UHF AEW RADAR OBSERVATIONS OF ELEVATED TRADEWIND DUCTS

Airborne uhf (435-Mc/s) propagation paths observed during the course of a 12-month study of elevated tradewind ducts (Project TRADEWINDS IV) varied from 240 to 1200 nautical miles (naut mi) as compared with less than 180 naut mi observed for the same system in a standard atmospheric propagation medium. Out of 18 flights spaced over a year, 17(94 percent) resulted in the radar detection of elevated ducts. Ten flights (55 percent) resulted in the discovery of ducts which permitted the radar detection of targets at ranges in excess of 500 naut mi. Radar data has been obtained which shows that the elevated ducts off the southern California coast can have an extent in longitude in excess of 1200 naut mi and a latitudinal extent of greater than 1000 naut mi. Average attenuation rates as low as 4 db/100 naut mi have been observed for pathlengths of over 1000 naut mi. The existence of ducts off the California coast capable of sustaining long range radio-radar propagation was not limited to the summer months. On the basis of data obtained during the 12-month study, there is evidence that the occurrence, strength, and extent of the ducts does not change significantly with the seasons of the year. The airborne uhf radar has proved to be a useful tool for the detection and observation of elevated ducts. Through the observation of ducting radar return signals, it was possible to determine the number, relative strength, height, and the thickness of elevated ducts. (Author)