Failed gyro glitch correction

Failed gyro glitch correction in obsid 8059

Summary

In ObsId 8059 a gyro glitch at around time=319932456.0 is not removed properly, resulting in a large discontinous jump in the aspect solution pointing attitude.

Processing workaround

One possible way to process obsid 8059 (pending resolution by CXCDS of this issue) would be to stop the aspect pipeline processing after the create_GYRODATA step and manually correct the errant value in the file:

pcadf0319928450N001_gdat1.fits

The time stamp of the bad record is 319932456.0037. Two column values should be modified:

 status1 : Change from 64 to 82.
 cts1corr: Change from 0 to -190645

Details

At around time=319932456.00 in ObsId 8059 there is a single instance of glitch data in gyro channels 0 and 1. The raw counts in both channels spike by about 1000 counts for one readout only. Channels 2 and 3 are unaffected.

The gyro_read_data (create_GYRODATA pipeline step) tool correctly marks this instance as BAD_DATA (status0=64 and status1=64). However, in the gyro_process (process_gyro_data pipeline step) tool the bad data value in channel 1 is not flagged in the sigma rejection step and does not get interpolated. This leaves a value of 0 in cts1corr, which subsequently induces a 2 degree jump in the aspect solution pointing attitude. In contrast, the glitch in the channel 0 data is correctly recognized (flagged with SIGMA_REJECT) and then interpolated. This is curious since the glitch values in the two channels occur at the same time and are qualitatively identical.

Initial reading of the relevant code in gyro_process.c and the S-G smoothing code in asputils.c doesn't show any obvious reason why the expected sigma rejection does not occur. It seems that closer reading of the code or investigation in a development/debug environment is necessary.

Data

The aspect pipeline was run locally for obsid 8059. In the first case the pipeline was stopped after gyro_read_data but before process_gyro_data. In the second case the full pipeline was run.

Case 1:
ciao-ccosmos% pwd
/proj/sot/ska/analysis/gyro_glitch/obs8059/ASP_L1_STD/out_stop_before_gyro_process

ciao-ccosmos% dmlist pcadf0319928450N001_gdat1.fits'[time=319932454.0:319932458.0][cols time,status0,status1,cts0raw,cts1raw,cts0corr,cts1corr]' data
 
--------------------------------------------------------------------------------
Data for Table Block GYRODATA
--------------------------------------------------------------------------------
 
ROW    time                 status0    status1    cts0raw    cts1raw    cts0corr   cts1corr
 
     1 319932454.2099660635          0          0      -2800       6050     455952    -190558
     2 319932454.4662160873          0          0      -2771       6037     455981    -190571
     3 319932454.7224660516          0          0      -2742       6025     456010    -190583
     4 319932454.9787160754          0          0      -2712       6013     456040    -190595
     5 319932455.2349660993          0          0      -2682       6000     456070    -190608
     6 319932455.4912161231          0          0      -2652       5988     456100    -190620
     7 319932455.7474661469          0          0      -2622       5975     456130    -190633
     8 319932456.0037161112         64         64      -3617       4939          0          0
     9 319932456.2599661350          0          0      -2564       5951     456188    -190657
    10 319932456.5162161589          0          0      -2535       5939     456217    -190669
    11 319932456.7724661827          0          0      -2505       5926     456247    -190682
    12 319932457.0287162066          0          0      -2475       5915     456277    -190693
    13 319932457.2849661708          0          0      -2445       5903     456307    -190705
    14 319932457.5412161946          0          0      -2416       5891     456336    -190717
    15 319932457.7974662185          0          0      -2387       5878     456365    -190730


Case 2:
ciao-ccosmos% pwd
/proj/sot/ska/analysis/gyro_glitch/obs8059/ASP_L1_STD/out_full_pipeline
ciao-ccosmos% dmlist pcadf0319928450N001_gdat1.fits'[time=319932454.0:319932458.0][cols time,status0,status1,cts0raw,cts1raw,cts0corr,cts1corr]' data
 
--------------------------------------------------------------------------------
Data for Table Block GYRODATA
--------------------------------------------------------------------------------
 
ROW    time                 status0    status1    cts0raw    cts1raw    cts0corr   cts1corr
 
     1 319932454.2099660635          0          0      -2800       6050     455952    -190558
     2 319932454.4662160873          0          0      -2771       6037     455981    -190571
     3 319932454.7224660516          0          0      -2742       6025     456010    -190583
     4 319932454.9787160754          0          0      -2712       6013     456040    -190595
     5 319932455.2349660993          0          0      -2682       6000     456070    -190608
     6 319932455.4912161231          0          0      -2652       5988     456100    -190620
     7 319932455.7474661469          0          0      -2622       5975     456130    -190633
     8 319932456.0037161112         82         64      -3617       4939     456157          0
     9 319932456.2599661350          0          0      -2564       5951     456188    -190657
    10 319932456.5162161589          0          0      -2535       5939     456217    -190669
    11 319932456.7724661827          0          0      -2505       5926     456247    -190682
    12 319932457.0287162066          0          0      -2475       5915     456277    -190693
    13 319932457.2849661708          0          0      -2445       5903     456307    -190705
    14 319932457.5412161946          0          0      -2416       5891     456336    -190717
    15 319932457.7974662185          0          0      -2387       5878     456365    -190730

Analysis data

The scripts and data used in this analysis are in /proj/sot/ska/analysis/gyro_glitch/obs8059

Last modified:02/22/08

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