!              Vitamin-D3 Irradiance
!              Eqn 6723  y=a+bx^2+cx^4+dx^6+ex^8
!              altitude from 0 to 4 km    e.g., U0 is 0 km U4 is 4 km
!              x = sza in degrees     x2=x*x                0 to 80
!              Fery = U * (O3/200)**(-R)           O3  = ozone 100 to 600 DU




U0=0.8815247634870993D0+x2*(-0.0003446297025320396D0+
    x2*(4.466455212482228D-08+x2*(-1.709320333122515D-12+
    x2*-2.888714586476976D-17)));
    
R0=1.116854091086787D0+x2*(7.340465959963418D-05+
    x2*(-1.309555521640900D-09+x2*(2.724436001963286D-12+
    x2*-2.330085149553069D-16)));
    

U1=0.9267310203283815D0+x2*(-0.0003593257688542949D0+
    x2*(4.561789738969226D-08+x2*(-1.596417454579047D-12+
    x2*-4.034672539440880D-17)));

R1=1.115478121579359D0+x2*(7.367505561248991D-05+
    x2*(-1.694117327632815D-09+x2*(2.842495887084427D-12+
    x2*-2.463800477819451D-16)));
    

U2=0.9682687822517592D0+x2*(-0.0003723834115887786D0+
    x2*(4.643503416861644D-08+x2*(-1.504080698964529D-12+
    x2*-4.928929634129989D-17)));

R2=1.115214683346364D0+x2*(7.370320824413805D-05+
    x2*(-2.110310018062394D-09+x2*(2.994906584698098D-12+
    x2*-2.651678828236242D-16)));
    

U3=1.008164616888194D0+x2*(-0.0003846105754356662D0+
    x2*(4.716986892302102D-08+x2*(-1.422126621475995D-12+
    x2*-5.679542858205005D-17)));

R3=1.115379308053167D0+x2*(7.335351389176717D-05+
    x2*(-1.937522857608918D-09+x2*(2.948031727326205D-12+
    x2*-2.646507078068413D-16)));
    

U4=1.047348088350274D0+x2*(-0.0003959548812501886D0+
    x2*(4.759203898774365D-08+x2*(-1.296962988029649D-12+
    x2*-6.639404041343815D-17)));

R4=1.115325183737295D0+x2*(7.357591989939739D-05+
    x2*(-2.184657093040342D-09+x2*(3.011693647185767D-12+
    x2*-2.715237892751160D-16)));