HDF-EOS5 File Structure Summary

1. Summary of HDF-EOS5 Files,Data Model and File Format Abe Taaheri, Raytheon IIS HDF & HDF-EOS Workshop XI November 2007

2. General HDF-EOS5 FileStructure • HDF-EOS5 file is any valid HDF5 file that contains: • a family of global attributes called: coremetadata.X Optional data objects: • family of global attributes called: archivemetadata.X • any number of Swath, Grid, Point, ZA, and Profile data structures. • another family of global attributes: StructMetadata.X • The global attributes provide information on the structure of HDF-EOS5 file or information on the data granule that file contains. • Other optional user-added global attributes such as “PGEVersion”, “OrbitNumber”, etc. are written as HDF5 attributes into a group called “FILE ATTRIBUTES”

3. General HDF-EOS5 FileStructure • coremetadata.X Used to populate searchable database tables within the ECS archives. Data users use this information to locate particular HDF-EOS5 data granules. • archivemetadata.X Represents information that, by definition, will not be searchable. Contains whatever information the file creator considers useful to be in the file, but which will not be directly accessible by ECS databases. • StructMetadata.X Describes contents and structure of HDF-EOS file. e.g. dimensions, compression methods, geolocation, projection information, etc. that are associated with the data itself. S

4. General HDF-EOS5 FileStructure • An HDF-EOS5 file • can contain any number of Grid, Point, Swath, ZonalAverage, and Profile data structures • has no size limits. • A file containing 1000's of objects could cause program execution slow-downs • can be hybrid, containing plain HDF5 objects for special purposes. • HDF5 objects must be accessed by the HDF5 library and not by HDF­EOS5 extensions. • will require more knowledge of file contents on the part of an applications developer or data user.

5. Swath Structure • Data which is organized by time, or other track parameter. • Spacing can be irregular. • Structure • Geolocation information stored explicitly in Geolocation Field (2-D array) • Data stored in 2-D or 3-D arrays • Time stored in 1-D or 2-D array, • Geolocation/science data connected by structural metadata

6. Swath Structure • For a typical satellite swath, an instrument takes a series of scans perpendicular to the ground track of the satellite as it moves along that ground track • Or a sensor measures a vertical profile, instead of scanning across the ground track

7. Swath Structure Data Field.1 Profile Field.1 Profile Field.n HDF5 Attribute Each Data Field object can have Attributes and/or Dimension Scales HDF5 Dataset “SWATHS” group • Swath_X groups are created when swaths are created • Data/Geo fields’ parent group are created when fields are defined. • Swath attributes are set as Object Attributes. • Attributes for Data, Profile, or Gelocation Fields groups are set as Group Attributes • Dataset related attributesset for each data field or geolocation field are called Local Attributes. They may contain attributes such as fillvalue, units, etc. “Swath_1” “Swath_N” Object Attribute <SwathName>: <AttrName> Geolocation Fields Profile Fields Data Fields Group Attribute <DataFields>: <AttrName> Data Field.n Longitude Latitude Local Attribute <FieldName>: <AttrName> Colatitude Time HDF5 Group

8. Swath Structure • Geolocation Fields • Geolocation fields allow the Swath to be accurately tied to particular points on the Earth’s surface. • At least a time field (“Time”) or a latitude/longitude field pair (“Latitude” and “Longitude”). “Colatitude” may be substituted for “Latitude.” • Fields must be either one- or two-dimensional • The “Time” field is always in TAI format (International Atomic Time) *DD = Decimal Degree

9. Swath Structure • Data Fields • Fields may have up to 8 dimensions. • For all multi-dimensional fields in scan- or profile-oriented Swaths, the dimension representing the “along track” dimension must precede the dimension representing the scan or profile dimension(s) (in C-order). ( e.g. “Bands, DataTrack, DataXtrack” ) • Compression is selectable at the field level within a Swath. All HDF5-supported compression methods are available through the HDF-EOS5 library. The compression method is stored within the file. Subsequent use of the library will un-compress the file. As in HDF5 the data needs to be chunked before the compression is applied. • Field names: • may be up to 64 characters in length. • Any character can be used with the exception of, ",", ";", " and "/". • are case sensitive. • must be unique within a particular Swath structure.

10. Compression Codes For Compression the data storage must be CHUNKED first

11. Compression Codes For Compression the data storage must be CHUNKED first

12. Swath Structure A “Normal” Dimension Map • Dimension maps are the glue that holds the SWATH together. They define the relationship between data fields and geolocation fields by defining, one-by-one, the relationship of each dimension of each geolocation field with the corresponding dimension in each data field. A “Backwards” Dimension Map

13. Grid Structure • Usage - Data which is organized by regular geographic spacing, specified by projection parameters. • Structure • Any number of 2-D to 8-D data arrays per structure • Geolocation information contained in projection formula, coupled by structural metadata. • Any number of Grid structures per file allowed.

14. Grid Structure • A grid contains grid corner locations and a set of projection equations (or references to them) along with their relevant parameters. • The equations and parameters can be used to compute the latitude and longitude for any point in the grid. • Important features of a Grid data set: the data fields, the dimensions, and the projection A Data Field in a Mercator-Projected Grid A Data Field in an Interrupted Goode’s Homolosine-Projected Grid

15. Grid Structure • Data Field characteristics: • Fields may have up to 8 dims • Dim order in field definitions: • - C: “Band, YDim, XDim” • - Fortran: “XDim, YDim, Band” • Compression is selectable at the field level within a Grid. Subsequent use of the library will un-compress the file. Data needs to be tiled before the compression is applied. • Field names must be unique within a particular Grid structure and are case sensitive. They may be up to 64 characters in length. • Any character can be used with the exception of, ",", ";", " and "/".

16. Grid Structure • Fields are Two - eight dimensional many fields will need not more than three: the predefined dimensions “XDim” and “YDim” and a third dimension for depth, height, or band. • Dimensions: • Two predefined dimensions for Data Fields: “XDim” and “YDim”. • - defined when the grid is created • - stored in the structure metadata. • - relate data fields to each other and to the geolocation information

17. Grid Structure • Projection: • Is the heart of the Grid structure. • Provides a convenient way to encode geolocation information as a set of mathematical equations, capable of transforming Earth coordinates (lat/long) to X-Y coordinates on a sheet of paper • General Coordinate Transformation Package (GCTP) library contains all projection related conversions and calculations. • Supported projections: * Sinusoidal is pseudocylinderical

18. HDF-EOS Point Structure • Data is specified temporally and/or spatially, but with no particular organization • Structure • Tables used to store science data at a particular Lat/Long/Height • Up to eight levels of data allowed. Structural metadata specifies relationship between levels.

19. Point Structure • Made up of a series of data records taken at [possibly] irregular time intervals and at scattered geographic locations • Loosely organized form of geolocated data supported by HDF-EOS • Level are linked by a common field name called LinkField • Usually shared info is stored in Parent level, while data values stored in Child level • The values for theLinkFiled in the Parent level must be unique

20. Point Structure • Point structure groups are created when user creates “Point_1”, ….. • Data and Linkage groups are created automatically when the level is defined • The order in which the levels are defined determines the (0-based) level index • FWDPOINTER Linkage will not be set (acutally first one is set to (-1,-1)) if the records in Child level is not monotonic in LinkFiekd • A level can contain any number of fields and records “POINTS” Group “Point_n” “Point_1” Object Attribute <SwathName>: <AttrName> Linkag Data Group Attribute <SwathName>: <AttrName> FWD POINTER Level n Level 1 BCK POINTER Local Attribute <SwathName>: <AttrName> HDF5 Group Level Data

21. Zonal Average (ZA) Structure • Generalized array structure with no geolocation linkage (basically a swath like structure without geolocation.) • The interface is designed to support data that has not associated with specific geolocation information. • Data can be organized by time or track parameter • Data spacing can be irregular • Structure • Data stored in multidimensional arrays • Time stored in 1-D or 2-D array “ZAS” group “Za_1” “Za_n” Object Attribute <SwathName>: <AttrName> Data Fields Group Attribute <DataFields>: <AttrName> Data Field.n Local Attribute <FieldName>: <AttrName> HDF5 Group

22. “h5dump” output of a simpleHDF-EOS5 file HDF5 "Grid.he5" { GROUP "/" { GROUP "HDFEOS" { GROUP "ADDITIONAL" { GROUP "FILE_ATTRIBUTES" { } } GROUP "GRIDS" { GROUP "TMGrid" { GROUP "Data Fields" { DATASET "Voltage" { DATATYPE H5T_IEEE_F32BE DATASPACE SIMPLE { ( 5, 7 ) / ( 5, 7 ) } DATA { (0,0): -1.11111,-1.11111,-1.11111,-1.11111,-1.11111, (0,5): -1.11111,-1.11111, ……………………………….. (4,0): -1.11111,-1.11111,-1.11111,-1.11111,-1.11111, (4,5): -1.11111,-1.11111 }

23. “h5dump” output of a simpleHDF-EOS5 file (cont.) ATTRIBUTE "_FillValue" { DATATYPE H5T_IEEE_F32BE DATASPACE SIMPLE { ( 1 ) / ( 1 ) } DATA { (0): -1.11111 } } } } } } } GROUP "HDFEOS INFORMATION" { ATTRIBUTE "HDFEOSVersion" { DATATYPE H5T_STRING { STRSIZE 32; STRPAD H5T_STR_NULLTERM; CSET H5T_CSET_ASCII; CTYPE H5T_C_S1; }

24. “h5dump” output of a simpleHDF-EOS5 file (cont.) DATASPACE SCALAR DATA { (0): "HDFEOS_5.1.10" } } DATASET "StructMetadata.0" { DATATYPE H5T_STRING { STRSIZE 32000; STRPAD H5T_STR_NULLTERM; CSET H5T_CSET_ASCII; CTYPE H5T_C_S1; } DATASPACE SCALAR DATA { (0): "GROUP=SwathStructure END_GROUP=SwathStructure GROUP=GridStructure GROUP=GRID_1 GridName="TMGrid" XDim=5 YDim=7

25. “h5dump” output of a simpleHDF-EOS5 file (cont.) UpperLeftPointMtrs=(4855670.775390,9458558.924830) LowerRightMtrs=(5201746.439830,-10466077.249420) Projection=HE5_GCTP_TM ProjParams=(0,0,0.999600,0,-75000000,0,5000000, 0,0,0,0,0,0) SphereCode=0 GROUP=Dimension OBJECT=Dimension_1 DimensionName="Time" Size=10 END_OBJECT=Dimension_1 OBJECT=Dimension_2 DimensionName="Unlim" Size=-1 END_OBJECT=Dimension_2 END_GROUP=Dimension

26. “h5dump” output of a simpleHDF-EOS5 file (cont.) GROUP=DataField OBJECT=DataField_1 DataFieldName="Voltage" DataType=H5T_NATIVE_FLOAT DimList=("XDim","YDim") MaxdimList=("XDim","YDim") END_OBJECT=DataField_1 END_GROUP=DataField GROUP=MergedFields END_GROUP=MergedFields END_GROUP=GRID_1 END_GROUP=GridStructure GROUP=PointStructure END_GROUP=PointStructure GROUP=ZaStructure END_GROUP=ZaStructure END " } } } } }