Changes between Version 3 and Version 4 of stacking_coverage.20130307

Timestamp:

Apr 16, 2013, 4:05:35 PM (13 years ago)

Author:

watersc1

Comment:

--

stacking_coverage.20130307

@@ -1 +1 @@
 == 2013-04-16 ==
 
+While testing the input FWHM cut, I discovered that an image that appeared valid by eye was being flagged during the PSF matching stage as having a overly deviant chi^2 value.  A study of the code revealed that the chi^2 value used is calculated in the following way:
+
+ 1. For all valid stamps in the PSF match, the flux and squared residual are fit with a quadratic function (x0 + x1 * flux + x2 * flux^2).
+ 2. This quadratic function is subtracted from the squared residual, providing a flux-neutral measurement of the squared residuals.
+ 3. The RMS scatter of these remaining residuals is saved as the chi^2 value for the PSF match (there's a sum over all used kernels, but the example case has only a single kernel).
+
+The following table shows the set of PSF match values, along with the parameters of the quadratic function:
+
+|| Nstamp || mean   || rms     || x0      || x1           || x2           || Image || Rejected? ||
+|| 27     || -1e-06 || 60.7719 || 19.8792 || 0.000116288  || -9.31452e-13 ||   0   || ||
+|| 119    || 1e-06  || 64.4908 || 57.5848 || -8.45089e-05 || 3.59486e-11  ||   1   || ||
+|| 26     || -1e-06 || 43.3212 || 27.068  || 5.53666e-05  || 1.7642e-13   ||   2   || ||
+|| 107    || -2e-05 || 2756.68 || 1273.49 || -0.00181565  || 1.34383e-10  ||   3   || At Input Stage ||
+|| 106    || -9e-06 || 1105.5  || 614.941 || -0.000711782 || 1.01758e-10  ||   4   || Yes ||
+|| 102    || -1e-06 || 105.827 || 18.7579 || 0.000123878  || -3.35511e-12 ||   5   || At Input Stage ||
+|| 101    || -0     || 51.924  || 27.2631 || 7.72215e-05  || 1.07841e-12  ||   6   || ||
+|| 100    || -6e-06 || 738.86  || 222.832 || -0.000305871 || 2.12201e-10  ||   
+|| 99     || 8e-06  || 273.861 || 95.194  || -0.000156691 || 2.03263e-10  ||   7   || Yes ||
+|| 124    || 4e-06  || 226.235 || 18.6949 || 0.000113144  || 4.15584e-12  ||   
+|| 122    || 2e-06  || 92.0136 || 18.5325 || 0.000110472  || 3.66559e-13  ||   8   || ||
+|| 123    || 1e-06  || 135.964 || -1.48911|| 0.000144198  || -2.92106e-12 ||  
+|| 121    || 1e-06  || 77.5818 || 7.60706 || 0.000104179  || 7.44259e-14  ||   9   || ||
+|| 103    || 3e-06  || 330.224 || -70.9388|| 0.000411208  || -5.42577e-12 ||   
+|| 101    || -3e-06 || 53.8796 || -7.55995|| 0.000204406  || 5.83814e-12  ||  10   || ||
+|| 116    || 0      || 55.2009 || 15.2849 || 4.40914e-05  || 6.08214e-12  ||    
+|| 116    || -0     || 23.573  || 32.1768 || 1.87319e-06  || 8.4501e-12   ||  11   || ||