parthity

parthity

stsdas.hst_calib.fos.y_calib

parthity

NAME · USAGE · DESCRIPTION · PARAMETERS · EXAMPLES · BUGS · REFERENCES
HELP · SEE_ALSO

NAME

parthity -- Locate particle hits and compute dark rate for science diodes.

USAGE

parthity input mask table1 table2 dark

This routine locates particle hits and determines the dark rate for the Faint Object Spectrograph (FOS) science diodes. Particle hits are located by determining the average count rate per diode, using all frames of data. Particle hits are then identified as individual data points where the count rate is greater than a specified threshold (i.e., the pthresh parameter) above the average rate for the diode. If pthresh = 0.0, then the program computes the value as pnsig times the standard deviation of the count rates for each diode over all frames of data. Consecutive diodes in the same data frame that have a count rate higher than pthresh are considered to be part of the same hit.

The dark rate is computed for each diode by averaging rates for all frames of data. Points determined to be particle hits are not used in the average. Noisy diodes are identified as those having a dark rate greater than dthresh above the average for all diodes. If dthresh = 0.0, then it is computed as dnsig times the standard deviation of the rates of all diodes.

PARAMETERS

input [file name template]: File names of the input dark observations. These files contain the raw data prior to any processing by the Routine Science Data Processing (RSDP) system. All input files must have the same values in their DETECTOR, NXSTEPS, FCHNL, NCHNLS, and OVERSCAN header keywords.

mask [file name template]: Optional data quality masks corresponding to each observation. If mask files are not used then all data are used, however, if data masks are used, there must be one mask file for each file specified in the input parameter.

table= "hits" [file name]

Name of the output table that is to contain the particle hit summary. The table will have one row for each hit found. The following columns are used:

   'TIME'        - Time of the hit (char*24).
   'FRAME'       - Frame number in which the hit occurred (integer).
   'COUNTS'      - Total counts in the hit (real).
   'DIODES'      - Number of consecutive diodes affected by the
		   hit (real).
   'FIRST_DIODE' - First diode affected by the hit (integer).

table= "frame_sum" [file name]

Name of the output table in which to place the frame summary. This table will have one row for each frame of data---it contains the following columns:

   'TIME'           - Frame time (char*24).
   'EVENTS'         - Number of particle hits in the frame 
			(real).
   'DIODES'         - Number of diodes affected by particle hits 
 			(real).
   'PCOUNTS'        - Total particle hit counts (real).
   'DARK_RATE'      - Average dark rate for the frame (real).
   'SELECTED_DIODE' - Count rate of the data point selected by
		        the 'dnum' parameter (real).

dark = "dark" [file name]: Name of the output file that will contain the average dark rate for each data point over all data frames. This file has the same length as the input file.

(pthresh = 0.0) [real, min=0.0]: Threshold in counts per second for identifying particle hits. A data point is considered a particle hit if its count rate is greater than pthresh above the average count rate for the diode. If pthresh = 0.0, then a threshold is computed for each diode using the value of pnsig.

(pnsig = 4.0) [real]: This parameter is used to compute the threshold for each diode when identifying particle hits. Thresholds are computed as the average count rate over all frames of data plus pnsig times the standard deviation of the count rates over all diodes. This parameter is used only if pthresh = 0.0.

(dthresh = 0.0) [real]: The threshold in counts per second for identifying noisy diodes. If the average count rate for the diode over all frames of data (excluding particle hit data points) is greater than dthresh, the diode is considered to be noisy. If dthresh = 0.0, then the threshold is determined using the value of dnsig.

(dnsig = 4.0) [real]: This parameter is used to compute the threshold for detection of noisy diodes when dthresh has a zero value. The threshold is set to dnsig times the standard deviation of the dark rate for all diodes.

(dnum = -1) [integer, min=-1, max=511]: This parameter is used to analyze an individual diode. If dnum is greater than or equal to zero, then the average dark rate for the selected diode is displayed to the terminal and the dark rate for each frame is included in the output table table2. The parthity task is best suited for locating noisy channels and particle hits in FOS observations that do not use overscanning. If overscanned data is used, small errors may occur in the mean count rate because undersampling at the ends of the diode array are not correctly taken into account. In addition, it is impossible to discern which diode corresponds to a certain pixel with overscanned data.

EXAMPLES

1. Process one observation file called darkobs. The particle hit and the noisy diode detection thresholds (i.e., pthresh and dthresh) will be computed using the pnsig and dnsig parameters.

hr> parthity darkobs[*] ""

2. Rerun the task using a particle hit threshold of 0.001 and place the results in tables ev1.tab and fs1.tab.

hr> parthity darkobs[*] "" ev1 fs1 pthresh=0.001