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AIRS Level 3 Beta Release Data Description


This page provides an overview of the AIRS Level 3 beta product as well as description of individual parameters contained in the AIRS Level 3 beta release. A description of the provided IDL reader can be found on the Reader page.


The AIRS Level 3 beta release is intended to help the user become familiar with the file interface and to get a feel for the AIRS Level 3 data products. Please note that at this time, the data files do not contain quality flags, attributes or metadata, these are under development. This release is also intended to generate feedback to aid in the development of the full set of AIRS Level 3 products. The beta release is limited to AIRS core geophysical parameters with the exception of clouds.

File Description

The data files are in HDF-EOS Grid format and each file is compressed using the gzip utility. To uncompress, type gunzip FILENAME at the command line. The files are 38 MB uncompressed. Data compression is not anticipated for the eventual production of Level 3 products at the DAAC.

Included in this beta release are daily, 8-day and monthly Level 3 files. The 8-day files correspond to the 16 day AQUA repeat cycle and monthly files are for calendar months.

The file-naming convention for the daily files is as follows:
Where yyyy = year of observation, mm = month of observation, dd = day of observation.
For the 8-day and monthly files the file-naming conventions is:
Where yyyy = year of observation, mm = month of observation, dd = beginning day, nnn = number of days in the file, usually 008, or 028 - 031.

Data Description

The Level 3 files contain geophysical parameters that have been averaged and binned into 1°x1° grid cells. Grid maps correspond to -180.0° to +180.0° longitude and -90.0° to +90.0° latitude. For each grid map of 4-byte floating-point mean values there is a corresponding 2-byte integer grid map of counts. The counts map provides the user with the number of points per bin that were included in the mean and can be used to generate multi-day maps from the daily gridded products.

The files contain both ascending and descending data for an entire day, 8-day period or month. The parameters are distinguished with either a '_desc' for descending or a '_asc" for ascending nodes appended to the parameter name given in the data description below.

AIRS Level 2 data products generated using v3.5 of the AIRS Level 2 PGE are the input for the AIRS Level 3 Beta products.

Individual Level 2 parameters are filtered using the retQAFlag within the Level 2 files on input to Level 3 processing. The retQAFlag is an unsigned 16-bit integer that is used as an aid to data selection. Bit values of the retQAFlag are shown in the table below. The V3.0 Level 2 Data Release definitions are given in strike-through format . Only values where the second byte of retQAFlag is equal to zero are included in the Level 3 beta products, the first byte of the flag is ignored, thus land values are included, some suspect SST values, etc. Missing or flagged data cells are filled with -9999.0 for float or -9999 for integer count values. In addition, profile data (TairStd and H2OMMRStd) are checked for data values below the surface using the Level 2 flag nSurfStd. The nSurfStd flag is the index of the last physically meaningful profile entry. Values below this index are filled with -9999.0.

11 - 15 Spare, currently zero filled
10 1024 lower part of profile not valid ( see the data fields bad_low_atm and Press_valid_bottom )
9 512 Sea Surface Skin Temperature retrieval is suspect
SST varies more than 3K from forecast
8 256 This record type not yet validate(Not open Ocean and/or outside validation latitude range of |lat| < 50°)
|lat| < 40°
5 - 7 Spare, currently zero filled
4 16 Final retrieval rejected or not attempted
3 8 Final Cloud Clearing rejected or not attempted
2 4 Regression First Guess rejected or not attempted
1 2 Initial Cloud Clearing rejected or not attempted
0 1 MW retrieval rejected or not attempted

The geophysical data products included in the Level 3 beta release are:

  • totO3Std Total ozone burden in air column (Dobson Units), dimension (360,180)
  • TSurfStd Retrieved surface skin temperature (K), dimension (360, 180)
  • TSurfAir Retrieved surface air temperature (K), dimension (360,180)
  • TAirStd Retrieved atmospheric temperature profiles (K) at 28 pressStd pressures. Array values below the surface are flagged as missing (-9999.0), dimension (360,180,28)
  • totH2OStd Total precipitable water vapor in air column (kg,m2), dimension (360,180)
  • H2OMMRStd Retrieved water vapor mass mixing ratio (gm/kg_dry_air) at 13 pressStd pressures. Array values below the surface are flagged as missing (-9999.0), dimension (360,180,13).

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Last updated: Sep 09, 2009 02:24 PM ET