An automatic SLR normal point analysis service has been set up as a collaboration between the UK's NERC Space Geodesy Facility at Herstmonceux and Monks Wood and with the Department of Satellite Geodesy, Austrian Academy of Sciences, in Graz, Austria. The process operates on a daily 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, Lageos-2 Etalon-1 and Etalon-2 normal points via a long-arc solution, but in particular concentrates on observations of many other satellites by the EUROLAS stations during a subsequent short-arc analysis.

The NP Quality Check Procedure

Long-arc orbits of duration 6-7 days 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 2 cm for each satellite is achieved, where a rejection level of 3-sigma is applied to eliminate outliers. A combined long-arc residual plot for Lageos-1, Lageos-2, Etalon-1 and Etalon-2 is created for every station. These plots show for each station the residual value from the fitted precise orbit for each normal point, and can be used to identify outliers at a level of a few cm. The residuals for Lageos-1 are plotted in RED, those for Lageos-2 in BLUE, those for Etalon-1 in GREEN and those for Etalon-2 in MAGENTA. Shown numerically on the plots are the residual mean and standard deviations for the accepted data for each of the four satellites.

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 from the best of the 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 sub-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 should be used by the stations as a basis for a quality assessment.

The entirety of the analysis results are published on the web to enable a quick and efficient access to these data for the SLR community.

Some Comments on the Web Pages

Selecting a Date of Analysis
Not more than the 32 most recent daily solutions are published. The main page of each date of analysis shows the total extent of the resulting data at a glance with all plots and tables represented as thumbnails which come along with useful information organized in tables underneath.

Daily Solution
The date 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 carried out.
The long-arc duration is set to 7 days.

* Best global stations used for the long-arc adjustment

1	7080	Mcdonald	6	7839	Graz
2	7090	Yarragadee	7	7840	Herstmonceux
3	7105	Greenbelt	8	7501	Hartebeesthoek
4	7110	Monument Peak	9	7810	Zimmerwald
5	7210	Haleakala	10	7845	Grasse