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Short-term Radio Propagation Forecasts in Southeast Asia

Ralph Jeffery SlutzT. N. GautierMargo Leftin

其他書名	Final Report
出版	U.S. Department of Commerce, Environmental Sciences Services Administration, Institutes for Environmental Research, Institute for Telecommunication Sciences and Aeronomy, 1967
URL	http://books.google.com.hk/books?id=rRIypwAACAAJ&hl=&source=gbs_api

註釋The report presents results of a 2-year program of development, test, and evaluation of short-term forecasts of maximum usable frequency (MUF) for Southeast Asia. The forecasts were designed for high frequency trunks of the U.S. Defense Communications System connecting Tokyo, Okinawa, Taipei, and points in the Philippines, Thailand, and South Vietnam, and for certain ship-shore and air-ground communications in that area. Development of the forecasts began in May 1965, and field testing was carried out from November 1966 to June 1967. The resulting techniques were described. Forecasts were issued from Boulder, Colorado, once each hour. They were based on MUF data transmitted hourly by teletype from vertical-incidence ionosphere sounding stations at Okinawa, Taipei, Manila, and Bangkok. A forecast lead time of 3 hours was necessary to allow for data transmission time plus the time necessary to prepare and transmit the forecasts to the user stations. The accuracy of the forecasts was estimated by comparison with the maximum observed frequency (MOF) on an oblique-incidence sounder operated by the Stanford Research Institute between Okinawa and Clark Air Base in the Philippines. For November 1966, averaged over all hours of the day, the rms error of the forecasts was 3.5 Mc/s. For the same month the rms error of the MUF for this path given by the world maps of ITSA's monthly "Ionospheric Predictions" issued 3-months in advance was 5.2 Mc/s. Thus the 3-hour forecast made an improvement of 33% in the rms error of the world map predictions. The errors were greater in summer because of the prevalence of sporadic -E ionization, not taken into account in either the world map predictions or the short-term forecasts. Reports from the user stations provided information on forecast accuracy and usefulness. Because of other factors affecting trunk operation, the user reports did not provide precise accuracy checks, but the accuracy implied appeared to be consistent with the accuracy estimated by comparison with the oblique-incidence sounder data. Analysis of usefulness was inconclusive because of factors such as interference, the considerable number of "no forecast" messages resulting from missing data, and inadequate understanding by many operators of propagation effects on trunk operation and the relationship of the forecasts to such effects on trunk operation and the relationship of the forecasts to such effects. The degree of enthusiasm for the forecasts expressed by the operators varied widely; some operators were very enthusiastic, other quite the contrary. Recommendations for future short-term forecasts for this area include: (1) basing forecasts upon data from more closely space sounding stations, including oblique-incidence as well as vertical-incidence stations: (2) including allowance for sporadic -E ionization; (3) providing faster communications to permit shortening the forecast lead time from 3 hours to 1 hour; and (4) providing additional training for the operators in the meaning and use of the forecasts