2nd meeting on the SCUBA Calibration Database (SCD)
  ===================================================  
                Minutes 2000 03 30
                Iain Coulson

Present : ENA (chair), IMC, WSH, TJ, EIR, RPT, JW

Introduction
------------

ENA : The document "Calculating Tau . . " needs to be released to the
      community. This meeting is to suggest any further edits.

WSH : worries about the amount of flak it will attract if it is seen
      as suggesting that all previous data are suspect.

EIR : The 'Introduction' needs to reflect the historical difficulty in
      analysing 450um skydips (& data).

TJ :  Skydip analysis now does proper error analysis.

Consensus : use of the old 450um:850um skydip relation (and old 850um
            skydip result) was better than using the old 450um skydip
            result. 'Introduction' should say "DON'T PANIC" in large,
            friendly letters, unless . . . observer used the 450um skydip
            *and* had calibrators and targets at different airmasses.
            There are intermediate scenarios for which the degree of
            panic ought to be proportional. Our job is to describe the
            likely impact under these scenarios and to suggest reanalysis
            wheer appropriate.

EIR : Are the changes of sign of the constants in the new (850-vs-CSO,
      850-vs-450) tau relations significant ?
 
TJ  : Is Fig. 1 necessary ?

EIR : . . . liked it.

TJ  : Ed Chapin's document (containing the Fig.1 data) is available
      via WWW.

ACTION on IMC : remove old tau relations from SCUBA web pages.
                Make them available only via Ed's document.

WSH : Suggest we plot tau_old  -vs- tau_new
                     ---------
                      tau_new 

ACTION on JW : rerun 450um skydips with old & new T_loads and create plot
               as described above.

All : Without the immediate effort of FJO to effect the VAX changes to
      T_hot = fn(filter), observers using SURF & ORACDR  need to be aware
      of the different values of T_hot & T_cold for all observing dates.

      on_line : calculations of tau_850 using current T_measured
                uncorrected (by -1K) will yield result that is accurate
                enough for the purposes of planning observing.
              : use tau relations to give tau_450
      SURF    : file headers will not be correct until FJO effort
                available.
      ORAC    : corrections will be made (Tim ?)

RPT : SURF & ORAC should give the same answers under the above correction
      schemes.

ACTION on JW : Produce time lag of T_hot (T_measured ?) and T_amb. 
               (low priority)

ACTION on ENA : Rewrite & recirculate "Calculating Tau . . ." document
                 by Apr 05.

All : Use of PARABOLA in the case of non-gaussian profiles (eg
      planets with diam > a few ") is not advised.

EIR?: What is the effect of a 1" change in the FWHM upon the results of
      'fluxes' ? - ACTION on IMC to find out, and liase with GMS re impact
      upon secondary calibrators.

All : Open actions from SCD001 need to be 'timelined' & prioritized.
      ACTION on ENA (although some concensus that the order of business
      of SCD001 reflected that order).

WSH : showed RR's plots of peak flux and integrated flux (of Uranus) vs
      time (6 hours of data), across a focus change : the latter stayed
      essentially constant, while the former faded during the approach to
      the focus and recovered its maximum afterwards. 
      This illustrates the danger of using just the peak of jiggle maps
      for calibration purposes. The (Z-)focus change was only 0.02mm
      while the peak flux dipped by (?) 10%.

      ACTION on TJ to implement mapping analysis using gaussian fit to
                      central image (including ? masking of central
                      image and median filtering of remainder for
                      sky background level).

end
--------------------------------------------------------------------------
ACTIONs from SCD002 :

 002001 : IMC : remove old tau relations from SCUBA web pages.
                Make them available via Ed's document.

 002002 : JW  : rerun 450um skydips with old & new T_loads and create plot
                as described above.

 002003 : JW  : Produce time lag of T_hot (T_measured ?) and T_amb. 
                (low priority)

 002004 : ENA : Rewrite & recirculate "Calculating Tau . . ." document
                 by Apr 05.

 002005 : IMC : What is the effect of a 1" change in the FWHM upon the
                results of 'fluxes' ? -  liase with GMS re impact
                upon secondary calibrators.

 002006 : ENA : Open actions from SCD001 need to be 'timelined' &
                prioritized.

 002007 :  TJ : to implement mapping analysis using gaussian fit to
                central image (including ? masking of central
                image and median filtering of remainder for
                sky background level).