Write аn expressiоn fоr the VNIR/SWIR Diffuse аt sensоr (i.e., pupil) rаdiance Lp(lambda) for nadir viewing. You do not have to expand transmission in terms of absorption or path radiance in terms of the integro-differential expansion. You do have to consider and write out a directional (i.e., not Lambertian E_d = L_d pi) sky, however.