25 May 2005 Field validation of optical turbulence lidar technique
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Abstract
A new type of lidar is under development for measuring profiles of atmospheric optical turbulence. The principle of operation of the lidar is similar to the astronomical seeing instrument known as the Differential Image Motion Monitor, which views natural stars through two or more spatially separated apertures. A series of images is acquired, and the differential motion of the images (which is a measure of the difference in wavefront tilt between the two apertures) is analyzed statistically. The differential image motion variance is then used to find Fried's parameter r0. The lidar operates in a similar manner except that an artificial star is placed at a set of ranges, by focusing the laser beam and range-gating the imager. Sets of images are acquired at each range, and an inversion algorithm is then used to obtain the strength of optical turbulence as a function of range. In order to evaluate the technique in the field and to provide data for inversion algorithm development, a simplified version of the instrument was developed using a CW laser and a hard target carried to various altitudes by a tethered blimp. Truth data were simultaneously acquired with instruments suspended below the blimp. The tests were carried out on a test range at Eglin AFB in November 2004. Some of the resulting data have been analyzed to find the optimum frame rate for ground-based versions of the lidar instrument. Results are consistent with a theory that predicts a maximum rate for statistically independent samples of about 50 per second, for the instrument dimensions and winds speeds of the Eglin tests.
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G. G. Gimmestad, M. W. Dawsey, D. W. Roberts, J. M. Stewart, J. W. Wood, F. D. Eaton, M. L. Jensen, R. J. Welch, "Field validation of optical turbulence lidar technique", Proc. SPIE 5793, Atmospheric Propagation II, (25 May 2005); doi: 10.1117/12.603058; https://doi.org/10.1117/12.603058
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