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Hubble Space Telescope
Same Visit, No Rotation, Large Shift

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
RootnameProposal IDTarget NameFilterExposure TimeDate of ObservationOrientatX PostargY PostargRA PostargDEC 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
FilterX ShiftY ShiftRotationScale
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
FilterX ShiftY ShiftRotationScale
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.