Abstract
This paper investigates the characteristic of the ionospheric delay and forecasting using modified statistical Holt-Winter method over Malaysia. This was carried out by using dual frequency GPS Ionospheric Scintillation and TEC Monitor (GISTM) receivers installed at the National University of Malaysia (UKM) (geographic coordinates 2.55°N, 101.46°E and geomagnetic coordinates 7.10°S, 174.05°E), and Langkawi national observatory (Langkawi) (geographical coordinates 6.19°N, 99.51°E and geomagnetic coordinates 3.39°S, 172.42°E), during 2011. In this work, the Holt-Winter forecasting method is modified to provide a better forecasting result over Malaysia. The diurnal, monthly, and seasonal variations of actual ionospheric delay have been analyzed and compared with forecasted ionospheric delay. Based on the results, the diurnal variability of ionospheric delay was maximal mostly between 12:00– 17:00 LT, and minimal nearly at 05:00 LT. The maximum monthly ionospheric delays occurred in October, which is attributed to the geomagnetic storm disturbance that caused increase in ionospheric delay. The lowest seasonal ionospheric delay occurred in the summer and the highest was during the equinox. The maximum ionospheric delay on a quiet day was around 41.9 TECU, while it reached up to 86.6 TECU during the geomagnetic storm. The Holt-Winter method exhibited the highest difference between the measurements and the forecasts in March, with an error of 6%. Hence, the modified Holt-Winter method forecast ionospheric delay effectively during quiet and disturbed periods over Malaysia.
Highlights
The Earth’s ionosphere is the ionized region of the upper atmosphere consisting of different ionized layers (D, E, and F)
The ionospheric Total Electron Content (TEC) is a notable source of error that disrupts the accuracy of the global positioning system (GPS) signals passing from the satellite to the ground by changing the velocity of the propagated signals causing ionospheric delay
The ionospheric delay is displayed on the vertical axis in TECU unit, and local time (LT) is displayed on the horizontal axis in hours
Summary
The Earth’s ionosphere is the ionized region of the upper atmosphere consisting of different ionized layers (D, E, and F). Investigation the ionospheric delay and identification of the precise and accurate forecasting model of transionospheric propagation errors are essential for precise measurements and further contributes valuable information to satellite and space probe navigation, space geodesy, radio astronomy and other applications. The ionospheric delay error correction for single frequency GPS receivers is done using the broadcast model, with the accuracy ranging from 50% to at most 60% [Klobuchar, 1996]. Since the study of the ionospheric delay and forecasting is a new subject in the equatorial region, in Malaysia, a precious model has become essential. The variations in the diurnal, monthly and seasonal ionospheric delay were estimated from the GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver and compared with the ionospheric delay forecast using the statistical Holt-Winter method over the UKM and Langkawi stations. Besides the differences in ionospheric delay observed during geomagnetic storm disturbances were investigated
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