1: Introduction
In this series of tests, we tested the performance of WFC3/UVIS instrument distortion coefficient table (IDCTAB) uab1537bi_idc.fits. This IDCTAB contains uniquely computed distortion solutions for 10 filters: F225W, F275W, F336W, F390W, F43W, F555W, F606W, F775W, F814W, and F850LP. All other filters use the values for F606W.
This test is designed to determine how the IDCTAB deals with a large shifts. To this end, we used two F606W observations taken during the same visit that are offset from one another by 80 arcseconds in X and Y. Details of the observations used in this test are listed in the table below. This test was designed to be more exploratory (rather than a more complex multi-filter survey) in nature, so we limited the scope to just the F606W filter.
| Summary of Relevant Observation Information | Rootname | Proposal ID | Target Name | Filter | Exposure Time | Date of Observation | Orientat | X Postarg | Y Postarg | RA Postarg | DEC Postarg |
|---|---|---|---|---|---|---|---|---|---|---|
| ibc307rgq | 11911 | OMEGACEN | F606W | 40.000000 | 2010-07-04 | -35.36287803869973 | 40.000000 | 40.000000 | 2.016928333333E+02 | -4.747905555556E+01 |
| ibc307sqq | 11911 | OMEGACEN | F606W | 40.000000 | 2010-07-04 | -35.32908736161019 | -40.000000 | -40.000000 | 2.016928333333E+02 | -4.747905555556E+01 |
2: Iteration I
| Iteration 1 Statistics Computed From Binned Vector Plots | X RMSY RMSVec Mag RMSVec Mag MeanVec Mag MedianVec Mag MaxVec Mag Min | |||||
|---|---|---|---|---|---|---|
| 0.0676794 | 0.0627527 | 0.0579025 | 4.81786 | 4.83664 | 4.92254 | 4.69430 |
| Shift.dat parameters by Filter | Filter | X Shift | Y Shift | Rotation | Scale |
|---|---|---|---|---|
| F606W | -2.30204 | 4.229031 | -0.00524999999999 | 1.000001 |
NOTE: In the above table, shift values are in units of drizzled image pixels, rotation values are in units of degrees, and scale values are dimensionless multipliers.
3: Iteration II
| Iteration 2 Statistics Computed From Binned Vector Plots | X RMSY RMSVec Mag RMSVec Mag MeanVec Mag MedianVec Mag MaxVec Mag Min | |||||
|---|---|---|---|---|---|---|
| 0.0226862 | 0.0251098 | 0.0286248 | 0.133966 | 0.137184 | 0.216614 | 0.0655949 |
| Shift.dat parameters by Filter | Filter | X Shift | Y Shift | Rotation | Scale |
|---|---|---|---|---|
| F606W | -0.09112655 | 0.09444429 | 0.00 | 0.9999986 |
NOTE: In the above table, shift values are in units of drizzled image pixels, rotation values are in units of degrees, and scale values are dimensionless multipliers.
4: Iteration III
| Iteration 3 Statistics Computed From Binned Vector Plots | X RMSY RMSVec Mag RMSVec Mag MeanVec Mag MedianVec Mag MaxVec Mag Min | |||||
|---|---|---|---|---|---|---|
| 0.0230103 | 0.0246496 | 0.0171515 | 0.0291133 | 0.0266959 | 0.0873291 | 0.00209974 |
5: Summary
This test demonstrates that for larger shifts, two iterations may not be sufficient to fully remove all systemics, and a third iteration of image processing is required to achieve image alignment.