IDB flare pipeline

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The frequency of observing calibrator sources during EOVSA solar observations is much less than that one typically would like to observe to properly take into account the instrumental gain variations. Hence self-calibration is often needed to calibrate the data to a level of satisfaction. A self-calibration pipeline suitable for generating calibrated dataset and quicklook images have been developed. Here we explain the various inputs of that pipeline and discuss various factors that is needed to be considered before supplying the input values. We also provide the steps for running the code on the pipeline machine.

Format of the pipeline

The pipeline for now consists of an input file and two codes. The input file is named as . The other two codes are and The code is used to generate the measurement set (MS) from the raw files and calibrate the data using the gaintables derived from the calibrator observations. The second script is where the self-calibration happens. The main reason for having two separate codes is that "" uses SUNCASA which for now runs on CASA versions<=5.4 . However, requires CASA >=5.6. Hence for now the user needs to run the codes using the appropriate CASA versions.

Description of the inputs

An example inputs file in given below.

## Task handlers ###
cal_disk = 0 ## apply calibration tables from full disc imaging
identify_data_gap=1  ### identify data gaps
doslfcal = 1  # main cycle of doing selfcalibration
doapply = 0  # apply the results

# ============ declaring the working directories ============
### remember / is necessary in all the folder names

workpath = '/data1/testing/20211101/'
slfcaldir = workpath+ 'slfcal_v3/'  # place to put all selfcalibration products
imagedir = slfcaldir + 'images/'  # place to put all selfcalibration images
caltbdir = slfcaldir+'caltables/'  # place to put calibration tables
slfdisktbdir = slfcaldir + 'slfdisktb/'

# ============= time to image =================
starttime='2017-08-20 19:20:00'   ### has strict formating rules
endtime='2017-08-20 19:48:00'

# ============ selfcal parameters ===============
refantenna = '0'
calc_cell=True ### If set to False use the value in beam given below
cell=[10]  ### size needs to be same as the number of spw listed in selfcal_spw
calc_imsize=True   ### is False uses the value given below
imsize=42  ### in solar radius, the full image size at the first frequency. Other frequencies, the value will be scaled.
           ### The default value of 42 solar radius is for ~1 GHz

max_frac_freq_avg=0.5  ### I will average at most this much fractional bandwidth

maxiter=10  ### maximum selfcal iterations
flag_antennas = '' ###anything except 13~15. Those antennas are always flagged. 

# ========== end of input parameters =================

The task handlers listed in the controls what functions will be performed by the A value of 0 means that functionality will be run. Please give 1 as input if the said task is desired. The next group of inputs are the working directories. After that, the time duration of interest should be provided. Please note that the format used when providing the starttime and endtime should be followed exactly as given in the above example. The next group of inputs are those which control different imaging and calibration parameters. refantenna is the index of the reference antenna which is used during the calibration. The user has the choice to either provide the cell size and manually, or the code can calculate it based on the maximum uv value. Please set the parameter calc_cell to True if automatic setting of parameter value is desired. If set to False, the user must provide the cell size for all the spws. Please note that the unit of the cell size is in arcseconds. Current the parameters calc_imsize and imsize are not used. The imsize is always set to 4096, which means that the total area imaged is equal to 4096xcell size. maxiter is the maximum number of selfcal iterations which can happen. During the self-calibration step, we use uv values above a cutoff. The cutoff is controlled by the parameter uvlim. The value of this parameter is in units of and corresponds to the value at spw 0. For other spws, the value is scaled with the corresponding frequency. During the self-calibration process, often spws are averaged to make an image. The two parameters named max_frac_freq_avg and avg_spw_max controls the maximum bandwidth over which this averaging can happen. max_frac_freq_avg is equal to the fractional bandwidth and is given by , where are the lower and upper edges of the band to be averaged. avg_spw_max is the maximum number of spws which can be averaged. During averaging both these parameters are calculated and the averaging stops when one of them is satisfied. If the user wants an antenna to be flagged other than antennas 13~15, that list should be supplied in flag_antennas . The image phasecenter is often shifted close to the location of the flare, so as to make a smaller image. Hence a custom phasecenter is used. The user has the option to provide the desired phasecenter in the input phasecenter or if left blank, the code will try to calculate it automatically.

Important steps in pipeline

  • Find time of self-calibration  : The flare times are first detected, because the self-calibration is performed only once by the pipeline for a dataset. If the user intends to perform self-calibration at multiple times, the dataset should be split around the times of interest. For each spw, the auto-correlations are extracted and the median and median absolute deviation of the timeseries are calculated. The times at which the auto-correlation value exceeds the threshold are noted down. The longest time interval for which the value is higher than the threshold is identified with the flare duration. A time interval of length duration/3 around the peak is chosen for self-calibration. The minimum time interval is chosen to be 10s and the maximum is chosen to be 1 minute. If no value is found above the threshold, we choose 1 minute around the peak for self-calibration. These times are identified as quiet times and other times are identified as flaring times.