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Frequently Asked Questions



Answers to  AIRS NRT Questions

  • How much AIRS NRT data sets are available?
    The NRT data sets stay for about 7 days from the time they are generated.
  • How soon are AIRS NRT data sets available?
    The NRT data is generally available within 3 hours of observations globally.
  • What's the difference between the AIRS NRT products and the AIRS routine Products?
  • The AIRS NRT data products are identical to the AIRS routine products except for the following.  The AIRS NRT products are produced;
    - whether or not the previous or subsequent granules are present.
    - with less accurate ephemeris/attitude data.
    - whether or not the forecast surface pressure is present.

    These differences have the following implications for the AIRS NRT Level 1B and Level 2 products.

    Level 1B The atmospheric surface pressure is not used in Level 1B processing, the AIRS Level 1b radiance data produced in the Near Real Time (NRT) system are nearly identical to the routinely processed AIRS data.  There may be small differences in the geolocation (i.e., longitude and latitude).  Also, since the NRT system does not wait as long for the previous or subsequent granule data to be present before processing there may be small differences in the radiances of NRT data that were processed without the previous or subsequent granules.  This can happen when AIRS is entering or leaving the range of a downlink station (usually are 17 times/day).  The reason for the differences is because the standard product uses the space view offset from the previous and subsequent granules for calibration purposes.

    Level2 The AIRS Level 2 NRT retrieval products can differ from the routine products because of small differences in assumed surface pressure and/or differences in the radiances.  Although it is rare, if the forecast surface pressure is not available when the NRT data are produced the NRT algorithm assumes a surface pressure based on a Digital Elevation Map (DEM) rather than the more accurate forecast surface pressure. The differences in the assumed surface pressure tend to be small (~ 10 mbar) near the equator but can become larger (~ 70 mbar) near synoptic weather events.  The pressure differences can also lead to differences in the retrieved temperature and water vapor.

    For more information, please read the following document,
    Difference between AIRS NRT and Standard Products *




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Last updated: Jan 24, 2012 04:51 PM ET