Changes between Version 2 and Version 3 of ZoologyInvestigations

Timestamp:

Aug 24, 2011, 11:56:02 AM (15 years ago)

Author:

rhenders

Comment:

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ZoologyInvestigations

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-Serge populated a database consisting of all the columns in the false detection fits files that were sent to us.  
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+[[PageOutline]]
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+= Introduction =
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+This page details the investigations into the high number of false detections reported by the Durham group. Durham reported around 400,000 false-detections across all exposures in the SAS footprint survey.
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+= Procedure =
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+We decided to populate a MySQL database consisting of all the columns in the false detection FITS files sent to us by the Durham group. This enabled us to easily query the data and experiment with various cuts on flags, flux errors etc. Serge populated the database on his desktop machine.  
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+= Cutting using flags =
 
 I made some cuts and found some things:
@@ -104 +115 @@
 
 This is AFTER I did the flag cuts.  Prior to that there were 8x as many detections, often landing on burntools and edges.
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+= Cutting using of flux error =
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+As seen above, cutting the data using both the 'FLAGS' and 'FLAGS2' fields, and rejecting those detections labelled with obvious faults, the original total of 400,000 false detections was brought down to around 56,000, a reduction of around 86%. Eye-balling the images confirmed that this removed the majority of 'obvious' false detections, such as those on the edges of chips or in areas of saturation from a bright star.
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+Next, we looked first to the error in the flux, specifically, FLUX_SIG compared to FLUX. By eliminating all those detections with a an error greater than 5% of the total flux, we were left with just 2000 detections, a reduction of about 96%.
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+So, by first rejecting those detections with flagged errors then further eliminating those with a high error in flux, the total of 400,000 can be brought down to 2000, a reduction of around 99%.