FURTHER EVALUATION OF FREQUENCY PREDICTIONS FOR SHORT-PATH RADIO COMMUNICATIONS IN THAILAND

Abstract

Abstract : Predictions derived by two methods for estimating F-layer critical frequency are evaluated by comparing 1967 predictions and measurements for Bangkok. One set of predictions has been obtained from a program developed at SRI (SRI/RPA predictions); the other has been obtained by scaling prediction contour maps prepared by ESSA. The SRI/RPA predictions have been corrected to take into account the error in prediction during 1966 compared to measurements at Bangkok, but because of a modification in ESSA predictions, including those for Southeast Asia, no local correction has been applied to 1967 ESSA predictions. Thus, for 1967 corrected SRI/RPA and uncorrected modified ESSA predictions are evaluated. The evaluation shows that the average error of both predictions of foF2 relative to ionosonde measurements is less than 1 MHz. The modified ESSA predictions are somewhat more accurate, averaging about 0.5 MHz higher than the observed median foF2 values. A comparison of uncorrected modified ESSA predictions for 1967 and ESSA predictions for previous years shows a definite improvement in accuracy of these uncorrected modified ESSA predictions relative to the uncorrected predictions made prior to 1967. Based on 1967 results, it is expected that future uncorrected ESSA predictions will be at least as accurate as SRI/RPA predictions that have been corrected using local Bangkok C-2 data. Furthermore, the anticipated error in uncorrected ESSA predictions (about 0.5 MHz average) is not serious enough to warrant applying a local correction for the vicinity of Bangkok. Consequently, the 3-month-term ESSA predictions would be preferred for Thailand.