We estimate the effective area available for cosmic-ray detection with a network of smartphones under optimistic conditions. To measure cosmic-ray air showers with a minimally-adequate precision and a detection area similar to existing ground-based detectors, the fraction of participating users needs to unrealistically large. We conclude that the prospects of cosmic-ray research using smartphones are very limited.
Charged particles of extensive air showers (EAS), mainly electrons and positrons, initiate the emission of fluorescence light in the Earths atmosphere. This light provides a calorimetric measurement of the energy of cosmic rays. For reconstructing the primary energy from an observed light track of an EAS, the fluorescence yield in air has to be known in dependence on atmospheric conditions, like air temperature, pressure, and humidity. Several experiments on fluorescence emission have published various sets of data covering different parts of the dependence of the fluorescence yield on atmospheric conditions. Using a compilation of published measurements, a calculation of the fluorescence yield in dependence on altitude is presented. The fluorescence calculation is applied to simulated air showers and different atmospheric profiles to estimate the influence of the atmospheric conditions on the reconstructed shower parameters.
