Changes between Version 12 and Version 13 of Durham_MDS_Testing4

Timestamp:

Dec 1, 2009, 7:55:31 AM (17 years ago)

Author:

shaun.cole@…

Comment:

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Durham_MDS_Testing4

@@ -32 +32 @@
 
 Show above are the x and y position offsets between two reductions of the ''same stack'' (30204). One is the from the standard cmf file provided, the other is from our own run of psphot on 30204 (from code taken from the SVN on Nov 25th). The rms is about 0.4 pixels, so as both methods used identical datasets this is a measure of the reproducability of psphot. The offset is of order 0.1-0.2 pixels. NOTE: although not shown, 29871 v 30204 shows a similar scatter, athough with a different overall offset.
+
+=== Noise in unconvolved stacks ===
+
+These figures show aperture magnitudes for a selected list of objects, with a local sky estimate (a mode) in an annulus around each object for the 30204 stack. The diameter of the aperture is 40 pixels and the inner and outer diameters of the annulus at 60 and 80 pixels.
+
+This first figure shows the magnitude against an error estimate based on the variation of the data in the annulus, the sky noise. Each pixel in the aperture is assumed to have at least the noise due to the sky, so these represent a lower limit on the true error in the aperture. 
+
+[[Image(ccdpack-v-ipp-gsky.png,400px)]]
+
+To check IPP stacking we also show the results of stacking the same warps using an independent software package (CCDPACK). The amount of clipping used in CCDPACK was greater, which explains the higher noise.
+
+Repeating the same apertures, but using the variances generated by the IPP analysis gives the following plot. Reassuringly what should be better estimates of the error lie above the sky noise estimate. 
+
+[[Image(gsky-ippvar.png,400px)]]