Solution Comparisons

The results of a VLBI global solution can depend on a great number of factors, including which observing sessions are used and how they were analyzed, the relative weights that stations are given based on how much data they contribute, the way that tides are modeled and earthquakes that shift station positions are treated, and many others.

Below are comparisons of the most recent USNO quarterly VLBI global solution with other solutions, including the C04, Bulletin A, and the previous USNO quarterly. Each comparison shows the differences in the values of the five Earth Orientation Parameters between the two solutions over time. Some scatter in the individual colored data points is expected, due to the variations in processing mentioned above - the overall trends in the time series are useful diagnostics of the differences. The time series tick marks denote days from January 1, 2000, with corresponding calendar year tick marks given at the top.

Comparisons of the current USNO global solution with the IERS C04 time series: 

Bulletin A Time Series
This is a comparison with the C04 series, the solution produced by the International Earth Rotation and Reference Systems (IERS) Center at Paris Observatory. The C04 is a long-term time series, with data reaching back to 1962 and derived using a variety of astrometric/geodetic techniques, not only VLBI. The current C04 EOPs (EOP 20 C04) are given with respect to the IAU 2006/2000A precession-nutation model and consistent with ITRF2020, and are updated twice weekly, ensuring a recent comparison set at the time the USNO quarterly VLBI solution is completed.

Comparisons of the current USNO global solution with the Bulletin A time series: 

Pole X&Y, UT1-UTC, Nutation Offset Longitude & Obliquity
This is a comparison with the Bulletin A series. IERS Bulletin A reports the latest determinations for polar motion, UT1-UTC, and celestial pole offsets at daily intervals based on a combination of contributed analysis results using data from Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Positioning System (GPS) satellites, and Lunar Laser Ranging (LLR). This publication is prepared by the IERS Rapid Service/Prediction Center.

Comparisons of the current USNO global solution with the previous USNO global solution: 

EOPS
This is a comparison of the current USNO quarterly VLBI global solution with the previous USNO quarterly solution. The variations between these quarterly solutions are expected to be quite small, as the main difference is the addition of new data sessions with the procedure and parameters largely staying the same.