Optical in-situ analysis of secondary reflectors in solar tower plants A. Timinger, T. Smith, M. Walther, W. Spirkl, A. Kribus, H. Ries and P. Doron J. Phys. IV France, 09 PR3 (1999) Pr3-117-Pr3-122 DOI: 10.1051/jp4:1999318