Status Report for Michael Richmond, Apr 1, 2004

  My job is to figure out how to obtain images with SNAP which
allow us to determine systematic errors in photometry across
the focal plane.  There are many possible sources of error, among
which are 

             A.  shutter timing
             B.  long-term changes in mirror coatings
             C.  chip-to-chip offsets
             D.  variations in filter transmission curves
             E.  vignetting
            
   
  My current plan is to create software which will allow me 
to simulate photometry performed in the presence of input
errors, and verify that I can determine those errors accurately.

  I have run a small simulation which includes the effects
of A, B, C.  It uses only three chips, 20 stars, and 81 images.
I verify that given NOISELESS input, I can identify image-to-image
timing errors and chip-to-chip zeropoint offsets properly. 
I can also determine the relative magnitudes of the input
stars accurately.

  Next is to make a set of tools which will allow me to compare quickly
a larger set of input quantities to their output values, so that
I can verify that a particular combination of observations will
give us all the information we need to the desired precision.
Once I have the tools, I can run larger simulations, and start
to add the effect of variations in filters (item D above).