A new backscatter-lidar forward operator was developed which is based on the distinct calculation of the aerosols' backscatter and extinction properties. The forward operator was adapted to the COSMO-ART ash dispersion simulation of the Eyjafjallajökull eruption in 2010. While the particle number concentration was provided as model output variable, the scattering properties of each individual particle type had to be determined by extensive scattering calculations. Sensitivity studies were performed to estimate the uncertainties related to the assumed particle properties. Therefore, scattering calculations for several types of non-spherical particles required the usage of t-matrix routines. Due to the distinct calculation of the backscatter and extinction properties of the models' volcanic ash size classes, the sensitivity studies could be resolved to each size class individually which is not the case for forward models based on a fixed lidar ratio. Finally, the forward modeled lidar profiles have been compared to ACL measurements both qualitatively and quantitatively while the attenuated backscatter coefficient was chosen as common physical quantity. As the ACL measurements were not calibrated automatically, their calibration had to be performed using CALIPSOs/CALIOP measurements. A slight overestimation of the model predicted volcanic ash number density was observed. By manually reducing the model predicted ash number density, the effect of simple data assimilation methods could be demonstrated. Major issues for future data assimilation of ACL data have been identified. The introduced forward operator offers the flexibility to be adapted to a multitude of model systems and measurement set-ups.