The KATRIN (Karlsruhe Tritium Neutrino) experiment aims to measure the mass of the electron anti-neutrino with a sensitivity of 200 meV/c2 by measuring the spectrum of the beta electrons close to the kinematic endpoint region. For monitoring the isotopic composition in the gaseous tritium source a custom-made Laser-Raman-System (LARA) has been developed at the Tritium Laboratory Karlsruhe. The two approaches used to calibrate the LARA system for trueness <3 % are: i) theoretical intensities together with a spectral intensity standard and ii) highly accurate gas mixtures. Latest efforts have improved the in-situ calibration via spectral standard with re-calculated theoretical uncertainties and uncertainty analysis. Recently, the TRIHYDE experiment has been setup which enables cross-checking of the calibration via gas mixtures of all six hydrogen isotopologues and further studies of systematic effects. This poster presents the benefits and status of both complementary approaches.