The Telescope Array observes cosmic rays with energies of 1019 eV and up. The cosmic rays are observed at three fluorescence sites and a separate ground array consisting of 507 detectors.
The three fluorescence sites observe air showers developing in the atmosphere. They are set about thirty kilometers apart from one another, forming an approximately equilateral triangle.
The 507 ground array detectors fill the area between the three fluorescence sites and are set 1.2 kilometers apart from one another. They are double layer scintillators which sample the charge particle density of the air shower footprint when it reaches the earth's surface.
TALE - TA's Low Energy Extension
TALE is the Telescope Array Low Energy extension. It is designed to observe cosmic rays with energies between 3x1016 eV and 1019 eV. TALE has two fluorescence sites placed about five kilometers away from TA-1 and TA-2. One of these is at Black Rock Mesa, and the other is at Long Ridge.
The TALE tower is a tower of fluorescence telescopes looking from near zenith to near horizon. These telescopes have three meter diameter mirrors to push the energy threshold of observable events as low as possible.
The TALE project also has an infill array of scintillator ground array stations spaced about 500 meters apart. These stations measure charged particle densities (the shower footprint) at the earth's surface for lower energy events approaching 3x1016 eV