Performance of GPS-TEC assisted NTCM-model to describe the East-African
equatorial Ionosphere
Abstract
NTCM is a simple and relatively faster global climatological model that
is developed, using ionospheric VTEC measurements from unevenly globally
distributed GNSS receivers, to mitigate ionospheric effects on GNSS
applications. As it is climatological, its ionospheric weather
characteristic specification capability is limited. Also, its nowcasting
and forecasting performance of the East-African equatorial ionosphere
has not yet been tested. Therefore, this paper demonstrates techniques
to change NTCM to ionospheric weather model to nowcast and forecast VTEC
for East-Africa. NTCM has been changed to ionospheric weather model
through adapting it to quiet days VTEC from nineteen GNSS receivers in
East-Africa in 2013 and 2014. Adaptation has been done by calculating
its driver, effective ionization level, when NTCM modeled VTEC fits the
best with observed VTEC. Then, performances of the model in nowcasting
and forecasting VTEC, before and after adaption, have been investigated
compared to observed VTEC. It is found that NTCM, after adaptation,
represents observed features of diurnal variations of VTEC and
equatorial ionization anomaly (EIA) much better than before adaptation.
After adaptation, the mean and standard deviation of daily mismodelings
are found comparable with the mean and standard deviation of yearly
mismodelings. It is demonstrated also that NTCM after adaptation to a
reference station performs better than before adaptation at the stations
nearby the reference station; however, its performance decreases at the
locations far away from the reference station. In addition, after
adaptation, one hour ahead prediction of NTCM is found to be the best
compared to its longer hours prediction.