source: branches/alma/tutorials/tutorial_4.rst@ 2072

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Tutorial 4 – Data Reduction for Parkes Methanol Multibeam
=========================================================

.. sectionauthor:: Jimi Green

Files
-----

* mmb-mx.rpf Data file (9.4 Mb)

Data Log
--------

* 7 Spectra taken with Parkes Methanol Multibeam

Instructions
------------

1. Work through the list of commands given in the text file to
   calibrate data taken with the Parkes Methanol Multibeam.
   Commands should be typed line-by-line into ASAP. Seek help
   from the tutors if there are any commands you don’t
   understand.
2. Write a python script to automate the calibration procedure for
   data taken with the Parkes Methanol Multibeam. Incorporate
   the list of commands used in step 1 as well as a routine to cycle
   through the 7 different beams.

   **Note:** Your python script should be executed in a terminal (and
   not within ASAP) with the following command::

       python -i myscript.py

Commands
--------

.. code-block:: python

        # Load data (with filename mmb-mx.rpf) into memory and display
        data = scantable("mmb-mx.rpf")
        print data
        # Set the polarisation feed type
        data.set_feedtype("circular")
        # Select just the first IF (the data actually contains two, the
        # methanol transition at 6.7GHz and the excited-state OH transition
        # at 6GHz, but we will only look at methanol).
        sel=selector()
        sel.set_ifs(0)
        data.set_selection(sel)
        # Set the rest frequency
        data.set_restfreqs(6.6685192e9)
        # Set the cal values for the 7 beams, both polarisations.
        calfact = (( 2.29, 2.28 ), ( 2.18, 1.93 ), ( 4.37, 4.37 ), \
             (2.53,3.20 ), ( 3.69, 3.89 ), ( 3.74, 3.51 ), ( 1.98, 1.70 ))
        # Apply cal factors to first beam, first polarisation
        sel.reset()
        sel.set_beams(0)
        sel.set_polarisations(0)
        data.set_selection(sel)
        data.scale(calfact[0][0], insitu=True, tsys=True)
        # Apply cal factors to first beam, second polarisation
        sel.reset()
        sel.set_beams(0)
        sel.set_polarisations(1)
        data.set_selection(sel)
        data.scale(calfact[0][1], insitu=True, tsys=True)
        # Now repeat above 10 steps for the other 6 beams
        # Reset selection parameter
        data.set_selection()
        # Set plotter output to show both polarisations on the same plot, 
        # but each beam on a separate plot.
        plotter.plot(data)
        plotter.set_mode("p","b")
        # Plot the first scan only
        sel = selector()
        sel.set_scans(1)
        plotter.set_selection(sel)
        # Average "off-source" scans for each beam, then use as the
        # reference scan to form a quotient.
        q = data.mx_quotient()
        plotter.plot(q)
        # Define the channel unit.
        q.set_unit("km/s")
        plotter.plot()
        plotter.set_range(-60,-10)
        # Average all the multiple beam data together to form 
        # a long integration spectrum.
        avb = q.average_beam()
        plotter.plot(avb)
        plotter.set_range()
        # Average polarisations together
        avp = avb.average_pol()
        plotter.plot(avp)
        # Fit a linear baseline (avoiding the maser feature)
        msk=avp.create_mask([-110,-70],[10,40])
        avp.poly_baseline(msk,order=1)
        plotter.plot(avp)
        # Make a nice file
        plotter.set_colors("black")
        plotter.set_legend(mode=-1)
        plotter.set_title("G300.969+1.148")
        plotter.save("G300p96.ps")