Ephemeris issue

[CorentinLouis]

How do we have to select the ephemeris

1. We need to take the ephemeris corrected from the observer distance, to obtain the correct longitude of the active magnetic field line at the moment of the emission (ephemeris from Horizons are ok; ephemeris from UIowa are not corrected from the light travel time)
2. Then we need to delay the observation of the emission by the light travel time of the signal from the emitting body to the observer.

[CorentinLouis]

Miriade ephemeris are corrected from the light travel time. Steps to obtain the corrects ephemeris:

• Jupiter's ephemeris seen from the observer at a SCET t1
• Since Miriade ephemeris are corrected from the light travel time, it gives us the ephemeris at the emission time t0
• To obtain the Jupiter's ephemeris seen from the moon at the emission time t0, we need to ask the ephemeris at t1-t_propagation / or ask ephemeris at t1 and then the moon must be moved back in time to get its position at the emission time t0 (supposing that the Jupiter-moon propagation time is negligeable - 1.4 sec for Io, which corresponds to 0.02029°)

[CorentinLouis]

(e.g., if this is not done correctly, it induces an error of ~4.2°-5.7° on the Io flux tube, for a light travel time of 30-40 min...)

[CorentinLouis]

The master branch used to take ephemerides correctly, until an update of MIRIADE (~2019), which no longer returns Jovian ephemerides in system III by default

[CorentinLouis]

The develop branch is now up to date.