2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/131736The current status and prospects of deducing the proton-air cross section from fluorescence telescope measurements of extensive air showers are discussed. As it is not possible to observe the point of first interaction, $X_ {\rm 1}$, directly, other observables closely linked to $X_{\rm 1}$ must be inferred from the measured longitudinal profiles. This introduces a dependence on the models used to describe the shower development. Systematic uncertainties arising from this model dependence, from the reconstruction method itself and from a possible non-proton contamination of the selected shower sample are discussed.Contribution to the 30th International Cosmic Ray Conference, Merida, Mexico, July 2007Astrophysicstext