@misc{eppel_a_multigrid_1990, 
author={Eppel, D. P.,Callies, U.},
title={A multigrid approach for variational data assimilation into hyperbolic model equations},
year={1990},
howpublished = {conference paper,conference lecture: Clermont-Ferrand (F); July 9-13, 1990},
note = {Online available at: \url{} (DOI). Eppel, D.; Callies, U.: A multigrid approach for variational data assimilation into hyperbolic model equations. In: International Symposium on Assimilation of Observations in Meteorology and Oceanography. Clermont-Ferrand (F). 1990. 37-41.}}