UV dose and UV index data file structure

Main data product pages:

Erythemal UV index | Daily erythemal UV dose

HDF data file structure

The data of UV index and UV dose fields is stored in HDF-4 data files.
Simply said, such a file has the following structure:

File header, with the file attributes
these specify the product name, data, version, units, etc.
Data sets:
1. Global UV index or UV dose field
2. Error in the global UV field
  due to the error in the ozone column value

There are several tools around on the web for viewing and treating HDF files, notably at the NCSA HDF Home Page. Software for reading HDF files is available at this page, where you can find a binary distributions for several operating systems (UNIX, Linux, Windows).
The HDF file can also be read with IDL; see below.

The following table gives as an example the header of the HDF file of the erythemal UV dose of 5 Feb. 2004, computed from SCIAMACHY ozone data [ image].

Global Attribute	Value
Product	Erythemal UV dose (kJ/m2)
Version	1.1
UV_field_date	2004, 2, 5, 0, 0, 0
Date_format	year, month, day, hour, minute, second (local solar time)
Cloud_info	Meteosat cloud cover fraction, 1-hourly observations
Authors	R.J. van der A & J.H.G.M. van Geffen
Affiliation	KNMI (Royal Netherlands Meteorological Institute)
E-mail	avander@knmi.nl & geffen@knmi.nl
Data_created_by	TM3-DAM (version 3.3) & temisuvdose (version 1.1)
Number_of_longitudes	720
Longitude_range	-179.75, 179.75
Longitude_step	0.50
Number_of_latitudes	360
Latitude_range	-89.75, 89.75
Latitude_step	0.50
Iuvfield	UV dose field
Iuverror	Error in UV dose due to error in ozone field
Units	UV dose unit kJ/m2
Note	UV dose = Iuvfield/100; Error = Iuverror/100
Product_code *	sdemdv
Data set	Rank --> dimensions
Iuvfield	2 --> 720 x 360
Iuverror	2 --> 720 x 360
) This product code is for internal use, to ease post-processing.*

Reading the HDF data file with IDL

The data file can also be read with IDL, for example with the routine uvhdfread.pro;
this particular routine has been tested at IDL versions 5.2, 5.4 and 5.5.
Once the data have been read, they can be plotted, exported to other formats, etc.
When running it with the erythemal UV dose of 5 Feb. 2004 [ image], the result looks like this:


IDL> .run uvhdfread
% Compiled module: UVHDFREAD.
IDL> uvhdfread

>>> Give the name of the HDF file to read
: uvdem20040205.hdf

    Product: Erythemal UV dose (kJ/m2)
    No. of global attributes: 21
    No. of datasets: 2

      id  Global Attribute (first five)
     -----------------------------------
       0  Product
       1  Version
       2  UV_field_date
       3  Date_format
       4  Cloud_info

    Details of the UV_field_date attribute:

       UV_field_date is of type LONG; no. of values:  6
       UV_field_date values stored :  2004    2    5    0    0    0
       UV_field_date as a nice date:  5 February 2004

    Reading data set Iuvfield ...
    Reading data set Iuverror ...

>>> Give a "return" to continue
: 

    Part of the data as example:

       ilat  latitude    ilon  longitude   UV_value
      ----------------------------------------------
        268    44.25      388    14.25       0.770
        268    44.25      389    14.75       0.740
        268    44.25      390    15.25       0.810
        268    44.25      391    15.75       0.850
        269    44.75      388    14.25       0.670
        269    44.75      389    14.75       0.700
        269    44.75      390    15.25       0.800
        269    44.75      391    15.75       0.830
        270    45.25      388    14.25       0.720
        270    45.25      389    14.75       0.780
        270    45.25      390    15.25       0.790
        270    45.25      391    15.75       0.750

>>> Extract the UV value at a certain longitude, latitude coordinate
>>> Give the longitude, range: [-180:180] degrees
    use -999 to end
: 12.23
>>> Give the latitude, range: [-90:90] degrees
: 41.80
    Given coordinates fall in the grid cell with centre:
      longitude =  12.25
      latitude  =  41.75
    The UV value for this cell is:  0.990

>>> Extract the UV value at a certain longitude, latitude coordinate
>>> Give the longitude, range: [-180:180] degrees
    use -999 to end
: 5.18
>>> Give the latitude, range: [-90:90] degrees
: 52.10
    Given coordinates fall in the grid cell with centre:
      longitude =   5.25
      latitude  =  52.25
    The UV value for this cell is:  0.210

>>> Extract the UV value at a certain longitude, latitude coordinate
>>> Give the longitude, range: [-180:180] degrees
    use -999 to end
: 0
>>> Give the latitude, range: [-90:90] degrees
: 0
    Given coordinates fall in the grid cell with centre:
      longitude =  -0.25
      latitude  =  -0.25
    The UV value for this cell is -1, meaning that
    there is no data available for this grid cell

>>> Extract the UV value at a certain longitude, latitude coordinate
>>> Give the longitude, range: [-180:180] degrees
    use -999 to end
: -999

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