| Date: | 1997-10-31 19:00:00 | |
| Sender: | Walter Hausleitner <[Mailed Walter Hausleitner <wh@ast.cam.ac.uk>]> | |
| Subject: | [SLR-Mail] No. 91: New Automatic SLR Normal Point Analysis Service | |
| Author: | Walter Hausleitner | |
| Content: | ******************************************************************************** SLR Electronic Mail 1997-10-31 19:00:00 UTC Message No. 91 ******************************************************************************** Author: Walter Hausleitner Subject: New Automatic SLR Normal Point Analysis Service New Automatic SLR Normal Point Analysis Service for EUROLAS Stations ==================================================================== A new automatic SLR normal point analysis service is set up at the Royal Greenwich Observatory which operates on both a daily and monthly basis. This makes it possible to carry out quality checks on the measurements from the SLR community on a very short timescale. This service includes a check on the global set of Lageos-1 and Lageos-2 normal points via a long-arc solution, but in particular concentrates on the observations of the EUROLAS stations during a subsequent short-arc analysis. The NP Quality Check Procedure ------------------------------ - The automatic service currently analyzes Lageos-1 and Lageos-2 normal points which are daily downloaded from NASA/CDDIS. - In the first step long-arc orbits are fitted to the normal points of a dozen of the most accurate global stations[*] using the RGO SATAN SLR package. A post-fit rms of about 6 cm for both satellites is achieved, applying a rejection level of 3-sigma to eliminate outliers. A combined long-arc residual plot for Lageos-1 and Lageos-2 including the mean values and standard deviations is created for every station. - In the subsequent part of the analysis Andrew Sinclair´s short-arc analysis procedure is used to solve for short-arc corrections. This method treats passes which are simultaneously tracked by at least two stations out of a set of some 5 very precise EUROLAS core stations[**]. These observations are used to correct the original long-arc during the period of simultaneous tracking. Typical values of the short-arc post-fit residual rms are at the 1 to 2 cm level. Short-arc residual plots are then generated, showing the residuals of all EUROLAS stations that tracked these arcs. - From the residuals of these short-arcs, time and range bias values for each participating station are deduced. These values are given in numerical summary tables along with the residual means and standard deviations. - These numerical summaries are taken as a basis for a quality assessment and information feedback procedure, which generates emails in the case of the occurrence of major irregularities and delivers it to the sourcing station. - The range and time biases of each SLR station are regularly compared with the corresponding values resulting from the weekly SLR normal point analysis performed by Richard Eanes at the University of Texas. - Finally the entirety of the analysis results are automatically published on the web to enable a quick and efficient access to these data for the SLR community. The address of the new web-site has changed and reads now as follows: http://www.ast.cam.ac.uk/~slr Note, that not more than the 32 most recent daily solutions and the latest two monthly solutions are published. Some Comments on the Operation of the Service --------------------------------------------- - Daily Solution The daily analysis procedure are scheduled to run between 1 and 3 am, preceded by some data acquisition routines. The daily updated web pages will be available by 7 am GMT. The date of any daily analysis refers to the last day of which measurements are included in the analysis and is equal to the day before the one on which the analysis was actually carried out. The long-arc duration is set to 7 days. Due to the existence of a delay of up to a few days in the normal point availability from CDDIS, an analysis delay currently set to 4 days is applied, which means that at day x the observations of day x-4 are involved in the short-arc analysis. However, short-arcs occuring after that day will again be treated in subsequent analyses, but no repeated feedback information will be generated for those passes. - Monthly solution The monthly analysis procedures are scheduled to run on the 4-th day of each month at 3 am. The long-arc covers the whole month plus a 3 days overlap before and after that month. Currently, no emails are generated based on these monthly results. [*] Best global stations used for the long-arc adjustment 1 7080 Mcdonald 6 7548 Cagliari 11 8834 Wettzell 2 7090 Yarragadee 7 7832 Riyadh 3 7105 Greenbelt 8 7839 Graz 4 7109 Quincy 9 7840 Herstmonceux 5 7210 Haleakala 10 7843 Orroral [**] EUROLAS core stations used to compute short-arc corrections 1 7832 Riyadh 2 7836 Potsdam 3 7839 Graz 4 7840 Herstmonceux 5 8834 Wettzell Any comments and suggestions are highly appreciated! Walter Hausleitner Department of Satellite Geodesy Austrian Academy of Sciences Graz, Austria on secondment to Royal Greenwich Observatory Space Geodesy Group Cambridge, England [Mailed From: Walter Hausleitner ******************************************************************************** |