Polar motion measurements: subdecimeter accuracy verified by intercomparison

Area of Science:

• Geophysics
• Astronomy
• Earth Science

Background:

• Accurate monitoring of Earth's polar motion is crucial for understanding various geophysical processes.
• Traditional techniques for polar motion determination include very long baseline interferometry (VLBI) and satellite laser ranging (SLR).
• Intercomparison of these techniques is essential for establishing accuracy bounds and identifying potential systematic errors.

Purpose of the Study:

• To establish an important bound on the accuracy of modern polar motion monitoring techniques.
• To intercompare measurement series from very long baseline interferometry (VLBI) and satellite laser ranging (SLR).
• To assess the potential impact of major earthquakes on polar motion.

Main Methods:

• Comparison of independent measurement series from VLBI and SLR observing techniques.
• Calculation of root-mean-square differences between pole position estimates from both techniques.
• Initial investigation for correlations between pole position variations and major seismic events.

Main Results:

• Root-mean-square differences between VLBI and SLR pole position estimates are approximately 2 milliseconds of arc (about 6 cm).
• These differences, in the absence of common systematic errors, bound the total errors in both measurement sets.
• No clear signature associated with major earthquakes was detected in the pole position data.

Conclusions:

• Modern VLBI and SLR techniques provide highly accurate measurements of polar motion.
• The established accuracy level promises to help resolve long-standing questions regarding the excitation mechanisms of polar motion.
• Further high-accuracy measurements are needed to fully understand polar motion dynamics and potential earthquake influences.