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<!DOCTYPE html>
<html>
<head>
<title>Exposure checker | Tutorial</title>
<link rel="stylesheet" media="screen" href="assets/bootstrap/css/bootstrap.min.css" type="text/css" charset="utf-8">
<link rel="stylesheet" media="screen" href="assets/eyeball.css" type="text/css" charset="utf-8">
<meta charset="utf-8">
<meta name="author" content="Peter Melchior, Erin Sheldon, Alex Drlica-Wagner">
<link rel="icon" href="assets/DESC_logo_trans.png" type="image/png">
<!-- Le HTML5 shim, for IE6-8 support of HTML elements -->
<!--[if lt IE 9]>
<script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
</head>
<body>
<div id="wrapper">
<div class='container'>
<div class="navbar">
<div class="navbar-inner">
<a class="brand" href="index.html">Exposure checker</a>
<ul class="nav">
<li><a href="viewer.html">Viewer</a></li>
<li class="active"><a href="#">Tutorial</a></li>
<li><a href="faq.html">FAQ</a></li>
<li><a href="statistics.html">Statistics</a></li>
<li><a href="api.html">API</a></li>
<li><a href="gallery.html">Gallery</a></li>
<li><a href="hodgepodge.html">Hodge-podge</a></li>
</ul>
</div>
</div>
<!-- content area -->
<div class="span12">
<h1>Tutorial</h1>
<a id="tutorial-anchor"></a>
</div>
<div class="span12">
<p>The primary interface for the Exposure Checker is the <a href="viewer.html">Viewer</a>, which displays half of an LSST CCD.
Initally three buttons are shown:</p>
<button id="skip-button" class="btn btn-primary skip">Skip</button>
<button id="fine-button" class="btn btn-success">Submit</button>
<!--#include file="problem_selector.shtml"-->
<p style="margin-top:10px">
If you are quickly scanning through images without assessing them, press the <span style="font-weight: bold; color:#006dcc">Skip</span> button to move to the next image.
If there are no obvious issues with the image displayed, press <span style="font-weight: bold; color:#46a546">Submit</span> to flag the image as good.
Otherwise, click the <span style="font-weight: bold; color:#9d261d">Problem</span> button and select one of the predefined problem categories.
Click on the location(s) of the problematic features to mark them on the image.</p>
<p>In the course of marking problems, two new buttons will appear:</p>
<div id="mark-buttons">
<button class="btn btn-primary" data-toggle="button">False</button>
<button class="btn btn-primary">Clear Last</button>
</div>
<p style="margin-top:10px">
With the <span style="font-weight: bold; color:#006dcc">False</span> button, you can report a non-existent problem that has been falsely flagged by data management (DM),
e.g. a mask that covers an area that appears totally fine.
Because DM interpolates over some features (cosmic rays, bleed trails, etc.) it can be very difficult to assess whether DM is performing properly.
If you do determine that a mask was added in error, choose the appropriate mask category click on this button to report it.
When you click on the image, a mark will appear to indicate that you are reporting a false positive.
After you've marked the first problem, another button <span style="font-weight: bold; color:#006dcc">Clear Last</span> will appear to let you undo your mark(s).
Once you are done marking all problems, click <span style="font-weight: bold; color:#46a546">Submit</span> to log the problems and advance to the next image.
</p>
<p>
The Exposure Checker provides a means to further investigate an image using these buttons:</p>
<p>
<div class="btn-group">
<button id="info-button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">Info</span><span class="caret"></span></button>
<ul class="dropdown-menu" role="menu" aria-labelledby="dLabel">
<li><a tabindex="-1" href="#tutorial-anchor" id="share-button">Share <u>l</u>ink</a></li>
<li><a tabindex="-1" href="#tutorial-anchor" id="desdm-button"><u>D</u>ownload original image</a></li>
<li><a tabindex="-1" href="#tutorial-anchor" id="fov-button">Show entire <u>F</u>oV</a></li>
<li><a tabindex="-1" href="#tutorial-anchor" id="reported-button">Show reported <u>p</u>roblems</a></li>
</ul>
</div>
<button class="btn btn-primary">Toggle <u>m</u>ask</button>
<button class="btn btn-primary">Toggle s<u>c</u>aling</button>
</p>
<p>
The <span style="font-weight: bold; color:#006dcc">Info</span> button opens a menu with a link to the image you are currently viewing, the path to the full resolution FITS file, and a PNG showing the entire focal plane. You can also overlay problems previously reported for this image by other users.
The <span style="font-weight: bold; color:#006dcc">Toggle Mask</span> button allows you to turn on and off the image mask, while the <span style="font-weight: bold; color:#006dcc">Toggle Scaling</span> button lets you change the image scaling.
</p>
<p>
You now have everything you need to start looking at images.
If you still have questions, go the <a href="faq.html">FAQ</a> page and see if we cover it already.<br>
The remainder of this tutorial goes into more detail about several common imaging artifacts. The <b>Simulation</b> section is geared towards issues in LSST DESC simulated images, while the other sections document common problems in real DES data.
</p>
</div>
<div class="span12">
<a id="simulation-anchor"></a>
<h2>Simulation</h2>
This section is for collecting feedback and issues on the simulation software. It is currently filled with problem classes (and examples) that were detected in DECam data from DES. Since we don't know exactly what issues we will run across with LSST, this section is open ended and evolving. If you see an issue that you don't know how to classify, mark it with "Other..." and report it on the <a href="https://lsstc.slack.com/messages/C932BQ550">#desc-dc2-eyeball</a> channel.
</div>
<div class="span7" >
<a id="speckle-anchor"></a>
<h4>Speckling</h4>
<p> Speckling can occur near bright objects and arises from a hardware-specific feature in PhoSim runs.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/speckle.png"><img src="material/speckle.png" /></a>
<small>Speckling around bright galaxies (LSST)</small>
</p>
</div>
<div class="span7" >
<a id="cosmic-anchor"></a>
<h4>Cosmic</h4>
<p> Issues with cosmic ray generation and simulation. May include (but is not limited to) the number of cosmics simulated. The length of cosmic rays, the scattering rate, the sharpness of cosmic ray edges, filter dependence, etc.
</p>
</div>
<div class="span7" >
<a id="star-anchor"></a>
<h4>Star</h4>
<p> Issues with star generation and simulation. May include (but is not limited to): the size of stars, the brightnesses of stars, bleed trails from the saturation of stars. If you start to see consistent artifacts please add a new description in the "Other" classification.
</p>
</div>
<div class="span7" >
<a id="galaxy-anchor"></a>
<h4>Galaxy</h4>
<p> Issues with galaxy generation and simulation. May include (but is not limited to): the size of galaxies, the brightnesses of galaxies, the orientation of galaxies. If you start to see consistent artifacts please add a new description in the "Other" classification.
</p>
</div>
<div class="span7" >
<a id="skybkg-anchor"></a>
<h4>Sky background</h4>
<p> Issues with sky background generation and simulation. May include (but is not limited to): the brightness, smoothness, and uniformity of the sky background. If you start to see consistent artifacts please add a new description in the "Other" classification.
</p>
</div>
<div class="span7" >
<a id="instrument-anchor"></a>
<h4>Instrument</h4>
<p> Issues with how the instrument is simulated. May include (but is not limited to): incorrect camera/ccd geometry, incorrect reflections/scattered light, saturation effects (i.e., edge bleeds), electronic noise, etc. If you start to see consistent artifacts please add a new description in the "Other" classification.
</p>
</div>
<div class="span12">
<a id="masking-anchor"></a>
<h2>Masking</h2>
</div>
<div class="span7" >
<a id="column-mask-anchor"></a>
<h4>Column Mask</h4>
<p> There are a number of columns that behave differently than their neighbors.
Often this occurs when a hot pixel in the column bleeds over during readout.
We attempt to mask these columns with a "bad pixel mask" and it is useful to know when we are missing bad columns.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/column_mask.gif"><img src="material/column_mask.gif" /></a>
<small>Partially masked bad column (DES)</small>
</p>
</div>
<div class="span7" >
<a id="cosmic-ray-anchor"></a>
<h4>Cosmic rays</h4>
<p> Unmasked cosmic rays should become apparent when you use
<button class="btn btn-small btn-primary">Toggle s<u>c</u>aling</button>
to switch to a scaling that emphasizes the bright aspects of the image and
<button class="btn btn-small
btn-primary">Toggle <u>m</u>ask</button> to blink the existing
mask. LSST DM interpolates masked cosmic ray pixels, which
makes it difficult to identify over-agressive masking.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/cosmic_ray.gif"><img src="material/cosmic_ray.gif" /></a>
<small>Several partially masked cosmic rays (DES)</small>
</p>
</div>
<div class="span7">
<a id="cross-talk-anchor"></a>
<h4>Cross-talk</h4>
<p>Cross-talk is a leakage of charge between electronic readout
channels. Cross-talk can usually be identified as long,
vertical features, typically several pixels wide and
often widest in the middle section. Cross-talk is generally
strongest between amplifiers on the same chip, and you should be
able to find a bright object that is the source of the charge.
Mark the widest region of the cross-talk feature (usually near the middle).
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/cross_talk.gif"><img src="material/cross_talk.gif" /></a>
<small>Cross-talk from several bright stars (DES)</small>
</p>
</div>
<div class="span7">
<a id="edge-bleed-anchor"></a>
<h4>Edge-bleed</h4>
<p> Very bright stars saturate the readout electronics leading
to bright bleeds on the readout side of the CCD. Edge-bleeds
should be automatically identified and masked with a
rectangular strip. If this mask is too big, too small, or not
present at all, please tag the location of the error.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/edge_bleed.gif"><img src="material/edge_bleed.gif" /></a>
<small>Edge-bleed on left side from bright star further right (DES)</small>
</p>
</div>
<div class="span7">
<a id="excessive-mask-anchor"></a>
<h4>Excessive mask</h4>
<p> Occasionally large regions of a CCD get masked for no
apparent reason. In LSST images, this is most commonly seen
from over-agressive cosmic ray masking. Toggle the mask and
flag excessive masks when you see them.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/excessive_mask.gif"><img src="material/excessive_mask.gif" /></a>
<small>Excessive masking likely due to a failed edge-bleed mask (DES)</small>
</p>
</div>
<div class="span12">
<h2>Sky Estimation</h2>
</div>
<div class="span7">
<a id="dark-rim-anchor"></a>
<h4>Dark rim</h4>
<p> It is fairly common for dark regions to appear in the corners and around the edges of images.
These reflect an over-subtraction of the sky background in these regions.
These dark rims are often correlated with bright stars or dense fields.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/dark_rim.gif"><img src="material/dark_rim.gif" /></a>
<small>Dark rim at the top-left corner (DES)</small>
</p>
</div>
<div class="span7">
<a id="dark-halo-anchor"></a>
<h4>Dark halo</h4>
<p> Dark halos occasionally appear surrounding bright objects.
This results from the sky background being over-estimated close to these objects.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/dark_halo.gif"><img src="material/dark_halo.gif" /></a>
<small>A dark halo appears around the bright star in this image (DES)</small>
</p>
</div>
<div class="span7">
<a id="Quilted-sky-anchor"></a>
<h4>Quilted sky</h4>
<p> Occasionally images show strong rectilinear patterning, and in the worst cases a CCD will appear as a 4x8 quilt of light and dark regions.
This quilting is introduced by a mismatch in the normalization factor between the pupil and illumination correction (both of which are calculated in 512 pixel blocks).
This artifact often appears strongest near the sides of the CCD, and can manifest itself as a single vertical line inset by roughly 1/8th of a CCD length.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/quilted_sky.gif"><img src="material/quilted_sky.gif" /></a>
<small>Quilted sky (downsampled by 2x) (DES)</small>
</p>
</div>
<div class="span7">
<a id="wavy-sky-anchor"></a>
<h4>Wavy sky</h4>
<p> Wavy sky appears as large-scale structures contributing a high-level of sky background.
These features are often correlated over the entire focal plane and can occur for several exposures in a row (they may be the result of poor observing conditions).
We don't understand the root cause of this yet...
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/wavy_sky.gif"><img src="material/wavy_sky.gif" /></a>
<small>Wavy sky (downsampled by 2x) (DES)</small>
</p>
</div>
<div class="span7">
<a id="anti-bleed-anchor"></a>
<h4>Anti-bleed</h4>
<p> Anti-bleeds are dark streaks extending from bright stars orthogonal to the readout direction.
They have a width roughly comparable to the masked region of the star.
They appear in the reduced images and are not purely an artifact of the sky background subtraction.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/anti_bleed.gif"><img src="material/anti_bleed.gif" /></a>
<small>Dark anti-bleed around bright stars (DES)</small>
</p>
</div>
<div class="span12">
<h2>Flat Field</h2>
</div>
<div class="span7">
<a id="ab-jump-anchor"></a>
<h4>Amp jump</h4>
<p>The LSST CCDs are read out by 16 different amplifiers (8 per exposure checker image).
The gains on these amplifiers are different leading to a different background level in different sections of each CCD.
Differences between amplifiers should be corrected in processing; however, a failure can lead to a strong change in the background level at the amplifier boundaries.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/amp_jump.png"><img src="material/amp_jump.png" /></a>
<small>Amplifier bias-level jump (LSST)</small>
</p>
</div>
<div class="span7">
<a id="fringing-anchor"></a>
<h4>Fringing</h4>
<p> Fringes are an interference pattern that occur at red wavelengths when the CCDs become transparent (think of the fringes on the surface of an oily puddle).
Fringes are known to be variable (relative to the rest of sky brightness) and they can be difficult to deal with.
They occur most commonly in the z- and y-bands.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/fringing.gif"><img src="material/fringing.gif" /></a>
<small>Strong fringing pattern (DES)</small>
</p>
</div>
<!-- Not in DC2
<div class="span7">
<a id="tape-bump-anchor"></a>
<h4>Tape bump</h4>
<p> The silicon wafers are attached to the CCD backplanes by six pieces of double-sided tape (three along each long edge of the CCD).
Physical stresses on the silicon lattice distort the electric field in these regions changing the effective size of the pixels in these regions.
A failure in flat-fielding can lead to one or often more of these tape bumps being visible in the reduced image.
For more information, see <a href="http://arxiv.org/abs/1403.6127">this paper</a>.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/tape_bumps.gif"><img src="material/tape_bumps.gif" /></a>
<small>Tape bump at the bottom center, together with fringing</small>
</p>
</div>
-->
<div class="span7">
<a id="tree-rings-anchor"></a>
<h4>Tree rings</h4>
<p> Tree rings are concentric, circularly symmetric features arising changes in the effective pixel size resulting from transverse electric fields in the CCDs.
Tree rings originate from variations in the doping impurities during single-crystal silicon growth.
Thus, the tree ring pattern of each CCD will depend on its relative position in the silicon wafer.
Tree rings appear most strongly in the z-band.
For more information, see <a href="http://arxiv.org/abs/1403.6127">this paper</a>.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/tree_rings.gif"><img src="material/tree_rings.gif" /></a>
<small>Strong concentric tree ring pattern (DES)</small>
</p>
</div>
<div class="span7">
<a id="vertical-jump-anchor"></a>
<h4>Vertical jump</h4>
<p>
Vertical jumps can arises from the incorporation of a few bad flats into the calibration sets.
These flats contain a strong gradient caused by the shutter failing to close during readout.
Due to the clipping algorithm when combining multiple flats, this results in a vertical "jump" near the center of flat-fielded images.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/vertical_jump.gif"><img src="material/vertical_jump.gif" /></a>
<small>Vertical jump from bad flats (DES)</small>
</p>
</div>
<div class="span12">
<h2>Reflections</h2>
</div>
<div class="span7">
<a id="bright-spray-anchor"></a>
<h4>Bright spray</h4>
<p> Light from bright off-axis stars can scatter at grazing incidence off of various surfaces in the optical train..
This leads to broad bright sprays fanning out from the edge of the focal plane.
These features can be most easily identified on the full focal plane images via the <button class="btn btn-small btn-primary">Info</button> button.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/bright_spray.gif"><img src="material/bright_spray.gif" /></a>
<small>Example of strong spray of scattered light (DES)</small>
</p>
</div>
<div class="span7">
<a id="ghost-anchor"></a>
<h4>Ghosts</h4>
<p>Ghost are reflections off the internal camera optics.
They dominantly appear when a bright object is in the field of view and often occupy very large areas (from parts of a chip to the entire focal plane).
Small ghosts can be identified on a single chip by their characteristic "tie-fighter window" pattern; however, often it is helpful to look at images of the full focal play.
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/ghost.gif"><img src="material/ghost.gif" /></a>
<small>Pupil ghost next to a bright star (DES)</small>
</p>
</div>
<div class="span7">
<a id="brush-strokes-anchor"></a>
<h4>Brush strokes</h4>
<p> In addition to "Bright Sprays", less intense scattered light features appear on smaller scales.
These have been termed "Brush Strokes" due to their diffuse, sweeping appearance.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/brush_strokes.gif"><img src="material/brush_strokes.gif" /></a>
<small>Brush strokes of scattered light (DES)</small>
</p>
</div>
<div class="span7">
<a id="bright-arc-anchor"></a>
<h4>Bright arc</h4>
<p> Bright arcs are another type of scattered light found in DES. They are believed to have arisen from reflections off the uncoated edge of the filters (a "Type II" spray) and scattering off of the filter cage.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/bright_arc.gif"><img src="material/bright_arc.gif" /></a>
<small>Bright arc of scattered light (DES)</small>
</p>
</div>
<!-- Not included in DC2
<div class="span12">
<h2>Tracks</h2>
</div>
<div class="span7">
<a id="satellite-anchor"></a>
<h4>Satellite</h4>
<p>Satellite, orbital stages of rockets, and other reflecting bodies
often cross our focal plane.
They create long, unsaturated streaks on the images, much longer and wider than cosmic rays. Since they are so
large, you can mark the track wherever you want. Sometimes, however,
the tracks are broken into segments (note: <a href="http://www.satobs.org/tumble/tumbleintro.html">rocket parts may tumble</a>),
in which case we'd like to have marks on each of the segments.
In Y1A1, be sure to keep an eye out for falsely masked streaks (i.e., streak masks when no streak is present).
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/satellite.gif"><img src="material/satellite.gif" /></a>
<small>Satellite streak</small>
</p>
</div>
<div class="span7">
<a id="airplane-anchor"></a>
<h4>Airplane</h4>
<p> Unfortunately, CTIO lies along a regional Chilean airline flight path.
We expect that roughly 15 planes will cross the DECam focal plane per season.
Planes have a much larger impact that satellites, often destroying the sky background estimation.
When lights on a airplane blink, they appear as out-of-focus donuts (and can be used to determine the height of the plane...).
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/airplane.gif"><img src="material/airplane.gif" /></a>
<small>An airplane trail (factor 2 downsampled)</small>
</p>
</div>
-->
<!-- Not included in DC2 (or probably any simulations)
<div class="span12">
<h2>Instrument/Telescope</h2>
</div>
<div class="span7">
<a id="guiding-anchor"></a>
<h4>Guiding Failure</h4>
<p> Failures in the telescope guiding can lead to extended and elongated sources.
These issues will hopefully be solved in Year 1.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/guiding.gif"><img src="material/guiding.gif" /></a>
<small>A guiding error leading to blurred sources.</small>
</p>
</div>
<div class="span7">
<a id="shutter-anchor"></a>
<h4>Shutter Failure</h4>
<p> Star bleeds are often symptomatic of the camera being readout with the shutter still open.
Star bleeds caused by shutter errors can be identified by looking at the full focal plane image, where the direction of the star bleeds will change between the top and bottom of the focal plane (due to a switch in the readout direction).
Shutter errors should be solved by Year 2.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/shutter.gif"><img src="material/shutter.gif" /></a>
<small>A shutter failure leading to star trails</small>
</p>
</div>
<div class="span7">
<a id="readout-anchor"></a>
<h4>Readout</h4>
<p>There are additional readout glitches, which are usually manifest as nearly vertical hatched lines near the edges of the CCDs.
These issues should be fixed early in SV.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/readout.gif"><img src="material/readout.gif" /></a>
<small>Image with a readout glitch on the left side</small>
</p>
</div>
<div class="span7">
<a id="haze-anchor"></a>
<h4>Haze</h4>
<p> Haze appears as large diffuse blurs around bright objects.
It affects the entire focal plane and can thus be seen well from the FoV images.
The reason could be a slightly overcast sky, but we don't fully understand the root cause of this yet...
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/haze.gif"><img src="material/haze.gif" /></a>
<small>Image with haze around bright stars (plus dark halos)</small>
</p>
</div>
<div class="span7">
<a id="vertical-stripes-anchor"></a>
<h4>Vertical stripes</h4>
<p> Some images contain a grainy vertical striping.
Sometimes, this striping can be so bad that the image gets excessively masked.
Vertical striping can be caused by a loose sync cable influencing the readout electronics.
The root cause can be both the individual images or the bias frame that is subtracted from each raw image.
Vertical striping is known to affect exposures taken in November, 2013 (specifically, CCDs on backplane 1).
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/vertical_stripes.gif"><img src="material/vertical_stripes.gif" /></a>
<small>Vertical stripes, resulting in excessive masking</small>
</p>
</div>
<div class="span7">
<a id="other-anchor"></a>
<h2>Other...</h2>
<p>Sometimes none of the existing categories fit.
In this case, you can describe the problem in your own words.
Please do so in a way that is as comprehensible and consistent as possible. To help you do that, we remember the descriptions you've used before and show them to you.
To get a sense of what other people have found, check out our <a href="hodgepodge.html">Hodge-podge</a> page that show you a list of free-word categories from all users.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/other.gif"><img src="material/other.gif" /></a>
<small>Image with "bizarre PSF" (possibly a guider fault)</small>
</p>
</div>
-->
<div class="span7">
<a id="awesome-anchor"></a>
<h2>Awesome!</h2>
<p>Rarely, you'll come across a truly phenomenal sight: a comet, a dense star cluster, a group of interacting galaxies, etc.
Report these objects by selecting "Awesome!" from the drop-down, then describe what you see and click on the object.
We collect these objects in our <a href="gallery.html">Gallery</a>.</p>
<p>If you'd like to help by inspecting Gallery entries
for our website and outreach purposes, please contact us.
</p>
</div>
<div class="span5">
<p class="img-polaroid">
<a href="material/awesome.gif"><img src="material/awesome.gif" /></a>
<small>Comet C/2010 R1 (DES)</small>
</p>
</div>
<div class="span12">
<h2>Want to help?</h2>
Help is always welcome! If you think you found a new class of artifacts, let us know. If you know where these artifacts come from, let us know. The best way to contact us is through the <a href="https://lsstc.slack.com/messages/C932BQ550">#desc-dc2-eyeball</a> channel or by opening a <a href="https://github.com/LSSTDESC/desc-exp-checker/issues">GitHub issue</a>.
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