| Date: | 2005-06-24 23:01:00 | |
| Sender: | Jim Ray <Jim Ray (NGS 301-713-2850 x112) <jimr@ngs.noaa.gov>> | |
| Subject: | [SLR-Mail] No. 1340: ocean tide loading model | |
| Author: | Jim Ray | |
| Content: | ******************************************************************************** SLR Electronic Mail 2005-06-24 23:01:00 UTC Message No. 1340 ******************************************************************************** Author: Jim Ray Subject: ocean tide loading model Dear Analysis Colleagues, According to the IERS Conventions, the instantaneous position of a terrestrial point can be modeled apriori as a function of time, t, by X_m(t) = X_o + V_o*(t - t_o) + SUM_i{dX_i(t)} where X_o and V_o are regularized coordinates and velocities (such as ITRF) at the reference epoch, t_o, and the summation includes various predictable motions, mostly tidal with periods near 12 and 24 hours. The largest tidal effect is that due to the solid Earth (body tide), with amplitudes in the few-decimeter range. The development of the IERS model for the solid Earth tide is very comprehensive but easily implemented using a subroutine kindly provided by V. Dehant and S. Mathews. The next largest tidal displacement, up to several centimeters, is due to ocean loading variations. Other effects that should conventionally be included in the summation above are the solid Earth pole tide (well modeled in the IERS Conventions), pole tide due to the oceans (IERS model under development), S1 and S2 atmospheric pressure loading (IERS model under development), and tidal geocenter motion (treatment unclear in Conventions). The IERS recommendations for ocean loading are so general and vague on critical points that it cannot be said that a ”conventional model” exists. It is recommended that users adopt the site-specific amplitudes and phases for the 11 largest partial tides generated by the website of M.S. Bos and H.-G. Scherneck (www.oso.chalmers.se/~loading/), preferably using the GOT00.2 tidal model of R. Ray. But a specific implementation to compute site displacements is lacking. This is a request for coded implementations of a modern ocean loading algorithm to be considered by the Advisory Board for IERS Conventions Updates for possible future use in the Conventions. The ideal routine should expect a station position and epoch as inputs and return the NEU displacements. If the Bos-Scherneck coefficients are not used, this should be clearly explained and justified. The code should be adequately documented internally, preferably with supporting references and any limitations explicitly described. Modulation of the main tides due to lunar nodal variation or some other interpolation method to account for lesser tides is recommended. On the other hand, the development should not be so elaborate that it is unnecessarily inefficient, considering realistic errors for the tidal amplitudes and phases. Any additional information you can provide to support your implementation would be appreciated. Please send submissions to me at your earliest convenience. Thanks very much for your help. --Jim Ray (Advisory Board chair) From: Jim Ray ”(NGS” 301-713-2850 ”x112)” ******************************************************************************** |