Data: CDS synoptic raster from March 1998
Fits data file: s10693r02
Read the data into a CDS data structure
To allow the software to recognise missing data, set a flag. Remember it is still necessary on some general routines to include the missing value explicitly.
Remove cosmic ray events (this step may be omitted if it takes too long).
will make the dataset 'data' available within your IDL session.
Calibrate the dataset using ergs/steradian as the output unit
Check the units by
Check which data window contains the OV line
Note that the OV data are in window number 3 and the window is 18 pixels wide and starts at detector pixel 989. Extract the OV data
Get a wavelength array to go with the OV spectrum
You should also investigate the routine gt_spectrum which can be used to extract a spectrum and wavelength array.
Average the spatial coordinates and plot the mean OV spectrum
Fit a single gaussian with linear background to the mean profile. Overplot the fit and print the fitted parameters
By creating a small IDL procedure, or on the command line, do the same fit for each pixel in the original OV data set and by saving the parameters create intensity, line-centroid and line-width maps. You may need to set a minimum intensity for the fit to avoid spurious fits. Eliminate any parameters that result from bad profile fits giving them a value that can be later specified as a 'missing' value.
The velocity map in particular will have systematic gradients both N/S and E/W owing to the tilt of the spectral line on the detector and the imaging of the scan mirror respectively. Derive corrections for these.
Translate the wavelength centroid map to a velocity map and look for any correlations between the map parameters.
Derive distributions for the map values. Investigate the shape of the intensity distribution.