Ahmad Faizal Mohd Zain

Forecasting of ionospheric delay over Parit Raja Station, Johor, using statistical method

GPS is of great importance in precise positioning, however, the accuracy is marked by error sources, i.e. ionospheric effects. The signal information is delayed and the carrier phase experiences an advance due to the dispersive character of the ionosphere. The delay can be more than 100 meters in the worst case scenario and tends to increase with increasing solar activity. This error can be corrected by processing the GPS data if it is known. This paper describes the possibility of using statistical methods to forecast the ionospheric delay which shows repeatable patterns in time series. The statistical method used is the Holt-Winter method due to its ability to forecast time series with repeated trends and seasonal patterns. Based on the TEC data collected during a period of a month, ionospheric delay forecast is generated for the following month, which is then compared with the real data. Results show that there is a 6% error between the forecast and the real ionospheric delay and the error correction for the delay can be more than 90%.

DGPS positional improvement by mitigating the ionospheric horizontal gradient and elevation angle effects

Over the equatorial region, the inhomogeneous formation of the ionosphere introduces greater ionospheric horizontal gradient which could give greater positioning error for a user station in a DGPS system. Furthermore, the difference in the elevation angle of the user station that ‘views’ the same GPS satellite as the reference station also introduces range measurement errors at mm to cm levels. In order to mitigate those two effects in a DGPS system, the Jones 3D ray tracing program was used to show final positioning improvement at the user station. Group delay and carrier phase advance measurements from 8 GPS satellites were used to determine and mitigate the effects of ionospheric horizontal gradient and the elevation angle. Positioning improvement of about 7 cm has been obtained by using both group delay and carrier phase advance measurements. This shows a good positioning improvement for the user station in a DGPS system that is located over the equatorial region.

Plasma drift during periods of low geomagnetic activity at UTHM's Parit Raja station

Measurements of data relating to ionospheric plasma drift have been collected at the Wireless and Radio Science centre (Waras) at UTHM Parit Raja station in Batu Pahat, Johor since 2004. This is done using a digital doppler interferometer which allows investigations into the dynamics of the ionosphere at this near equatorial station to be carried out. These measurements include Doppler shifts, angles of arrival, as well as virtual heights from significant numbers of ionospheric echo sources simultaneously at the same time. By employing Doppler inteferometry reception technique at four receivers connected to four spaced antennas nearby, it is possible to identify the three dimensional locations of various scattering points reflected back from the ionosphere as a result of vertically-incident HF waves. These waves are transmitted at frequencies of 5.9MHz, 7MHz, and 8MHz which cover the local Flayers since the critical frequencies lie between 6MHz and 8MHz.

Analysis of reflectarrays printed above variable substrate thicknesses

This paper presents a thorough investigation of the effects of substrate thickness on the performance of infinite reflectarrays. The reflectarrays designed in the X-band frequency range are investigated in terms of electric field intensity, reflection loss and reflection phase performance. It has been demonstrated that the electric field intensity decreases from 3.42e5V/m to 2.34e5V/m as the thickness of the substrate is increased from 0.2mm to 2.0mm. The measured reflection loss has been shown to decrease from 15dB to 2.25dB as the substrate thickness is changed from 0.127mm to 0.381mm. Furthermore the effect of substrate thickness on the reflection phase performance has also been demonstrated by waveguide scattering parameter measurements.

Total Electron Content During Travelling Ionospheric Disturbance in Parit Raja, Johor

Travelling ionospheric disturbance (TID) is a phenomenon caused by solar activity and TID strength varies by locations, especially in equatorial regions. This phenomenon affects the local total electron content (TEC), especially during the daytime. Because of this, research regarding augmenting TEC values during TID is done by comparing TEC values obtained from the IRI2001 and NeQuick models with IONEX data. By using Global Positioning System (GPS) data obtained from the Parit Raja station in the southern part of Malaysia (1o 52’ N, 103o 06’ E) as reference, research was conducted during geomagnetic quiet day as well as on the disturbed day. The occurrence of TID can clearly be seen when using the real TEC data from IONEX and WARAS. Result obtained from Parit Raja station shows a much more significant effect of TID occurrence on TEC than what was shown by IONEX data. However, the TEC values obtained from the IRI2001 and NeQuick models were influenced by the number of sunspots and were only applicable in geomagnetic quiet days. In order to obtain more accurate TEC values, it is necessary to ensure that TID condition is included in the IRI2001 and NeQuick models.