Reply to Lanari, R., et al. Comment on “Pre-Collapse Space Geodetic Observations of Critical Infrastructure: The Morandi Bridge, Genoa, Italy” by Milillo et al. (2019)

Abstract

We would like to thank our colleagues for their comment, as we believe that this discussion further highlights the importance of innovative research in the emerging field of InSAR applications to civil engineering structures. We discuss the statement from Lanari et al. (2020): “Our analysis shows that, although both the SBAS and the TomoSAR analyses allow achieving denser coherent pixel maps relevant to the Morandi bridge, nothing of the pre-collapse large displacements reported in Milillo et al. (2019) appears in our results”. In this reply we argue that (1) they cannot detect the pre-collapse movements because they use standard approaches and (2) the signals of interest become observable by changing the point of view.

Electron acceleration driven by the lower-hybrid-drift instability

“…In the following we assume an unperturbed electron temperature of 50 eV (typical values at Mercury's magnetopause being ∼20−100 eV (Ogilvie et al 1974;Uritsky et al 2011)). This acceleration process is well in the range of observations of the electron instrument MPPE/MEA onboard the Mio spacecraft of the BepiColombo mission (Saito et al 2010), since this instrument includes two electron analyzers that can measure the three-dimensional energy distribution of electrons in the range 3-3000 eV (in solar wind mode) or 3-25 500 eV (in magnetospheric mode), with a time resolution of 1 second (Milillo et al 2020). Here, we simulate the instrumental response of MPPE/MEA when encountering electrons accelerated by a LHDI at Mercury's magnetopause, as shown in Fig.…”

“…First, we discuss the features of the LHW that are expected to be generated by the development of the LHDI at Mercury's magnetopause. These waves have a frequency of f ≈ f LH ≈ 5-20 Hz (in the frame of the drifting ions) and wavelength λ ≈ 2πρ e ≈ 5−15 km (hereafter using typical magnetic field values at Mercury's magnetopause of 10-30 nT, ion temperature 30-70 eV, and density 10-30 cm −3 ; see Milillo et al 2020). In the reference frame of the spacecraft, given that those waves are advected by the shocked solar wind flow, estimated to have a speed V SW ≈ 100 km s −1 , and with an ion drift speed v Di ≈ v thi ≈ 50−80 km s −1 , the Doppler-shifted frequency of the LHW, expected to be observed in the spacecraft frame, lies in the range f = f ± k(v Di + V SW ) ≈ 50−200 Hz.…”

Electric field measurements at the plasma frequency around comet 67P by RPC-MIP on board Rosetta

“…Similar mutual impedance experiments will be carried by future missions. The Hermean magnetosphere will be studied by the Active Measurement of Mercury's Plasma (AM 2 P; Trotignon et al 2006) instrument as part of the Plasma Wave Investigation (PWI; Kasaba et al 2020) on board BepiColombo (Milillo et al 2020). The Mutual Impedance Measurement (MIME) will be part of the Radio and Plasma Wave Investigation (RPWI) carried by the Jupiter ICy Moons Explorer (JUICE; Grasset et al 2013) mission that will observe plasma properties in the Jovian system.…”

Electron acceleration driven by the lower-hybrid-drift instability: an extended quasilinear model

“…In the following we assume an unperturbed electron temperature of 50 eV (typical values at Mercury's magnetopause being ∼ 20 − 100 eV (Ogilvie et al 1974)). This acceleration process is well in the range of observations of the electron instrument MPPE/MEA onboard the Mio spacecraft of the BepiColombo mission (Saito et al 2010), since this instrument includes two electron analyzers that can measure the three-dimensional en-ergy distribution of electrons in the range 3-3000 eV (in solar wind mode) or 3-25500 eV (in magnetospheric mode), with a time resolution of 1 second (Milillo et al 2020). Here, we simulate the instrumental response of MPPE/MEA when encountering electrons accelerated by a LHDI at Mercury's magnetopause, as shown in Fig.…”

“…First, we discuss the features of the LHW that are expected to be generated by the development of the LHDI at Mercury's magnetopause. These waves have frequency f ≈ f LH ≈ 50-100 Hz and wavelength λ ≈ 2π/ρ e ≈ 5-15 km (using hereafter typical magnetic field values at Mercury's magnetopause of 10-30 nT, ion temperature 30-70 eV, and density 10-30 cm −3 , see Milillo et al (2020)). Assuming that those waves are advected by the shocked solar wind flow with a speed V S W ≈ 100 km/s, the Doppler-shifted frequency of the LHW lies in the range f = f ± kV S W ≈ 0-200 Hz.…”