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# Minutes of the TELCAL kickoff meeting (May 2004)

    Introduction:
    -------------

    Goal:
      - NCS delegates the telescope calibration to reduction packages
      - need a telescope calibration library, perhaps inside GILDAS

    "Desirable" Features
      - Re-use what is available
      - avoid duplication of efforts
      - Standardization
      - Easy maintenance

    Contraints
      - many actors
      - short timescales
      - Portability
      - backward compatibility (must be able to process old data)
      - new ATM version

    Alternative(s)
      - per package solution ? leads to maintenance issues, and serious loss of time...
      - make a common library
            - requires to define needs and interfaces
            - requires clients to adapt to the library constraints

    Beware:
      - RED lifetime was 20 years...
      - Wide distribution of the library through GILDAS
      - IRAM has a record of success, which leads to high expectations
      - Failure is not an option (success is easily forgotten)

    For a library, we need to define:
      - Functionalities
      - Interfaces with outside world (ATM / Reduction packages / NCS / other libraries)
      - Internal data format
      - Internal design (backend handling, fitting, ...)

    ***************************************************************************

    Conclusions:
    ------------

    - A somewhat cryptic table of the current situation is attached.

    - List of desirable library functionalities:
       * Focus
       * Pointing
       * Chopper
       * Skydips
       * Sideband rejection
       * Array geometry
       * Array gains
       * Baseline
       * Regridding
       (* Fitting maybe for specialized algorithms)

    - J.Penalver is now in charge of Pointing Models for the 30m. Pointing
      models thus are outside the scope of the library at least in its first
      iteration.

    - Language to be used: F90 with derived types, modules for at least derived
      types and definition of function interfaces.

    - Goals:
       * 1st version of library should be available by end of year
         (November 2004 if possible).
       * 1st version meaning same functionalities as providing now by red:
         focus, pointing, chopper (for spectra), skydips (for spectra),
         sideband rejection
       * Priorities in library building:
           1 Focus
           2 Pointing
           3 Chopper
           4 Skydips
           5 Sideband rejection

    - Work distribution:
       o Related work without timescale:
          * A.Sievers to distribute an example of 30M-FITS file with corresponding
            documentation for each back-end as soon as they become available
            starting with bolometer and then 4MHz.
          * H.Wiesemeyer to provide translation from 30M-FITS to CLASS data
            format.
          * A.Bacmann and S.Guilloteau to make a memo on bandpass calibration
            at the 30m and PdBI to take into account bandwith increase and new
            ATM possibilities.
       o Library work:
          * Small description of sideband rejection measurement at the 30m.
             => A.Sievers (ASAP)
          * Iteration on interfaces and practical derived types:
             => J.Pety and S.Guilloteau 31.05.2004
          * Test on minimization routines (eg can we realiably use a 2-D
            minimization routine to fit a 1-D problem?):
             => S.Guilloteau 30.06.2004
          * One fully working example (focus):
             => J.Pety and H.Wiesemeyer 30.06.2004
          * A point will then be made enabling new work distribution round.

    ***************************************************************************

    Pointing Methods

       - least square fit
            * Input
                - lambda offsets
                - beta   offsets
                - lambda derivatives
                - beta   derivatives
                - intensities
                - weights
                - fitting shape (e.g. Gaussian,n-Gaussians)
                  Parameters, Guesses, Fixed/Fitted, Boundaries???

            * Output
                - parameters
                - errors
                - quality flags

       - evalute fitted function
            * Input
                - fitting shape, parameters
                - input coord (lambda,beta)

            * Output
                - intensities

       - plotting: Fit overplotted over data for two crosses
            * Input:
                - System, Units

            * Output:
                - Screen plot

       - results for NCS
            * Input:
                - Output of fit
                - Logging info

            * Output:
                - XML file
                - sic procedure (OBS)

    Comments:
       - dealing with spillover on multi-beam receivers ?
       - start with "single-pixel" version
       - can deal with multi-pixel in two different ways
       - changing the lambda(i), beta(i) for each pixel
       - or putting the relative positions of the beams into the fitting function
       - is there a gain to be obtained by fitting a broadened beam for
         planets ?  need to evaluate that issue separately.

    ---------------------------------------------------------------------------

    Focus Methods: Very similar to pointing...

    ---------------------------------------------------------------------------

    Sideband Rejection:

     - currently being done using the Martin-Pupplet settings, by coupling one
       of the sidebands with the cold load, the others with the hot load.
     - is the method accurate enough ?
     - can we rely on the  engineer tables ?
     - measurement seems to be the most accurate method, but the precision is
       unknown ?
     - should it be frequency dependent ?

    First step: transfert what is currently done in RED into the library ..

    ---------------------------------------------------------------------------

    Chopper:

       * Input:
           - El
           - sideband rejection(i)
           - RF Frequency nu(i) and Bandwidth dnu(i)
           - Signed IF Frequency
           - Hot,Cold,Sky,Offset(dark count) temperature T(i)
           - Hot and Cold Temperatures T(i) and coupling coefficients f(i)
           - Telescope specific: Pamb, Water scale height, altitude, latitude
           - Date

           Pin = fhot B(Thot) + (1-fhot) B(Tamb) = B(Teff)

       * Output:
           - Trec(i)
           - Water
           - Water and Others Zenith Opacities(i)

    Tcal:

       * Input:
           - El
           - RF Frequency nu(i)
           - Signed IF Frequency
           - Sideband rejection
           - Set of Tamb (cabine, ground) and coupling coefficients f(i)
           - Water
           - (Interpolated) Trec(i) for dual load

       * Output
           - Tcal(i)
           - Water and Others Zenith Opacities(i) for DSB analysis

    ---------------------------------------------------------------------------

    Skydip

       * Input:
           - El(j)
           - sideband rejection(i)
           - RF Frequency nu(i) and Bandwidth dnu(i)
           - Signed IF Frequency
           - Hot,Cold,Offset(dark count) temperature T(i) TSky(i,j)
           - Hot and Cold Temperatures T(i) and coupling coefficients f(i)
           - Telescope specific: Pamb, Water scale height, altitude, latitude
           - Date
           - Bolometer bandpass(i)

       * Output:
           - Value and errors of Water vapour(i)
           - Value and errors of Feff(i)
           - Quality flag

    ---------------------------------------------------------------------------

    Baseline 1-D

       - Fitting:
           * Input
               - Abscissa(i)
               - Ordinate(i)
               - Weights(i) (may be 0 to exclude a window)
               - Fitting shape (eg polynomial,spline)

           * Output
               - Fitted parameters
               - RMS

       - Baseline computation:
           * Input
               - Abscissa(i)
               - Fitting shape
               - Fitted parameters

           * Output
               - Baseline(i)

       - Baseline application
           * Input
               - Baseline(i)
               - Ordinate(i)

           * Output
               - Baseline(i)-Ordinate(i)

    ---------------------------------------------------------------------------

    Baseline 1-D: On-Off => To be discussed later.

    ---------------------------------------------------------------------------

    Baseline 2-D: spectral x time

       - Fitting:
           * Input
               - Frequency nu(i)
               - Space      x(j)
               - Ordinate   y(i,j)
               - Weights(i,j) (may be 0 to exclude a window)
               - Fitting shape:
                     * Factorized polynomials
                     * Box averaging of independant polynomials
                     * Cubic spline interpolation of independent polynomials
                     * Cubic spline interpolation of independent cubic spline
                     * sinusoidal(nu) with coefficients being polynomials(t)

           * Output
               - Fitted parameters
               - RMS

       - Baseline computation:
           * Input
               - Abscissa(i)
               - Fitting shape
               - Fitted parameters

           * Output
               - Baseline(i)

       - Baseline application
           * Input
               - Baseline(i)
               - Ordinate(i)

           * Output
               - Baseline(i)-Ordinate(i)

    On-off: simultaneous fitting of background and baseline

    ---------------------------------------------------------------------------

    Baseline 2-D: Spatial data => to be discussed later

    ---------------------------------------------------------------------------

    Regridding 1-D

           * Input
               - Abscissa(i)
               - Ordinate(i)
               - Weights(i)
               - New reference pixel, value, increment, dimension
               - Algorithm

           * Output
               - New abscissa(i)
               - New ordinate(i)
               - New weights(i)
               - Transformation matrix for signal and weight

    Comment: Special case for already regularly sampled data

    ---------------------------------------------------------------------------

    Regridding 2-D

        - If it can be factorized (eg space x spectral), then use 1-D
          regridding

        - Else
           * Input
               - Abscissa(i)
               - Ordinate(i)
               - Weights(i)
               - New reference pixel, value, increment, dimension
               - Algorithm

           * Output
               - New abscissa(i)
               - New ordinate(i)
               - New weights(i)
               - Transformation matrices for signal and weight

    ---------------------------------------------------------------------------

    Array geometry: No consensus yet. In the first iteration of the library,
    this functionality will be delivered by MOPSIC.