towers can furnish data on the variation in wind direction and speed with height; those data provide a measure of the dispersing capacity of the atmosphere.

Radar and lidar techniques can be used to provide data for wind measurements at rates that are orders-of-magnitude smaller than those available from operational measurement systems. Given the need for wind fields with high temporal resolution, particularly in areas of complex terrain, this technology is promising. However, it can only measure winds at one location, so spatial interpolation is still necessary. Also, the technique is expensive and requires a technically well-trained staff. With the continuing advances in computers and hardware, however, the cost of remote sensing systems will inevitably decrease.

Ideally, a meteorological measurement program would include the use of remote sensing to measure temporal variations of winds above the surface. Remote sensing would be complimented by balloons, either tethered or free-rise, depending on the problem being studied.

The extinction of light by hygroscopic airborne particles generally increases with increasing relative humidity because of the increase in particle size. Consequently, detailed information about humidity must be obtained during field programs. The relative humidity (or the dew point temperature) should be measured at all surface meteorological stations and in vertical profiles from balloons as well. Such measurements are usually inexpensive and can provide information for testing the ability of meteorological models to reproduce the vertical and spatial extent of water vapor transport; that information also is needed for modeling the wet removal of pollutants.