The Rate of TEC index (ROTI) is defined as standard deviation of the rate of TEC (ROT) assuming the ionosphere as a thin layer. Hence the index provides information about temporal ionospheric irregularities. DLR's ROTI is calculated for the European region between 25 degrees N - 75 degrees N and 20 degrees W - 45 degrees E.

These data is used to calculate relative TEC as input for the ROTI processing. The standard deviation is calculated over a one minute window and the ROT is calculated each second. The ROTI measurements are mapped into a regular grid (2 degrees x2 degrees lat/lon). Each grid cell presents the mean of the ROTI measurements located in this cell.