| Description: observed_event_tdb indicates the instant at which photons were received at the instrument. It is represented in the 'Barycentric Dynamical Time' system, as a number of elapsed seconds since the J2000 epoch. This is consistent with the definition of 'ephemeris time' as used in the SPICE toolkit. In a label the corresponding values are given by the optional start_observed_event_tdb and stop_observed_event_tdb attributes. At least one of either observed_event_time or observed_event_tdb, must be a table field for occultation data. Both may be used. observed_event_time is equivalent to spacecraft_event_time for spacecraft data and to earth_received_time for Earth-based data. It is always the photon arrival time, so in this regard we treat typical spacecraft radio occultation data as Earth-based, referring to the time at the DSN receiving station. For an uplink radio occultation, this is the spacecraft event time. |