Here are the three questions in Orbit refinement:

**What is orbit refinement?**Suppose I know the Keplerian orbital elements at 6:00:00 on a certain day as the initial orbit and use SGP4 to propagate it to 8:00:00 on the same day, obtaining the orbital elements at 8:00. However, this is still obtained through numerical integration, and there is a discrepancy between this and the true orbital elements at 8:00. If I use the orbital elements obtained through SGP4 as the initial orbit and then incorporate some measurement data (e.g., azimuth, range, elevation, time from 8:00 to 9:00) to refine the orbit at 8:00, does this count as orbit refinement?Also, suppose I know the Keplerian orbital elements at 6:00:00 on a certain day as the initial orbit and also have observation data from 6:00 to 8:00. If I use the initial orbit at 6:00 and iteratively fit the observation data to propagate it forward, obtaining the orbital elements at 8:00, is this considered orbit refinement?Which of the two scenarios is considered orbit refinement?**Given the initial orbit at 6:00:00 and observation data from 6:00 to 8:00, if I use BatchLSEstimate to obtain a refined orbit, should I compare the refined orbit against the initial orbit at 6:00 or against the true orbital elements at 8:00 for validation?****Given the initial orbit at 6:00:00 and observation data from 6:00 to 8:00, if I use BatchLSEstimate to obtain a refined orbit, I printed the refined orbital elements at 7:20, 7:40, and 8:00. I found that only the true anomaly differs while the other orbital elements remain the same. Why is that?**