David L. Fried

David L. Fried is an American scientist, best known for his contributions to optics. Fried described what has come to be known as Fried's seeing diameter, or r0 (usually pronounced r-naught). The seeing diameter is effectively a limiting aperture due to atmospheric turbulence, and is found either empirically or statistically. The seeing diameter limits optical resolution. Note that it is a diameter, not a radius, even though r is used as the variable.
Typical values for Fried's seeing diameter in the visible spectrum may range from less than 1 cm (you can detect turbulence with your eye) to 20 cm on Mt. Haleakala.
Life and professional career.
David L. Fried was born in Brooklyn, New York, on April 13, 1933. He received the AB, MS, and PhD degrees in physics from Rutgers University, New Brunswick, New Jersey, in 1957, 1959, and 1962, respectively. From 1957 to 1959 he was with RCA Astro-Electronics Division, Princeton, N. J., where he worked on computer applications analysis. In 1961 he was employed by Rockwell International, where he held the position of Manager in the Electro-Optical Laboratory of the Autonetics Division (Anaheim, Calif.), where, as head of the Laser Techniques Group, he was engaged in the study of devices necessary for laser applications, and in the analysis of system concepts for laser application. He also did extensive work in the study of optical propagation in a randomly inhomogeneous atmosphere and the consequent effects on optical system performance. In 1966 he joined the technical staff of the North American Aviation Science Center, Thousand Oaks, Calif., where he was engaged in a study of the microwave reflectivity and emissivity of rough surfaces.
Fried served for 20 years on the U.S. Army Science Board (ASB). For many years, he served on the ASB’s standing committee on ballistic missile defense. In the 1960s, Fried published a series of papers on the optical effects of atmospheric turbulence that provided much of the analytic foundations for the development of adaptive optics systems, and that resulted in the definition of the quantity now known as Fried’s parameter. In addition, his 1966 paper, "Limiting Resolution Looking Down Through the Atmosphere," was important in showing a basic limit, about five centimeters, to how sharply space-based telescopes can image objects on the ground. In 1981, Fried carried out the first analysis evaluating and establishing the feasibility of the use of atmospheric laser back scatter to control adaptive optics—a concept which now goes by the name of laser guide-star. He then designed, managed the development of the hardware for, and supervised an experiment that successfully demonstrated the validity of the laser guide-star concept.
From 1970 (when he founded the company) until 1993 (when he sold the company), Fried was the president of the Optical Sciences Company (Placentia, California). In 1993, he received the SPIE Technology Achievement Award for his initial laser guide-star work. From 1993 to 1995 he was a professor of physics at the Naval Postgraduate School, Monterey, California. Currently, he works as an independent consultant.
In addition to his work related to optical propagation/turbulence effects/adaptive optics, Fried has done work in a variety of other electro-optics related fields such as the suppression of infrared background clutter in moving target detection systems; analysis of laser speckle statistics; analysis of the effect of photo-detection-event driven shot noise upon the precision of various types of optical measurements; the design and development of low-temperature-optics long-wavelength infrared sensors for use in mid course ballistic missile defense; and in the design and performance analysis for space-based infrared sensors for missile and aircraft detection. He has also been involved in the search for a sound approach to the mid-course decoy discrimination problem for ballistic missile defense.
Honors.
1993 – David L. Fried, Optical Sciences Company, SPIE Technology Achievement Award. 
External links.
Biographical data extracted from: