International Laser Ranging Service
10th General Assembly

Data Formats and Procedures Working Group

San Fernando, Spain
Monday, June 7, 2004
18:00-19:00

Agenda

Notes

Attendees: Werner Gurtner, Stefan Riepl, Maury Dube, David Carter, Jan McGarry, Julie Horvath, Mark Davis, Bud Donavan, Randy Ricklefs, John Luck, Chris Moore, Mike Pearlman, Wolfgang Seemüller

1. Welcome and Introduction

W. Seemüller welcomed the attendees, and gave short remarks about the work done since the last Working Group meeting in Nice, April 2003.

2. Membership

Roger Wood has retired and is withdrawn from the list of WG members. Thanks to him for his excellent work done in this group. Maury Dube was added to the membership list.

3. Review of CB Activities

Mike Pearlman gave a short report on the activities of the Central Bureau. He reports that SLR is not getting proper recognition in papers and reports that are being issued by the analysis and science community. A notification should be put on the ILRS web site and at the EDC web page too. The Station Qualification procedure has been implemented. The recent NASA budget reduction result in closure of the SLR stations Arequipa and Maui, and cutbacks for stations Monument Peak and McDonald. Concerning the satellite predictions some duplications occur. CB will prepare a list of recommended prediction sets. The formerly report cards were produced by Van Husson, who is not working anymore for the ILRS. This work will be replaced by RITSS soon.

4. Refraction Study Group and 5. Format Study Group

The most important work is done in these two Study Groups of the DF&P WG. See the two special reports by the chairs of   these Study Groups Stefan Riepl and Randy Ricklefs .

6. Full-Rate data delivery

Still some problems are existing with some SLR stations due to format, filenaming and delivery errors. Automatic archiving and handling is problematic therefore. AI: E-mail to the corresponding stations

7. Filenaming and directory change at CDDIS (and EDC)

Carey Noll and Maury Dube presented a poster in San Fernando about these changes. The changes have to be fitted to requests of the ACs

8. Normal point data format and integrity check

Wolfgang Seemueller reports about the normal point data format and integrity check at EDC. It is implemented, and the program and a description is put to the ftp server at EDC/DGFI.

9. Pass list format for Gravity Probe - B

A first format description of the pass list for Gravity Probe - B was given by Werner Gurtner. The final format will be available soon. A similar pass list is necessary for problematic satellites due to damages of other satellite equipments (e.g. ICESAT).

10. More frequent ONP data exchange

The same exchange frequency of ONP data should be at both Global ILRS Data Centers CDDIS and EDC. Wolfgang Seemüller will make the correspondent arrangements for coordination of the equal data exchange at both centers.

11. Urgent Mail/Prediction Exploder satisfying?

After the transition of the Prediction Exploder from CDDIS/HTSI to EDC nobody is blaming, so all seem to be satisfied. No comments were given.

12. Working Group Charter/WG Activities

No changes Finally our former chair of the DF&P WG John Luck presented his research about the multi-colour normal point generation. He was asked to formulate a recommendation about this item (see attachment). The recommendation is under review by the members of the DF&P WG. Additionally he formulates a workshop resolution (see attachment). Thanks to John for his excellent work.

RECOMMENDATION

From : DATA FORMATS AND PROCEDURES WORKING GROUP
To : ILRS Central Bureau
On: The 1997 ILRS Normal Point (NP) Algorithm

Considering that:
Item (1) of the published algorithm reads:
"Use high precision predictions to generate prediction residuals PR j = O j - P j where j indexes all returns in the pass . ."; and that:
Item (3) of the published algorithm reads:
"Solve for a set of parameters . . . to remove the systematic trends of the prediction residuals, giving the trend function f(PR); and that:
Item (4) of the published algorithm reads:
"Compute fit residuals FR j = PR j - f(PR j ) and omit outliers"; and

Noting that:
inappropriate interpolation methods can introduce serious errors in the predictions P j and therefore in the prediction residuals PR j leading to errors in Normal Points as great as one-third of the amplitude of the prediction error in any bin,

Recommends that :

1. Interpolations be performed on Cartesian X,Y,Z coordinates, not on azimuth, elevation and range, at each instant of observation. Geocentric X,Y,Z is preferable, but topocentric X,Y,Z (e.g. East, North, Up) is adequate; and
2. The tabular interval used as the basis of interpolations be no larger than the intervals for each satellite recommended by ILRS for its new predictions format, and that orbit integrator step sizes which produce the tabular points for interpolation be no greater than these intervals; and
3. Such tabular intervals be less than the ILRS Normal Point bin sizes; and
4. The interpolation mechanism be at least Lagrangian of order 8 or equivalent (8-point, i.e. degree 7). In particular, cubic splines should never be used; and/or
5. Alternatively, separate trend functions in each NP bin may be computed from observations accepted in steps (3) and (4), from which new fit residuals FR j are computed for the generation of the Normal Point. Such separate trend functions need only be of low order, e.g. quadratic; and
6. Each station and Operations Centre rigorously examines its own software and ensures that it complies with this recommendation; and
7. Any station that amends its NP generation software to accord with this Recommendation must update its System Change Indicator as of the date of implementation; and
8. The ILRS Central Bureau updates the NP Algorithm document forthwith.

Reference :   http://ilrs.gsfc.nasa.gov/products_formats_procedures/normal_point/np_algo.html

JMcKL, 10 June 2004
Item 7 added 19 June 2004

WORKSHOP RESOLUTION

The 14 th International Workshop on Laser Ranging,

• Recognizing that inappropriate interpolation methods into tables of range predictions can introduce significant errors in Normal Point values which may behave as unidentifiable random errors; and that inappropriate interpolation methods into tables of pointing predictions can produce substantial tracking errors leading to unnecessary loss of data; and
• Considering that software for Normal Point generation and for telescope pointing at some stations might still employ such inappropriate interpolation methods as legacies from bygone days when the errors were viewed as less important,
• Implores the people responsible for maintaining operational software at or for each and every ILRS station to examine the interpolation schemes employed for Normal Point generation and for tracking predictions, and to adopt the Recommendation dated 10 June 2004 from the Data Formats and Procedures Working Group to the ILRS Central Bureau.

JMcKL, 19 June 2004

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