A comparison of three methods of measuring the atmospheric coherence length

In the fall of 1996, we had the opportunity to measure the atmospheric coherence length (Fried's r(o) parameter) at the Starfire Optical Range using three instruments. Each instrument measured r(o) using a different theory and technique. The first instrument, designed and built by Dr Donald Wafters of the Naval Postgraduate School, is based on measuring the MTF of the atmosphere using a stellar image on a one dimensional detector. The second instrument, designed and built by Lockheed Martin engineers at White Sands Missile Range, is based on measuring the differential motion of stellar images. The third technique in this study used short exposure star images taken through the 1.5m telescope and processed by matching the images to short exposure theory values of r(o). All of the instruments were located at the Starfire Optical Range and data were collected during both day and night hours. This paper presents the results of these measurments and discusses the different techniques in terms of the results obtained.