artobs image exptime ccdtype
image
Observation to be created.
exptime
Exposure time of observation.
ccdtype
CCD image type of observation. This type is one of the standard types
for the CCDRED package.
ncols = 132, nlines = 100
The number of columns and lines in the full image created including
bias section.
filter =
Filter string for the observation.
datasec = [1:100,1:100]
Data section of the observation.
trimsec = [3:98,3:98]
Trim section for later processing.
biassec = [103:130,*]
Prescan or overscan bias section.
imdata =
Image to be used as source of observation if specified. The image must
be at least as large as the data section.
skyrate = 0.
Sky counting rate. The total sky value will be scaled by the exposure time.
badpix =
Bad pixel region file in the standard CCDRED bad pixel file format.
biasval = 500.
Mean bias value of the entire image.
badval = 500.
Bad pixel value placed at the specified bad pixel regions.
zeroval = 100.
Zero level of the data section.
darkrate = 1.
Dark count rate. The total dark count will be scaled by the exposure time
zeroslope = 0.01
Slope of the zero level per pixel.
darkslope = 0.002
Slope of the dark count rate per pixel. This is also scaled by the exposure
time.
flatslope = 3.0000000000000E-4
The mean flat field response is 1 with a slope given by this value.
sigma = 5.
Gaussian noise sigma per pixel.
seed = 0
Random number seed. If zero new values are used for every observation.
overwrite = no
Overwrite an existing image? If no a new observation is not created.
There is no warning message.
This script task generates artificial CCD observations which include bad pixels, bias and zero levels, dark counts, flat field response variations and sky brightness levels. Optionally, image data from a reference image may be included. This task is designed to be used with the ccdred package and includes appropriate image header information.
First the task checks whether the requested image exists. If it does exist and the overwrite flag is no then a new observations is not created. If the overwrite flag is set then the old image is deleted and a new observation is created.
An empty image of the specified size and of pixel data type short is first created. If a noise sigma is specified it is added to the entire image. If a reference image is specified then image section given by the datasec parameter is copied into the data section of the observation. Next a sky level, specified by the skyrate parameter times the exposure time, is added to the data section. The flat field response with a mean of one and a slope given by the flatslope parameter is multiplied into the data section. If a dark count rate and/or a zero level is specified then these effects are added to the data section. Then the specified bias level is added to the entire image; i.e. including the bias section. Finally, the pixels specified in the bad pixel region file, if one is specified, are set to the bad pixel value.
The CCD reduction parameters for the data section, the trim section, the bias section, exposure time, the CCD image type, and the filter are added to the image header (if they are specified) using ccdhedit to apply any keyword translation.
1. To create some test CCD images first set the task parameters such as number of columns and lines, data, bias, and trim sections, and data values. The images are then created as follows:
cl> artobs.filter = "V" # Set the filter cl> artobs zero 0. zero # Zero level image cl> artobs dark 1000. dark skyrate=0. # Dark count image cl> artobs flat 1. flat skyrate=1000. # Flat field image cl> artobs obj 10. object # Object image
Note that the CCD image type is not used explicitly so that for a dark count image you must set the sky count rate to zero.