We report on the simultaneous observation of atmospheric erenkov light by a prototype five telescope array, GRACE, (Gran Sasso Air erenkov Experiment) with deep underground muons in the MACRO (Monopole Astrophysics and Cosmic Ray Observatory). The telescope array was deployed at Campo Imperatore above the Gran Sasso Laboratory for a run completed in the fall of 1992. The total live time for the combined surface-underground operation was ∼100 h during which more than 300 events were seen in coincidence. The efficacy of this technique to monitor the electromagnetic and penetrating muon components of a cosmic-ray-induced cascade is discussed.
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