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Show the anemometer mast. The lower end will terminate in a junction box adjacent to the recorder inside an appropriate office space. Any splices along the cable will be brought above ground and made on a terminal board inside a securely supported junction box. If possible, it is useful to have these splice boxes above the maximum expected snow depth. If not, their position should be marked for easy location when buried under snow. All cable exiting from the ground will be run through pipe or conduit into the junction boxes. It is possible, though much more complicated and expensive, to use radio links instead of cables for wind system telemetry. Cables are much to be preferred because of their reliability. If peculiarities of terrain or distance make a buried cable impractical, radio transmission of wind data can be considered. A reliable system will cost from $ 10,000 on up. If such a system is contemplated, expert advice on its selection and installation should be sought. The Forest Service Electronics Center in Beltsville, Maryland 20705 ( Telephone: ( 301) 474- 4800) has made a study of radio telemetry systems suitable for this use and can advise National Forest users. Radio telemetry makes almost exclusive use of digital data transmission, therefore contact- type anemometers are much more compatible with such systems. It is possible to transmit analog data via radio links, but this involves considerable more complication and expense. Rime The accumulation of rime ( freezing of supercooled cloud droplets onto solid objects) leads to serious calibration and maintenance problems with anemometers and wind vanes. Small amounts of rime quickly alter the response of the instruments to the wind, so that accurate data cannot be obtained. As the amount of rime increases, response of the instruments slows down until a point is reached where they cease to function. If large amounts of rime accumulate while high winds are blowing, serious damage may occur. Extra weight on rotating anemometer cups may damage the bearings; if too much weight accumulates, the cups can actually break off. The most serious damage occurs when only part of the adhering rime falls off the cups. The resulting unbalance can quickly destroy the anemometer if wind velocity is high. Seriousness of the riming problem varies widely with climate. It is most severe where the supply of supercooled clouds is most abundant, namely in maritime climates. At some higher elevations along the Cascade or Sierra Nevada mountains riming is so frequent and heavy that it is extremely difficult to maintain anemometer 46 |