Place for sodars in a high-technology environment

摘要

In an era of increasingly complex technology, some of the atmospheric quantities211u001emost difficult to measure and observe are yielding their secrets to increasingly 211u001ecomplex instruments and combinations of instruments. For example, water vapor 211u001eprofiles, a long-time nemesis to detailed examination, have become measurable 211u001ewith the use of Raman lidar; temperature profile measurements are becoming 211u001erelatively routine with radio acoustic sounding systems (RASSs) or infrared 211u001eFourier transform instrumentation such as the atmospheric emitted radiance 211u001einterferometer (AERI); and radar, lidar, or combinations of the two are enabling 211u001ewind profile measurements to increasing altitudes. What, then, is the role of the 211u001erelatively pedestrian sodar in such an era. Because the sodar's propagation speed 211u001ein the atmosphere is six orders of magnitude smaller than that of its 211u001eelectromagnetic counterparts (3 x 10(sup 2) vs. 3 x 10(sup 8) m/s), severely 211u001elimiting its rate of interrogation, and because the sodar's signal limit 211u001efrequency modulation techniques, many high-technology advances associated with 211u001eenormous increases in computation speed and available memory have had relatively 211u001elittle direct impact on acoustic remote sensing. However, the principal elements 211u001eof acoustic remote sensing continue to make it a useful, even essential, tool for 211u001eobtaining a better understanding of the physics of the lower atmosphere. The 211u001esodar's 'slow' propagation speed provides relatively easy access to the region 211u001ebetween 10 m and several hundred meters above the surface that is often 211u001einaccessible to other instruments. This is the region of the atmosphere where 211u001econditions often change radically with height, the 'matching' region between 211u001elarge-scale forcing and small-scale surface heterogeneities that can have large 211u001eeffects on human activity. The atmosphere provides signals for sodars that are 211u001erich in content because the phase speed of sound is dependent on the atmosphere 211u001eitself and is tied directly to the atmosphere's temperature and wind structure. 211u001eHence, the signals from acoustic remote sensing instruments can provide boundary 211u001econditions crucial for the proper operation of numerical models of the atmosphere 211u001ewhose output is becoming increasingly important in individual and business 211u001edecision making.