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					       ISSI LLR Workshop, Berne, February 14-17, 2011




Criteria for Validation of
(new) LLR Sites
Jürgen Müller*
Institut für Erdmessung (Institute of Geodesy)
Leibniz Universität Hannover (University of Hannover)
Germany
*with input from J. Williams, P. Shelus, E. Pavlis and
others
         Contents
Background
  - open questions
  - sites’ status
  - available LLR analysis software

Definiton of critieria for
  - lunar tracking
  - data quality
  - data analysis?

Conclusions
Requirements for LLR analysis and tracking
    Should we have standards for
      - normal point (NP) computation?
      - LLR data processing?


    Criteria for tracking (new) LLR sites
       - number of reflector arrays to be observed ?
       - successful observation days/nights per month ?
       - normal points per year: ?
       - normal point accuracy: ?
       - post-fit residual of single NP to global solution: ?


    Further constraints to be considered?
             Retro-reflectors and observatories

                                        First reflector deployed on
Luna 17
          Apollo15           Luna 21
                                        July 21, 1969 (Apollo 11)
                                        “Continuous” LLR
                 Apollo14
                            Apollo11
                                        observations for 41 years
Luna17 retro-reflector

       Lunokhod 1 has been re-discovered
       in April 2010
           Number of normal points
 1970 - 2010: ca.17,000 normal points
   Status, perspective at the LLR sites

 McDonald continued lunar tracking (at low level only),
  as well as LRO tracking
 APOLLO also started LRO tracking
 Grasse is back into the game since end of 2009
 Matera re-started LLR tracking in spring 2010, but not
  routinely at the moment
 Wettzell plans (see talk of U. Schreiber)
         LLR telescopes

                                      McDonald




             Wettzell, old




APOLLO                       Grasse
            Hawaii
           LLR – returned photons

Wettzell, 0.7m telescope   APOLLO, 3.5m telescope




    Can we use the same normal point software?
NP calculation – application of pulse pattern
                 Normal point calculation

NP software
  - As baseline tool: NP software from OCA?
  - Or, SLR NP software
http://ilrs.gsfc.nasa.gov/products_formats_procedures/normal_point/np_algo.html
      adapted?
   - In any case, refined NP calculation in some cases, e.g.,
     • APO (filtering, pulse shape…),
     • WLRS (semi-pulse train)
    Weighted annual residuals
          weighted residuals (observed - computed
          Earth-Moon distance), annually averaged




Should we use some standard processing software?
Is this feasible at all?
Available software at the analysis centers

 Software packages for LLR data analysis
  Hannover: LUNAR
  Paris: INPOP
  Pasadena: JPL software (cooperation with NAOJ)
  Harvard CFA: PEP
  MIT: PEP
  Austin, Univ. Texas: a version of PEP (in the past)

 Comparison of post-fit residuals in 2010 (ISSI inspired
 and Boston workshop) showed major differences.
Comparison of post-fit residuals




    Presented at Boston workshop 2010
Comparison of post-fit residuals




    Presented at Boston workshop 2010
Comparison of post-fit residuals




    Presented at Boston workshop 2010
Comparison of post-fit residuals




    Presented at Boston workshop 2010
         Requirements for LLR analysis

LLR data processing
  - Document for ephemeris integration available;
      chapter in Explanatory Supplement,
      see http://iau-comm4.jpl.nasa.gov/XSChap8.pdf
  - Analysis models are very different (IERS conventions
     for Earth, but none for solar system and lunar rotation);
     differences collected at Boston workshop (several
     pages)
     ..\WORD\LLR\2010\Murphy_Workshop\matrix.html
  - Different LLR analysis packages should be accepted
Requirements for lunar tracking?




  We are happy with each single
  LLR measurement at all.
          Statistics of LLR measurements
 Year   Numb rms     rms    Number by station Number by reflector
              nsec    cm     OCA MLR APO Ap11 Lk1 Ap14 Ap15 Lk2
  1995   1018 0.143   2.14    575 443     0    89 0 99 810 20
  1996   1015 0.112   1.68    609 406     0    86 0 91 822 16
  1997    819 0.107   1.60    577 242     0    54 0 35 726         4
  1998    695 0.104   1.56    353 342     0    62 0 58 573         2
  1999    844 0.095   1.43    663 181     0 103 0 94 634 13
  2000    895 0.112   1.68    809 86      0    93 0 68 733         1
  2001    375 0.148   2.22    285 90      0    31 0 17 326         1
  2002    242 0.157   2.35    174 68      0    21 0    5 214       2
  2003    245 0.129   1.94    185 55      0    18 0 10 216         1
  2004    487 0.102   1.54    446 35      0    60 0 56 356 15
  2005    331 0.116   1.73    273 58      0    34 0 47 246         4
  2006    166 0.112   1.67      0 82 84       23 0 14 129          0
  2007    209 0.101   1.52      0 48 161       33 0 35 137         4
  2008    369 0.134   2.01      0 66 303       66 0 70 210 23
  2009    239 0.147   2.20     25 51 163       45 0 36 147 11
  2010    263 0.099   1.49     19   8 230      42 30 43 135 13
                 Numbers from Jim Williams, JPL
 JPL post-fit residuals




Presented at Boston workshop 2010
     Requirements for lunar tracking

Criteria for tracking (new) LLR sites
 number of reflector arrays to be observed:
  at least Apollo15, then LK1, the others if possible
 successful observation days/nights per month:
  no hard constraint, but try 1 - 4
 normal points per year:
  no hard constraint (~12 to Ap15), but try 100
 normal point accuracy:
   < 0.1 ns (goal < 0.05 – 0.01 ns)
 post-fit residual of single NP to global solution:
   < 1 ns
          Further activities, procedure

   Agree about „tracking criteria“
    finally, to be accepted by ILRS GB
   Apply criteria and check quality of new LLR data with
    the help of a ‚qualification‘ website (Paris website?)
    and in close cooperation with a LLR AC (biases,
    systematics, internal/external accuracy)
   After test phase: routine operation
   Official acceptance of a LLR site in ILRS?
   Consequences in case of failure?
                 Further constraints

Further constraints (according to ILRS standards)
  - LLR sites should observe LAGEOS and/or should
      have a GNSS receiver co-located at the site
  - Prepare LLR website providing
     • „general“ rules
     • tracking criteria
     • NP software (OCA or adapted SLR NP s/w)
     • some documentation (e.g. ephemeris integration)
     • list of Boston workshop?
     • …
  - The LLR data should be freely available at ILRS data
      centers in official ILRS format CRD
           CRD Consolidated laser Ranging Data format
           CPF Consolidated Prediction Format
                 Conclusions

We should try to get as many LLR sites as possible.

Some formal and quality requirements have to be met.

The general rules and required standards should be
  documented at the ILRS website.

The LLR community could/should cooperate with the
  SLR community more closely, e.g., concerning
  normal point calculation (NP length), formats.
Statistics - Reflectors and Observatories

				
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