HIRDLS-Aura_L2_v07-00-20-c01_2008d001.cdl

// Purpose: A simplified CDL example the Level 2 Aura HIRDLS product files in
// HDF5-based HDF-EOS format archived in NASA GES DISC. This file shows how a
// Level 2 vertical profile swath data file is usually encoded in the HDF-EOS
// convention and how they can be converted to a netCDF structure with CF
// convention.

// Please notice that many HDF products contains variables with the "units"
// attribute value being set as "NoUnit". In this example, Value "1" is used
// instead. See the comment before the last variable "temperatureQuality".

// Please also notice that the file, though being compliant with HDF-EOS
// standard, also uses HDF5's "Dimension Scale" approach in associating data
// point with coordinates. This is reflected by the HDF5 reserved attribute
// name "DIMENSION_LIST". The value in this attribute are the references of
// HDF5 objects from which the coordinate datasets can be identified. In this
// example, this attribute is included in variables to demonstrate how HDF5
// deals with dimension mapping. But the attribute must be comment out when
// using ncgen to convert it to NetCDF-4. NetCDF-3 is OK.

// This file can be converted to a nc3 or a nc4 file, but the DIMENSION_LIST
// attribute must be commented out in case of nc4. The output nc3/nc4 file
// should pass CF checker except that no actual data values are included in the
// file.
// ncgen -b HIRDLS-Aura_L2_v07-00-20-c01_2008d001.cdl
// ncgen -k netCDF-4 -b HIRDLS-Aura_L2_v07-00-20-c01_2008d001.cdl

// Contact: Wenli Yang, GES DISC, wenli.yang@nasa.gov


netcdf HIRDLS-Aura_L2_v07-00-20-c01_2008d001 {

 // Template source:
 // ftp://acdisc.sci.gsfc.nasa.gov/ftp/data/s4pa/Aura_HIRDLS_Level2/HIRDLS2.007/2008/HIRDLS-Aura_L2_v07-00-20-c01_2008d001.he5

 :Title = "Example of 2D vertical profile Swath based on Aura HIRDLS Level 2 HDF-EOS file" ;
 :Conventions = "CF-1.6.0" ;
 :Institution = "NASA-GSFC" ;

 // Dimensions
 // Note: in HDF-EOS, the dimension names are stored in the structure metadata.
 // If one uses ncdump to dump a HDF-EOS file, the dimension names in its
 // structure will not be recognized by ncdump and the names will be shown as
 // phony_dim_0, phony_dim_1, etc.

 dimensions:
   nLevels = 121 ; // number of pressure layers. This is the profile height.
   nTimes = 5554 ; // number of time steps in a swath, the same as number of along track data points, "Track". This is the profile length.


 variables:

 // Coordinate variables.

 // They are originally included in the "/HDFEOS/SWATHS/HIRDLS/Geolocation
 // Fields/" group and are moved to the top here as coordinate variable, with
 // some changes to attributes in order to be compliant with CF-1.6.
 // It should be noticed that
 // 1) There are only two the real coordinates, one being "time", whose size is
 //    the number of the along track points in the swath, and the other is
 //    "pressure" which defines the profile's vertical coordinate along which
 //    measurements are taken. The altitude, latitude, and longitude variables
 //    provide the location of of swath points in the 3D space.
 // 2) In addition to the variables listed here, there are more than a dozen
 //    additional variables the science team considered as "geolocation"
 //    variables, among which are the solar and viewing geometry variables that
 //    can be found in most L1/L2 NASA EOS swath data files.
  double time(nTimes) ;
     time:long_name = "time" ;
     time:units = "seconds since 1993-01-01 00:00:00" ;
     // time:DIMENSION_LIST = "1-58650071";
  float pressure(nLevels) ;
     pressure:long_name = "pressure level" ;
     pressure:units = "hPa" ;
     // pressure:DIMENSION_LIST = "1-58649775";
  float altitude(nTimes, nLevels) ;
     altitude:standard_name = "altitude" ;
     altitude:long_name = "height above mean sea level" ;
     altitude:units = "m" ;
     // altitude:DIMENSION_LIST = "1-58650071,1-58649775";
  float longitude(nTimes) ;
     longitude:units = "degrees_east" ;
     longitude:long_name = "Geodetic longitude (deg)" ;
     // longitude:DIMENSION_LIST = "1-58650071,1-58649775";
  float latitude(nTimes) ;
     latitude:units = "degrees_north" ;
     latitude:long_name = "Geodetic latitude (deg)" ;
     // latitude:DIMENSION_LIST = "1-58650071,1-58649775";


 // Data variables.

 // There are more than six dozens of "data" variables included in this HIRDLS
 // HDF-EOS file. They are either of two-dimensional, i.e., along the time and
 // pressure coordinate, or only of one-dimension, i.e., changes only along the
 // time coordinate but not along the vertical pressure coordinate. Only one of
 // each such variables are included in this example.
 float temperature(nTimes, nLevels) ;
    temperature:coordinates = "longitude latitude altitude" ;
    temperature:_FillValue = -999.f ;
    temperature:missing_value = -999.f ;
    temperature:long_name = "temperature" ;
    temperature:units = "K" ;
    // temperature:DIMENSION_LIST = "1-58650071,1-58649775";

 // CF recommands, although not requires, "units" for all variables. Many HDF-
 // EOS data include variables without unit, such as some index based variables
 // and quality variables. It is a common practice in HDF-EOS community to use
 // "NoData" as the value of such variables but the "NoData" value is
 // considered as not CF compliant. It seems that simply using "1" as unit
 // value might be a good option. It will be vary appropriate in some index
 // based variable, such as the popular "Normalizaed Difference Vegetation
 // Index" in the land remote sensing area, where people sometimes using a
 // longer "1 NDVI unit" as a unit. In this example, I use "1" to replace the
 // original "NoUnit".
 byte temperatureQuality(nTimes) ;
    temperatureQuality:coordinates = "longitude latitude altitude" ;
    temperatureQuality:_FillValue = -99b ;
    temperatureQuality:missing_value = -99b ;
    temperatureQuality:long_name = "temperature quality" ;
    temperatureQuality:units = "1" ;
    // temperatureQuality:DIMENSION_LIST = "1-58650071";


 // Data values are not included in this example
 data:

}