6993 32 archive 306 disk0/00/00/69/93 2008-07-25 03:23:21 2008-07-25 03:23:21 2008-07-25 03:23:21 article show Christopher.Watson@utas.edu.au King MA Watson CS Christopher.Watson@utas.edu.au Penna NT Clarke PJ pub 040499 040402 969902 restricted GPS; sub-daily signals; geophysical loading Copyright 2008 by the American Geophysical Union. Estimates of seasonal geophysical loading from GPS may be biased by propagated unmodeled subdaily signals. Although the major geophysical signals at semidiurnal and diurnal frequencies are now routinely modeled in GPS analyses, the characteristics of unmodeled or mismodeled subdaily signals are not well known. Here, using site coordinates estimated every 5 minutes, we examine the subdaily coordinate spectral characteristics for ~90 global GPS sites. Unmodeled signals with amplitudes at the 10 mm level are present at frequencies between ~1/day and the Nyquist frequency. 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