l_gal, b_gal, r_pc -> Av
Berdnikov and Pavlovskaya, 1991, SvAL 17, 215
Interstellar extinction at Galactic longitudes 65 - 165 degree

Needs: l_gal, b_gal, r_pc

Ranges: l [65,165]
        b [abs(b)>10]
        r [0,1500]

Av = [beta * (b * sin(l - phi) + a0)/|sin(b)|] * [1 - exp(-|z|/beta)]