  The excitation spectrum of the nucleon consists of several overlapping
resonances. To identify these resonances and their contributions to the
measured cross sections, a partial wave analysis is used. A set of at least
eight, well chosen, single and double polarisation observables is needed to
derive an unambiguous solution. With the Crystal Barrel/TAPS setup at ELSA,
single and double polarisation observables can be measured in different
reaction channels, by using the combination of a linearly or circularly
polarised photon beam and a longitudinally or transversely polarised butanol
frozen spin target. Results of the G asymmetry measurement, using linearly
polarised photons and longitudinally polarised protons, for pion and eta
photoproduction are presented. This project is supported by the DFG (SFB/TR16).
