or an outline.  The labeling of the non-existent corner OTAs is provided to orient the focal plane.}
    11401336  \label{fig: pattern row cells}
    11411337\end{figure}
    11421338
    11431339\begin{figure}
    1144   \caption{Example of pre/post pattern row application.}
     1340  \centering
     1341  \begin{minipage}{0.45\hsize}
     1342    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5379g0103o_XY57_nopat.png}
     1343%    \caption{(a)}
     1344%  \end{subfigure}%
     1345%  \begin{subfigure}[]{.45\hsize}
     1346  \end{minipage}%
     1347  \begin{minipage}{0.45\hsize}
     1348    \includegraphics[width=0.9\hsize,angle=0,clip]{images/o5379g0103o_XY57_pat.png}
     1349%    \caption{(b)}
     1350%  \end{subfigure}
     1351  \end{minipage}
     1352  \caption{Example of the PATTERN.ROW correction on exposure o5379g0103o OTA57 cell xy00 (i-filter 45s).  The left panel shows the cell with all appropriate detrending except the PATTERN.ROW, and the right shows the same cell with PATTERN.ROW applied.  The correction reduces the correlated noise on the right side, which is most distant from the read out amplifier.  There is a slight over subtraction along the rows near the bright star. \czwdraft{which I can't seem to find proper ranges to highlight.}}
    11451353\end{figure}
    11461354
    … …  
    11701378background gradient variations along the rows of the cells that is not
    11711379stable enough to be completely fit by the dark model.  This common
    1172 feature across the columns of cells results in a ``sawtooth'' pattern
     1380feature across the columns of cells results in a ``saw tooth'' pattern
    11731381horizontally across an OTA, and as the background model fits a smooth
    11741382sky level, this induces over and under subtraction at the cell
    … …  
    11771385this higher order issue.
    11781386
    1179 The replacment for PATTERN.CELL is the PATTERN.CONTINUITY correction,
     1387The replacement for PATTERN.CELL is the PATTERN.CONTINUITY correction,
    11801388which attempts to match the edges of a cell to those of its neighbors.
    11811389For each cell, a thin box 10 pixels wide on each edge is extracted and
    … …  
    11891397neighbors.
    11901398
    1191 For OTAs that initially show the sawtooth pattern, the effect of this
     1399For OTAs that initially show the saw tooth pattern, the effect of this
    11921400correction is to align the cells into a single ramp, at the expense of
    11931401the absolute background level.  However, as we subtract off a smooth
    … …  
    11961404smoother than it would be otherwise also allows for the background
    11971405subtracted image to more closely match the astronomical sky, without
    1198 significant errors at cell boundaries.  An example of the image before
    1199 and after this correction is shown in figure \ref{fig: continuity
    1200   example}.
    1201 
    1202 \begin{figure}
    1203   \caption{Continuity example, with background issue.}
    1204   \label{fig: continuity example}
    1205 \end{figure}
     1406significant errors at cell boundaries.  An example of the effect of
     1407this correction on an image profile is shown in Figure \ref{fig:dark switching}.
     1408
     1409%% \begin{figure}
     1410%%   \centering
     1411%%   \caption{Continuity example, with background issue.}
     1412%%   \label{fig: continuity example}
     1413%% \end{figure}
    12061414
    12071415\subsection{Fringe correction}
    … …  
    12431451
    12441452\begin{figure}
    1245   \caption{Example of y-filter fringe pattern, before and after correction.}
     1453  \centering
     1454  \begin{minipage}{0.5\hsize}
     1455    \includegraphics[width=1.0\hsize,angle=0,clip]{images/o5220g0025o_XY53_nofringe.png}
     1456%    \caption{(a)}
     1457%  \end{subfigure}%
     1458%  \begin{subfigure}[]{.45\hsize}
     1459  \end{minipage}%
     1460  \begin{minipage}{0.5\hsize}
     1461    \includegraphics[width=1.0\hsize,angle=0,clip]{images/o5220g0025o_XY53_fringe.png}
     1462%    \caption{(b)}
     1463%  \end{subfigure}
     1464  \end{minipage}
     1465  \caption{Example of the y-filter fringe pattern on exposure o5220g0025o OTA53 (y-filter 30s).  The left panel shows the OTA mosaic with all detrending except the fringe correction, while the right shows the same including the fringe correction.  Both images have been smoothed with a Gaussian with $\sigma = 3$ pixels to highlight the faint and large scale fringe patterns. \czwdraft{See if there's a way to have mana produce images larger than the screen size.}}
    12461466  \label{fig: fringe example}
    12471467\end{figure}
    … …  
    13021522overlap.
    13031523
    1304 Foreach output skycell, all overlapping OTAs and the calibrated
     1524For each output skycell, all overlapping OTAs and the calibrated
    13051525catalog are read into the \ippprog{pswarp} program.  Each input image
    13061526is examined in order, and the same transformation performed.  This
    … …  
    14641684% @ISIS.ORDERS    S32     6    4    2     # Polynomial orders for ISIS kernels
    14651685
    1466 Once the convolution kernels are defind for each image, they are used
     1686Once the convolution kernels are defined for each image, they are used
    14671687to convolve the image to match the target PSF.  Any input image that
    14681688has a $\chi^2$ value greater than 4.0$\sigma$ larger than the median
    … …  
    17641984\label{sec:discussion}
    17651985
     1986\czwdraft{Although the detrending and image combination algorithms
     1987  work well to produce a consistent and calibrated images, having the
     1988  full PV3 data set allows issues to be identified and solutions
     1989  created for future improvements to the IPP pipeline.  In addition,
     1990  the existence of the final calibrated catalog can be used to look
     1991  for issues that appear dependent on focal plane position.}
     1992
     1993An obvious way to make use of the PV3 catalog is to do a statistical
     1994search for electronic crosstalk ghosts that do not match a known rule.
     1995Given that bright stars do not equally populate all fields, choosing
     1996exposures to examine to look for crosstalk rules is difficult.  The
     1997current crosstalk rules were derived from expectations based on the
     1998detector engineering, supplemented by rules identified largely based
     1999on unmatched transients.  With the full catalog, identification of new
     2000rules can be done statistically, looking at detection pairs that
     2001appear more often than random. 
     2002
     2003There is some evidence that we have not fully identified all of these
     2004crosstalk rules, based on a study of PV3 images.  For example,
     2005extremely bright stars \czwdraft{exp o5677g0123o has this rule, find a
     2006  magnitude} may be able to create crosstalk ghosts between the second
     2007cell column of OTA01 and OTA21, with possibly fainter ghosts appearing
     2008on OTA11.  Despite the symmetry observed in the main ghost rules,
     2009there do not appear to be clear examples of a similar ghost between
     2010OTA47 and OTA66.  Examining this further based on the PV3 catalog
     2011should provide a clear answer to this, as well as clarify brightness
     2012limits below which the ghost does not appear.
     2013
     2014The PV3 catalog may also allow better determination of which date
     2015ranges we should use to build the dark model.  The date ranges
     2016currently in use are based on limited sampling of exposures, and do
     2017not have strong tests indicating that they are the best.  By examining
     2018the scatter between the detections on a given exposure and the catalog
     2019average, we can attempt to look for increases in scatter that might
     2020suggest that the dark model used is not completely correcting the
     2021camera.  Looking at this based on the catalog would allow this
     2022information to be generated without further image level processing.
     2023
     2024In addition to improving the quality of the catalog for any future
     2025reprocessing, there are a number of possible improvements that could
     2026fix the image cosmetics.  A study of the burntool fits on stars that
     2027have been badly saturated suggest that we may be able to improve the
     2028trail fits by considering not the star center, but rather the edge of
     2029saturation.  This restricts the fit to only consider the data along
     2030the trail, and may improve the fit quality.  Implementing this change
     2031would require additional bookkeeping of which pixels were saturated,
     2032as the fits on subsequent exposures will need to skip these pixels
     2033before fitting the persistence trail.  This is unlikely to seriously
     2034impact the photometry of objects, but may improve the results of
     2035stacks if fewer pixels need to be rejected.
     2036
     2037The fringe model used currently is based on only a limited number of
     2038days of data \czwdraft{one, I believe}.  This means that the model
     2039calculated may not be fully sensitive to the exact spectrum of the
     2040sky.  This may make the model quality differ based on the date and
     2041local time of observation.  There is some evidence that the fringe
     2042model does fit some dates better than others, and so improving this by
     2043expanding the number of input exposures may improve a wider range of
     2044dates.
     2045% o5818g0349o is a good example of bad fringe correction.
     2046
     2047Finally, a large number of issues arise due to the row-to-row bias
     2048issues.  The PATTERN.ROW correction is used on a limited number of
     2049cells, to minimize any possible distortion of bright stars or dense
     2050fields by the fitting process.  As the row-to-row bias changes very
     2051quickly in the y pixel axis and slowly along the x, it may be possible
     2052to isolate and remove this signal in the Fourier domain.  Preliminary
     2053investigations have shown that there is a small peak visible in the
     2054power spectrum of a single cell, but determining the optimal way to
     2055clip this peak to reduce the noise in the image space is not clear.
     2056
     2057
     2058\czwdraft{I need a good concluding thing to say, so it doesn't end with, ``we should do better next time.''}
     2059
     2060The Pan-STARRS1 Surveys (PS1) have been
     2061made possible through contributions by the Institute for Astronomy, the
     2062University of Hawaii, the Pan-STARRS Project Office, the Max-Planck
     2063Society and its participating institutes, the Max Planck Institute for
     2064Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial
     2065Physics, Garching, The Johns Hopkins University, Durham University,
     2066the University of Edinburgh, the Queen's University Belfast, the
     2067Harvard-Smithsonian Center for Astrophysics, the Las
     2068Cumbres Observatory Global Telescope Network Incorporated, the
     2069National Central University of Taiwan, the Space Telescope Science Institute, and the National
     2070Aeronautics and Space Administration under Grant No. NNX08AR22G issued
     2071through the Planetary Science Division of the NASA Science Mission
     2072Directorate, the National Science Foundation Grant No. AST-1238877,
     2073the University of Maryland, Eotvos Lorand University (ELTE),
     2074and the Los Alamos National Laboratory.
     2075
    17662076
    17672077\end{document}
Note: See TracChangeset for help on using the changeset viewer.