Initial ILRS AWG Meeting (Florence 1999)

Minutes of Analysis Working Group Meeting
Florence, Italy
September 22, 1999


  1. welcome
  2. actions since The Hague
  3. membership
  4. tasks of ILRS/ILRS AWG
    4a) QC of Laser Ranging (LR) observations
    4b) specification of guidelines for analysis standards
    4c) QC of analysis products
    4d) official ILRS product as contribution to IERS
  5. 5)actions
  6. 6)closure


AWG members: Graham Appleby Cinzia Luceri Ron Noomen Toshi Otsubo Bernd Richter Pete Shelus Mark Torrence

guests: Van Husson Matti Paunonen Randy Ricklefs

2) Actions (since the Hague):

The existence and organization of the web page was reported. In particular, the page ilrs.gsfc.nasa.gov/science.html was mentioned. It was acknowledged that the current contents are not very good. Cinzia Luceri will update the description of the phenomena.

3) Membership:

current membership: consists of 2 LLR and 14 SLR analysts

Graham Appleby Richard Biancale Richard Eanes Ramesh Govind Rolf Koenig Hiro Kumimori Cinzia Luceri Vladimir Mitrikas Juergen Mueller Ron Noomen (coordinator) Toshi Otsubo Bernd Richter Remko Scharroo Pete Shelus (deputy coordinator) Tim Springer Mark Torrence

4) Tasks:

4a) Quality Control of laser ranging observations

- level 1: at station (# raw obs/NP, noise, outliers, ....

- level 2: at data center (ibidem + format compliance, ....

- level 3: at analysis centers goal: detection of systematic errors (RB, TB, FB, tropo, etc.)


LAG-1 LAG-2 ERS-1 ERS-2 Aji.GPS35/36 CODE x CRL x x x CSR x x Delft x xx x MCC x x NERC x x

questions: - are QC results transferred to stations? others? - (need for) storage at central location? - (need for) inclusion in one document? - results in accordance with quality of data? - consequences for scientific analysis? - more satellites? - LLR data?

answers: - SLR/LLR stations, SLR/LLR analysis centers

==> discussion:

NERC's analysis is done every day with 6 day arc. There is an automatic Email to EUROLAS stations to warn them of obvious data problems.

There was a discussion of how to report RB, TB, FB, trop; whether or not to report the analyses; and how to attach a meaning to the results. (which show differences).

Van Husson showed some CSR results which show differences in the station's RB, TB, for LAGEOS 1 and 2. These differences were generally attributed to station position errors. The same may apply to results reported by other groups. There was no consensus on whether or not the individual analysis centers should use their own or a standard set of station positions. Every RB, TB, FB, trop bias report should now be sent to Van at ATSC on Tuesday of each week. He will combine the reports to issue one report and have this available on the next day (Wednesday). At this moment (some of) this work is done on an informal basis, but it should be made more structured. Definition of pilot project 1. The individual analysis center's reports will still be available through the ILRS. (Van asked DUT to place the station monument number in each record of the DUT report.)

4b) analysis standards

options: - IERS Conventions 1996 - ERS Standard - ...

necessity? - goal of analysis: best description of physical truth - differences in dataset (target satellite, screening, ---) - differences in analysis technique - date of analysis standard

conclusion: - clear definition of product is important - allow for freedom/progress in analysis

==> discussion:

Discussion of standards centered around the desire of each analysis center to maintain their own "style" of analysis and quality control, and whether or not a set of standards should exist. The group decided to use ITRF97 as the definition of the frame and its time evolution, by using this input as a priori for station position and velocities.

4c - i) analysis products: definition of products

- distinguish between internal and external purposes?

- station positions: - use DOMES id - refer to monument instead of optical centers - main monument at station? - parameters: cartesian components + epoch - units [m] - reference system?....ITRF97?

- station velocities: - use DOMES id - parameters: cartesian comp. (+ epoch) - units: [m/yr] - reference system? ITRF97, NNR or ??

- earth orientation parameters: - definition? - units? - individual components or pairs of 3? - reference epoch: central date + internal length? - epoch for LLR: mean observations? - SLR intervals inconsistent with intervals used by other space geodetic technique(s)?

- gravity field coefficients: - normalized values - sign? - static terms: epoch? - temporal terms: epoch?

- geocenter: - definition? - units: [m]?

- satellite/lunar ephemerides: - parameters: epoch + cartesian position + velocity - reference: true of date system - units:: [m], [m/sec] and [MJD + fraction] - spacing?

- lunar librations - ?

- lunar orientation parameters: - ?

- other: - ? ==> discussion:

Due to time constraints a detailed discussion of this extensive list was deferred until another meeting. General consensus on the need to use the SLR monument position as the reference point, and the DOMES numbers as station id for reporting station position and velocity information. ITRF97 will be used for a priori information on position and velocity. As for EOPs, these parameters will be identical to the parameters that are submitted to IERS, always in pairs of 3. Epoch is center of interval, with the latter running from 12.00 to 12.00 hrs. Discussions on other parameters (gravity field coefficients etc.) was not held because of time constraints.

4c - ii) analysis products: format


SINEX + satisfies requirements for station positions, velocities, EOPs (not LLR?),---- + "open" to new products + constraints + ascii + international standard - big - "overkill" for ephemerides

ERS GPM satellite ephemerides many additional parameters

IRVs satellite ephemerides

IERS format for EOP

==> discussion:

There was general consensus to use SINEX for reporting station position and velocity information and EOP (Xp, Yp, and UT/LOD, depending on IERS requirements). For EOPs, the SINEX format has the advantage of allowing for a full covariance matrix.

4c - iii ) analysis products: Quality Control

benefits: - detection of errors/blunders in analysis - definition of products - overall improvement of SLR/LLR community

drawback: - work

questions: - reference? - weight of individual contributions? - format? - dataset? - technique? - feedback? - .....

==> discussion:

see notes on item "4e".

4d) official ILRS product as contribution to IERS

time series of station position solutions - interval per solution? - total period? - satellite? - combination of individual contributions? - dataset? screening? model differences? - format/definition/reference? - who?

position at epoch + velocity - total period? - satellite? - combination of individual contributions? - dataset? screening? model differences? - format/definition/reference? - who?

- other products?

- calibration against "external" solutions?

- time schedule?

- pilot project?

==> discussion:

Due to time constraints a detailed discussion of this agenda item was deferred until another meeting, though it was generally agreed that the ILRS should work towards one coordinated product to submit to the IERS.

4e) analysis products: proposal for pilot projects:

i) station positions

- dataset: - Lageos-1 ??? - LLR? - screened data? - global network - station motions? - format/definitions? - contributions from whom? - comparison:

ii) EOP - dataset: - screened data? - global network - station position/motions? - format/definition? - contributions from whom? - comparison: who?

==> discussion:

Before the two proposed pilot projects were discussed, another was suggested: to combine existing analysis centers RB, TB, FB, and trop bias analyses into one report. As discussed in 4a above: Every RB, TB, FB, trop bias report should now be sent to Van Husson at ATSC on Tuesday of each week. He will combine the reports to issue one report. As from now on, this is referred to as pilot project 1.

The station position and EOP pilot projects were discussed (from now on to be called "pilot project 2" and "...3", respectively. There will be a solution based upon LAGEOS-1 (only!) for a 28 day period beginning at 0 hr Sept 5 and going through 24 hr on Oct 2. For pilot project 2, the product will be a global station coordinates solution at epoch September 19. For pilot project 3, this will be a time-series (at 3-day intervals) of EOPs. The final file of edited data should also be made available with the solution for station positions and/or EOP.

Dr Philip Moore (formerly at Aston University, now at Newcastle upon Tyne), being one of the Associated Analysis Centers, has volunteered to compare and combine the station position solutions. Additionally, Ron Noomen will ask the MCC if they will compare the station position solutions. Ron Noomen will try to find another analysis or associate analysis center to analyze the EOP solutions. Ron Noomen will send email through the ILRS AWG exploder to inform each analysis center about these pilot projects.

5) Action Items

1) inventory of analysis activities. who? when? 2) discussion + agreement on format etc. 3) definition of pilot projects. 4) data analysis in pilot projects. 5) pparation QC at AAC/ACs to have S/W for analysis 6) QC individual solution at AAC/ACs 7) workshop ==> discussion:

Item 1: Van Husson will get the information provided through the initial proposals to the ILRS from John Degnan and put the information on the ILRS web site.

Item 2: per discussion in 4c-ii, SINEX will be used for station position, velocity, and EOP exchange. ITRF97 will be a priori for station positions and velocities.

Item 3: see pvious notes ("4e") on the three pilot projects. action item Ron Noomen

Item 4: Results from pilot project analyses should be made available by Nov 15 through the ILRS web site (Mark Torrence will coordinate this with the ILRS central bureau)

Item 5: Pilot position project analyses will be done by Newcastle upon Tyne, and (perhaps) MCC; analyses center(s) for EOPs not yet determined. Deadline for pparation November 15.

Item 6: Results of comparison of the pilot project contributions (Item 5) are to be available through the ILRS web site by Dec 15.

Item 7: Though Suryia Tatevian and Ramesh Govind has suggested through Ron Noomen that an analysis working group meeting be held in Russia and Australia, respectively, it was decided to have a meeting in Frankfurt either Jan 17 and 18 or Jan 24 and 25.

Further discussion was about the need for the ILRS to come to one coordinated product to submit to the IERS. The selected approach was to let this evolve from the currently defined pilot projects. Mark Torrence was designated to coordinate web related activities of the analysis working group with the central bureau.