Now at: Korea Polar Research Institute (KOPRI), Incheon, Korea.
GRACE's spatial aliasing error
Article first published online: 22 NOV 2007
© 2007 The Authors Journal compilation © 2007 RAS
Geophysical Journal International
Volume 172, Issue 1, pages 41–48, January 2008
How to Cite
Seo, K.-W., Wilson, C. R., Chen, J. and Waliser, D. E. (2008), GRACE's spatial aliasing error. Geophysical Journal International, 172: 41–48. doi: 10.1111/j.1365-246X.2007.03611.x
- Issue published online: 22 NOV 2007
- Article first published online: 22 NOV 2007
- Accepted 2007 September 10. Received 2007 September 10; in original form 2006 December 1
- Satellite geodesy;
- Time variable gravity
The GRACE satellite mission provides a near-continuous sequence of approximately 30-d gravity field solutions in the form of spherical harmonics (SH). Because SH functions are global while GRACE measurements are sensitive mainly to variations along the ground-track, undersampling (alias contamination) occurs. Here we investigate how geophysical signals are likely to cause alias error in GRACE gravity fields. We use actual GRACE orbits and systematically sample several types of time-varying signals that might represent either errors in geophysical models such as tide models, or unmodelled geophysical signals. We show how error in semi-diurnal tides like S2 can alias into long period variations in particular harmonics, particularly as a possible error source in the degree 2, order 0 term (C20) of GRACE fields. We also show that aliasing associated with non-tidal geophysical model errors is significant at order 15 or multiples of 15, due to the GRACE ground track spacing in longitude. This can be predicted from Kaula's resonance formula and might be reduced by suppressing amplitudes of affected harmonics.