**Acknowledgements**

The author acknowledges the Office of the Surveyor General of the Federation (OSGF) of Nigeria for making the NIGNET GPS data available. Thanks to Dr. Gopi Seemala for providing software that was used in processing of the GPS RINEX data and for his immeasurable support during the period of carrying out the work in this chapter. The author also appreciates developers of the NeQuick and IRI-Plas models for making their models available. I thank the WDC and the WDC-SILSO for, respectively, making DST index and SSN data available. Thanks to developers of the Apex Coordinate Conversion Utility Software that was also used in this chapter. Most importantly, I thank the Centre for Atmospheric Research, the Indian Institute of Geomagnetism, and the CV Raman Fellowship for providing support and opportunity to carry out the work in this chapter. I heartily appreciate the Mathworks® for providing me with sponsored license for the MATLAB software that was used for this chapter.
