PART IV — DYNAMICS OF THE ATMOSPHERE-OCEAN SYSTEM 



High-Resolution Acoustic Radar is 

 another candidate for clear-air WIT 

 detection from ground-based stations. 

 Such radars have detected thin inter- 

 nal surfaces and stable and breaking 

 wave activity to heights of 2 kilo- 

 meters. The potential to reach 15 

 kilometers in the vertical direction 

 can probably be realized, although the 

 effect of strong winds aloft on the 

 refraction of the acoustic beam re- 

 mains an open question. Unfortu- 



nately, acoustic radar cannot be used 

 on board fast-flying aircraft because 

 of the slow speed of sound and the 

 high acoustic noise levels. 



Future Teclmologx/ — Finally, a real 

 hope still remains for the develop- 

 ment of a coherent laser radar (or 

 LIDAR) sufficiently sensitive to de- 

 tect the small background concentra- 

 tions of aerosols in the high tropos- 



phere and capable of measuring 

 turbulence intensity through the dop- 

 pler velocities. Although a theoretical 

 feasibility study of such a device in 

 1966 indicated that the then available 

 LIDARs could not accomplish the 

 task, more recent developments in 

 laser technology may now make such 

 a system feasible. The National Aero- 

 nautics and Space Administration is 

 presently conducting research and de- 

 velopment along these lines. 



A Note on Acoustic Monitoring 



As is well known, the propagation 

 of sound waves through the atmos- 

 phere is strongly affected by wind, 

 temperature, and humidity. The pos- 

 sibility therefore exists that measure- 

 ments of the propagation of sound 

 waves could be used to derive infor- 

 mation on important meteorological 

 parameters. 



The potential of these methods has 

 been analyzed and some experimental 

 results published. It has shown that 

 acoustic echoes can readily be ob- 

 tained from the atmospheric turbu- 

 lence and temperature inhomogenei- 

 ties always existing in the boundary 

 layer of the atmosphere. The equip- 

 ment required is relatively simple; it 



involves a radar-like system in which 

 pulses of acoustic signal, usually 

 about 1kHz in frequency, are radi- 

 ated from an acoustic antenna, with 

 echoes from the atmospheric structure 

 obtained on the same or on a second 

 acoustic antenna. 



This field of acoustic echo-sounding 

 of the atmosphere is very new and 

 appears to hold considerable promise 

 for studies of the boundary layer of 

 the atmosphere — i.e., the lowest sev- 

 eral thousand feet. Specifically, re- 

 search is now being undertaken to 

 identify its usefulness for the quanti- 

 tative remote measurement of wind, 

 turbulence, humidity, and tempera- 

 ture inhomogeneity. If, as expected, 



the technique is shown capable of 

 measuring the structure of the bound- 

 ary layer and the vertical profiles of 

 these meteorological parameters, it 

 will represent a major breakthrough 

 in remote measurement of the atmos- 

 phere, which should be of great value 

 to meteorological observations and 

 research. Its primary application is 

 likely to be in the monitoring of 

 meteorological parameters in urban 

 and suburban areas, for use by air- 

 pollution and aviation agencies. In 

 addition, it is already providing the 

 research worker with totally new in- 

 sight into the detailed structure and 

 processes controlling the atmospheric 

 boundary layer in which we live. 



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