Difference: 20152010MsciPhotometryAnalysis (1 vs. 2)

Revision 220 Oct 2015 - ElenaCukanovaite

Line: 1 to 1
 
META TOPICPARENT name="StewartBoogertPhotometry2015"

Initial histogram

The dark frames were analysed by plotting a histogram of all the photoelectron values. However, specifying too many bins will mean that some of the bins inside the peak will have values equal to 0, since the bin width is so small. This can be seen in the figure below. This deviates the Gaussian from the curve.

Changed:
<
<
example.png
>
>
example.png
  To fix this the values of 0 inside the peak were set to nan. The peak was defined such that it starts above 1000 bin counts. The plot without the zeros in the peak can be seen below. As can be seen the distribution can be described well by the Gaussian distribution.
Changed:
<
<
no_zeros_histogram.png
>
>
no_zeros_histogram.png
  This was done for the various exposure time images. What we wanted to compare was the sigma found from the fitting procedure (sigma_fitting) and the sigma as derived from Poission distribution, i.e. sigma_poisson = square root of the mean pixel value given from the fit. The plot below shows the difference, sigma_fitting - sigma_poisson = delta(sigma).
Changed:
<
<
difference_between_sigmas.png
>
>
difference_between_sigmas.png
  Therefore, as the exposure time increases the background signal deviates from Poissonian. To check this, the mean from fitting was plotted as a function of exposure time below.
Changed:
<
<
mean_as_function_of_time.png
>
>
mean_as_function_of_time.png
  The mean also increases with the exposure time in approximately linear fashion. This could explain why the delta(sigma) increases with exposure time, because as the mean increases so does the numerical value of its standard deviation, therefore allowing more deviation between values.

-- ElenaCukanovaite - 20 Oct 2015

Changed:
<
<
META FILEATTACHMENT attachment="example.png" attr="" comment="The Gaussian fitted to overbinned histogram." date="1445346845" name="example.png" path="example.png" size="33806" user="zxap014" version="1"
META FILEATTACHMENT attachment="no_zeros_histogram.png" attr="" comment="Fixed histogram with no overbinning, curve fitted with a Gaussian." date="1445347888" name="no_zeros_histogram.png" path="no_zeros_histogram.png" size="34321" user="zxap014" version="1"
META FILEATTACHMENT attachment="difference_between_sigmas.png" attr="" comment="Delta(sigma) as a function of exposure time." date="1445348165" name="difference_between_sigmas.png" path="difference_between_sigmas.png" size="24258" user="zxap014" version="1"
META FILEATTACHMENT attachment="mean_as_function_of_time.png" attr="" comment="Mean pixel value found from the fit as a function of exposure time." date="1445348467" name="mean_as_function_of_time.png" path="mean_as_function_of_time.png" size="24958" user="zxap014" version="1"
>
>
META FILEATTACHMENT attachment="example.png" attr="" comment="" date="1445369310" name="example.png" path="example.png" size="35967" user="zxap014" version="1"
META FILEATTACHMENT attachment="no_zeros_histogram.png" attr="" comment="" date="1445369328" name="no_zeros_histogram.png" path="no_zeros_histogram.png" size="38004" user="zxap014" version="1"
META FILEATTACHMENT attachment="mean_as_function_of_time.png" attr="" comment="" date="1445369334" name="mean_as_function_of_time.png" path="mean_as_function_of_time.png" size="27838" user="zxap014" version="1"
META FILEATTACHMENT attachment="difference_between_sigmas.png" attr="" comment="" date="1445369339" name="difference_between_sigmas.png" path="difference_between_sigmas.png" size="27181" user="zxap014" version="1"

Revision 120 Oct 2015 - ElenaCukanovaite

Line: 1 to 1
Added:
>
>
META TOPICPARENT name="StewartBoogertPhotometry2015"

Initial histogram

The dark frames were analysed by plotting a histogram of all the photoelectron values. However, specifying too many bins will mean that some of the bins inside the peak will have values equal to 0, since the bin width is so small. This can be seen in the figure below. This deviates the Gaussian from the curve.

example.png

To fix this the values of 0 inside the peak were set to nan. The peak was defined such that it starts above 1000 bin counts. The plot without the zeros in the peak can be seen below. As can be seen the distribution can be described well by the Gaussian distribution.

no_zeros_histogram.png

This was done for the various exposure time images. What we wanted to compare was the sigma found from the fitting procedure (sigma_fitting) and the sigma as derived from Poission distribution, i.e. sigma_poisson = square root of the mean pixel value given from the fit. The plot below shows the difference, sigma_fitting - sigma_poisson = delta(sigma).

difference_between_sigmas.png

Therefore, as the exposure time increases the background signal deviates from Poissonian. To check this, the mean from fitting was plotted as a function of exposure time below.

mean_as_function_of_time.png

The mean also increases with the exposure time in approximately linear fashion. This could explain why the delta(sigma) increases with exposure time, because as the mean increases so does the numerical value of its standard deviation, therefore allowing more deviation between values.

-- ElenaCukanovaite - 20 Oct 2015

META FILEATTACHMENT attachment="example.png" attr="" comment="The Gaussian fitted to overbinned histogram." date="1445346845" name="example.png" path="example.png" size="33806" user="zxap014" version="1"
META FILEATTACHMENT attachment="no_zeros_histogram.png" attr="" comment="Fixed histogram with no overbinning, curve fitted with a Gaussian." date="1445347888" name="no_zeros_histogram.png" path="no_zeros_histogram.png" size="34321" user="zxap014" version="1"
META FILEATTACHMENT attachment="difference_between_sigmas.png" attr="" comment="Delta(sigma) as a function of exposure time." date="1445348165" name="difference_between_sigmas.png" path="difference_between_sigmas.png" size="24258" user="zxap014" version="1"
META FILEATTACHMENT attachment="mean_as_function_of_time.png" attr="" comment="Mean pixel value found from the fit as a function of exposure time." date="1445348467" name="mean_as_function_of_time.png" path="mean_as_function_of_time.png" size="24958" user="zxap014" version="1"
 
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