Calibration Access and Data Handbook

Generation from Ground Calibration Data

The keyword THRESH is the setting of the event detection threshold used by the BPE to recognize events. THRESH describes the threshold for which the fraction of detected events PHDFRAC was calculated. The fraction of detected events is derived from the OM engineering data subtype 6 (Intensifier characteristics).
Given a event detection threshold THRESH the fraction of detected events is approximated using e.g. the IDL functions gaussfit and gauss_pdf:

pro phd_ana, name,ll_fit,ul_fit,i_thresh,PHDFRAC
 ; INPUT: 
 ; name     string name of datafile
 ; ll_fit   integer lower limit of fit
 ; ul_fit   integer upper limit of fit
 ; i_thresh integer event detection threshold
 ; OUTPUT:
 ; PHDFRAC  real   fraction of detected events
 
 ; read data
 rdtable,name,x,y  
 
 ; gaussian fit
 yfit=gaussfit(x(ll_fit:ul_fit),y(ll_fit:ul_fit),a1,nterm=3)
 
 ; calculate fraction of detected events 
 PHDFRAC= 1.-gauss_pdf((i_thresh-a1(1))/a1(2))
 
return
end

The CCD parameters stored in the field PARAM00 were already derived from laboratory measurements at MSSL and are listed above. No further update is intended.