Design and co-ordination of multi-station international neutron monitor networks

The world's neutron monitor network was initiated about 50 years ago. It grew to a peak of almost 100 stations towards the end of the 1960s and at present about half of these are still active. Many of the original questions about the production of atmospheric secondaries, geomagnetic effects, and neutron monitor response in general, have been settled satisfactorily. Due to their long- term reliability and automated data acquisition, the remaining neutron monitors in the network are well suited for important future contributions in several areas. Amongst these are (a) spectral measurements, which require an optimal distribution along cutoff rigidities; (b) anisotropy studies, which require a set of neutron monitors with well-defined, narrow cones of acceptance for charged particles, covering all directions as evenly as possible; and (c) solar neutron measurements, which primarily require an even distribution in longitude, at high altitude and near the equator. Steps have already been taken to improve the network with these goals in mind, and to standardize methods. This contribution describes some of these steps and suggests further strategies to achieve the most optimal network.