Abstract
The ionospheric layer is an essential source of error that changes the signal velocity of the Global Positioning System (GPS), causing signal delay. Therefore, studying ionospheric delay and forecasting is essential to understand the ionospheric delay behaviour and to identify an accurate
forecasting approach to enhance the GPS positioning accuracy by reducing the errors. This research focused on the implementation of the statistical Holt-Winter method to forecast ionospheric delay, using the data derived from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver
located at Universiti Kebangsaan Malaysia (UKM) station at the geographic coordinate of 2.55 N, 101.46 °E and geomagnetic coordinate of 7.10 °S, 174.05 °E, during 2011. The forecast was carried out on a diurnal, monthly and seasonal variation. The peaks of the ionospheric delay
were observed in the post-noon time while the minimum was observed in the early morning time. A comparison of the monthly actual ionospheric delay with the forecasted one showed that the maximum difference in variation between the actual ionospheric delay and forecasted was around 0.16 m.
The efficiency of the Holt-Winter in forecasting ionospheric delay was proven with an accuracy of between 95-98%.