A modified Kramers-Kronig integral is derived, which offers greater convergence than the conventional expression when reflectance data are available over a limited range. The modified expression produces good convergence when applied to synthetic spectra.
R. K. AHRENKIEL, "Modified Kramers-Kronig Analysis of Optical Spectra," J. Opt. Soc. Am. 61, 1651-1655 (1971)