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A series of experiments was conducted in January, 1993, in which a pulsed laser beam was propagated from one aircraft to a receiver on board another aircraft. At the receiver, the resulting turbulence induced scintillation patterns across an 80 cm aperture were recorded. The measured irradiance patterns were used to infer the fundamental performance limits imposed by turbulence induced amplitude scintillation on imaging systems and laser transmitters employing adaptive optics to perform phase only compensation. From the data, point and aperture averaged scintillation statistics and amplitude correlation functions were also obtained.We describe the theoretical basis for the measurements. A theoretical analysis, applicable in the weak scintillation regime, is presented. Predictions based on wave optics computer simulations are also presented, and comparisons of the empirical results with the analysis and simulation predictions are shown. The methodology used to analyze the data recorded during the ABLEX tests is also detailed. A description of the experiment and a discussion of the results obtained are presented in a companion paper1.

ABLEX, or Airborne Laser Experiment, was a series of airborne experiments conducted in December, 1992 and January, 1993 in which a pulsed laser beam was propagated between two aircraft flying at high altitude. In these experiments, the scintillation patterns resulting from propagation through atmospheric turbulence were recorded. From these scintillation patterns, the fundamental performance limits of phase-only adaptive optics systems could be determined.Rather than field a highly complex, and expensive, airborne testbed equipped with a state-of-the art adaptive optics system, the physics-limited performance was determined by a novel, and quite simple, method which used a Fresnel lens collection system. The aircraft flew at separations ranging from 25 to 200 km. Data was obtained below, through, and above the tropopause. This paper describes those experiments, the experimental hardware, and the results obtained. Though there was a wide range of turbulence, as evidenced from scintillation statistics, the SireN values inferred from these experiments provided direct evidence that atmospheric scintillation does not present a fundamental limitation to phase-only compensation. EXPERIMENT DESCRIPTIONThe ABLEX experiment was conducted using two aircraft, a source aircraft, HARP, and a receiver aircraft known as ARGUS. HARP is a Lear 36A operated by the Aeromet Corporation, Tulsa, Oklahoma. ARGUS is an Air Force NC -135E operated by the Phillips Laboratory Flight Test Branch. sAir I Harp Airpbnel ______ lI, Figure 1. ABLEX objectives.The principle hardware subsystems for ABLEX are: laser, laser pointing system, receiver telescope and gimbal, science sensor, and receiver pointing system. Additionally, both aircraft had laser diode beacons which served as track sources for each other. Figure 2 depicts the main elements of HARP while Figure 3 depicts the main elements of the ABLEX receiver.

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