Changes between Version 3 and Version 4 of Image_Artifacts

Timestamp:

Jul 28, 2009, 4:06:25 PM (17 years ago)

Author:

Paul Price

Comment:

More details about artifacts

Image_Artifacts

@@ -1 +1 @@
 == PS1 Image Artifacts ==
 
-== Burntool ==
+== Burns ==
 
-Three different patterns that can arise from burntool.  The first has a bright streak that burntool should have removed.  The second has the burn from a star on a previous image oversubtracted either due to a bad fit or the images being processed in the wrong order.  The third shows an oversubtraction of the burn.
+"Burns" are the result of bright sources landing on the detector in the image under consideration, or a recent image, causing trails along the detector columns.  It seems that lots of excess charge upsets the pixels.  When this charge is clocked out, some of it remains, causing a burn trail that goes upward (away from the amplifier) in the image with a bright source.  Then in subsequent exposures, the angry pixels slowly leak charge, causing burn trails that go downward (towards the amplifier).
+
+'burntool' has been developed by the Camera group (specifically, John Tonry) to attempt to remedy these artifacts in software.  Since it requires operation on images in the order in which they were observed, it must be run on data in the IPP after registration but before the chip stage is executed (output is named *.burn.fits, set rawImfile.user_1 = 1.0, and then turn on USE.DEBURNED.IMAGE in the PPIMAGE recipe).  Efforts are underway in the Camera group to fix these artifacts in hardware.
+
+Three different artifact patterns can arise from burntool.  The first has a bright streak that burntool should have removed but didn't.  The second has the burn from a star on a previous image oversubtracted either due to a bad fit or the images being processed in the wrong order.  The third shows an oversubtraction of the burn.
 
 [[Image(burntoolP.png)]]
@@ -13 +17 @@
 == Ghost image ==
 
+The origin of these is unknown.  Are they true ghosts (due to multiple partial reflections), or are they electronic (crosstalk or burns)?
+
 [[Image(ghost.png)]]
 
-== Glint from star at edge of camera ==
+== Star glint ==
 
-See discussion here: [[wiki:PS1_GPC1_GlintMasks]]
+A bright star just beyond the edge of the populated focal plane can cause a glint.  See discussion here: [[wiki:PS1_GPC1_GlintMasks]].
 
 [[Image(glint_s0.25.png)]]
 
-== Improperly masked halo ==
+Moon glints may also be seen, due to light from the moon avoiding the baffles and hitting the detector.
+
+== Ghost ==
+
+Ghosts are due to reflection of a bright star off the focal plane, and re-reflection and focusing back on the focal plane by L1 or L2.  This results in an out-of-focus image (image of the pupil) on the detector.  We attempt to mask these using the astrometric model and a star catalogue, but the model of the position, size and exact shape is not particularly precise.  This results in a partially masked ghost.
+
 
 [[Image(halo_s0.5.png)]]