EVERYTHING YOU NEED TO KNOW FOR DOWNWARD FLUX AT SURFACE

 Notation;
  mu0=cosine(solar zenith angle at the surface)
  f0=exoatmospheric solar flux through a surface perpendicular to the direction
     of propagation.
  f0atten=the attenuated downward solar flux at the surface through a surface
          perpendicular to the direction of propagation.  This does NOT
          include the cosine(solar zenith angle) factor.
  gg=downward diffuse flux at the surface for 0 surface reflectance
  sb=reflectance of atmosphere when illuminated by upward isotropic flux @ sfc.
  ggp=actinic flux due to downward diffuse at the surface for 0 surface
         reflectance
  sbp=reflectance of atmosphere (in terms of actinic flux) when illuminated
         by upward isotropic flux @ sfc.

  Total downward flux at sfc for reflectance rho =
     (f0atten*mu0+gg)/(1-rho*sb)

  Total actinic flux (4pi) at sfc for reflectance rho =
     f0atten + ggp + rho*(sbp+2)*(f0atten*mu0+gg)/(1-rho*sb)

  Total downward actinic flux at sfc for reflectance rho =
     f0atten + ggp + rho*sbp*(f0atten*mu0+gg)/(1-rho*sb)

wavelength Solar  f0    f0atten    gg        sb        ggp       sbp
           Zenith
           [deg]
*****************************************************************************
 3419.00  7.8 1.00E+00 4.927E-001 2.376E-01 3.635E-01 4.760E-01 8.627E-01
 3420.00  7.8 1.00E+00 4.932E-001 2.374E-01 3.632E-01 4.757E-01 8.622E-01
 3421.00  7.8 1.00E+00 4.936E-001 2.372E-01 3.629E-01 4.754E-01 8.616E-01
 3422.00  7.8 1.00E+00 4.940E-001 2.370E-01 3.626E-01 4.751E-01 8.610E-01
 3423.00  7.8 1.00E+00 4.944E-001 2.368E-01 3.623E-01 4.748E-01 8.604E-01
 3424.00  7.8 1.00E+00 4.949E-001 2.367E-01 3.620E-01 4.745E-01 8.598E-01
 3425.00  7.8 1.00E+00 4.954E-001 2.365E-01 3.617E-01 4.743E-01 8.594E-01
 3426.00  7.8 1.00E+00 4.958E-001 2.363E-01 3.614E-01 4.740E-01 8.588E-01
 3427.00  7.8 1.00E+00 4.962E-001 2.361E-01 3.611E-01 4.736E-01 8.581E-01
 3428.00  7.8 1.00E+00 4.965E-001 2.359E-01 3.608E-01 4.732E-01 8.576E-01
 3429.00  7.8 1.00E+00 4.969E-001 2.356E-01 3.605E-01 4.728E-01 8.570E-01
 3430.00  7.8 1.00E+00 4.972E-001 2.354E-01 3.602E-01 4.724E-01 8.564E-01
 3431.00  7.8 1.00E+00 4.975E-001 2.351E-01 3.599E-01 4.720E-01 8.559E-01
 3432.00  7.8 1.00E+00 4.977E-001 2.348E-01 3.596E-01 4.715E-01 8.553E-01
 3433.00  7.8 1.00E+00 4.981E-001 2.346E-01 3.593E-01 4.711E-01 8.546E-01
 3434.00  7.8 1.00E+00 4.985E-001 2.344E-01 3.590E-01 4.708E-01 8.541E-01
 3435.00  7.8 1.00E+00 4.989E-001 2.343E-01 3.587E-01 4.706E-01 8.537E-01
 3436.00  7.8 1.00E+00 4.994E-001 2.341E-01 3.585E-01 4.704E-01 8.534E-01
 3437.00  7.8 1.00E+00 4.997E-001 2.338E-01 3.583E-01 4.700E-01 8.530E-01
 3438.00  7.8 1.00E+00 4.997E-001 2.335E-01 3.580E-01 4.693E-01 8.524E-01
 3439.00  7.8 1.00E+00 4.996E-001 2.330E-01 3.577E-01 4.685E-01 8.519E-01
 3440.00  7.8 1.00E+00 4.995E-001 2.326E-01 3.574E-01 4.677E-01 8.513E-01
 3441.00  7.8 1.00E+00 4.997E-001 2.323E-01 3.571E-01 4.672E-01 8.509E-01