titles_meda

                                 Titles:  MEDA
                                 =============
 
        Contact:        S. Biller, Oxford.
 
        Revision History:-
        ================
 
        2.04    N. West         Convert to sparse table of physical media.
        2.05    N. West         Document tidy-up.
	2_07	Mike Lay	Changes to the way attenuation is handled
	2_08    Mike Lay        Complete Overhall to include specular/diffuse
                                reflections.
        2.09    N. West         Correct mistake in the HTML file.
        3.00    M. Thorman      KMEDA_NW_ENT now included at start of bank.
                                Added KMEDA_RAYL_SCF word.
	3.02    M. Thorman      Added diffuse transmission probability and
                                scaling factor for diffuse scattering in air.
        5.00    N. Tagg         Add addivives. (Scintillator and WLS)
	5.03    J. Wilson	Added scintillation flag

 
Titles Files
------------
 
media.dat
 
 
Verification
------------
 
 
Description
-----------
 
     This bank contains a table of physical media optical properties data. See
media.html for more information. The KMEDA_* bank addresses used below are
defined in the file:-
 
      snoman/n_nn/code/media_data.inc
 
Some symbolic commands are available.
 
Data Words
----------
 
      I = integer, F = floating point, H = hollerith 4 char
 
        Fixed length Database Header. See DBHDR
 
        KMEDA...
 
  +1  I  _NW_ENT    Number of words per entry
 
        The following structure is repeated for each type of media. The
        address mnemonics are relative to the start of the entry e.g.:-
             LEMEDA = MEDP_MEDA( I_PHYS_MEDIA_CODE )
             icons(LEMEDA + KMEDA_ISO_COMP) is the isothermal compressibilty
 
i+...   i = 1, 84, 167, 250, 333, 416 , ...

  +1  H _NAME      Name 5 word array (20 characters).
  +6  I _MEDP_CODE Physical media code. See media.html and id_media.html
  +7  I _OPTI_FLAG Optical media flag
  +8  F _REFX_MEAN Mean refractive index.
  +9  F    ..._IMG Mean imaginary refractive index
  +10 F _REFX_POLY Refractive index polynomial array. KMEDA_NW_REFX_POLY words
                   See note 2.
                   KMEDA_NW_REFX_POLY = 10.
  +20 F _REFX_POLY Imaginary Refractive index polynomial array.
           ..._IMG KMEDA_NW_REFX_POLY words. See the routine REFIDX.
                   KMEDA_NW_REFX_POLY = 10.
  +30 F _ATTN_POLY Attenuation array. First word is scale factor, second word
		   is number of data points, then the data points.
		   KMEDA_NW_ATTN_POLY words.
                   See the routine ABSINT.
  +62 F _RAYL_SCF       Rayleigh scattering scaling factor (see note 1.)
  +63 F _ISO_COMP       Isothermal compressibility (units N^-1 m^2).
  +64 I _SPEC_FLAG      Specular reflection flag   (see note 3) 
  +65 F _SPEC_POLY      Specular Reflection data
  +74 I _DIFF_FLAG      Diffuse reflection/transmission flag    (see note 3)
  +75 F _DIFF_POLY      Data for diffuse reflection/transmission in water. 
  +82 I _SCINT     Scintillation flag 1 = 0, 0 = off
  +83 F _DIFF_SCF_AIR   Scaling factor for diffuse reflection/trans. in air.

 
Notes
-----
 
1) The Rayleigh scattering scaling factor would usually be set to a value
   greater than 1.0 to simulate scattering above that of the Rayleigh limit
   (due to impurities etc.) as long as it follows a Rayleigh Energy^4 law.
 
2) The refractive index is calculated from the formula: n = c1 + c2*exp( c3*E )
   where c1,c2,c3 are the values from _REFX_POLY and E is the photon energy in
   eV. See REFIDX for more details.

3) Diffuse Transmission and Reflection
   -----------------------------------

   The words in _DIFF_POLY hold data for diffuse reflection and transmission
   from surfaces in water. By default only the first two words are used:-
     _DIFF_POLY   reflection probability
     _DIFF_POLY+1 transmission probability
   The outgoing direction is isotropic in a backward or forward hemisphere
   respectively. In air, the probabilities are scaled by the scaling
   factor in word _DIFF_SCF_AIR.

   There are special cases such as Nickel where _DIFF_POLY holds data giving
   the wavelength dependence of the reflection probability. This is dealt with
   in diff_refl_prob.for. Also see the entries in media.dat for more 
   information.
   
   Specular Reflection and Refraction1.9
   ----------------------------------

   For optical media, the probability of specular reflection and refraction
   is calculated according to Fresnel coefficients. If any diffuse reflection
   or transmission is switched on then the specular values are renormalized:-

     R = R*(1-DR-DT)
     T = T*(1-DR-DT)

   ( R=spec refl. T=refraction DR=diffuse refl. DT=diffuse trans. )

   The calculated probabilities can be overridden with fixed user
   values by setting _SPEC_FLAG and then filling the _SPEC_POLY array:-
     _SPEC_POLY   reflection probability
     _SPEC_POLY+1 transmission probability
   These values are scaled as above if diffuse scattering is also specified.
	
   For non-optical media (eg Stainless Steel), the _SPEC_POLY array is
   used to give the probability of reflection and absorption (ie transmitted
   photons get absorbed). See SPEC_REFL_PROB.FOR for more info.

4) The last of the 8 words allocated for KMEDA_DIFF_POLY has been canabalised to
   accommodate the scintillation flag (since it was never used). Now only 7 
   words are available for  KMEDA_DIFF_POLY.