Reckoning ionospheric scintillation S4 from ROTI over Indian region

Abstract

• Study of Ionospheric scintillations indices S4 and ROTI in Indian region. • Relation between ROTI & S4 is useful for standard GNSS receivers to estimate S4. • Correlation of ROTI & S4 is better than 0.6, yet an estimate of S4 is unreliable. • Using obtained relation, a range of S4 values can be estimated from ROTI value. Ionospheric irregularities cause fluctuations (scintillations) in received satellite signal strength, degrading communication and navigation signals. The scintillation strength depends on the scale sizes of the irregularities and the frequency of the radio signal. The parameter S4 index describes the scintillation strength derived from the amplitude of high rate received signal sampled at 50 Hz, usually from special GNSS receivers. Most GNSS receivers have a lower data sampling rate, so an alternate parameter, Rate of Change of TEC Index (ROTI), is derived from the total electron content (TEC) sampled at 30 s. Here, the correlation between ROTI and S4 is performed for the Indian ionospheric region, with different elevation mask angles and ROTI calculated over different averaging intervals. An estimate of the S4 value from ROTI is unreliable even though the correlation between them is better than 0.6. Different elevation mask angles and ROTI with varying averaging intervals do not significantly affect the correlation between S4 and ROTI. Further, the correlation and occurrence percentages of S4 corresponding to ROTI are analyzed. An 80% confidence range is obtained to correlate the observed ROTI with the corresponding S4 index. These probability estimates of S4 values derived from ROTI values also vary with latitude. This relation between ROTI and S4 will be beneficial in using standard GNSS receivers for the studies of ionospheric scintillations.