Rate ot TEC Index (ROTI)

The ROTI, as proxy for a measure of scintillation, was introduced in [Pi et al., 2013], and basically consists in computing the standard deviation of the rate of TEC over a certain time interval. It can be easily computed using the ionospheric (geometry-free) combination of GNSS carrier phase measurements. In short, the steps to compute it are described in Algorithm .

Algorithm (Satellite ROTI calculation)

Inputs Carrier-phase GNSS measurements at two bands (e.g. L1 and L2)

Output Time series of ROTI (TECU/minute)

1. For each GNSS satellite

   1. Compute the ionospheric (geometry) free combination of carrier phases at frequencies \(f_1\) and \(f_2\): \(LI = L1 - L2\)

   2. Compute the time difference of \(LI\): \(\Delta LI = \frac{\delta LI}{\delta t}\)

   3. Compute the time difference of \(STEC\): \(\Delta STEC = \Delta LI / \alpha_{LI}\), where \(\alpha_{LI} = 40.3 \cdot (\frac{1}{f_2^2} - \frac{1}{f_1^2})\)

   4. Compute the standard deviation of the \(\Delta STEC\) across consecutive time intervals of e.g. 5 minutes

An example of the ROTI calculation for a 1Hz dataset of SEY1 station (2014, doy 58) can be found in [Juan et al., 2017]