February 8, 2013

The issue with the cell-to-cell continuity is likely a result of the interaction between PATTERN.MEDIAN and the non-linearity correction. Disabling NONLIN allows for the 3-phase OTAs (which have fewer nonlinearity issues) to retain continuity. I am not fully clear on how this interaction is working, as NONLIN is applied with the other detrend steps (DARK/FLAT/etc) before the PATTERN functions are called. I would have not have expected that this would cause discontinuities to remain.

SAS footprint test52
Current trunk + PATTERN.MEDIAN - NONLIN

February 7, 2013

Conclusions based on the initial ppImage implementation

  1. Cosmetic evaluation. OTA00 is in lower right corner. Click to zoom in to larger image.
  • Pro:
    • Butterfly effect around stars is removed.
    • OTAs which were not being corrected with PATTERN.ROW (ie OTA45, OTA55) see improvement.
    • Definite improvement in some "bad OTAs" (OTA67 in particular).
    • Corner glows are mitigated (OTA12)
    • Cross talk effect in OTA61 improved.
  • Con:
    • Print through of bright sources into median correction (ghost in OTA11, star in OTA24, all of OTA06, etc).
    • Incomplete removal of row-to-row variations (OTA15, OTA27, OTA45, etc).
    • Cell-to-cell continuity no longer maintained for unknown reason (OTA11, many others).
SAS footprint test48. SAS footprint test51
Effectively current trunk Current trunk + PATTERN.MEDIAN

  1. Individual row-by-row solutions are not stable between exposures. The following image shows a series of median solution images for OTA56/row 0 for the SAS footprint and for a series of similar science exposures taken after that date (highlighted frame is the first non-SAS footprint exposure). There are clear differences between the row-to-row patterns even within the short time frame of the SAS footprint.

  1. Applying only the PATTERN.MEDIAN to exposures (without DARK, FLAT, or PATTERN.CONTINUITY) yields a clear x-pixel direction gradient curve. This is effectively a result of solving for the DARK contribution on a per exposure basis. Applying DARK + FLAT removes this gradient on OTAs that are well behaved. This illustrates that the DARK model is not a significant problem for these OTAs.
Science images, PATTERN.MEDIAN only, OTA56/row 0
Dark images, PATTERN.MEDIAN only, OTA56/row 0
Science images, PATTERN.MEDIAN/DARK/FLAT, OTA56/row 0
  1. Applying only PATTERN.MEDIAN to a series of bias frames helps explain why the cell-column structures are not well removed by this correction. The larger scale ripples have a period that is not constrained to a cell. For example, in the highlighted bias (OTA31, PATTERN.MEDIAN only) below, I count ~11 ripples in the 4th (from left) column of cells. Whatever is driving these ripples is independent of the cell structure, and as such, these ripples do not reinforce in the PATTERN.MEDIAN calculation.

February 5, 2013

I have an initial implementation in ppImage/psModules of this correction.

Cell Mode Science OTA20 OTA27 OTA67 - Dark OTA20 OTA27 OTA67
Pre Post Pre Post Pre Post Pre Post Pre Post Pre Post
xy00 0 - 19.1360 16.2163 18.2377 12.3995 19.1727 14.1483 - 6.1285 4.4151 6.0682 3.7090 6.6669 4.6517 -
xy00 1 - 16.2163 17.1696 12.3995 15.3510 14.1483 9.2773 - 4.4151 3.6588 3.7090 3.2176 4.6517 3.0194 -
xy01 0 - 19.0460 14.9990 18.0620 13.3894 18.4362 13.6208 - 6.1873 4.3626 6.0671 4.1361 6.3822 4.3927 -
xy01 1 - 14.9990 15.1816 13.3894 15.1782 13.6208 9.1863 - 4.3626 3.5922 4.1361 3.4309 4.3927 2.8451 -
xy02 0 - 18.9513 15.8220 17.1856 12.7766 18.2383 12.7415 - 6.1805 4.5006 5.7957 3.9339 6.8098 4.2825 -
xy02 1 - 15.8220 13.9137 12.7766 10.9814 12.7415 8.2730 - 4.5006 3.6908 3.9339 3.2501 4.2825 2.8721 -
xy03 0 - 18.5051 15.0910 16.6074 12.9144 18.9350 15.1614 - 6.0329 4.1954 6.1399 4.2113 6.8538 4.3345 -
xy03 1 - 15.0910 11.8479 12.9144 10.4689 15.1614 9.3123 - 4.1954 3.4928 4.2113 3.5075 4.3345 2.7423 -
xy04 0 - 18.0283 14.2967 17.2791 13.1565 17.9581 10.2001 - 6.0211 4.2602 6.0691 4.2499 6.5565 3.5076 -
xy04 1 - 14.2967 11.4103 13.1565 10.6392 10.2001 10.0613 - 4.2602 3.5722 4.2499 3.4626 3.5076 2.3275 -
xy05 0 - 18.0424 13.6410 17.0563 12.8031 18.5023 nan - 5.8812 4.0306 6.1444 4.1855 6.5560 nan -
xy05 1 - 13.6410 12.0317 12.8031 12.7779 18.5023 nan - 4.0306 3.3730 4.1855 3.4577 6.5560 nan -
xy06 0 - 17.7460 12.4594 17.6375 15.2400 18.0741 nan - 6.0368 3.9447 6.2297 4.3317 6.5286 nan -
xy06 1 - 12.4594 14.6684 15.2400 12.3931 18.0741 nan - 3.9447 3.3657 4.3317 3.5709 6.5286 nan -
xy07 0 - 17.4767 11.9081 17.0315 12.6593 0.0000 nan - 5.7820 3.7218 6.1509 4.1284 0.0000 nan -
xy07 1 - 11.9081 14.7872 12.6593 15.5990 0.0000 nan - 3.7218 3.1714 4.1284 3.4052 0.0000 nan -
xy10 0 - 18.2514 14.1018 18.3373 11.8626 19.3578 18.0667 - 5.8554 4.2808 5.8761 3.4812 7.1169 4.9970 -
xy10 1 - 14.1018 16.0846 11.8626 15.5814 18.0667 14.8097 - 4.2808 3.5589 3.4812 3.0692 4.9970 3.2849 -
xy11 0 - 18.5462 13.9435 17.9536 12.7593 18.6224 16.8352 - 6.1133 4.3305 5.8202 3.9862 7.1274 4.8184 -
xy11 1 - 13.9435 14.1660 12.7593 14.4832 16.8352 13.8805 - 4.3305 3.5792 3.9862 3.2806 4.8184 3.1085 -
xy12 0 - 18.4375 15.0417 17.5258 12.4371 19.0663 15.5909 - 6.0537 4.3680 5.7809 4.0517 7.1838 4.4087 -
xy12 1 - 15.0417 12.8425 12.4371 10.8093 15.5909 8.5315 - 4.3680 3.6009 4.0517 3.2822 4.4087 2.9466 -
xy13 0 - 18.2929 14.1276 17.3519 13.8896 17.1998 13.0043 - 5.5887 3.8780 5.8373 4.2403 7.1461 4.2662 -
xy13 1 - 14.1276 12.2511 13.8896 11.6127 13.0043 14.0887 - 3.8780 3.2592 4.2403 3.5201 4.2662 2.7240 -
xy14 0 - 17.9325 13.1143 17.8327 13.3869 17.7430 14.2839 - 5.7602 4.0778 6.1397 4.5782 7.0328 3.6044 -
xy14 1 - 13.1143 10.8539 13.3869 10.8322 14.2839 9.6809 - 4.0778 3.4093 4.5782 3.6551 3.6044 2.4486 -
xy15 0 - 17.9928 12.8740 16.7583 12.2736 17.2278 nan - 5.7530 3.9591 6.0022 4.3926 7.1338 nan -
xy15 1 - 12.8740 12.1617 12.2736 13.1751 17.2278 nan - 3.9591 3.2744 4.3926 3.5546 7.1338 nan -
xy16 0 - 18.0439 12.0950 17.2752 12.8557 18.6109 nan - 5.7624 3.6545 6.2035 4.4541 6.8946 nan -
xy16 1 - 12.0950 13.6971 12.8557 14.2169 18.6109 nan - 3.6545 3.1643 4.4541 3.6680 6.8946 nan -
xy17 0 - 17.3371 11.5769 19.4375 14.8047 0.0000 nan - 5.6314 3.5134 6.4868 4.6869 0.0000 nan -
xy17 1 - 11.5769 14.2065 14.8047 16.9240 0.0000 nan - 3.5134 2.9966 4.6869 3.9870 0.0000 nan -
xy20 0 - 19.4929 15.1833 17.2820 12.2914 18.8305 14.4255 - 5.8749 4.1899 6.2832 3.6105 6.5996 4.3940 -
xy20 1 - 15.1833 16.8889 12.2914 14.7989 14.4255 9.1376 - 4.1899 3.4093 3.6105 3.1802 4.3940 2.8409 -
xy21 0 - 18.8188 14.3427 18.2276 12.8475 18.6053 13.7738 - 6.0194 4.0294 6.3746 4.1167 7.0766 4.7348 -
xy21 1 - 14.3427 14.8981 12.8475 14.4139 13.7738 8.4585 - 4.0294 3.4695 4.1167 3.4340 4.7348 3.0959 -
xy22 0 - 18.4371 14.4400 17.7528 12.8034 18.8758 13.2251 - 6.1783 4.2438 6.2803 4.0339 6.9602 4.0829 -
xy22 1 - 14.4400 13.7328 12.8034 11.1047 13.2251 9.4503 - 4.2438 3.5118 4.0339 3.3759 4.0829 2.7076 -
xy23 0 - 18.3282 13.5068 17.9319 13.1245 18.3186 13.5902 - 6.0390 4.0628 6.3250 4.2480 6.9023 4.2354 -
xy23 1 - 13.5068 11.3889 13.1245 10.8052 13.5902 8.1498 - 4.0628 3.3967 4.2480 3.4674 4.2354 2.7378 -
xy24 0 - 18.5331 13.9161 17.4129 12.5379 16.8786 10.5109 - 5.9910 4.0248 6.2760 4.1768 6.9114 3.3142 -
xy24 1 - 13.9161 11.7017 12.5379 10.3224 10.5109 12.8027 - 4.0248 3.3709 4.1768 3.3658 3.3142 2.2545 -
xy25 0 - 18.8492 13.7972 16.9552 12.2764 16.8643 nan - 5.9284 3.9407 6.4132 4.1226 6.7820 nan -
xy25 1 - 13.7972 12.2562 12.2764 12.7897 16.8643 nan - 3.9407 3.3190 4.1226 3.3770 6.7820 nan -
xy26 0 - 17.8476 12.0684 17.2714 11.9061 0.0000 nan - 5.7852 3.5705 6.4087 4.1523 0.0000 nan -
xy26 1 - 12.0684 14.4886 11.9061 13.5854 0.0000 nan - 3.5705 3.0873 4.1523 3.4065 0.0000 nan -
xy27 0 - 17.6855 11.6663 16.6421 12.2780 0.0000 nan - 5.4959 3.7763 6.4091 4.1174 0.0000 nan -
xy27 1 - 11.6663 14.5230 12.2780 14.9671 0.0000 nan - 3.7763 3.0864 4.1174 3.4885 0.0000 nan -
xy30 0 - 18.4763 13.6104 18.3649 12.0178 16.8053 14.8654 - 5.7268 4.2020 6.2051 4.4402 7.3537 4.9785 -
xy30 1 - 13.6104 15.7799 12.0178 15.0555 14.8654 8.9357 - 4.2020 3.4855 4.4402 3.8393 4.9785 3.1229 -
xy31 0 - 19.3674 14.7158 17.9415 13.2576 19.0805 14.7440 - 6.0188 4.2763 6.3727 4.8845 7.9630 5.5280 -
xy31 1 - 14.7158 16.1925 13.2576 14.1147 14.7440 10.2556 - 4.2763 3.5746 4.8845 3.9310 5.5280 3.6413 -
xy32 0 - 18.3466 13.6634 17.8306 13.2970 18.0555 10.9673 - 6.0750 4.4342 6.5418 4.8183 7.8396 4.9507 -
xy32 1 - 13.6634 12.6847 13.2970 12.2090 10.9673 8.8627 - 4.4342 3.5512 4.8183 3.9323 4.9507 3.1904 -
xy33 0 - 18.4171 12.9474 17.5620 14.0882 18.1302 13.0712 - 6.0303 4.2300 6.4342 4.9112 7.9225 4.9694 -
xy33 1 - 12.9474 10.6324 14.0882 11.1242 13.0712 8.0515 - 4.2300 3.5418 4.9112 3.9866 4.9694 3.1990 -
xy34 0 - 17.9496 13.0746 17.3083 13.1250 18.4269 10.6724 - 6.0228 4.1859 6.2401 4.8411 8.1413 4.5869 -
xy34 1 - 13.0746 10.9876 13.1250 11.4894 10.6724 8.4659 - 4.1859 3.4852 4.8411 3.8676 4.5869 2.9100 -
xy35 0 - 18.4303 13.0714 17.4326 15.6595 0.0000 nan - 5.7687 3.9480 6.2028 4.8671 0.0000 nan -
xy35 1 - 13.0714 12.0987 15.6595 12.2467 0.0000 nan - 3.9480 3.2420 4.8671 3.8953 0.0000 nan -
xy36 0 - 17.6417 11.8336 17.1183 15.5740 0.0000 nan - 5.8034 3.7506 6.3231 4.6842 0.0000 nan -
xy36 1 - 11.8336 14.3535 15.5740 13.2449 0.0000 nan - 3.7506 3.1686 4.6842 3.9192 0.0000 nan -
xy37 0 - 17.7989 11.8550 16.8804 13.4954 0.0000 nan - 5.9150 3.8859 6.3897 4.7409 0.0000 nan -
xy37 1 - 11.8550 13.3849 13.4954 15.3119 0.0000 nan - 3.8859 3.3115 4.7409 4.0454 0.0000 nan -
xy40 0 - 18.5319 14.1220 18.5072 11.5330 18.0607 13.3059 - 6.1715 4.4447 6.1677 3.6401 6.3359 4.4088 -
xy40 1 - 14.1220 15.5400 11.5330 15.7441 13.3059 10.8456 - 4.4447 3.6159 3.6401 3.2119 4.4088 3.0171 -
xy41 0 - 18.3665 14.5400 17.6085 12.7655 17.0868 13.1887 - 6.1858 4.2359 5.7857 3.6231 6.4787 4.3623 -
xy41 1 - 14.5400 14.7101 12.7655 14.0190 13.1887 13.4015 - 4.2359 3.4932 3.6231 2.9904 4.3623 3.0141 -
xy42 0 - 18.5093 13.6799 17.4195 12.3168 17.4092 15.9769 - 6.0979 4.3039 5.8623 3.7256 6.8841 4.4221 -
xy42 1 - 13.6799 12.2633 12.3168 11.5988 15.9769 10.0928 - 4.3039 3.4998 3.7256 3.0495 4.4221 3.0557 -
xy43 0 - 18.0734 12.9225 16.9227 14.3226 18.3046 14.0339 - 6.3452 4.4203 6.0097 3.9800 6.4185 3.9673 -
xy43 1 - 12.9225 10.4091 14.3226 11.9042 14.0339 8.8871 - 4.4203 3.6298 3.9800 3.2304 3.9673 2.7529 -
xy44 0 - 18.3202 13.5666 17.4369 13.0589 17.2433 12.3189 - 6.3044 4.4849 6.0454 3.9135 6.4449 3.2703 -
xy44 1 - 13.5666 10.8389 13.0589 10.4720 12.3189 10.9676 - 4.4849 3.6020 3.9135 3.2339 3.2703 2.3119 -
xy45 0 - 17.6807 12.9688 16.9089 12.3285 0.0000 nan - 5.9951 4.0661 6.1289 3.9398 0.0000 nan -
xy45 1 - 12.9688 13.4718 12.3285 13.3575 0.0000 nan - 4.0661 3.3636 3.9398 3.1533 0.0000 nan -
xy46 0 - 17.4889 11.7468 18.1185 13.6169 0.0000 nan - 5.9795 3.8890 6.2004 3.9215 0.0000 nan -
xy46 1 - 11.7468 14.0915 13.6169 12.7394 0.0000 nan - 3.8890 3.1813 3.9215 3.2310 0.0000 nan -
xy47 0 - 17.2549 12.2509 17.0664 13.1579 0.0000 nan - 6.1473 3.9337 6.5688 4.2108 0.0000 nan -
xy47 1 - 12.2509 14.2660 13.1579 13.8481 0.0000 nan - 3.9337 3.3917 4.2108 3.7338 0.0000 nan -
xy50 0 - 19.1672 14.3945 19.1031 13.6655 17.7989 13.4743 - 5.8081 4.2717 6.1104 3.8799 6.4406 4.2570 -
xy50 1 - 14.3945 16.4193 13.6655 16.6419 13.4743 10.1684 - 4.2717 3.3874 3.8799 3.2374 4.2570 3.3138 -
xy51 0 - 17.5836 13.4868 18.6964 13.2541 17.8646 13.0439 - 5.8572 4.1488 5.7090 3.8340 6.6715 4.3907 -
xy51 1 - 13.4868 11.8247 13.2541 15.9136 13.0439 10.6652 - 4.1488 3.2842 3.8340 3.1090 4.3907 3.4019 -
xy52 0 - 18.1610 13.1693 17.5781 12.6718 17.9637 12.2584 - 5.5796 3.9051 5.4741 3.4871 6.7154 3.9766 -
xy52 1 - 13.1693 11.1376 12.6718 13.0346 12.2584 10.1146 - 3.9051 3.1355 3.4871 2.8429 3.9766 3.3090 -
xy53 0 - 17.8415 13.2155 17.0598 12.4405 17.7597 13.9421 - 5.5153 3.7380 5.3750 3.5125 6.7748 4.2158 -
xy53 1 - 13.2155 10.8081 12.4405 9.7693 13.9421 10.6826 - 3.7380 2.9665 3.5125 2.9122 4.2158 3.2870 -
xy54 0 - 17.8132 12.8345 16.4835 13.2793 0.0000 nan - 5.5682 3.8162 5.3923 3.5193 0.0000 nan -
xy54 1 - 12.8345 11.0486 13.2793 11.0388 0.0000 nan - 3.8162 3.0777 3.5193 2.8222 0.0000 nan -
xy55 0 - 18.3738 13.1667 16.4079 12.1191 0.0000 nan - 5.5168 3.6796 5.4315 3.4924 0.0000 nan -
xy55 1 - 13.1667 12.1194 12.1191 11.7436 0.0000 nan - 3.6796 3.0129 3.4924 2.8222 0.0000 nan -
xy56 0 - 17.9210 12.8984 16.9084 11.9762 0.0000 nan - 5.7195 3.9752 5.4183 3.4499 0.0000 nan -
xy56 1 - 12.8984 14.2478 11.9762 13.0840 0.0000 nan - 3.9752 3.2214 3.4499 2.8536 0.0000 nan -
xy57 0 - 17.9643 12.5860 16.4967 12.6264 0.0000 nan - 5.4871 3.6574 5.3740 3.4181 0.0000 nan -
xy57 1 - 12.5860 14.3727 12.6264 13.5046 0.0000 nan - 3.6574 3.0978 3.4181 2.7987 0.0000 nan -
xy60 0 - 18.5754 14.3014 19.7871 16.1240 18.2467 13.6199 - 5.7715 4.1062 7.6085 5.8120 6.8863 4.9200 -
xy60 1 - 14.3014 15.4722 16.1240 16.7295 13.6199 3.5696 - 4.1062 3.1894 5.8120 4.3245 4.9200 0.8764 -
xy61 0 - 18.4149 14.1142 19.0320 13.4497 18.5325 13.8615 - 6.0880 4.1860 7.2236 4.9619 7.1891 5.1303 -
xy61 1 - 14.1142 12.1579 13.4497 16.1997 13.8615 7.5957 - 4.1860 3.1970 4.9619 3.7255 5.1303 1.1089 -
xy62 0 - 17.9743 13.8208 17.8738 12.7798 17.9593 12.1875 - 5.5695 3.8447 6.7363 5.0456 7.0439 4.6350 -
xy62 1 - 13.8208 10.9875 12.7798 15.3255 12.1875 4.8085 - 3.8447 3.0123 5.0456 3.6803 4.6350 0.9223 -
xy63 0 - 17.5187 14.5204 17.3614 14.7514 0.0000 nan - 5.7046 3.7578 6.4055 4.6858 0.0000 nan -
xy63 1 - 14.5204 11.6832 14.7514 11.0854 0.0000 nan - 3.7578 2.9840 4.6858 3.6345 0.0000 nan -
xy64 0 - 17.6017 14.6413 17.3987 16.2023 0.0000 nan - 5.7881 3.8969 6.7611 4.9196 0.0000 nan -
xy64 1 - 14.6413 12.5936 16.2023 11.4374 0.0000 nan - 3.8969 3.0256 4.9196 3.7609 0.0000 nan -
xy65 0 - 18.1412 13.8778 16.4766 14.6702 0.0000 nan - 5.7909 3.8372 6.5445 4.5016 0.0000 nan -
xy65 1 - 13.8778 12.7789 14.6702 12.5641 0.0000 nan - 3.8372 3.1923 4.5016 3.4447 0.0000 nan -
xy66 0 - 17.7994 13.3668 16.2286 14.9296 0.0000 nan - 5.8586 3.9755 6.5579 4.5374 0.0000 nan -
xy66 1 - 13.3668 13.7715 14.9296 14.7816 0.0000 nan - 3.9755 3.2770 4.5374 3.5710 0.0000 nan -
xy67 0 - 18.6031 12.7620 16.5695 12.3977 0.0000 nan - 5.8040 3.6758 6.3274 4.2493 0.0000 nan -
xy67 1 - 12.7620 13.5308 12.3977 13.6571 0.0000 nan - 3.6758 3.1162 4.2493 3.5995 0.0000 nan -
xy70 0 - 18.6224 16.8280 0.0000 nan 17.9232 13.5220 - 6.4643 4.8306 0.0000 nan 6.2814 4.7851 -
xy70 1 - 16.8280 10.8186 0.0000 nan 13.5220 nan - 4.8306 2.2564 0.0000 nan 4.7851 nan -
xy71 0 - 18.0627 16.2561 19.2449 14.9796 18.4076 13.6569 - 6.2000 4.3428 6.5232 4.8270 6.4697 4.7545 -
xy71 1 - 16.2561 11.4097 14.9796 16.7605 13.6569 nan - 4.3428 3.1694 4.8270 3.5373 4.7545 nan -
xy72 0 - 17.9131 16.1474 20.6421 19.7244 0.0000 nan - 6.1307 4.2060 6.5394 4.7448 0.0000 nan -
xy72 1 - 16.1474 10.5407 19.7244 22.3510 0.0000 nan - 4.2060 2.9494 4.7448 3.5783 0.0000 nan -
xy73 0 - 17.6573 15.5024 17.1247 15.9317 0.0000 nan - 6.1636 4.9120 6.2946 5.0910 0.0000 nan -
xy73 1 - 15.5024 12.1165 15.9317 17.2715 0.0000 nan - 4.9120 3.9651 5.0910 3.4171 0.0000 nan -
xy74 0 - 19.5564 16.1072 17.5456 14.3083 0.0000 nan - 6.3147 4.3845 6.5893 5.2462 0.0000 nan -
xy74 1 - 16.1072 13.0130 14.3083 13.3359 0.0000 nan - 4.3845 3.5398 5.2462 3.7716 0.0000 nan -
xy75 0 - 17.8748 15.3014 16.4173 12.4891 0.0000 nan - 6.2100 4.3155 6.8408 5.2154 0.0000 nan -
xy75 1 - 15.3014 13.1325 12.4891 9.7654 0.0000 nan - 4.3155 3.4496 5.2154 3.5053 0.0000 nan -
xy76 0 - 18.0350 13.6841 16.1565 14.2040 0.0000 nan - 6.1736 4.1423 6.3203 5.1315 0.0000 nan -
xy76 1 - 13.6841 12.0662 14.2040 14.8797 0.0000 nan - 4.1423 3.3137 5.1315 3.4352 0.0000 nan -
xy77 0 - 17.3479 16.0663 16.5455 15.2718 0.0000 nan - 6.7330 4.7866 6.7884 5.4040 0.0000 nan -
xy77 1 - 16.0663 16.7648 15.2718 18.0559 0.0000 nan - 4.7866 3.7874 5.4040 3.9781 0.0000 nan -

September 5, 2012

Based on Nigel's email this morning (details at http://ps1sc.ifa.hawaii.edu/PS1wiki/index.php/DRAVG_telecon#Correlated_bias_structure_between_cells), I spent part of the afternoon looking at this structure again, starting from Nigel's point that adjacent cells seemed to have the same structure.

The OTA chosen by Nigel is OTA57, which has PATTERN.ROW applied to columns 0,1,2,6,7, leaving 3,4,5 with no PATTERN.ROW correction. The oversubtraction PATTERN.ROW leaves is clearly visible in the first image, in the cell one up and right of the bottom left corner. As columns 345 had lower row-to-row offsets, these cells were left unmodified. It's also clear from this image (and other investigations) that the cells we do not apply PATTERN.ROW to still have some level of row-to-row variations.

My study used bias images from OTA67, as I had them on disk locally (an MHPCC power outage prevented grabbing new data). For this study, I constructed row models by subtracting the median value for each cell from that cell, and then calculating the median "stack" across a row of cells. This results in 8 cell sized models appropriate for removing the bias variations from a row of cells. Subtracting this row model from each cell should remove the row-to-row variations. The following image shows these models for one bias frame, showing the variations between different cell-rows for one image.

A similar process can be done on a science image, with two result cells shown below. Both images show the original raw image, the row model subtracted image, and a similar model generated from columns of cells.

This method seems to do a decent job of minimizing row-to-row variations, without the oversubtraction around bright stars that PATTERN.ROW introduces. However, there are still some issues that need to be considered before this can be implemented.

1. The first science image shows a ghosting due to bright pixel columns that cause an oversubtraction in the background level in vertical bands. This can probably be mitigated by including the static mask data when making the median stack.

2. This structure appears to change between each bias frame that I examined, suggesting that this is not something that can be precalculated. This variation makes sense, as any static feature would be included in the dark model.

3. These tests were done on raw images, without any dark correction. Some thought needs to be done to determine where in the detrending process this kind of correction should be applied.

4. Bright extended objects will need to be checked closely to ensure that this does not damage those objects.

Attachments