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Optical Engineering

Middle atmosphere slant-path optical turbulence conditions derived from very high-frequency radar observations
Author(s): Frank D. Eaton; Gregory D. Nastrom; Anthony R. Hansen
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Paper Abstract

Slant path calculations are shown of the transverse coherence length (r0), the isoplanatic angle (?0), and the Rytov variance (?2R), using a 6-yr data set of refractive index structure parameter (C2N) from 49.25-MHz radar observations at White Sands Missile Range, New Mexico. The calculations are for a spherical wave condition; a wavelength (?) of electromagnetic radiation of 1 ?m; four different elevation angles (3, 10, 30, and 60 deg), two path lengths (50 and 150 km); and a platform, such as an aircraft, at 12.5 km MSL (mean sea level). Over 281,000 radar-derived C2N profiles sampled at 3 min intervals with 150-m height resolution are used for the calculations. The approach, an ''onion skin" model, assumes horizontal stationarity over each entire propagation path and is consistent with Taylor's hypothesis. The results show that refractivity turbulence effects are greatly reduced for the three propagation parameters (r0, ?0, and ?2R) as the elevation angle increases from 3 to 60 deg. A pronounced seasonal effect is seen on the same parameters, which is consistent with climatological variables and gravity wave activity. Interactions with the enhanced turbulence in the vicinity of the tropopause with the range weighting functions of each propagation parameter is evaluated. Results of a two region model relating r0, ?0, and ?2R to wind speed at 5.6 km MSL are shown. This statistical model can be understood in terms of upward propagating gravity waves that are launched by strong winds over complex terrain.

Paper Details

Date Published: 1 February 1999
PDF: 8 pages
Opt. Eng. 38(2) doi: 10.1117/1.602079
Published in: Optical Engineering Volume 38, Issue 2
Show Author Affiliations
Frank D. Eaton, Air Force Research Lab. (United States)
Gregory D. Nastrom, St. Cloud State Univ. (United States)
Anthony R. Hansen, St. Cloud State Univ. (United States)

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