Micro cavity plasma arrays have numerous applications, such as the treatment of volatile organic compounds (VOCs) or the generation of new species. In recent years, the focus has also shifted to plasma catalysis, in which catalytic surfaces are combined with plasmas. The key to all of these applications is the generation of reactive species such as atomic oxygen within the plasma. Typically, atomic oxygen densities can be measured by laser spectroscopic methods. In the case of a micro plasma array, which consists of thousands of cavities with a diameter between 50-200 µm, optical access is limited. For this reason, an optical emission spectroscopy (OES) approach, helium state enhanced actinometry (SEA), is used. 2D resolved narrow bandwidth measurements are performed by using an ICCD camera in combination with a tunable bandpass filter (550-1000 nm). The discharge is operated in helium with an oxygen admixture of 0.1%. An argon admixture of 0.05% is used as actinometer gas. The triangular excitation voltage is varied between amplitudes of 400 and 800 V at a frequency of 15 kHz. Very high dissociation degrees up to nearly complete dissociation are observed. Time resolved measurements show significant differences in oxygen density between the increasing and the decreasing potential phase.