A variable-frequency, spinning reticle photometer has been used to measure the spatial-frequency modulation of stellar images in the Cassegrain focal plane of a 1.22 m telescope at the AMOS observatory atop Haleakala on the island Maui, Hawaii. This data, processed in real time, provides information on the statistical properties of the image size which, in turn, yields an estimate of the atmospheric correlation scale <i>r</i><sub>o</sub>. Data was collected on 24 nights over a period of eight months. Values of <i>r</i><sub>o</sub> ranged from 5.3 to 17.8 cm with a mean value of 9.6 cm at 5000 Å. A variety of temporal behavior was also observed.
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