Changes between Version 2 and Version 3 of PS1_MD04_RefStack

Timestamp:

Jun 20, 2010, 11:41:52 AM (16 years ago)

Author:

eugene

Comment:

--

PS1_MD04_RefStack

@@ -27 +27 @@
 }}}
 
+==== Ingesting the images ====
+
 The selected images were ingested into 2 dvo databases (one for griz and a second for y-band).  Below, I give the addstar commands used for the ingest.  In this case, the 'NOMINAL' zero point was applied; this means that the on-the-fly calibrations were ignored and the expected zero points were used.  
 
@@ -46 +48 @@
 }}}
 
+==== Relative Photometry and Astrometry ====
+
 After the databases were created, I ran the full-scale relative astrometry and photometry analysis on them.  The relative photometry analysis currently runs separately for each target average photcode (grizy).  The analysis determines the average magnitudes of the stars in the images, based on the available measurements, then uses these averages to determine the relative offsets of the image zero points.  It stabilizes the system of equations by re-setting the photometric clusters of images to 0.0.  The program performs a requested number of iterations on the photometry.  As the analysis proceeds, the code attempts to identify outlier detections for individual stars, then outlier stars (variable stars) from the sample, and finally outlier images -- those with excessively large scatter (ie, poor photometric conditions).  As these outlier / poor entries are discovered, they are excluded from the constraints on the average magnitudes.  I ran 20 iterations of relative photometry, using the commands listed below.  Note that only the high signal-to-noise measurements were used to determine the relative photometry (SIGMA_LIM), and that the zero points were calculated for the full GPC1 exposures, with the individual chips held fixed relative to one another (-imfreeze -mosaic).  The -statmode option specifies how the averaging is performed; in this case, the analysis performs a weighted mean of the inner 50% of the available measurements.
 
@@ -61 +65 @@
 }}}
 
+==== Photometry and Astrometry Accuracy ====
 
+(show some figures here of the residuals)
 
+==== High-Quality Database ====
+
+Once the relative photometry and astrometry were calculated, I created subset high-quality photometry databases for both griz and y-band.  These databases are restricted to only the stars with many repeated, high-accuracy measurements.  By creating subset databases like this, the eventual on-the-fly calibrations using these databases will not be slowed by needed to load large numbers of sources which do not contributed much to the quality of the calibration.  The following 'photdbc' commands extract the high-quality data.  Note that the griz database, with 4x as many visits, has a higher requirement on the minimum number of measurements for a high-quality source than the y-band database.
+
+{{{
+photdbc $region -D CATDIR catdir.v1 -D PHOTDBC_JOIN_RADIUS 1.0 -D AVE_SIGMA_LIM 0.025 -D NMEAS_MIN 40 catdir.ref.griz
+photdbc $region -D CATDIR catdir.yband -D PHOTDBC_JOIN_RADIUS 1.0 -D AVE_SIGMA_LIM 0.025 -D NMEAS_MIN 10 catdir.ref.yband
+}}}
+
+Finally, I merged the griz and y-band database at this point:
+
+{{{
+rsync -auv catdir.ref.griz/ catdir.ref/
+dvomerge catdir.ref.yband into catdir.ref
+}}}
+