7.3 Impact on Signal-to-Noise Ratio
Signal-to-Noise Ratio (SNR) of normalized TIPs and CIPs were computed
for each aliasing and artifact free signal portion (δw ) along the
satellite tracks considering noise level as ±1.5 units in the normalized
scale. The noise level was obtained from maximum peak-to-peak amplitude
(range) of the ionospheric perturbations computed along the satellite
tracks on a quiet day (i.e. previous day of the tsunami and earthquake).
– (14)
where IP is ionospheric perturbation (TIP or CIP), N is
noise level.
Comparison of SNR of TIPs and CIPs derived using all the three methods
(Fig. 18, Table 1 and Table 2) shows that the SNR is better for the
perturbations derived using SPLA. Average SNR of aliasing and artifact
free TIPs and CIPs obtained using SPLA is 2.6, whereas average SNR of
the perturbations obtained by adopting residual and differential methods
are 1.4 and 2.0, respectively (Fig. 18, Top). Further, it is evident
from Fig. 18 (bottom) that the average increase in gain of the
perturbations detected by SPLA compared to residual (rTEC) and
differential (dTEC) methods are 149.1% and 38.6 %, respectively.
Similarly, the average SNR of all TIPs and CIPs (including those which
suffers aliasing and artifacts) derived using SPLA is also higher than
the TIPs derived using the differential and residual methods (Table 1
and Table 2). Further, range of SNR variation (1.68) and standard
deviation (0.43) of gROT manifest the consistency in obtaining TIPs
using SPLA. However, among the three methods, the range of SNR and
standard deviation are very high for rTEC (Table 2) which reveals that
TIPs obtained using the residual method is highly inconsistent.
Similarly, in the case of CIPs, strength of the signals detected by the
residual method differs from corresponding ones detected by SPLA (Table
2). Results of the SNR comparisons reveal the magnitude of impact of
aliasing and artifacts on the signal strength of the perturbations.
Further, this analysis reveals the efficiency of SPLA on increasing the
signal strength of the ionospheric perturbations detected using GPS
apart from removing aliasing and artifacts.