difx:amplitudescaling

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difx:amplitudescaling [2010/11/19 04:47] adamdeller |
difx:amplitudescaling [2015/10/21 10:08] (current) |
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===== Amplitude scaling in General ===== | ===== Amplitude scaling in General ===== | ||

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The level of correction done online by DiFX is controlled by the TSYS entry in the DATASTREAM table entries of the .input file. If TSYS < = 0, only the first two steps are done. If TSYS=1.0, all steps excepting the last two are done. If TSYS = (some nominal tsys value), then all steps except the last are performed. | The level of correction done online by DiFX is controlled by the TSYS entry in the DATASTREAM table entries of the .input file. If TSYS < = 0, only the first two steps are done. If TSYS=1.0, all steps excepting the last two are done. If TSYS = (some nominal tsys value), then all steps except the last are performed. | ||

- | Each step will now be considered in more detail | + | Each step will now be considered in more detail. |

==== 1. Forming unnormalised correlation counts ==== | ==== 1. Forming unnormalised correlation counts ==== | ||

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==== 2. Scaling the unnormalised correlation to correct for the length of integration ==== | ==== 2. Scaling the unnormalised correlation to correct for the length of integration ==== | ||

- | At the end of one accumulation period the correlator calculates the number of valid samples accumulated and divides the visibilities by this number. a visibility at this stage should be actual correlation coefficient of the reconstructed datastreams,the expectation value of a sample squared. | + | At the end of one accumulation period the correlator calculates the number of valid samples accumulated and divides the visibilities by this number. an autocorrelation at this stage should be the expectation value of a sample squared. |

This step is skipped in DiFX when TSYS>0 - as we shall see, the division by autocorrelations later on makes it redundant, since this same correction is applied to both autocorrelations and cross correlations | This step is skipped in DiFX when TSYS>0 - as we shall see, the division by autocorrelations later on makes it redundant, since this same correction is applied to both autocorrelations and cross correlations | ||

- | ==== 3. Correcting for the nominal occupation of sampler levels ==== | + | ==== 3. Correcting for the nominal occupation of sampler levels, and for the unpack values chosen ==== |

This is where things start to get muddled. | This is where things start to get muddled. | ||

difx/amplitudescaling.1290102466.txt.gz · Last modified: 2010/11/19 04:47 by adamdeller