Gain Correction of TRACE Images
The IDL procedure trace_prep is intended to assist in the processing of TRACE data from raw to level 0. It resides as a part of SolarSoftWare (SSW) on the TRACE tree, as does the databases it utilizes. The procedure can read in raw data images or can use images already read in. The main default processing steps are the dark pedestal subtraction and the CCD gain correction. At present it performs the following steps:
| * Read image(s) either from the raw database or a data cube and image structure |
| * Fill pixels of value = 0 with mean pixel value of entire image |
| * Replace near-saturated pixels with a value > 4095 |
* Subtract the dark pedestal (ADC offset) from each image |
* Perform CCD gain calibration using flatfielding on each image |
| * Output the corrected image(s) in an updated structure and data cube |
The CCD gain correction for UV and EUV images is determined by temporally interpolating between the two appropriate smoothed flat field images and between both of their corresponding power and multiplicative factor parameters, then applying the resulting parameters to the resulting flat field,
followed by multiplying by the proper WL flat field, and finally dividing the resultant into the image to be gain corrected. If the correction time is past that of the last flat field, then the latter is used for correction along with its associated parameters. The correction for WL images is to divide them by the appropriate WL flat field.
Optionally, the following corrections can be applied if the appropriate keywords are used:
| * Remove radiation belt spikes and streaks from each image (/unspike), /destreak) |
| * Remove background diffraction pattern (and readout herringbone) (/deripple) |
| * Normalize each image for exposure (/normalize) |
| * Correct pointing in the index structure for each channel (for image alignment in other SSW routines (/wave2point) |
| * Extract a subimage from each image (keywords /sllex, /slley, /subimgx, /subimgy) |
Assuming that the index and data records have already been read in, a call to trace_prep is:
trace_prep,index,data,outindex,outdata [,/unspike][,/destreak]
or to read images 0,1,2,4,8 from hourly files in the raw database:
trace_prep,file_list(indir,infile),[0,1,2,4,8],index,data, [,/unspike][,/destreak]
More detailed information can be found in the TRACE Analysis Guide and in the header of the trace_prep procedure
Modified 20-Apr-2006 20:00