Device-specific thresholds for various aviation-related operational frequencies. RSTN data are marked with yellow dots. The discrete frequencies at which the RSTN data is observed are indicated on the top axis. Data points from observations in Marqué et al. (2018) (cyan x’s) at GPS frequencies (1–1.5 GHz) are added. The data from Marqué et al. (2018) consists of e-Callisto data which has been flux-calibrated using data from the ORFEES (Nancay) and HSRS (Humain) observatories. The radar and GPS frequencies which are used in the study region are marked by magenta and dark blue solid and dashed lines. There are no data at these frequencies from the RSTN network. ^{These frequencies can} be monitored by using e-Callisto spectral data but no flux-calibrated data is available from e-Callisto for these frequencies. The dashed green curve along the top of the shaded region in Figure 4 is generated by using a cubic spline of the most intense observations at each discrete frequency. The spline values are used for the upper bound column in Table 2.