KI V2 -- Description of Quality Assessment (QA) grade

Overview

Each sum line should have a single QA metric which can be used for data evaluation and selection in the Level 2 calibration. The current QA system calculates percentile scores for a list of data attributes at the sum, integration and nightly levels (see http://msc.caltech.edu/KISuppo../../../QAoverview.html). The grade is designed to incorporate this information as well as other factors to assign a value that less experienced interferometry users can use in calibrating their data.

Format

Similar to 2MASS, each grade will be a 3 digit field where the digits run from 0 to 3 with the following meanings: 

  0 = good data with no known issues or problems
  1 = fair data which may have minor issues but will still calibrate normally
  2 = poor data (weather or instrument) that will need very careful calibration
  3 = data severely comprised by weather or instrument problems, should only
    be used with extreme caution

Each digit will represent a given time span:

1st: this record
2nd: this integration
3rd: this night

Thus the 2nd digit will be the same for all records in an integration and the 3rd digit will be the same for all records in a night.

The grades will NOT be normalized. That is, there will be no effort to make 1/4 of the grades be 0.

Assigning grades

The grades digit assignment will have two phases. In the first phase, a preliminary grade will be assigned at each level based on the percentile scores from that level.

Preliminary grade assignment

In the preliminary grade assignment, each level attribute contributes to the grade. This is derived simply from the percentile score with the data in the top 25% getting a grade of 0, data in the middle 50% getting a grade of 1 and data in the lowest 25% getting a grade of 2. The flux attribute is not included in this calculation.

The preliminary grade at each level is the (rounded) average of the attribute grades.

Grade modifications

In the second phase, the preliminary grades are modified based on data aspects not covered by the QA percentiles, or by absolute values for some attributes which we know to be bad.

These modifications are given for each level

Record

  1. Modifications based on cal flag value 
    cal flag	 grade
0 or 1		 no change
2 thru 5         grade = 2 (unless was already a 3)
  2. Mofications based on ratio value 
    ratio correction < 1        grade = 3
ratio correction > 2        grade = 3
  3. Modifications based on numerically bad values 
    photon flux < 0   grade = 3
V2 < 0             grade = 3
V2 > 2             grade = 3

Integration

  1. The integration grade must be equal to or greater than the average record grade.
  2. If integration is a science target and no calibration data are available within a specified interval, the grade is set as given below: 
      +/- 30 minutes grade = 2
  +/- 1 hour     grade = 3
  3. Modications based on ratio value 
     
  mean ratio correction < 1      grade = 3
  mean ratio correction > 2      grade = 3
  4. Modifications based on numbers of records in this scan (Note: the nominal number of records per scan is 25) 
      number of records = nr

  nr >= 15       no change
  7 >= nr > 15   grade = grade - 1
  nr < 7         grade = grade - 2

Night

  1. The night grade must be equal to or greater than the average integration grade.

In exceptional circumstances, grades will be modified as needed by the V2 contact scientist to reflect instrument problems. In general this will apply to whole integrations and nights only.

Return to the KI Support page Return to QA Overview

last updated Mar 30, 2005