Development of an Acoustic Echosounder for Detection of Lower Level Atmospheric Turbulence.
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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Atmospheric density fluctuations induce phase perturbations that upgrade the spatial coherence of a laser beam propagating through the atmosphere. These degradations spread the laser beam alter the centroid and intensity profile stochastically. Turbulent conditions arising from various environmental situations and meteorological phenomena are found at virtually all levels of the atmosphere. A substantial fraction of the optical turbulence along a vertical path arises from the surface heat flux within the first 100-200 meters above the ground. This thesis seeks to measure and analyze atmospheric turbulence within the first 100-200 meters above the ground with extremely high accuracy. The echosounder design incorporated a 25 element, square, planar array housed within a lead and foam insulated, acoustic shroud. This acoustic echosounder was employed to collect real-time, low level atmospheric data at two sites. This data should prove useful in determining whether the performance of laser and electro-optical systems could be increased by raising sensors and transmitters well above the local turbulent layer through the use of towers or other such structures.
- Acoustic Detection and Detectors