Astroparticle Physics

160 7 Secondary Cosmic Raysatmosphericair showerprimaryinteractionisotropicscintillation lightFig. 7.29Principle of the measurement ofthe scintillation light of extensiveair showersFly´s EyeAir Watchprecise energy assignments, however, it has a big disadvantagecompared to the classical air-shower technique thatit can only be operated in clear moonless nights. Figure7.30 shows an arrangement of mirrors and photomultipliers,as they have been used in the original Fly’s Eye setup of theUtah group. In the Auger experiment the array of samplingdetectors is complemented by such a number of telescopeswhich measure the scintillation light produced in the atmosphere.Much larger acceptances could be provided if such aFly’s Eye detector would be installed in orbit (‘Air Watch’,Fig. 7.31).Fig. 7.30Arrangement of mirrors andphotomultipliers in the originalFly’s Eye experiment of the Utahgroup {25}radio detection of showersApart from these detection techniques it has also beentried to observe air showers via the electromagnetic radiationemitted in the radio band. It is generally believed thatthis radio signal is caused by shower electrons deflected in