Gap filling strategies for long term energy flux data sets. - Falge, ,E.,.; Baldocchi, ,D.,.; Oldson, ,R.,.; Anthoni, ,P.,.; Aubinet, ,M.,.; Bernhofer, ,C.,.; Burba, ,G.,.; Ceulemans, ,R.,.; Clement, ,R..; Dolman, ,H.,.; Granier, ,A.,.; Gross, ,P.,.; et al. (Agricultural and Forest Meteorology, 2001)