Speaker
Description
The International VLBI Service for Geodesy and Astrometry (IVS) conducts both 24-hour and 1-hour geodetic VLBI sessions. The 24-hour sessions utilize global VLBI networks to estimate all five Earth Orientation Parameters (EOP), but they generate large volumes of data, resulting in product delays of several weeks. In contrast, the 1-hour intensive sessions are designed to provide more timely estimates of the Earth rotation angle (UT1-UTC), which is known to vary more over shorter time scales. These sessions use only 2–3 telescopes and offer faster results, but are more sensitive to short-term variations and suffer from limited troposphere modeling due to sparse observations and reduced mutual sky coverage. For instance, tropospheric gradients—routinely estimated in 24-hour sessions—cannot be reliably determined in intensives.
Previous studies have explored enhancing both session types by incorporating GNSS data from co-located stations, using either co-located combination on the observation level (CCOL) or combination at the normal equation (NEQ) level. Some of these approaches showed improvements in UT1-UTC and/or UT1-UTC derived Length of Day (LOD) estimates. However, they primarily relied on Legacy VLBI data combined with final and rapid GNSS products using NEQ-level methods, or on VGOS data combined with final GNSS products using CCOL.
In this study, we investigate the impact of using different GNSS orbit and clock product types—ultra-rapid (same-day), rapid (within 2 days), and final (12–19 days)—in CCOL solutions with VGOS for VLBI intensive sessions. We compare the integrated solutions across GNSS product types and against standalone VGOS processing to evaluate the trade-offs between timeliness and accuracy.
