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.