The Postage Stamp Pipeline Flow Charts

December 1997

  • Determination of bias, sky and flat field
  • Characterization of the point spread function
  • Preliminary astrometric and photometric calibration

  • Determination of bias, sky and flat field

     
    Initialise Modules, Read Plan/Parameter Files
    
    Foreach filter {
    
        Read 2D (Nframes x Ncolumns) bias structure from idB*.fit file 
     
        Read data quartiles for all frames from scFang*.fit files
    
        Calculate bias drift, flat-field and sky for all frames
    
        Foreach frame {
        
            Smooth and interpolate bias drift, flat-field and (sky)  
    
            Write flat-field to file psFF*.fit
        }
    
        Cleanup
    }
    
    
    

    Characterization of the point spread function

     
    Initialise Modules, Read Plan/Parameter Files
    
    Foreach filter {
       
        Determine mean (over all frames) gains and dark variances
      
    }
    
    Retrieve information on 200x200 stamps
    
    Foreach filter {
    
        Foreach frame {
    
            Read the flat-field vector (from a psFF*.fit file)
    
            Read 65x65 stamps (from a scFang*.fit file) 
    
            Extract profiles for 65x65 stamps 
    
            If available { Read 200x200 stamps
    
                           Extract profiles for 200x200 stamps
            }
             
        }
    
        Reject objects with any of individual flags set on
     
    }
    
    /* these two loops over filters are separated beacuse the above is
    coded at Tcl level, and the following one in C */
    
    Foreach filter {
    
        Foreach frame {
    
            Form a subsample of objects 
         
            Clip the subsample on the deviation from a median in each cell
    
            Clip the subsample on the extracted profile shape  
     
            Clip the subsample on the extracted profile size    
    
            Clip the subsample by using a best-fit model PSF 
    
            Clip the subsample until it is uniform 
     
            Determine the mean PSF profile and the best-fit model PSF
    
            Determine composite profile
    
            Add bright objects' profiles to the composite profile 
    
            Calculate photometric corrections (aperture corrrection etc.)
    
        }       
              
    }
    
    Cleanup
    
     
    
    
    

    Preliminary astrometric and photometric calibration

     
    Read astrometric transformation coefficients for each frame and filter
      (from asTrans*.fit file) 
    
    Calculate time and airmass for each frame and filter 
      (by using information from scFang*.fit files headers) 
    
    Read zero points, extinction coefficients and color terms for each filter 
      (from exPhotom*.par file) 
    
    Read positions and magnitudes (in each filter) of objects detected in the MT pipeline
      (from kaCalObj*.fit files, aka patch files) 
    
    Read color terms for each filter from psParam.par file
      (to be used in log(flux20) = a + color_term * color_index)
    
    Read counts in each filter for a 20th mag object 
      (from an old calibration file, psCT*.fit)
     
    Setup extinction arrays for interpolation 
      (extinction coefficient as a function of time and color) 
    
    Foreach frame {
    
        If No MT patches 
    
            Use old calibration(time) from psCT*.fit  
    
        Else {
    
            Foreach patch file {
                
                Match PS stars with MT stars
                    
                Determine calibration(time) for this patch file
    
            }
             
        }
    
        Interpolate calibration(time) to each frame       
    
    }
    
    
    
    

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    Please send any comments or suggestions to Zeljko Ivezic


    ZI, December 1997