| Date: | 1999-01-21 09:00:00 | |
| Sender: | John J. Degnan <[Mailed John Degnan <jjd@ltpmail.gsfc.nasa.gov>]> | |
| Subject: | [SLR-Mail] No. 228: Extension of GEOS-3 Tracking Campaign | |
| Author: | John J. Degnan | |
| Content: | ******************************************************************************** SLR Electronic Mail 1999-01-21 09:00:00 UTC Message No. 228 ******************************************************************************** Author: John J. Degnan Subject: Extension of GEOS-3 Tracking Campaign by ltpmail.gsfc.nasa.gov (8.8.8/8.8.8) with SMTP id NAA09348 for Frank Lemoine has submitted a request to the ILRS Governing Board for three months additional tracking of GEOS-3 by the SLR network. The ILRS Governing Board has voted via email to approve this request. All ILRS stations and operations centers are therefore requested to continue GEOS-3 tracking support until April 20, 1999. The full text of Frank´s request follows. Sincerely, John J. Degnan Chairperson, ILRS Governing Board John and Mike: I recommend extension of the GEOS-3 tracking campaign for an additional three months, to April 1999. The response from the stations has been excellent, both in terms of the quality of the data, and distribution of the passes, with the exception of a dearth of tracking by Arequipa. As of this morning (January 14, 1999), we have about 9900 useful normal points. To make a proper assessment of these data on gravity field determination, though, more than just three months of data are required. Remember, when SLR/DORIS data to TOPEX were used to tune JGM-1 and create JGM-2, some six months of data were used [Nerem et al., 1994]. Other comments: 1. The k=4 resonance (m=57) for GEOS-3 is about 25 days. It´s not clear we can pull it out or separate it from drag effects, but more data would help. [The other resonsances periods are ~4 days (m=14), ~2 days (m=28), ~2 days (m=29), ~3.6 days(m=43)]. 2. With more data we could test whether there is any benefit from the estimation of dynamical tide coefficients using the new GEOS-3 data, which have the following periods for this satellite: Mm (27.55 days); Mf (13.66 days); 01 (15.2 days); N2 (10.6 days); M2 (17.2 days); K2 (66.2 days). I point out that papers exist in the literature that used the ”old” GEOS-3 data to estimate M2 [Cazenave and Daillet, 1981; Felsentreger et al., 1979, and Goad and Douglas, 1978]. I realize that the ILRS has many demands for laser tracking at the present time, however I hope due consideration will be given to this request. Best regards, Frank Lemoine Space Geodesy Branch NASA GSFC [Mailed From: John Degnan ******************************************************************************** |