Guide to ISO Data Products:
Data Quality Report

All standard observations in the routine phase were individually inspected and an assessment of the quality of the data products was made. It should be noted that the quality refers to whether the data are useful from the technical point of view; no attempt were made to judge whether the data serve the particular science goal.

A more detailed quality analysis is available since version 7.0 of the ISO Data Archive. Every standard observation in the archive has a new product called "Data Quality Report" which compiles the whole quality information available. Simultaneously a more extended and refined list of flags has been defined for a better characterization of the observations.

The "Data Quality Reports" include:

A list of flags which affect a given observation:

General:

• - Telemetry Drop
  Data were heavily affected by an interruption of the telemetry.

• - Pointing Problem
  The actual pointing was significantly off the target, or the target was not acquired at all.

• - High glitch rate
  The measurement suffered an anomalously high glitch rate.

• - Suspicious pointing
  The pointing may not be accurate and/or the object may not be well centered.

Per instrument:

A list of flags is now available to characterize the observations taken with a given ISO instrument. More specific problems that can affect the observations like saturation, fringes, calibration problems, etc...are assessed. The whole list of available flags per instrument can be found below.

These flags may apply to the whole observation or only to certain part of it (certain measurement, wavelength, band or raster position). Note that not all observations affected by a particular flag have been identified so far.

Queries based on these flags are possible from the "Search Quality Flags" button of the ISO Data Archive.

Observations which were never executed or for which no data products could be derived are not displayed in the ISO Data Archive any more.

CAM Flags:

• - Saturation
• - Remnant pattern
  (The observation is affected by a previous very bright source or saturated observation)
• - Wrong instrument configuration
• - Instrument disabled/failed

LWS Flags:

• - Significant transient effects
• - Strong mismatch between detectors
• - Presence of strong fringes
• - Known extended source
  
• - Significant strong-source effects present (in 1 or more raster points)
• - Near-infrared leak features
• - 57.16 micron feature in SW2
• - Detector warm-up features
• - Abnormally high dark current
• - Low number of scans
  
• - Low sampling
  
• - Slow scanning
  
• - Large number of negative fluxes
• - Wheel Position Problem
  
• - Saturation

PHT Flags:

• - Off-centre pointing
• - Incomplete Raster Maps
• - Exposure time reduced due to TM drop
• - Saturation Sky Measurement
• - Saturation FCS Measurement
• - Possible Cirrus Confusion
• - Straylight Feature
• - Inconsistent filter combinations
• - Less efficient deglitching
• - Fatal glitch event
• - Wrong Chopper Angle
  (The chopper off-beam was located on a source instead of the blank sky)
• - Latch-up
  (The cold read-out electronics for the P2 detector went into a noisy state)
• - Wrong instrument configuration
• - Instrument disabled/failed

SWS Flags:

• - Detector jumps identified in band 1
• - Detector jumps identified in band 2
• - Detector jumps identified in band 3
• - Detector jumps identified in band 4
• - Detector jumps identified in band 5
• - Detector jumps identified in band 6
• - Scan jumps identified in band 1
• - Scan jumps identified in band 2
• - Scan jumps identified in band 3
• - Scan jumps identified in band 4
• - Scan jumps identified in band 5
• - Scan jumps identified in band 6
• - Light leakage at 28 microns
  (The efficiency of the order selection filters in the light path of band 3D is low)
• - Increased noise due to preceding CAM-CVF observation
  (A CAM-CVF observation preceding a SWS observation led to an increase in the detector dark current in band 3)
• - Extended source: check photometry
• - No simultaneous SW gratting scan
  (Simultaneously observe with the SW grating and the Fabry Perots was not possible)
• - Post-helium observation
  (This observation was made after ISO's Helium coolant was depleted)
• - Wrong instrument configuration
• - Instrument disabled/failed

The second part of the Data Quality Report compiles the quality information associated to the Off-Line Processing Pipeline (OLPv10.1) which includes a list of caveats affecting a particular instrument, instrument mode and/or instrument configuration. Also, a list of quality flags per instrument related to pipeline processing and calibration scheme restrictions have been defined. They are:

General:

• - Pipeline Problem
  Problems during different processing steps meant that a number of products are missing.

Per instrument:

CAM Flags:

• - Bad Dark Subtraction
• - Bad flat-fielding
• - Bad deglitching
  (The deglitching algorithm has overidentified the number of glitches)

LWS Flags:

• - Original pipeline data affected by scan-numbering problem
  

PHT Flags:

• - Default responsivity used
• - Zero Signals
• - Flat-field Features
• - Systematic Flux Offsets
  (The measurement contains a filter which shows a systematic flux offset)
• - Source in Off-beam
  (Bad definition of on-source and off-source position in a rectangular chopped measurement during the performance verification phase)
• - Temperature out of range
  (The dynamic spectral response calibration was established for the temperature range 2.7K < T < 3.1K)
• - Static Default RSRF (Relative Spectral Response Function) applied
  (This can introduce spurious features)
• - Memory Effects
  (The measurement suffers a memory effect to a previous illumination or a strong radiation hit of the PHT-S detector)
• - FCS signal not stable (transients)
• - Signals not stable
• - Only 1 FCS measurement for map
• - Straylight Feature
• - Responsivity Offset due to By-passing Skylight
  (Observations with anomalously high responsivity values on bright sky backgrounds)
• - Less efficient deglitching

SWS Flags:

• - Glitch tails identified in band 1
• - Glitch tails identified in band 2
• - Glitch tails identified in band 3
• - Glitch tails identified in band 4
• - Glitch tails identified in band 5
• - Glitch tails identified in band 6
• - Fringe residuals identified in band 1
• - Fringe residuals identified in band 2
• - Fringe residuals identified in band 3
• - Fringe residuals identified in band 4
• - Fringe residuals identified in band 5
• - Fringe residuals identified in band 6
• - Check dark subtraction

Some of these pipeline processing problems/restrictions can be solved by means of an interactive analysis of the data. The resulting products are called Highly Processed Data Products (HPDP) and the full documentation of the reduction steps, improvement of the final products and their quality is also included in the Data Quality Reports.

Finally the Data Quality Reports include also general comments by experts.