README FILE

                 Erythemal Exposure and Irradiance Data Products

 ---->  This site is mirrored from the Finnish ftp://ftp.fmi.fi ftp site  <----
                 
The erythemal noontime irradiance in a 1x1 degree grid in located in 

/pub/omi/data/uv/ery_noon

in units of milli-watts/m^2/nm



- Documentation for Noontime Irradiances and Daily Erythemal Exposure -

in the directory /pub/omi/data/uv/ery_noon and /pub/omi/data/uv/ery_dose

All of the data in this directory are on a 1x1 degree grid

The units for erythemal_noon irradiances are

milli-watts/m^2/nm


The units for the erythemal exposure are

joules/m^2



  Each value code consists of three digits: a 1 digit exponent (E), 
and a 2 digit mantissa (M).  A decimal point is implied between the 
two digits of the mantissa.  Together,  E  and  M  encode a value 
of  M*10^E .  For example, the value code "342" represents the value 
4.2*10^3 .  Note that a value code of "999" is a fill-value, used
where OMI data were unavailable.

Contact (at Goddard Space Flight Center)

Dr. Jay. R. Herman
Code 613.3
NASA Goddard Space Flight Center
Greenbelt, MD 20771
Jay.R.Herman@nasa.gov

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Data Product

  The Erythemal Exposure data product is an estimate of the daily
integrated ultraviolet irradiance, calculated using a model for the
susceptibility of caucasian skin to sunburn (erythema).  This can 
be interpreted as an index of the potential for biological damage 
due to solar irradiation, given the column ozone amount and cloud 
conditions, as determined from measurements made with the Ozone
Monitoring Instrument (OMI), on each day.


  The solar irradiances used in the calculation have units of
nW m^{-2} nm^{-1} (nanowatts per square meter per nanometer; the
"square meter" refers to the area on a horizontal surface, the 
"nanometer" refers to the wavelength of the light).  Thus, after
integrating over wavelength and time, one is left with units of
J m^{-2} (Joules per square meter).  Please see the section in the
complete documentation (erynotes.ps or erynotes.pdf) titled "A note
on the units of the exposure" for a discussion.



Format of the Data Files

  Each file consists of 3 header records, followed by 2700 data 
records.  The data records are organized in 180 groups of 15 
records.  The first 14 records in each group contain 25 three-digit 
value codes; the 15th record contains 10 value codes, followed by 
the numerical value of the center latitude of the band.  Each group 
corresponds to a single 1 degree wide latitude band, and each value 
code corresponds to a cell of dimensions 1 degree latitude by 1 degree 
longitude.

  Each value code consists of three digits: a 1 digit exponent (E), 
and a 2 digit mantissa (M).  A decimal point is implied between the 
two digits of the mantissa.  Together,  E  and  M  encode a value 
of  M*10^E .  For example, the value code "342" represents the value 
4.2*10^3 .  Note that a value code of "999" is a fill-value, used
where OMI data were unavailable.

  The following format specifications are recommended for reading 
the data records (all at once) from an Erythemal Exposure data file.

The value codes may be read as integers into a single integer array
of dimensions (360,180) (using the FORTRAN or IDL subscripting 
convention).  They must then be decoded into the values they represent.
The recommended format specification for reading the data is

   (179(14(1X,25I3,/),1X,10I3,/),14(1X,25I3,/),1X,10I3)

Alternatively, the values may be read into an integer array of 
dimensions (2,360,180), where the element (1,ilon,ilat) (FORTRAN)
or (0,ilon,ilat) (IDL) is the exponent  E  for the value at 
the grid cell (ilon,ilat), and the element (2,ilon,ilat) (FORTRAN)
or (1,ilon,ilat) (IDL) is the mantissa  M .  The recommended format 
specification in this case is

   (179(14(1X,25(I1,I2),/),1X,10(I1,I2),/),14(1X,25(I1,I2),/),1X,10(I1,I2))