NAME: synflat PURPOSE: Create a synthetic flat frame with optional overscan DESCRIPTION: Using a base flat field array, a signal level in photons, and a gain, a flat image array is created with the flat aberrations and the photon (Poisson) statistics. We add to this a base dark image and a bias frame that is created by synbias, which adds a bias level (overscan level) and simulated read noise - an optional overscan area is created that contains bias and read noise only. The sigma is specified for the read noise, which is normally distributed wih a mean of 0. The final output is an integer array. CATEGORY: CCD data processing CALLING SEQUENCE: synflat,flatbase,slvl,darkbase,etime,gain,biasbase,biaslevel,rdnoise,seed,$ flatframe INPUTS: flatbase = 2-D float input array. This is conceptually a constant and consists of dimensionless values between 0 and 1.0 that multiply the base signal (sky or screen) level of the flat. slvl = flat signal level in counts. darkbase = 2-D integer float input array. This is conceptually a constant and is multiplied by the exposure time to generate the ideal dark image (units are counts per second) etime = exposure time in seconds gain hypothetical gain (e-/DN) for statistics biasbase = 2-D input array. This is conceptually a constant, normally floating point, with each pixel in units of D/N (counts). It represents the bias structure introduced by the electronics. biaslevel bias (overscan) level, in units of D/N (counts) rdnoise value in electrons/pixel. Sigma for bias is rdnoise/gain. seed for random number generator- both input and output. seed for random number generator- both input and output. OPTIONAL INPUT PARAMETERS: KEYWORD INPUT PARAMETERS: OVERSCAN - integer, number of columns for the explicit overscan area. If less than or equal to 0, there is no overscan area generated and the dimensions of the output array matches biasbase. FITSFN - Fits file for the flat frame. The exposure time is included in the header. The default is to generate no file. CRSNUM - number of cosmic ray strikes per ccd area of image. The units are strikes per megapixel per image. Cosmic rays will not be placed in the overscan area, if one is defined. The count of CRS for an image is chosen as a Poisson deviate with the given mean. CRSMIN - minimum D/N for cosmic ray strikes that will be added to the output. CRSMAX - maximum D/N for cosmic ray strikes that will be added to the output. Intensity of each CRS is drawn uniformly over the range [CRSMIN,CRSMAX]. STARRATE - mean number of stars added per image. Stars are gaussian PSF's as computed by synstar. Stars will not be placed in the overscan area, if one is defined. The number of stars for an image is chosen as a Poisson deviate with the given mean. STARMIN - minimum flux- as passed to synstar- for stars that will be added to the output. STARMAX - maximum flux- as passed to synstar- for stars that will be added to the output. Flux of each star is drawn uniformly over the range [STARMIN,STARMAX]. KEYWORD OUTPUT PARAMETERS: CRSOUT - Output, number of cosmic rays added to the image. STARSOUT - Output, number of stars added to the image. OUTPUTS: flatframe - 2-D int array that is the synthetic flat image. Its dimensions are n x (m + o) where n, m are the dimensions of flatbase and o is the number of overscan columns created. The overscan area of the flat is flatframe[n:n+o-1, *]. Pixels are in units of D/N counts. Pixel values are calculated in floating point and rounded to nearest integer. They are truncated at 32767. COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: Only handles single images- the darkbase, flatbase and biasbase must be identically dimensioned. PROCEDURE: MODIFICATION HISTORY: 2006 June 28, Written by Peter L. Collins, Lowell Observatory 2006/07/10 PLC, reorder arguments for consistency 2006/07/12 PLC, CRS keywords- other documentation and argument cleanups. 2006/07/12 PLC, add keywords CRSOUT and STARSOUT. 2006/07/14, MWB, final cleanup and addition to library.