NAME: syndark PURPOSE: Create a synthetic CCD dark frame with optional overscan DESCRIPTION: Adds a base dark image to a bias frame that is created by synbias, which adds a bias level (overscan level) and simulated read noise to an arbitrary base image- an optional overscan area contains bias and read noise only. The sigma is specified for the read noise, which is normally distributed wih a mean of 0. The output is an integer array. CATEGORY: CCD data processing CALLING SEQUENCE: syndark,darkbase,etime,gain,biasbase,biaslevel,rdnoise,seed,darkframe INPUTS: darkbase = 2-D input array. This is conceptually a constant, normally floating point, with each pixel in units of counts/sec. etime = exposure time in seconds, which is a multiplier for darkbase 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 represent the bias structure introduced by the electronics. biaslevel integer or float, bias (overscan) level, in units of D/N (counts) rdnoise integer or float, in electrons/pixel. Sigma for bias is rdnoise/gain. 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 match biasbase. FITSFN - Fits file for the output dark frame. Exposure time is included in the header. The default is to generate no file. CRSNUM - Average number of cosmic ray strikes per ccd area of image. 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]. CRSMIN - minimum D/N for cosmic ray strikes that will be added to the output. KEYWORD OUTPUT PARAMETERS: CRSOUT - Output, number of cosmic rays added to the image. OUTPUTS: darkframe - 2-D int array that is the synthetic dark image. It's dimensioned n x (m + o) where n, m are the dimensions of darkbase and o is the number of overscan columns created. The overscan area of the dark is darkframe[n:n+o-1, *]. Pixels are in units of D/N counts. Pixel values are calculated in floating point and rounded and rounded to nearest integer. They are truncated at 32767. COMMON BLOCKS: COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: Only handles single images- the darkbase 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 2006/7/12 PLC, CRS keywords- other documentation and argument cleanups. 2006/07/13 PLC, add keyword CRSOUT. 2006/07/14, MWB, final cleanup and addition to library.