| | 1 | The ISP data from late 2006 / early 2007 makes a good demo case for building and testing detrend images. |
| | 2 | |
| | 3 | Some notes from the analysis: |
| | 4 | |
| | 5 | * the shutter correction can be measured and applied, but there are some limitations: |
| | 6 | * the input images with excessive saturated pixels should be excluded - this is especially an issue for the ISP since it seems to saturate with a severe non-linear regime (>60k). |
| | 7 | * the correction does not work below ~0.05 sec. The correction image ranges from -4 msec to +45ms. |
| | 8 | * the correction appears to have some variations as a function of time: |
| | 9 | the residual images include a term which appears to be the difference between the shutter correction at two small offsets. |
| | 10 | I conclude that the shutter, detector, and optics are not remaining co-aligned. this effect appears at below the 1% level. |
| | 11 | |
| | 12 | * flat-field residual images (verify mode) |
| | 13 | * g,r,i images are easy to explain |
| | 14 | * short exposures (<0.05) show the effect of the shutter correction hitting its limits |
| | 15 | * some images show large scale gradients, perhaps clouds or sky illumination pattern |
| | 16 | * some images show the effect of non-linearity / saturation |
| | 17 | |
| | 18 | * z band images have some peculiarities |
| | 19 | * the show all the expected features above (not peculiar) |
| | 20 | * images from 2007/1/18 seem to be very poor |
| | 21 | ** most of these are 240 sec exposures - bad dark correction?? |
| | 22 | ** some of these have stars (ie, night, not twilight) - IR sky glow? |
| | 23 | |
| | 24 | * y band images show similar issues |
| | 25 | * problem from 2007/1/18 |
| | 26 | |
| | 27 | '''looking in detail, it is clear that the dark correction is poor for long exposures''' |
