[1636] | 1 | =========================== |
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| 2 | Tutorial #5 - ASAP advanced |
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| 3 | =========================== |
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| 4 | |
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| 5 | .. sectionauthor:: Maxim Voronkov |
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| 6 | |
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| 7 | **Main goal:** To understand how to handle the data manually by building a quotient |
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| 8 | without using mx quotient |
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| 9 | |
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| 10 | Files |
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| 11 | ----- |
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| 12 | |
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| 13 | * 2009-04-02 2240 MMB-MX-11.9-0.13333.rpf data file |
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| 14 | |
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| 15 | * Script 1: tutorial.py general reduction script |
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| 16 | |
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| 17 | * Script 2: systemquotient.py script doing built-in quotient (to be copied and modified) |
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| 18 | |
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| 19 | * Script 3: userquotient.py the result (youâre not supposed to look into itunless desperate) |
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| 20 | |
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| 21 | |
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| 22 | Instructions |
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| 23 | ------------ |
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| 24 | |
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| 25 | 1. Load the data from RPFITS file |
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| 26 | |
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| 27 | 2. Play with various methods to get access to the data |
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| 28 | |
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| 29 | 3. Run the reduction script using the built-in quotient |
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| 30 | |
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| 31 | 4. Copy the template script doing the quotient |
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| 32 | |
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| 33 | 5. Modify makeQuotient method to replicate the functionality of the built-in mx quotient |
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| 34 | |
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| 35 | **Help:** Use help method in asap to get information about parameters, etc |
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| 36 | |
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| 37 | .. code-block:: python |
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| 38 | |
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| 39 | %run tutorial.py |
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| 40 | |
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| 41 | Copy *systemquotient.py* to a new name, change the import statement at the |
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| 42 | top of *tutorial.py* to load your file instead of the *systemquotient.py*. |
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| 43 | |
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| 44 | .. code-block:: python |
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| 45 | |
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| 46 | from myquotient import * |
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| 47 | |
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| 48 | Now your version of `makeQuotient` will be called from *tutorial.py*. |
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| 49 | Use the following to load the data into a scan table called sc |
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| 50 | |
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| 51 | .. code-block:: python |
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| 52 | |
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| 53 | sc=scantable("2009-04-02_2240_MMB-MX-11.9-0.13333.rpf") |
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| 54 | |
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| 55 | Inspect the content. |
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| 56 | |
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| 57 | .. code-block:: python |
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| 58 | |
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| 59 | sc.summary() |
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| 60 | |
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| 61 | The file contains 7 scans. Each scan corresponds to observations of a source |
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| 62 | with a different beam of a 7-beam receiver. We want to use the median |
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| 63 | spectrum from all other scans as a reference when constructing the quotient |
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| 64 | using the formula |
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| 65 | |
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| 66 | .. code-block:: none |
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| 67 | |
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| 68 | Result = Toff * (On/Off - 1), |
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| 69 | |
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| 70 | where Toff is the system temperature measured during the reference scan, On |
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| 71 | is the signal spectrum, Off is the reference spectrum. We want to construct |
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| 72 | Result for each individual beam (out of 7 beams available) and average all |
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| 73 | these spectra together. |
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| 74 | |
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| 75 | To do the selection |
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| 76 | |
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| 77 | .. code-block:: python |
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| 78 | |
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| 79 | sel=sc.get_selection() |
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| 80 | sel.set_beams(0) |
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| 81 | sel.set_scans(0) |
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| 82 | sel.set_polarisations(0) |
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| 83 | sc.set_selection(sel) |
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| 84 | selected_sc = sc.copy() |
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| 85 | selected_sc.summary() |
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| 86 | |
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| 87 | To average or compute the median use one of |
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| 88 | |
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| 89 | .. code-block:: python |
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| 90 | |
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| 91 | ref.average_time(weight="median") |
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| 92 | scans.average_time() |
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| 93 | |
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| 94 | To merge the scans together (i.e. individual quotients for each beam) build |
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| 95 | a python list first and then use merge and average time |
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| 96 | |
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| 97 | .. code-block:: python |
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| 98 | |
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| 99 | res=[] |
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| 100 | for b in range(7): |
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| 101 | res.append(myFunctionReturningAScanTable(beam)) |
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| 102 | averaged_scantable = average_time(merge(res)) |
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| 103 | |
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| 104 | Note that merge will fail if the list has only 1 element. An if-statement may |
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| 105 | be necessary |
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| 106 | To scale the scantable with the constant factor use:: |
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| 107 | |
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| 108 | scan.scale(factor,tsys=False, insitu=True) |
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| 109 | |
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| 110 | To add a constant use:: |
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| 111 | |
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| 112 | scan.add(constant_to_add, insitu=True) |
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| 113 | |
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| 114 | To get the tsys use:: |
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| 115 | |
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| 116 | scan.get_tsys() |
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| 117 | |
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| 118 | Note that some selection of data is usually necessary. Otherwise `get_tsys()` |
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| 119 | returns too many numbers. |
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| 120 | To divide two spectra simply divide one scan table to another:: |
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| 121 | |
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| 122 | quotient = signal / ref |
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