Subject: [SLR-Mail] No. 891: Removal of systematic bias in Herstmonceux SLR range data
From: Graham Appleby & Philip Gibbs <slr@slrb.rgo.ac.uk (SLR Herstmonceux)>

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SLR Electronic Mail          2002-01-30 08:34:00 UTC           Message No. 891 
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Author: Graham Appleby & Philip Gibbs
Subject: Removal of systematic bias in Herstmonceux SLR range data

    NERC Space Geodesy Facility
    REMOVAL OF SYSTEMATIC BIAS IN HERSTMONCEUX SLR RANGE DATA

    REASON FOR CHANGE
    We are now confident that we understand the characteristics of a 
    range-dependent range bias that has been in our SLR measurements since
    1994 October 1. It is caused by subtle non-linear effects in the
    Stanford SR620 counters that we use to make the range measurements;
    the range bias values (amounting for example to some 8-10mm at the
    distance of LAGEOS) continue to be stable and predictable at a level
    of uncertainty of about 20ps (3mm in 1-way range).

    DATE OF CHANGE
    From 2002 February 1 00:00 UT we will apply range corrections to our
    data before they are submitted to EDC and CDDIS and no further
    corrections will be required by users. 

    CONSISTENCY WITH PREVIOUS DATA
    For maximum accuracy in interpretation of Herstmonceux (7840) data
    obtained in the period 1994 October 1 until 2002 January 31 inclusive,
    the following table should be used to determine the appropriate
    range-dependent correction that must be ADDED TO the time-of-flight
    given in the normal point data.


    Range (ms)      Correction (ps)
                 to 2-way time-of flight

        0                 0      
        2                35      
        4                48      
        6                52      
        8                73
       10                77
       12                91
       14                92
       16               100
       18               120
       20               109
       22               120
       24               111
       26               115
       28               112
       30                97
       32               100
       34                87
       36                82
       38                75
       40                72
       42                73
       44                62
       46                61
       48                50
       50                54
       52                48
       54                53
       56                52
       58                54
       60                74
       62                71
       64                75
       66                84
       68                86
       70                87
       72               101
       74               100
       76                83
       78                80
       80                76
       82                78
       84                84
       86                74
       88                79
       90                82
       92                73
       94                85
       96                79
       98                80
      100                76
      102                83
      104                79
      106                78
      108                73
      110                85
      112                82
      114                76
      116                75
      118                78
      120                75
      122                62
      124                72
      126                67
      128                56
      130                70
      130                70

    Please contact us if further details are required.

                                                               |
    ========================================================= -O- =========
    |  NERC Space Geodesy Facility                            /|          |
    |  Herstmonceux Castle                                   /            |
    |  Hailsham                                             /             |
    |  East Sussex                                  (    / /  /)         |
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    |  Tel:   +44 (0)1323 833888                  (     |O| /    )       |
    |  Fax:   +44 (0)1323 833929                  =================       |
    |  Email: slr@slrb.rgo.ac.uk                  ==             ==       |
    |  Web:   http://nercslr.nmt.ac.uk/           =               =       |
    =======================================================================

From: slr@slrb.rgo.ac.uk (SLR Herstmonceux) 

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