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

2. Page 2 General HDF-EOS5 File Structure 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. Page 3 General HDF-EOS5 File Structure S 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.

4. Page 4 General HDF-EOS5 File Structure An HDF-EOS5 file – can contain any number of Grid, Point, Swath, Zonal Average, 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. Page 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. Page 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. Page 7 Swath Structure Data Field.1 Profile Field.1 Profile Field.n HDF5 Attribute HDF5 Dataset Each Data Field object can have Attributes and/or Dimension Scales 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 attributes set for each data field or geolocation field are called Local Attributes. They may contain attributes such as fillvalue, units, etc. Geolocation Fields “SWATHS” group “Swath_N” “Swath_1” Data Fields Profile Fields Object Attribute : Group Attribute : Local Attribute : Longitude Latitude Time Colatitude Data Field.n HDF5 Group

8. Page 8 Swath Structure Field NameData TypeFormat Longitudefloat32 or float64DD*, range [-180.0, 180.0] Latitudefloat32 or float64DD*, range [-90.0, 90.0] Colatitudefloat32 or float64DD*, range [0.0, 180.0] Timefloat64 TAI93 [seconds until(-) / since(+) midnight, 1/1/93] 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. Page 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. Page 10 Compression Codes Compression Code ValueExplanation HDFE_COMP_NONE 0No Compression HDFE_COMP_RLE 1 Run Length Encoding Compression (not supported) HDFE_COMP_NBIT 2NBIT Compression HDFE_COMP_SKPHUFF 3Skipping Huffman (not supported) HDFE_COMP_DEFLATE 4gzip Compression HDFE_COMP_SZIP_CHIP 5 szip Compression, Compression exactly as in hardware HDFE_COMP_SZIP_K13 6 szip Compression, allowing k split = 13 Compression HDFE_COMP_SZIP_EC 7szip Compression, entropy coding method HDFE_COMP_SZIP_NN 8 szip Compression, nearest neighbor coding method HDFE_COMP_SZIP_K13orEC 9 szip Compression, allowing k split = 13 Compression, or entropy coding method For Compression the data storage must be CHUNKED first

11. Page 11 Compression Codes Compression Code ValueExplanation HDFE_COMP_SZIP_K13orNN 10 szip Compression, allowing k split = 13 Compression, or nearest neighbor coding method HDFE_COMP_SHUF_DEFLATE 11shuffling + deflate(gzip) Compression HDFE_COMP_SHUF_SZIP_CHIP 12 shuffling + Compression exactly as in hardware HDFE_COMP_SHUF_SZIP_K13 13 shuffling + allowing k split = 13 Compression HDFE_COMP_SHUF_SZIP_EC 14shuffling + entropy coding method HDFE_COMP_SHUF_SZIP_NN 15 shuffling + nearest neighbor coding method HDFE_COMP_SHUF_SZIP_K13orEC 16 shuffling + allowing k split = 13 Compression, or entropy coding method HDFE_COMP_SHUF_SZIP_K13orNN 17 shuffling + allowing k split = 13 Compression, or nearest neighbor coding method For Compression the data storage must be CHUNKED first

12. Page 12 Swath Structure A “Normal” Dimension Map A “Backwards” 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.

13. Page 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. Page 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. Page 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. Page 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. Page 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 : Geographic MercatorTransverse Mercator Universal Transverse Mercator Cylindrical Equal area Hotin Oblique Mercator Space Oblique Mercator Sinusoidal*Integerized Sinusoidal Interrupted Goode’s Homolosine Polar Stereographic Lambert Azimuthal Equal Area PolyconicAlbers Conical Equal AreaLambert Conformal Conic * Sinusoidal is pseudocylinderical

18. Page 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. Page 19 Point Structure Usually shared info is stored in Parent level, while data values stored in Child level The values for the LinkFiled in the Parent level must be unique 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

20. Page 20 Point Structure Object Attribute : “POINTS” Group “Point_1” Group Attribute : Local Attribute : Level 1 Level n Data Linkag “ Point_n” FWD POINTER BCK POINTER HDF5 Group 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 Level Data

21. Page 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_n” “Za_1” Object Attribute : Group Attribute : Local Attribute : Data Fields HDF5 Group Data Field.n

22. Page 22 “h5dump” output of a simple HDF-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. Page 23 “h5dump” output of a simple HDF-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. Page 24 “h5dump” output of a simple HDF-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. Page 25 “h5dump” output of a simple HDF-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. Page 26 “h5dump” output of a simple HDF-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 " }